I just discovered your video and I know it is 6+ years old now. Thank you very much for the time and effort you put into your production. I have never seen as good of a schematic in terms of simplicity and thoroughness of the relationship between the various components found in the overhead power lines and the transfer of that power to a typical home. I will be committing your schematic to memory. And your demonstration of the isolation transformer was the best I have yet seen. Well done & thank you again.
Good video. I took my isolation transformer apart right after I got it to make it completely floating as well. There seems to be a lot of arguments back n forth on whether or not to float the scope though.
have used isolation transformers all throughout my career! They are an absolute necessity when working on hot chassis tv's! I have a few. my best ones are the ones i have built into my variacs
Mine is ahead of my variac, so it accomplishes the same thing.They are the first piece of test equipment a tech needs to buy. You can't take chances with electricity.
Be careful medical isolation transformers are not really isolated. Check it with a meter before you trust it. Watch Todd Harrison's video on how to modify one. /th-cam.com/video/11Yve2ijWyk/w-d-xo.html
Hello I would like to thank you for this video ! I needed to watch it several times to understand (well) process, before doing it by myself...without a big bang in the cellar In France, 230 v, and 30 ma security on the line...But with a maximum care i tried to connect mys scope Rigol 1102, behind my 600 W transformer. So, no fire, no explosion, and i have always the cellar too Many many thanks cause it was difficult for me to prevent misunderstanding around ground, secondary line, and scope. That's ok now and very happy to do this in real life, after many tests to control all connections on the transformer and to verify all separations between them, i decided to run experiment, and i could see (with happyness) the same result on my rigol and the beautiful waveform for the secondary 230v AC So this test makes me understand some rules and gives me basis for the future GREAT ! rgds Eric.
You correct that misapprehension that some techs have, who say that they do not need an isolation transformer when working on a valve guitar amplifier, because it has it's own transformer in its power supply and is therefore 'already isolated'. They fail to understand that the secondary of the PSU transformer is grounded, and thus not isolated from the mains. They need to watch your well-informed video to put them right.
yes, that how every non ground referenced transformer protect you if you touch one of the outputs. That how two mains powered devices protect themselves from shorting the mains when you connect one to another. But you still have to remember, that floating voltage might be dengerous if you close the floating loop Here in Europe we have 230V in every socket, so hot chasis are not that common but you still expected to use insolation transformer for measurent on serviced equipment. To not blow up your scope or yourselves. One thing you forget to mention Insolation transformer not only insolates you if you touch one output, but also limit the power you could recieve if you close the loop to the power output of the transfotmer, so if you close the loop it won't be the full breaker current, but only its fraction. Closing the loop on the output side also would not flick your mains breaker if the transformer is not some kind of behemoth, so you would be expected to install one breaker on the output in case of catastrophic failure of serviced equipment.
a grounding at 230v would require much thicker ground wires and small shunt on the neutral its doable for low power devices such home audio equipment but not on high power motors and still have the same level of safety
Thanks for the demo. Although here in the UK we have a slightly different arrangement with the mains supply (just three conductors provided from the supplier -240v Live, Neutral and Earth) all the same safety precautions apply, as do your comments on isolation. Strangely enough I was looking at mains isolation transformers yesterday and I think I'm going to get one with a combined variac, essentially an AC power supply, but one with a ground isolation switch so I can control whether earth ground is connected which better suits my needs.
good work, like the refresher course , it made me want get my my old text books out again also may me sad ,i took apart my Tektronix 2445 about a year ago and still have not found the time or the energy to put back together .
The only difference in the uk is the distribution transformer is massive and it often lives in a brick building, it supplys many streets. Also its only 240v tappings, same idea though. ive known about isolation transformers for a long time. We cant do your test in the uk, our earth leakage or/and rcd breakers wont allow power direct to earth, they trigger and cut the supply.
We have GFI breakers here too. They are used on outdoor outlets and circuits where the outlet Is located around sinks. We also have CFCI wall plugs which are the same thing in a wall plug you it can be reset without having to go to the breaker box. I know in the UK and many other countries you have 240V single phase, so 2 conductors and an earth ground. Line and Neutral.Here we have 240 with a center tap neutral so we can have 120 phase to ground, and 240 phase to phase..My garage heater that you hear running in the background is a 240V unit. Only 3 wires, 2 hot, and earth ground.My hot tub and dryer on the other hand has 4 wires. 2 hot, plus neutral and earth ground. The phase to phase powers things like the heating element, and then 1 phase to neutral for things like the control panel, lights ect.1 distribution transformer typically feeds 12 homes. We have underground facilities in some areas where the transformer is mounted in a big steel box on the ground. What is your 3Phase voltage there?Here it is 208V phase to phase. They just use the center tap and 1 leg so between any phase and neutral it is 120, and between phases 208.
Pass i dont know the full info, 400v for 3 phase, as far as i can remember, only businesses tend to use 3 phase. Houses dont have access to 3 phase, no need. At 240v we only need half the current you get from a 120v outlet to do the same job.
We don't have access to 3 phase either. Mostly business or apartments were they need to run elevators. Motors much more efficient on 3phase.We have 208/3, and then it goes to 600/3 for larger businesses. That is what feeds the CO I work out of.You are right at 240 only half the current, but it is a moot point because you pay for KWh, so the cost is the same to operate. My electric car charges on 240, but I can charge it on 120 as well if I need to, but it takes all night on 12 amp 120V, and only 3.5 hours on 15A 240..
We also have an odd way of wiring up 13 amp mains outlets, i think just after the war we had a shortage of copper, or it just cost too much. So rather than using spur wiring for every outlet, we started using a ring main from the fusebox all around the sockets then back to the fusebox, uses thinner copper wire. I personally like spur wiring, i think canada and the usa still have that, but i cant be sure, i cant see that far LOL :-D. We use spur wiring for electric showers. And radial wiring that jumps to every light fitting. My brain still locks up when i see an american call black "live", surely red would have made more sense, red meaning danger in the animal kingdom, as we are also animals.
Red and black is used.Remember that we have split phase 240V.For 120 runs the wire color is Black (hot) and White (neutral).For 240 single phase such as for water heaters and baseboard heaters, again only 2 wires, Red and Black (both hot) and of course the bare earth conductor.For 240V with neutral, which is used on kitchen outlets, RED Black and White. Outlets are wired Black to top outlet, and Red on bottom.That way 2 appliances can be run simultaneously on a 15 amp circuit.Also there is the sheath color. Wire designed for 240 single phase is red, whereas the rest of the wiring is white.For 3 phase they use Red/Black/Blue for the hot, and White for neutral.
12voltsvids, You are very wise and understand these power systems at a level I have not seen from anybody outside the power distribution industry. So don't think I'm trying to degrade your wealth of knowledge because I'm not. Your first light bulb test was with no isolation and it showed that clear danger. Your second light bulb test showed how a technician isolation transformer protects you and your equipment. I'm not talking about either of those situations. I'm saying once you connect the scope ground clip to your TV chassis your technician isolation transformer is 100% not isolating you from high energy any more. I now see how your system is wired in Canada and the problem is clearly the same as I have tested in the USA. Don't do this test but! Power your TV with the technician isolation transformer, then connect your ground clip from your scope to either the line or the neutral on the TV to take normal measurements with your scope. At this point your scope is safe, just as you showed in test two, but you are no longer protected by the isolation transformer as the scope ground has strapped one leg of your isolation transformer to your home's ground system. If you reach out with one hand and touch any part of the TV circuitry that is on the opposite line side with respect to your scope ground clip and your isolation transformer you will get zapped "by the energy delivered by the isolation transformer's secondary side through your home's grounding system" just as if your TV was connected directly to mains and you were getting a zap from the mains. Yes, some point of your body has to be grounded to your home's grounding system or just good old ground under your feet if you don't have rubber sole shoes, but that's just as true with direct mains as well. Meaning your not any more safe working on the TV once the grounded scope is connected then if you didn't use the isolation transformer in the first place. This is the scope/DUT/IT testing I'm trying to warn people about. People get injured by this type of DUT setup testing all the time because they think they are isolated from mains power, which they are, but this normal testing situation exposes the technician to 100% exact same danger from their isolation transformer energy just as if it was mains energy or just as if it was a Hospital grade isolation transformer as you clearly noted in your drawings showing the secondary strapped to chassis ground. Trust me, do the test as I describe here which is a normal way people use a scope on a DUT that is isolated but please use a light bulb not your hand. ;)
Yes I know that if you connect your "earthed" scope to the chassis, and then you touch a hot point on the chassis while you are touching ground you will get zapped, but you don't need to ground the chassis to accomplish this.If you are touching a ground point on the chassis, such as a shield cover, and you touch an energized point on the chassis at the same time you will still get zapped.The isolation transformer does protect your scope from accidentally creating a short circuit. I connected it to both sides of the line, no sparks. Sure I am now tying that side of the transformer to ground, and if I was poking my fingers around in the set while standing in bare feet on wet cement I am asking to get bit, but if you are following safe servicing procedures, and that means wearing insulated shoes, and keeping your free hand away from anything conductive when working, a pocket is the safest place, you are safe. At least you don't have to worry that a hot chassis is going to blow your scope probe up. When I work I normally have my scope floating free as well. Safety first. I have extensive electrical training. Not just in this field, which I have done for 32 years, but I work now for a major telecom, so I deal with working in proximity of secondary grid power every day. In my career in the business I was zapped twice in 20 years. One time because my assistant didn't know not to talk to me while I was working and I was distracted. (This is why you should never talk to a linesman that is working, as working around electricity takes 100% concentration) The only reason I wasn't hurt was because I followed safety procedures. One hand in pocket, rubber soul shoes. No path for electricity to travel across heart. Just like a bird sitting on a wire.
Our local Target had a Toshiba TV similar to that one for customers to know they are on CCTV when they walked in. Ran for about 20 years 24x7 until they decided it was a little outdated in looks for the entry way.
why don't you touch the secondary wire and ground with your hands instead of the lightbulb to demonstrate the safety of an isolation transformer. that would impress more .
Why does virtually every isolation transformer on Amazon have grounded receptacles? I totally get what you're saying which begs the question as to what the value of a grounded isolation transformer is. What are they used for?
That defeats the purpose.round prong needs removing on those for sure. A proper serviceman's isolation transformer like mine has a 2 prong cord and 2 prong receptical on the transformer. Actually it has 3. The secondary has 3 taps, 90%, 100% and 110% outputs. For 120 in that makes the 3 outputs 105, 120 and 135 approximately. I use the high side and rum it into my variac so I can go from 0 to 150 volts.
You said something at both the beginning and end of the video that may have "clicked" in my head. Either side of the isolation transformer can be pulled to ground. WHAT? Really? I'm interpreting this as, if you touch one side of the isolating transformer to ground, you aren't forcing voltage to or from the ground but instead you're stabilizing one of the transformer legs, causing the AC voltage fluctuations to occur only on the opposite leg. So if I ground wire 1, then wire 1 becomes stable and wire 2 carries the oscillating AC voltage. If I instead ground wire 2, then wire 2 becomes stable and wire 1 carries the oscillating voltage. I've been trying to figure out how any isolation transformer works, because I feel that the voltage is just going to go through you to ground. I never thought that maybe the ground is more powerful than either leg by itself and will force it to stabilize. Or maybe I've thought of the earth as a giant capacitor capable of endless dumping of electricity, and that might not necessarily be the case. Argh. Now I have to rethink everything.
My hand wound isolation transformer does not pass enough power. Does it need a resonant capacitor in series with primary to match the 20khz AC input? I even tried impedance matching that did not work either.
some years ago I bought a hallicrafters S38 and was told I should run it off a isolation transformer. I never did that but I think I see why I should and will get one.
I also have a Hallicrafters, will have to dig it out and see the model. I believe the one I have has a power transformer. It works too, at least it did the last time I used it.
Hi 12voltvids ,I thinking that you have small mistake (but very dangerous!! ) whan you connect the oscilloscope probe ground (which is main ground) you referance the Isolated side of the transformer to the ground again so you canceling the Isolation!!. I am using the two oscilloscope probe with math function and not the oscilloscope probe ground!!
haimt1464 yes connecting a grounded scope probe will ground the isolation for sure. This demo was to show that accidental contact with live side will pose no risk because the live side would be pulled low. there will be other points on chassis that would then become energized. this demo was done specifically for this demo to show that the isolation transformer does indeed provide protection against accidental shorting. ultimately you want your scope floating as well. My scope has no ground connection normally. so connecting it would give me no light regardless if I connected the ground to line or neutral, (without transformer) however this would bring the scope chassis to line potential because it is floating which is very dangerous. with the isolation transformer protecting the unit under repair, even if your scope ground was on a line connected reference, the scope would not be energized. So for safety, an isolation transformer is mandatory AND the earth ground prong on the scope needs to be removed. I can demo this too if people want to see my scope chassis go up to 120 v. that was the purpose. with the scope grounded and the bulb connected to line it lit up. if the ground pin was removed the bulb wouldn't light but the scope chassis would be hot. that is very dangerous. on iso transformer and the ground pin on scope removed, unit under test is fully isolated and floating. this is the only way I work.
Can I please ask you a question... How can I generate composite video using basic logic chips? I.e 74HC series. Should I just build a counter for the pixel clock, and then derive the sync pulses from there by counting clock pulses? I love your videos. Youre one of the best on youtube... Please keep it up.
Hello, I read that measuring with an oscilloscope, you need an amplifier, you need galvanic separation, I ask from what point of view, when today's amplifiers have only 2 wires. Thank you for any knowledge
I just got an old VIZ Isotap isolation transformer. The isolated output is 2 prong. I have 2 questions: One, if I am working on a modern tube amplifier which has a three prong plug, do I still need the isolation transformer? Two, if I do need it; should I use the infamous 2/3 prong adapter to plug it in? I can't think of any other way to do it.
I bought a new isolation transformer for my 14 year old future electrical engineer. I am wondering why I bought it! Perhaps because I have seen so many TH-cam videos on I/T’s. Such a gadget will not prevent electrocution when working on 240 vac projects. It will only protect the scope and other equipment. I use a RCD (residual current device) also referred to as a (DCD, differential current device on all my circuits, in fact 22 of them. In Australia we have 240 vac and the common ground (neutral) is tied to the ground stake as a safety measure, same as in many other countries. If I am working on any 240 vac equipment and I for some reason touch the active wire, the power goes off within 30 m/s when a differential of 15 mA is detected. So the scope is off and I am safe. Why do I need an I/T ? I am going to test this out on my own equipment by shorting something out when connected to the scope. I paid $250 for the I/T. The RCD’s cost about $15. I see someone suggested a $400 device on the probe to protect the scope, yes, but that doesn’t protect your life. I am not getting it, can someone please explain to me why a $15 gadget will not only protect the scope and my life?
A proper isolation transformer has no reference to neutral or ground on the isolated side. Both prongs on the plug are isolated. If you touch either side while grounded you will not receive a shock because there is no return path to ground. If you touch both at the same time then you will receive a shock. If you grab one wire on one hand and the other with the other then you have completed a path across the heart and you could end up electrocuted. The big safety factor is accidental shock. That is you touching something live (mains connected ) and the current running through your body and out your feet into earth. This is where the isolation transformer protects you. It also protects your scope from damage. Your ground fault interrupters are good, but when you have a fault in the device you are working on and the breaker trips every time you try to power it up for testing you become very frustrated 😡. Isolation transformer keeps you safe from accidental shock. Your GFCI by the way I only protects from ground leakage. You will still like with an isolation transformer get zapped if you grab Live and neutral. I can speak from experience. I wouldn't be commenting here had it not been for my transformer. When I was as working in the business a cable tv (grounded) connector dropped off the tv I was working on and onto my forearm startling me. I jumped and in the process contacted a hot chassis directly connected to power. I could have received a major shock but because the tv was plugged into my isolation. Transformer i didn't as much as receive a tingle of voltage. Nothing. Also when the connector fell into the chassis it didn't short out again because the set was isolated.
@@12voltvids Thanks for a very lengthy explanation all of which I knew. But please explain to me why a RCD which will save your scope and other equipment as well as your life isn't better than an I/T,,, thanks.
@@cookieboi4449 you will still become the conductor until the current is cut off and that jolt is enough to send your heart into fibulation. They are safer than no protection but you still get zapped for an instant of a second until the circuit trips. With an isolation transformer there is no current flow at all, you float just like a bird on a wire.
are there additional specs for the transformer, current , watts etc. and do you use or can you use 240v also. thanks again for all your work really enjoy the learning, also anyplace special you get these transformers from? ty j
Isolation transformers are available from transformer manufactures for both 120 and 240 volts. You should be able to get them from electrical suppliers or order them from the manufactures such as Hammond Transformer, Alanson Transformer ect. You pay more for large capacity. Mine is rated at 600 watts, so I can operate the largest plasma sets on mine no problem.
You would get the same exact result if the secondary of the isolation transformer DID have a ground to the case as long as the neutral isn't bonded as well. It's done this way in every single operating room in the US. There is still a ground(bonding) jumper that puts every piece of stainless equipment at the same potential. This ground however is NOT bonded to the secondary winding AT ALL. You can touch a hot lead and touch ground and 0 current will flow. Take your hot from the secondary of the iso transformer put it on the bulb, take the wire from the neutral side of the bulb and ground it. Does the bulb light? No.
You can earth equipment for sure. The problem is many so called isolation transformers also tie the neutral side of the secondary to ground and that defeats the purpose.
@@12voltvids if that's the case it shouldn't be called an isolation transformer because that is in fact defeating the purpose. In that case it's simply a 1:1 transformer and probably some type of false advertising. Eta- the drawing made of the first grounded type isolation transformer is in fact a fully isolated transformer that will completely isolate you from earth or any grounded surface- even with the ground wire as long as it's not bonded. Thus is exactly how operating room iso systems are designed and wired. It's MORE dangerous to not have that bonding wire.(Again, it absolutely can not be bonded to the winding though)
@@xprocharged1 My isolation transformer has no ground. There is no ground prong on primary or secondary. 2 prong cord on primary and 2 prong receptical on secondary. Totally isolated.
@@12voltvids I get that. My point is you're JUST as isolated even with a 3 wire / 3 prong setup. It can be argued, and has been, that an isolated system with a ground is safer than without due to capacitive coupling and leakage current. Leakage current is much lower when a ground wire is used- hence the reason they are done this way in operating rooms where current that a normal person couldn't even feel could easily kill an infant or someone with their chest opened up with metal instruments touching their heart.
My Isolation I made works perfect, no earthg grounds, but i was thinking could I just ground the chassie in case of a faulty primary so as not to receive a shock in such a event?
Excellent explanation and demo! Not sure if it has been brought up earlier, but how come outlets in North America are polarized (one pin is wider than the other)? On AC it shouldn't matter what orientation the plug has. Most of my friends that see some of my import USA stuff and notice the outlet on my power strip/transformer always ask "Why on earth is it like that? It shouldn't matter since it is AC."
Depends on the type of device being powered, but polarized plugs generally ensure that it is the hot/active lead that is being switched and not the neutral. They do this for safety reasons.
Good question, and to answer it for you it is for safety.Many items they connect the chassis ground directly to one side of the AC line. The wider blade is the neutral side and the smaller one is the HOT.This ensures that the chassis is tied to neutral, and not the hot side.Also, if there is a power switch in line, you want to ensure that the hot side is switched and not the neutral side as that would leave AC still live inside the device. Operation wise it wouldn't matter, but if one of the capacitor that tie say the antenna ground to the chassis were to short and the hot side was tied to the chassis ground, well you can see that the antenna connector would be now be hot. Parts like the tuner shield would be directly connected to 120V.Not everything is polarized. None of the power supplies for equipment I install at work is polarized. This is because it goes to a switching type power supply, and both sides of the DC output are isolated by transformer, and the entire AC side is double insulated.
Does that means that after the insulation transformer there is no Live/Gnd anymore? I mean, are those two wires after the transformer exactly the same, or do is there any difference between them?
Hi, just wanted to ask you a question about AC outlet dirty power. I'm a musician the several guitar amps in my house that I use. I seem to have a problem with the these amps displaying high frequency harmonic distortion. I've tried everything to alleviate this problem, but nothing seems to work. I heard of an audio isolation transformer called a Topaz ultra isolation transformer 32 series that you can plug your equipment in and it will filter out any noise problems. Do you know if something like this would be a good idea to buy? Thanks Michael Newell from Niagara Falls, Ontario
I'm having similar issues with my recording studio setup. ugly mud creeps into the guitar tracks as soon as any gain is added. I've tried everything - power conditioners (got the Panamax), UPS online double conversion (TrippLite), and now about to try isolation transformer (got the Tripplite IS1000). I have seen other videos that modify the iso transformer by removing the ground to neutral on the secondary... but is it as easy as using a cheater plug on both sides?!?
In Germany every fuse box has a ground fault circuit interrupter, so when a short occurs, the power automatically cuts. Do you not have this in the US?
Thanks. So in plain english you're protecting your scope's integrity by isolating the input of the device under test by means of an isolation transformer. You're not removing ground in the input of the scope, or feeding the scope from the transformer, that is what many people typically would think should be done. Right?
No I am isolating my work bench from Earth ground. The secondary of the isolation transformer is not referenced to earth or neutral at all. My scope also floats.
@@12voltvids Oh, OK with the first part of your answer, but you mean the "measure side" of the scope floats?, or you also removed ground from the scope's power input. I read many times scope's ground (in the power side) shouldn't be neutralized because in that case scope will be floating at the same voltage level of the measure side, no matter were no chance of make a ground fault, but chasis therefore we also will be floating at high voltage. Please your final comments.
@@ramirosuarez9537 yes scope floats so yes the chassis could be hot but remember it is isolated from earth ground so you won't get a shock even if you touch it. Just like a bird on a wire.
My isolation transformer was shipped to me grounded. I think all in the USA are shipped that way to protect the manufacturer and vendor. But, there were no docs or warning labels stating that it was grounded to mains. Seems very wrong. It does not provide isolation. Have heard that the scope should remain mains grounded. Confusing situation.
Surging Circuits I removed my scope ground and it sits on a wooden bench. never remove scope ground unless you are working with an isolation transformer. doing so could create a very dangerous situation as the scope chassis could become energized. at least on isolation transformer the "floating" scope is never going to become mains energized. it could become DC energized if you are working on a power supply on the DC side of the transformer so services need to be aware of this. I actually have a ground wire that I can earth the scope if needed but usually I don't as I am aware of what I am doing, and take every precaution when working.
+Surging Circuits There are different types of isolation transformers though; ie medical and audio isolation transformers for example will be mains earth referenced and will usually have the output neutral tied to ground, and they are supposed to be grounded for safety. "Isolation" in this sense is being used to protect sensitive equipment, but you have to modify them to make them "tech" isolation transformers.
CORRECT. These type of transformers are there to limit spikes and noise on the line. The pass through ground and bonding of the neutral to earth ground on the secondary removes any safety from shock factor. You need to cut the ground pin, and remove that bond from the neutral to case on the output plug.As I said in a previous message measure with a meter to be sure.
Question regarding the information about the ground prong, at 10:24: If making my own isolation transformer setup (off-the-shelf transformer per se, but making an enclosure for it with switches and fuses and things), would it make sense to tie the "ground" prong of the outlet to the neutral side of the outlet, as long as neither of them is tied to anything actually referenced to earth ground? If not, why would that be a problem? Like, I'm thinking it would be a "ground" that floats with the neutral side, and the live side would have 120v between it and either the neutral or the "ground" (I keep using quotes to emphasize that I don't mean actually ground-tied), but could also be (real-)ground referenced thus making the "neutral" and "ground" effectively live... would this be reasonable? Or should I just leave it completely non-connected? My thought is to do this for DUT's that have a grounding plug, to just give them something to connect to...... But I'm not entirely sure if it's reasonable. Any input is welcome! Thanks for the video!
A serviceman's isolation transformer has 2 wires. Hot and neutral only. No ground. The ground prong can not be connected to a thing or you are defeating the safety the isolation transformer gives you. Mine is a commercial transformer that cost a bloody fortune. It has a 2 prong non polarized line cord and just a 2 prong secondary receptacle. Can not plug a 3 prong plug into it. Have to cut it off. Mine is a Hammond and it originally cost about a buck a watt. (500 watts, 500.00)
@@12voltvids I don't want to cut off the ground prong on my DUTs, as I'll want to use them safely when not under test, as well. I know there are only two output wires from the secondary (well, assuming a single transformer voltage, though of course there are multi-tap isolation transformers, too), the question is, would it make sense to wire the "neutral" (though that's arbitrary, as both sides are floating) wire to the "ground" wire of the output socket -- not grounding it, it's still galvanically isolated from the mains, it'd just be that if, say, the DUT had a chassis ground that connected to what it expected to be an earth ground, that "ground" would be connected to one side of the secondary (which we'll call the neutral). Does that somehow lose safety? If so, how/why?
@@DavidLindes a short extension cord solves this delemina. You can get short 1 to 3 foot cords. The ground pin comes off easy. Then you can plug your DUT into the 3 prong receotical on the short cord.
@@12voltvids ok. But is there any danger in shorting the "ground" pin to the neutral side? Seems innocuous to me, but I wonder if I'm missing something.
@@DavidLindes you don't want to connect the ground pin to anything. It is totally open. With the neutral unbonded it will float as well. Your meter will still read accurately on the DC side of the power transformer. If measuring on AC side then one probe goes to neutral not ground.
I was demonstrating how it works. To show that the isolated side is fully isolated from the line. Naturally you wouldn't test to line, you test to ground. The line is isolated. Testing to line would remove that isolation.
Q) Since my isolation transformer is mains grounded, I have used a 6inch pigtail 2-wire extension to connect the device I'm working on to the iso-transformer. Do you see a problem doing it this way vs opening the iso-transformer and removing the ground connection? Thx.
That will work just fine IF, the plug on your isolation transformer is totally isolated from the earth ground.Take a meter and put it in ohms mode.Put one probe on the ground lug on the power cord to your isolation transformer. Then measure to both prongs on the output plug.You should see infinite resistance. If you measure anything between the ground terminal on the power cord and either of the power prongs on the output then the secondary is strapped to the earth, and you have no protection. You need to cut the ground prong off the power cord in this case to isolate the transformer from earth ground.
So since I salvaged my transformer from my Karaoke Machine, is there a way that I can use my own transformer as a isolation transformer when servicing the electronics?
Could you please post the link to your recent video where you showed how to connect a light bulb as current limiter? I tried to search for it in your videos but I did not find it. Thanks!
Some TV's use hot chassis, I'm confused why they would even want to make a TV hot chassis for what reasons to put very high voltage on the chassis is just poor designing but it was common in arcade game monitors that if you hand was touching the chassis and your other hand was touching the circuit boards ground or oscilloscope chassis you would get a major shock. I don't know why the benefits of the TV designers to use hot chassis just doesn't make sense to me, any reasons why?
One word. Cost. Power transformers are expensive. Since there is already a big transformer inside for the high voltage it is easier and much cheaper just to add some low voltage windings to that flyback. For the end user it doesn't add any risk, just service people need to use an isolation transformer which any tech worthy if calling himself a tech already has and is using.
@@12voltvids But most EE techs say that only isolation transformers are Galvantic isolation, and that Non Isolation transformers don't have Galvantic Isolation. I'm not sure what inside the transformer is causing the transformers to be Galvantic Isolation, do you know?
@@waynegram8907 A full isolation transformers do not have a ground lug or ground pin on the secondary. Mine has a 2 prong cord and 2 prong outlet. 100% isolation. Some have the secondary bonded to neutral which is not isolated at all. Might as well not even be there.
@@12voltvids arcade monitors isolation transformers has a 3 prong cord/outlet primary and the secondary is 2 prong outlet going to the monitors circuit boards and hot chassis. I'm not sure why they design it to have a hot chassis having very high voltage on the chassis frame metal
Where do you find these transformers? I would like to try myself and to learn to connect devices to repair. And it seems to me wise, when I first an isolation transformer create or find. These transformers are somewhere in a or other device? Or where can you find them?
I bought the the one I have way back when I worked in the business from the electronic parts supplier (now closed after the owner passed), it was about 125.00 as it is a big one. Will handle 500 watts easily
12voltvids Thank you, for the quick response. Is there any other way to keep yourself safe? Or is the only way this transformer? Yes itself very well pay attention, but that's normal. We have 220 volt in Netherlands.
@@Repair5700 Remember you can still receive a jolt with an isolation transformer if you contact a ground on the chassis and hot on the chassis, but an isolation transformer will protect you from receiving a shock from any energized part on the device under repair and earth ground. Without an isolation transformer you can get a nasty shock. It also protects your expensive test equipment like oscilloscope. The scope must also be floating though, so no connection to earth on the scope. I plug my scope into the same transformer so it is isolated as well. An isolation transformer is a key piece of safety equipment that everyone working on electronics should invest in. It could save your life. It has certainly saved me from countless shocks or damage to test equipment.
What if we install an inline fuse of maybe 500 mah on the crocodile clip of the scope like those that comes on car stereos to help causing an accident to those who don't own a isolation transformer or simply forger to use it on a determinate moment.
Not that I am recommending this but...and if you do it, you do so at your own risk. The very first shop I worked for was run by a very smart, ex military electrical engineer. He didn't believe in isolation transformers. He cut the ground off his scope (that would be that big old 1963 HP that I now have) so the scope chassis was not directly connected to earth. He then wired up a small red light bulb, a little 5 watt xmas type bulb between the scope chassis and earth ground. This way, if the scope ground probe inadvertently made contact with an energized hot ground, there would be no sparks, no blown equipment, the little red light would light up. The red light was a warning that the scope chassis was HOT and not to touch it. Now that was him, for me, once I finished my training with him, and got into the next shop (Sony Canada) and the next one after that where I stayed for 20 years, I had an isolation transformer and would not service without it. I have an isolation transformer on my bench now, my variac is plugged into the isolated output, and that feeds my test power bar. Isolation is the safest, but cutting the ground prong will prevent you from blowing up your test gear or melting your scope probe. Just if you do that, and I am not telling you to, I am telling you not to, but if you do, remember the light bulb trick and you will know if the ground is clipped onto a hot point without sparks and the subsequent cursing that follows.
12voltvids No no, i never intended or tried to said the fuse thing was the solution or the way to get rid of the transformer ,but i do know it would help a lot to mitigate fire hazards or equipment damaged like you just said, i know the isolation transformer its important but i just was making a point in those cases when you don't have one at hand or taking meaurements out of the shop etc, also some or all commercial transformers come with the ground atached to the one lead of the secundary making it a neutral since they are intended for power conditioning purposes and some folks don't modify then to make it truly isolated or don't know so still i think the fuse thing or even better the lightbul trick should even be part of the osciloscope and be buil in already, heck should even be a code regulation i think.
That was great thanks mate. I'm a 3rd year apprentice electrician and am constantly trying to understand electricity. So current always wants to go back to the original transformer that it came from?
Electricity always goes back yo it's source. That is a closed circuit. It can't go back to another source. Regardrless if you are talking batteries or mains. In a battery you have a + and - terminal. Electrons flow from the - terminal, go through the circuit, and return to the + terminal. In mains you have your generator and load. Transformers are just a way to step the voltage up and down. The power company steps the voltage up to a high voltage for long distance transmission for 2 reasons. A higher voltage requires less current, therefore the conductor can be smaller, and there are always losses in the transmission line. These losses are less when dealing with higher voltages. The transformer that feeds your house is the last step in the transmission line from the generator. On the secondary winding one side is grounded in single phase 240V countries. In north america we have split phase 120V, so the center tap is grounded and there is an A and B phase. These are 180' out of phase with each other. If you connect across the 2 hot lines you have 240V. This is what ranges, HVAC, Dryer, hot water and heat uses. The danger comes from that neutral line, the center tap being tied to ground. Now either conductor, if it is grounded will complete the circuit, and becomes a potential risk for anyone servicing electronics connected to the mains. A proper isolation transformer has NO GROUND REFERENCE in the secondary winding. The primary side will have one side of the winding tied to ground through the grounded neutral, and of course the hit wire, but the secondary is floating. You can touch one wire and be grounded, and nothing will happen, because there is no complete circuit. No complete circuit no shock. Yes if you were to grab both the secondary wires then you will get a shock, bt not from touching a single wire and ground because the load is balanced. Now, if you were to ground one side of the transformer, well then the other one would be just as dangerous, because the hot side is no longer isolated. The real reason to use isolation transformer is to protect your scope and other grounded equipment. On non polarized old radios for example one of the power wires is connected to the chassis. If you happened to plug that radio in directly, and the side that was connected to the hot was the chassis connected wire, now the chassis is floating at line potential. Touch your grounded scope probe and sparks will fly, and at a minimum you will be buying a new scope probe, and possible a new scope. Plug that same radio into an isolation transformer and it is safe to connect your scope, just remember that as long as your scope is connected you are removing the safety factor for you. If you are grounded and touch a hot wire you will be the path to ground. I not only have my bench isolated, but I also don't have my scope grounded. I just found an old isolation transformer in my storage unit, so perhaps a tear down video of that one is in order.
Alot of what you just said I've heard before at trade school and from other tradies but each time I hear it it sinks in a bit deeper so thanks for that I appreciate it!
Joshua Caldwell Work safe around electricity and give it the respect it requires as it can kill you in an instant. I work at my day job around utility wires as I have to climb utility poles to hook up phone lines and fiber optic drops. I see contractors doing really dumb things that leaves me shaking my head at times. Like using metal ladders in the close vicinity of power. HELLO! Wood or fibreglass only for safety sake.
12voltvids thanks Mate yeah I did my first 2 years of my apprenticeship changing the overhead services from the open power lines to the point of attachment at the house end so I know exactly what you mean. I was either on a fiberglass ladder with insulated gloves or I was in an insulated bucket cherry picker. Our overhead open LV mains have 3 phases and a neutral (in Aus) Just one more question if I may but you said on the big trasmition HV lines that it carries a small amount of current because it's very high voltage but my question is that ohms law says if you increase the voltage doesn't the current increase? Its got something to do with power or something doesn't it?
No the opposite. For the given load as you increase the voltage the current goes down. So if you are drawing 100 watts at 100 volts it would take 1 amp. At 200 volts it would only dray .5 amps to provide that same 100 watts of power. Ohm's Law: States the relationships between current (amps), resistance (ohms) and voltage. Volts = Amps x Ohms Amps = Volts / Ohms Ohms = Volts / Amps Watt's Law: States the relationships between power (watts), current (amps) and voltage. Watts = Volts x Amps Volts = Watts / Amps Amps = Watts / Volts
My isolation transformer is isolated between primary and secondary but gives me 120v between secondary and house neutral. I’m in a 220v environment by the way. Isn’t this enough to get electrocuted or destroy the scope I wonder? I thought it was safe enough but after those measurements I’m getting worried. Is there also a faston connector on the transformer body and the maker suggested me to connect it to primary hot ground in order to shunt to ground parassital current... even with the ground connected to the primary it doesn’t change a lot and I still getting 120v between secondary phase and house heart. Ohmmeter still reporting hight isolation between chassy ground and the rest of the secondary output. That’s weird to me at this point... can you explain what’s the reason I’m getting those results?
Your transformer is not isolated. There is probably a center tap that is groinded. This needs to go. You should see 0 volts between either side of the secondary and ground, neutral or hot. You should only see voltage between the 2 secondary terminals. Anything else is not isolated and you can still get a nasty shock and blow up your scope.
I asked about the center tap to the maker and he told me that there’s just a sort of shield that need to be connected to ground... I give a try and isolate the cable that is connected to the chassis and that seems to come from an internal winding (don’t know if is the center tap or whatever...) thank you for the suggestions.
12voltvids here is the answer I just got from the maker: ...Two positive voltages to earth in an isolation transformer are absolutely normal, indeed it proves that the winding is isolated, therefore it does not have a neutral reference to earth. You will see that if you put one pole of the secondary to ground it is with that pole (obviously) at 0V to earth and the other pole at (about) 230Vac, but this turns out to be in practice a "first fault" that increases the risk for the user and therefore must be practiced only if a neutral reference is required on the secondary and only if adequate protections are arranged for the user who is no longer isolated following an earth fault.
@@ictrepairs6963 Huh? An isolation transformer will have no reference to any earth or neutral on the secondary. Therefore, if your secondary winding is not connected to anything there will be no voltage measured whatsoever on the output as the secondary is floating. If you tape your meter in ohms mode, you will see resistance when measuring the primary coil, and secondary coil. You will see infinite resistance between primary and secondary, and between secondary and ground, or neutral. If either of the secondary wires has ANY resistance at all to any terminal other than the other end of the secondary then the transformer is NOT an isolation transformers. Many so called isolation transformers are NOT because they pass the earth terminal through, which incidentally removes isolation. A real isolation transformer will have no connection on the earth terminal. Mine does not even have an earth terminal period. It has a 2 prong cord on the primary, and a 2 prong receptical on the output. I had to cut the 3rd prong off to my Variac, which is what is plugged into the transformer. 100% isolation. I have demonstrated this.
@@ictrepairs6963 I I have previously demonstrated, if t here is an earth connection, that is passed to the output then it is not fully isolated. There are many medical isolation transformers on the market that pass the ground through, and have one side of the secondary tied to earth ground. This defeats the purpose. and these need to be modified to restore isolation. A service technician, or engineers grade transformer has no electrical connection between primary and secondary.
I can tell you what will happen. You will loose your isolation. Neutral is strapped to earth ground. so tying one side of the secondary to ground, or neutral will effectively remove the isolation transformer from a safety perspective. You need that floating neutral, so that if you make contact with an energized conductor, that conductor will be pulled to ground and become the ground reference.
sir whether one should connect crt tv to isolation transformer and connect oscilloscope directly on main 220 v line and carry out the test or vice versa .which way is the better
My scope is connected directly to mains however my scope had had the ground (earth) prong removed from the cord. My scope floats. If you don't want to remove the earth pin then plug it into the isolation transformer as well. The whole point if using isolation transformer is safety while servicing and that means no equipment under test can be earth referenced. It has to float so that an accidental touch to live circuit will not result in you becoming the complete path to ground. Even if you are grounded the unit under test is isolated.
Did people really told you that you get no protection using an isolation transformer?, man, what kind of moron would say that? Great explanation as always.
There are those that will argue that connecting your grounded scope removes protection. It doesn't remove protection. You can still get a shock with an isolation transformer if you contact 2 different potentials on the circuit.What an isolation transformer protects you from is a direct line shock with a return to earth from touching an earth and live circuit, because the reference to earth is removed by an isolation transformer. The argument is that if your scope is grounded you restore that ground, and then you can be shocked.Partially true, yes you restore the ground reference if your scope is bonded to earth, and that is why it is safest to unbond the scope from earth as well.What it does, if your scope is bonded to earth is remove the dead short line to ground if your ground lead gets connected to hot, because the hot and neutral is floating, so the hot will be pulled to ground potential, and no sparks.If you remove the ground pin on the scope then the scope will not provide a ground reference, and you are as safe as you can be. Never remove the ground pin on a scope without using an isolation transformer though, because if you do, and the scope ground lead comes in contact with a hot circuit the entire scope chassis will become hot, and if you were to touch the scope chassis, you could become the path to ground :(That could ruin your day.So, to recap the lesson, for safety. No earth ground on the scope, and all equipment under repair plugged into isolation transformer.FYI I plugged my scope into a grounded cord specifically for this demo, because if I didn't, when I connected the light bulb between hot and the scope ground it would not have lit up, but my scope chassis would have become live. I never have my scope grounded.
this is also an issue if you use your scope analyze your mains if you want to do this without an isolation transformer use an inverted that is not grounded same result no ground the grounding works great when our hands are not inside the device when our hands are inside a device the ground is a threat but even standing on concrete floor with shoes on you can still get a nice a zap if you have any amount of oil on your shoes or if the concrete is wet
My bench plug is isolated from ground, and neutral, as is my scope. It is the safest way to work on equipment. I would never work on any equipment with isolating it, and I still practice safe operating procedures, and that includes keeping one hand in my pocket, and wearing CSA certified footwear at all times when working in the shop.
A grounded 1:1 is not isolated. You can remove the bond to ground and float the secondary winding to make it an isolation transformer. These type are usually used in medical devices where they what to isolate from mains connection but need to remain earthed. They are not a serviceman isolation transformer until the earth bond is completely isolated.
Somebody is skipping ahead because the very first thing that shows up after the intro is guess what? A schematic showing what an isolation transformer and an explanation on how it works and why you need one.
@@12voltvids Sorry, I did see that schematic... I do see what you were trying to illustrate by using the light bulb and isolation transformer but got a a bit lost trying to follow what you were connecting to what
No, but when you are working on a hot chassis you don't want to be that path to ground. With an isolation transformer you allow your equipment under test to float isolated from both earth and the live wires so a short to ground either through s scope probe or you won't harm you or your test equipment.
@@12voltvids But why is is only safer when working on electronics? Why not for all appliances? Say for instance you have one of those dodgy Chinese rechargeable camping lights (that Big Clive has featured), where the USB outlet becomes live at mains voltage whilst the unit is charging. From my understanding of your explanation in this video, if you plugged the light into an isolation transformer and touched the USB port, you wouldn't get zapped, but if you plugged it into a regular socket instead you certainly would.
@@man_eating_monkey Yeah you could plug one of those dodgy camping lights with no isolation into an isolation transformer and it would be safe. That camping light should have had a transformer inside. They went for a capacitor dropper.
Mine is a Hammond if I remember. Allison manufacturing also makes them. Just be sure you get one that does not have a pass through ground. 2 prong cord only. If it has a ground prong on the cord it must be cut off so there is no bond to ground whatsoever. This is very important. If there is any bond to ground then the safety provided by an isolation transformer are lost.
@@12voltvids I got a TrippLite IS-1000 I would like to plug in front of all of my pro audio recording gear. Can I just use a couple of cheater plugs (one on each side) to make it truly isolated? I see some people doing modifications to remove the secondary ground to neutral, which I what I was going to try until I saw this video. Thanks in advance!
@@crossdynamix7176 got exact same situation and query as CrossDynamix. did the mod,removing grnd from secondary neutral, but am stuck in the same place as CrossD. If the secondary hot and neutral wires are floating then how would passing ground from mains counteract the separation of ground from neutral on the output? Furthermore, would severing connection to output ground be enough to float the output entirely, without disconnecting chassis ground from primary? Thanks
Well it isn't like I didn't know they were live.You don't see me touching them, and there are no animals, or small children around. Nothing wrong with my handling of them, you do notice that I am making sure they don't touch anything.
No negative and positive on AC. Neutral is the return (grounded) side, and hot is the supply. On the output transformer there is no neutral as the secondary is not connected or referenced to earth ground. Both sides float, so either side could be grounded and not cause a short to ground because it is totally isolated from the supply.
@@12voltvids ahh ok thank u when u say hot supply what do u mean by that and thanks for replying larrning about isolation transformers before hooking up to crt arcade cabinet
@@gamingo_gguyverx6812 The mains supply at the wall plug will have 1 "hot" wire and a neutral which is at ground potential, but not ground. It is the return wire that runs back to the transformer. The ground wire is just that, earth. Now the neutral is also earthed at the transformer as well, but there will be currents on the neutral wire and not normally on the ground wire.. If you take your meter in AC mode and put one probe in the ground port on the plug and then measure the other 2, you will see one measuring 0 and the other showing the line voltage, 120 in north america, 240 in europe. In north america the 2 blades for the plug are different size. The larger blade is neurtal, and the smaller one is the hot side.
I just discovered your video and I know it is 6+ years old now. Thank you very much for the time and effort you put into your production. I have never seen as good of a schematic in terms of simplicity and thoroughness of the relationship between the various components found in the overhead power lines and the transfer of that power to a typical home. I will be committing your schematic to memory. And your demonstration of the isolation transformer was the best I have yet seen. Well done & thank you again.
I have videos older than this that people still find.
Sir high respect for your knowledge and professional dedication.
Thanks very much for this, you filled an essential gap in my safety knowledge.
That is the exact explanation I was looking for! So simply and yet well layed out; thanks!!!
Good video. I took my isolation transformer apart right after I got it to make it completely floating as well. There seems to be a lot of arguments back n forth on whether or not to float the scope though.
Excellent demonstration and explanation...Thank you sir....thumbs up...
have used isolation transformers all throughout my career! They are an absolute necessity when working on hot chassis tv's! I have a few. my best ones are the ones i have built into my variacs
Mine is ahead of my variac, so it accomplishes the same thing.They are the first piece of test equipment a tech needs to buy. You can't take chances with electricity.
Isolation transformer are bit hard to find....maybe it's more expensive to manufacture.
I have found used ones on Ebay. Apparently hospitals use them.
Be careful medical isolation transformers are not really isolated. Check it with a meter before you trust it. Watch Todd Harrison's video on how to modify one. /th-cam.com/video/11Yve2ijWyk/w-d-xo.html
This is a great video.... I've been going back and viewing some of your older stuff... this is really really excellent. Very clear.
Hello
I would like to thank you for this video ! I needed to watch it several times to understand (well) process, before doing it by myself...without a big bang in the cellar
In France, 230 v, and 30 ma security on the line...But with a maximum care i tried to connect mys scope Rigol 1102, behind my 600 W transformer. So, no fire, no explosion, and i have always the cellar too
Many many thanks cause it was difficult for me to prevent misunderstanding around ground, secondary line, and scope.
That's ok now and very happy to do this in real life, after many tests to control all connections on the transformer and to verify all separations between them, i decided to run experiment, and i could see (with happyness) the same result on my rigol and the beautiful waveform for the secondary 230v AC
So this test makes me understand some rules and gives me basis for the future
GREAT !
rgds Eric.
You correct that misapprehension that some techs have, who say that they do not need an isolation transformer when working on a valve guitar amplifier, because it has it's own transformer in its power supply and is therefore 'already isolated'. They fail to understand that the secondary of the PSU transformer is grounded, and thus not isolated from the mains.
They need to watch your well-informed video to put them right.
yes, that how every non ground referenced transformer protect you if you touch one of the outputs. That how two mains powered devices protect themselves from shorting the mains when you connect one to another.
But you still have to remember, that floating voltage might be dengerous if you close the floating loop
Here in Europe we have 230V in every socket, so hot chasis are not that common
but you still expected to use insolation transformer for measurent on serviced equipment. To not blow up your scope or yourselves.
One thing you forget to mention
Insolation transformer not only insolates you if you touch one output, but also limit the power you could recieve if you close the loop to the power output of the transfotmer, so if you close the loop it won't be the full breaker current, but only its fraction. Closing the loop on the output side also would not flick your mains breaker if the transformer is not some kind of behemoth, so you would be expected to install one breaker on the output in case of catastrophic failure of serviced equipment.
a grounding at 230v would require much thicker ground wires and small shunt on the neutral its doable for low power devices such home audio equipment but not on high power motors and still have the same level of safety
Every tech should know 👏
Thanks for the demo. Although here in the UK we have a slightly different arrangement with the mains supply (just three conductors provided from the supplier -240v Live, Neutral and Earth) all the same safety precautions apply, as do your comments on isolation.
Strangely enough I was looking at mains isolation transformers yesterday and I think I'm going to get one with a combined variac, essentially an AC power supply, but one with a ground isolation switch so I can control whether earth ground is connected which better suits my needs.
Earth does not provided by the DNO
good work, like the refresher course , it made me want get my my old text books out again also may me sad ,i took apart my Tektronix 2445 about a year ago and still have not found the time or the energy to put back together .
The only difference in the uk is the distribution transformer is massive and it often lives in a brick building, it supplys many streets.
Also its only 240v tappings, same idea though.
ive known about isolation transformers for a long time.
We cant do your test in the uk, our earth leakage or/and rcd breakers wont allow power direct to earth, they trigger and cut the supply.
We have GFI breakers here too. They are used on outdoor outlets and circuits where the outlet Is located around sinks. We also have CFCI wall plugs which are the same thing in a wall plug you it can be reset without having to go to the breaker box. I know in the UK and many other countries you have 240V single phase, so 2 conductors and an earth ground. Line and Neutral.Here we have 240 with a center tap neutral so we can have 120 phase to ground, and 240 phase to phase..My garage heater that you hear running in the background is a 240V unit. Only 3 wires, 2 hot, and earth ground.My hot tub and dryer on the other hand has 4 wires. 2 hot, plus neutral and earth ground. The phase to phase powers things like the heating element, and then 1 phase to neutral for things like the control panel, lights ect.1 distribution transformer typically feeds 12 homes. We have underground facilities in some areas where the transformer is mounted in a big steel box on the ground. What is your 3Phase voltage there?Here it is 208V phase to phase. They just use the center tap and 1 leg so between any phase and neutral it is 120, and between phases 208.
Pass i dont know the full info, 400v for 3 phase, as far as i can remember, only businesses tend to use 3 phase.
Houses dont have access to 3 phase, no need.
At 240v we only need half the current you get from a 120v outlet to do the same job.
We don't have access to 3 phase either. Mostly business or apartments were they need to run elevators. Motors much more efficient on 3phase.We have 208/3, and then it goes to 600/3 for larger businesses. That is what feeds the CO I work out of.You are right at 240 only half the current, but it is a moot point because you pay for KWh, so the cost is the same to operate. My electric car charges on 240, but I can charge it on 120 as well if I need to, but it takes all night on 12 amp 120V, and only 3.5 hours on 15A 240..
We also have an odd way of wiring up 13 amp mains outlets, i think just after the war we had a shortage of copper, or it just cost too much.
So rather than using spur wiring for every outlet, we started using a ring main from the fusebox all around the sockets then back to the fusebox, uses thinner copper wire.
I personally like spur wiring, i think canada and the usa still have that, but i cant be sure, i cant see that far LOL :-D.
We use spur wiring for electric showers.
And radial wiring that jumps to every light fitting.
My brain still locks up when i see an american call black "live", surely red would have made more sense, red meaning danger in the animal kingdom, as we are also animals.
Red and black is used.Remember that we have split phase 240V.For 120 runs the wire color is Black (hot) and White (neutral).For 240 single phase such as for water heaters and baseboard heaters, again only 2 wires, Red and Black (both hot) and of course the bare earth conductor.For 240V with neutral, which is used on kitchen outlets, RED Black and White. Outlets are wired Black to top outlet, and Red on bottom.That way 2 appliances can be run simultaneously on a 15 amp circuit.Also there is the sheath color. Wire designed for 240 single phase is red, whereas the rest of the wiring is white.For 3 phase they use Red/Black/Blue for the hot, and White for neutral.
12voltsvids, You are very wise and understand these power systems at a level I have not seen from anybody outside the power distribution industry. So don't think I'm trying to degrade your wealth of knowledge because I'm not. Your first light bulb test was with no isolation and it showed that clear danger. Your second light bulb test showed how a technician isolation transformer protects you and your equipment. I'm not talking about either of those situations. I'm saying once you connect the scope ground clip to your TV chassis your technician isolation transformer is 100% not isolating you from high energy any more. I now see how your system is wired in Canada and the problem is clearly the same as I have tested in the USA. Don't do this test but! Power your TV with the technician isolation transformer, then connect your ground clip from your scope to either the line or the neutral on the TV to take normal measurements with your scope. At this point your scope is safe, just as you showed in test two, but you are no longer protected by the isolation transformer as the scope ground has strapped one leg of your isolation transformer to your home's ground system. If you reach out with one hand and touch any part of the TV circuitry that is on the opposite line side with respect to your scope ground clip and your isolation transformer you will get zapped "by the energy delivered by the isolation transformer's secondary side through your home's grounding system" just as if your TV was connected directly to mains and you were getting a zap from the mains. Yes, some point of your body has to be grounded to your home's grounding system or just good old ground under your feet if you don't have rubber sole shoes, but that's just as true with direct mains as well. Meaning your not any more safe working on the TV once the grounded scope is connected then if you didn't use the isolation transformer in the first place. This is the scope/DUT/IT testing I'm trying to warn people about. People get injured by this type of DUT setup testing all the time because they think they are isolated from mains power, which they are, but this normal testing situation exposes the technician to 100% exact same danger from their isolation transformer energy just as if it was mains energy or just as if it was a Hospital grade isolation transformer as you clearly noted in your drawings showing the secondary strapped to chassis ground. Trust me, do the test as I describe here which is a normal way people use a scope on a DUT that is isolated but please use a light bulb not your hand. ;)
Yes I know that if you connect your "earthed" scope to the chassis, and then you touch a hot point on the chassis while you are touching ground you will get zapped, but you don't need to ground the chassis to accomplish this.If you are touching a ground point on the chassis, such as a shield cover, and you touch an energized point on the chassis at the same time you will still get zapped.The isolation transformer does protect your scope from accidentally creating a short circuit. I connected it to both sides of the line, no sparks. Sure I am now tying that side of the transformer to ground, and if I was poking my fingers around in the set while standing in bare feet on wet cement I am asking to get bit, but if you are following safe servicing procedures, and that means wearing insulated shoes, and keeping your free hand away from anything conductive when working, a pocket is the safest place, you are safe. At least you don't have to worry that a hot chassis is going to blow your scope probe up. When I work I normally have my scope floating free as well. Safety first. I have extensive electrical training. Not just in this field, which I have done for 32 years, but I work now for a major telecom, so I deal with working in proximity of secondary grid power every day. In my career in the business I was zapped twice in 20 years. One time because my assistant didn't know not to talk to me while I was working and I was distracted. (This is why you should never talk to a linesman that is working, as working around electricity takes 100% concentration) The only reason I wasn't hurt was because I followed safety procedures. One hand in pocket, rubber soul shoes. No path for electricity to travel across heart. Just like a bird sitting on a wire.
Our local Target had a Toshiba TV similar to that one for customers to know they are on CCTV when they walked in. Ran for about 20 years 24x7 until they decided it was a little outdated in looks for the entry way.
Thanx for sharing , very informative
why don't you touch the secondary wire and ground with your hands instead of the lightbulb to demonstrate the safety of an isolation transformer. that would impress more .
Nice explaination, Now, I made already
GOOD FAST EXPLAINATION THANK YOU !!!
Why does virtually every isolation transformer on Amazon have grounded receptacles? I totally get what you're saying which begs the question as to what the value of a grounded isolation transformer is. What are they used for?
That defeats the purpose.round prong needs removing on those for sure. A proper serviceman's isolation transformer like mine has a 2 prong cord and 2 prong receptical on the transformer. Actually it has 3. The secondary has 3 taps, 90%, 100% and 110% outputs. For 120 in that makes the 3 outputs 105, 120 and 135 approximately. I use the high side and rum it into my variac so I can go from 0 to 150 volts.
Cool video again, sir. Hope the festive season was good to you.
Thank you so much for clarifying this concept.
You said something at both the beginning and end of the video that may have "clicked" in my head. Either side of the isolation transformer can be pulled to ground. WHAT? Really? I'm interpreting this as, if you touch one side of the isolating transformer to ground, you aren't forcing voltage to or from the ground but instead you're stabilizing one of the transformer legs, causing the AC voltage fluctuations to occur only on the opposite leg. So if I ground wire 1, then wire 1 becomes stable and wire 2 carries the oscillating AC voltage. If I instead ground wire 2, then wire 2 becomes stable and wire 1 carries the oscillating voltage.
I've been trying to figure out how any isolation transformer works, because I feel that the voltage is just going to go through you to ground. I never thought that maybe the ground is more powerful than either leg by itself and will force it to stabilize.
Or maybe I've thought of the earth as a giant capacitor capable of endless dumping of electricity, and that might not necessarily be the case. Argh. Now I have to rethink everything.
My hand wound isolation transformer does not pass enough power. Does it need a resonant capacitor in series with primary to match the 20khz AC input? I even tried impedance matching that did not work either.
some years ago I bought a hallicrafters S38 and was told I should run it off a isolation transformer. I never did that but I think I see why I should and will get one.
I also have a Hallicrafters, will have to dig it out and see the model. I believe the one I have has a power transformer. It works too, at least it did the last time I used it.
Hi 12voltvids ,I thinking that you have small mistake (but very dangerous!! ) whan you connect the oscilloscope probe ground (which is main ground) you referance the Isolated side of the transformer to the ground again so you canceling the Isolation!!.
I am using the two oscilloscope probe with math function and not the oscilloscope probe ground!!
haimt1464
yes connecting a grounded scope probe will ground the isolation for sure. This demo was to show that accidental contact with live side will pose no risk because the live side would be pulled low. there will be other points on chassis that would then become energized. this demo was done specifically for this demo to show that the isolation transformer does indeed provide protection against accidental shorting. ultimately you want your scope floating as well. My scope has no ground connection normally. so connecting it would give me no light regardless if I connected the ground to line or neutral, (without transformer) however this would bring the scope chassis to line potential because it is floating which is very dangerous. with the isolation transformer protecting the unit under repair, even if your scope ground was on a line connected reference, the scope would not be energized. So for safety, an isolation transformer is mandatory AND the earth ground prong on the scope needs to be removed.
I can demo this too if people want to see my scope chassis go up to 120 v. that was the purpose. with the scope grounded and the bulb connected to line it lit up. if the ground pin was removed the bulb wouldn't light but the scope chassis would be hot. that is very dangerous. on iso transformer and the ground pin on scope removed, unit under test is fully isolated and floating. this is the only way I work.
Very good demo!
Can I please ask you a question... How can I generate composite video using basic logic chips? I.e 74HC series. Should I just build a counter for the pixel clock, and then derive the sync pulses from there by counting clock pulses?
I love your videos. Youre one of the best on youtube... Please keep it up.
I used an RCA CD22402E which is a sync pulse generator for TV camera.That Is the heart of my macrovision scrubber.
Hello, I read that measuring with an oscilloscope, you need an amplifier, you need galvanic separation, I ask from what point of view, when today's amplifiers have only 2 wires. Thank you for any knowledge
I just got an old VIZ Isotap isolation transformer. The isolated output is 2 prong. I have 2 questions: One, if I am working on a modern tube amplifier which has a three prong plug, do I still need the isolation transformer? Two, if I do need it; should I use the infamous 2/3 prong adapter to plug it in? I can't think of any other way to do it.
So you are saying remove the case or any other ground from the "line" side also and not just the receptacle (plugs) side?
I bought a new isolation transformer for my 14 year old future electrical engineer. I am wondering why I bought it! Perhaps because I have seen so many TH-cam videos on I/T’s. Such a gadget will not prevent electrocution when working on 240 vac projects. It will only protect the scope and other equipment. I use a RCD (residual current device) also referred to as a (DCD, differential current device on all my circuits, in fact 22 of them. In Australia we have 240 vac and the common ground (neutral) is tied to the ground stake as a safety measure, same as in many other countries. If I am working on any 240 vac equipment and I for some reason touch the active wire, the power goes off within 30 m/s when a differential of 15 mA is detected. So the scope is off and I am safe. Why do I need an I/T ? I am going to test this out on my own equipment by shorting something out when connected to the scope. I paid $250 for the I/T. The RCD’s cost about $15. I see someone suggested a $400 device on the probe to protect the scope, yes, but that doesn’t protect your life. I am not getting it, can someone please explain to me why a $15 gadget will not only protect the scope and my life?
A proper isolation transformer has no reference to neutral or ground on the isolated side. Both prongs on the plug are isolated. If you touch either side while grounded you will not receive a shock because there is no return path to ground. If you touch both at the same time then you will receive a shock. If you grab one wire on one hand and the other with the other then you have completed a path across the heart and you could end up electrocuted. The big safety factor is accidental shock. That is you touching something live (mains connected ) and the current running through your body and out your feet into earth. This is where the isolation transformer protects you. It also protects your scope from damage. Your ground fault interrupters are good, but when you have a fault in the device you are working on and the breaker trips every time you try to power it up for testing you become very frustrated 😡. Isolation transformer keeps you safe from accidental shock. Your GFCI by the way I only protects from ground leakage. You will still like with an isolation transformer get zapped if you grab Live and neutral. I can speak from experience. I wouldn't be commenting here had it not been for my transformer. When I was as working in the business a cable tv (grounded) connector dropped off the tv I was working on and onto my forearm startling me. I jumped and in the process contacted a hot chassis directly connected to power. I could have received a major shock but because the tv was plugged into my isolation. Transformer i didn't as much as receive a tingle of voltage. Nothing. Also when the connector fell into the chassis it didn't short out again because the set was isolated.
@@12voltvids Thanks for a very lengthy explanation all of which I knew. But please explain to me why a RCD which will save your scope and other equipment as well as your life isn't better than an I/T,,, thanks.
@@cookieboi4449 you will still become the conductor until the current is cut off and that jolt is enough to send your heart into fibulation. They are safer than no protection but you still get zapped for an instant of a second until the circuit trips. With an isolation transformer there is no current flow at all, you float just like a bird on a wire.
great video. besides adults, good for kids getting into electronics.
are there additional specs for the transformer, current , watts etc. and do you use or can you use 240v also. thanks again for all your work really enjoy the learning, also anyplace special you get these transformers from? ty j
Isolation transformers are available from transformer manufactures for both 120 and 240 volts. You should be able to get them from electrical suppliers or order them from the manufactures such as Hammond Transformer, Alanson Transformer ect. You pay more for large capacity. Mine is rated at 600 watts, so I can operate the largest plasma sets on mine no problem.
Where do you get one??? I've been searching and I'm only looking for 12vac
You would get the same exact result if the secondary of the isolation transformer DID have a ground to the case as long as the neutral isn't bonded as well.
It's done this way in every single operating room in the US. There is still a ground(bonding) jumper that puts every piece of stainless equipment at the same potential. This ground however is NOT bonded to the secondary winding AT ALL. You can touch a hot lead and touch ground and 0 current will flow.
Take your hot from the secondary of the iso transformer put it on the bulb, take the wire from the neutral side of the bulb and ground it. Does the bulb light? No.
You can earth equipment for sure. The problem is many so called isolation transformers also tie the neutral side of the secondary to ground and that defeats the purpose.
@@12voltvids if that's the case it shouldn't be called an isolation transformer because that is in fact defeating the purpose. In that case it's simply a 1:1 transformer and probably some type of false advertising.
Eta- the drawing made of the first grounded type isolation transformer is in fact a fully isolated transformer that will completely isolate you from earth or any grounded surface- even with the ground wire as long as it's not bonded. Thus is exactly how operating room iso systems are designed and wired. It's MORE dangerous to not have that bonding wire.(Again, it absolutely can not be bonded to the winding though)
@@xprocharged1
My isolation transformer has no ground. There is no ground prong on primary or secondary. 2 prong cord on primary and 2 prong receptical on secondary. Totally isolated.
@@12voltvids I get that. My point is you're JUST as isolated even with a 3 wire / 3 prong setup. It can be argued, and has been, that an isolated system with a ground is safer than without due to capacitive coupling and leakage current. Leakage current is much lower when a ground wire is used- hence the reason they are done this way in operating rooms where current that a normal person couldn't even feel could easily kill an infant or someone with their chest opened up with metal instruments touching their heart.
My Isolation I made works perfect, no earthg grounds, but i was thinking could I just ground the chassie in case of a faulty primary so as not to receive a shock in such a event?
If the chassis is not grounded it is double insulated. Do not ground it.
Excellent explanation and demo! Not sure if it has been brought up earlier, but how come outlets in North America are polarized (one pin is wider than the other)? On AC it shouldn't matter what orientation the plug has. Most of my friends that see some of my import USA stuff and notice the outlet on my power strip/transformer always ask "Why on earth is it like that? It shouldn't matter since it is AC."
Depends on the type of device being powered, but polarized plugs generally ensure that it is the hot/active lead that is being switched and not the neutral. They do this for safety reasons.
Good question, and to answer it for you it is for safety.Many items they connect the chassis ground directly to one side of the AC line. The wider blade is the neutral side and the smaller one is the HOT.This ensures that the chassis is tied to neutral, and not the hot side.Also, if there is a power switch in line, you want to ensure that the hot side is switched and not the neutral side as that would leave AC still live inside the device. Operation wise it wouldn't matter, but if one of the capacitor that tie say the antenna ground to the chassis were to short and the hot side was tied to the chassis ground, well you can see that the antenna connector would be now be hot. Parts like the tuner shield would be directly connected to 120V.Not everything is polarized. None of the power supplies for equipment I install at work is polarized. This is because it goes to a switching type power supply, and both sides of the DC output are isolated by transformer, and the entire AC side is double insulated.
Interesting video.You should show a schematic diagram connection between tv, scope and bulb.
Does that means that after the insulation transformer there is no Live/Gnd anymore? I mean, are those two wires after the transformer exactly the same, or do is there any difference between them?
There is no difference in the large scale. If you view it in any tiny time unit there is voltage between them that varies -170...+170 volts
I have a powervar troital transfer power conditioner sometimes i hear a loud hum for 2 seconds is that it leveling the voltage?
Hmm, a digram of your demonstration would have helped. I can't tell from what you're doing.
Hi, just wanted to ask you a question about AC outlet dirty power. I'm a musician the several guitar amps in my house that I use. I seem to have a problem with the these amps displaying high frequency harmonic distortion. I've tried everything to alleviate this problem, but nothing seems to work. I heard of an audio isolation transformer called a Topaz ultra isolation transformer 32 series that you can plug your equipment in and it will filter out any noise problems. Do you know if something like this would be a good idea to buy? Thanks Michael Newell from Niagara Falls, Ontario
I'm having similar issues with my recording studio setup. ugly mud creeps into the guitar tracks as soon as any gain is added. I've tried everything - power conditioners (got the Panamax), UPS online double conversion (TrippLite), and now about to try isolation transformer (got the Tripplite IS1000). I have seen other videos that modify the iso transformer by removing the ground to neutral on the secondary... but is it as easy as using a cheater plug on both sides?!?
In Germany every fuse box has a ground fault circuit interrupter, so when a short occurs, the power automatically cuts. Do you not have this in the US?
We have ground fault interrupters but they are only required for outdoor plugs and plugs located in bathrooms or around water.
Thanks. So in plain english you're protecting your scope's integrity by isolating the input of the device under test by means of an isolation transformer. You're not removing ground in the input of the scope, or feeding the scope from the transformer, that is what many people typically would think should be done. Right?
No I am isolating my work bench from Earth ground. The secondary of the isolation transformer is not referenced to earth or neutral at all. My scope also floats.
@@12voltvids Oh, OK with the first part of your answer, but you mean the "measure side" of the scope floats?, or you also removed ground from the scope's power input. I read many times scope's ground (in the power side) shouldn't be neutralized because in that case scope will be floating at the same voltage level of the measure side, no matter were no chance of make a ground fault, but chasis therefore we also will be floating at high voltage. Please your final comments.
@@ramirosuarez9537 yes scope floats so yes the chassis could be hot but remember it is isolated from earth ground so you won't get a shock even if you touch it. Just like a bird on a wire.
@@12voltvids Thanks a lot for confirming that. Best regards.
My isolation transformer was shipped to me grounded. I think all in the USA are shipped that way to protect the manufacturer and vendor. But, there were no docs or warning labels stating that it was grounded to mains. Seems very wrong. It does not provide isolation.
Have heard that the scope should remain mains grounded. Confusing situation.
Surging Circuits
I removed my scope ground and it sits on a wooden bench.
never remove scope ground unless you are working with an isolation transformer. doing so could create a very dangerous situation as the scope chassis could become energized. at least on isolation transformer the "floating" scope is never going to become mains energized. it could become DC energized if you are working on a power supply on the DC side of the transformer so services need to be aware of this. I actually have a ground wire that I can earth the scope if needed but usually I don't as I am aware of what I am doing, and take every precaution when working.
+Surging Circuits There are different types of isolation transformers though; ie medical and audio isolation transformers for example will be mains earth referenced and will usually have the output neutral tied to ground, and they are supposed to be grounded for safety. "Isolation" in this sense is being used to protect sensitive equipment, but you have to modify them to make them "tech" isolation transformers.
CORRECT. These type of transformers are there to limit spikes and noise on the line. The pass through ground and bonding of the neutral to earth ground on the secondary removes any safety from shock factor. You need to cut the ground pin, and remove that bond from the neutral to case on the output plug.As I said in a previous message measure with a meter to be sure.
Question regarding the information about the ground prong, at 10:24:
If making my own isolation transformer setup (off-the-shelf transformer per se, but making an enclosure for it with switches and fuses and things), would it make sense to tie the "ground" prong of the outlet to the neutral side of the outlet, as long as neither of them is tied to anything actually referenced to earth ground? If not, why would that be a problem? Like, I'm thinking it would be a "ground" that floats with the neutral side, and the live side would have 120v between it and either the neutral or the "ground" (I keep using quotes to emphasize that I don't mean actually ground-tied), but could also be (real-)ground referenced thus making the "neutral" and "ground" effectively live... would this be reasonable? Or should I just leave it completely non-connected?
My thought is to do this for DUT's that have a grounding plug, to just give them something to connect to...... But I'm not entirely sure if it's reasonable. Any input is welcome! Thanks for the video!
A serviceman's isolation transformer has 2 wires. Hot and neutral only. No ground. The ground prong can not be connected to a thing or you are defeating the safety the isolation transformer gives you. Mine is a commercial transformer that cost a bloody fortune. It has a 2 prong non polarized line cord and just a 2 prong secondary receptacle. Can not plug a 3 prong plug into it. Have to cut it off. Mine is a Hammond and it originally cost about a buck a watt. (500 watts, 500.00)
@@12voltvids I don't want to cut off the ground prong on my DUTs, as I'll want to use them safely when not under test, as well. I know there are only two output wires from the secondary (well, assuming a single transformer voltage, though of course there are multi-tap isolation transformers, too), the question is, would it make sense to wire the "neutral" (though that's arbitrary, as both sides are floating) wire to the "ground" wire of the output socket -- not grounding it, it's still galvanically isolated from the mains, it'd just be that if, say, the DUT had a chassis ground that connected to what it expected to be an earth ground, that "ground" would be connected to one side of the secondary (which we'll call the neutral).
Does that somehow lose safety? If so, how/why?
@@DavidLindes a short extension cord solves this delemina. You can get short 1 to 3 foot cords. The ground pin comes off easy. Then you can plug your DUT into the 3 prong receotical on the short cord.
@@12voltvids ok. But is there any danger in shorting the "ground" pin to the neutral side? Seems innocuous to me, but I wonder if I'm missing something.
@@DavidLindes you don't want to connect the ground pin to anything. It is totally open. With the neutral unbonded it will float as well. Your meter will still read accurately on the DC side of the power transformer. If measuring on AC side then one probe goes to neutral not ground.
Wouldn't it be simpler to test both sides of the isolation by touching one lead to either side of the isolation transformer to line ground or neutral?
I was demonstrating how it works. To show that the isolated side is fully isolated from the line. Naturally you wouldn't test to line, you test to ground. The line is isolated. Testing to line would remove that isolation.
Q) Since my isolation transformer is mains grounded, I have used a 6inch pigtail 2-wire extension to connect the device I'm working on to the iso-transformer. Do you see a problem doing it this way vs opening the iso-transformer and removing the ground connection? Thx.
That will work just fine IF, the plug on your isolation transformer is totally isolated from the earth ground.Take a meter and put it in ohms mode.Put one probe on the ground lug on the power cord to your isolation transformer. Then measure to both prongs on the output plug.You should see infinite resistance. If you measure anything between the ground terminal on the power cord and either of the power prongs on the output then the secondary is strapped to the earth, and you have no protection. You need to cut the ground prong off the power cord in this case to isolate the transformer from earth ground.
Thx good to know this!
So since I salvaged my transformer from my Karaoke Machine, is there a way that I can use my own transformer as a isolation transformer when servicing the electronics?
Need to be a 1:1 ratio not a step down as most devices would have.
Climbing a pole for a living sure beats swinging from one. ;)
Thanks for the video. Very informative.
bootersdad my ex girlfriend is a pole climber... The union pays her really well but for some reason, it’s always in $1 bills... 😐🤷🏻♂️
Don’t think you would make much swinging on a pole....then again there are some weird people out there...
Could you please post the link to your recent video where you showed how to connect a light bulb as current limiter?
I tried to search for it in your videos but I did not find it.
Thanks!
You mean this one:
th-cam.com/video/vXlWSKU_lPI/w-d-xo.html
Yes, thanks!
Some TV's use hot chassis, I'm confused why they would even want to make a TV hot chassis for what reasons to put very high voltage on the chassis is just poor designing but it was common in arcade game monitors that if you hand was touching the chassis and your other hand was touching the circuit boards ground or oscilloscope chassis you would get a major shock. I don't know why the benefits of the TV designers to use hot chassis just doesn't make sense to me, any reasons why?
One word. Cost. Power transformers are expensive. Since there is already a big transformer inside for the high voltage it is easier and much cheaper just to add some low voltage windings to that flyback. For the end user it doesn't add any risk, just service people need to use an isolation transformer which any tech worthy if calling himself a tech already has and is using.
@@12voltvids But most EE techs say that only isolation transformers are Galvantic isolation, and that Non Isolation transformers don't have Galvantic Isolation. I'm not sure what inside the transformer is causing the transformers to be Galvantic Isolation, do you know?
@@waynegram8907
A full isolation transformers do not have a ground lug or ground pin on the secondary. Mine has a 2 prong cord and 2 prong outlet. 100% isolation. Some have the secondary bonded to neutral which is not isolated at all. Might as well not even be there.
@@12voltvids arcade monitors isolation transformers has a 3 prong cord/outlet primary and the secondary is 2 prong outlet going to the monitors circuit boards and hot chassis. I'm not sure why they design it to have a hot chassis having very high voltage on the chassis frame metal
@@waynegram8907 one word. Cost.
Where do you find these transformers? I would like to try myself and to learn to connect devices to repair. And it seems to me wise, when I first an isolation transformer create or find. These transformers are somewhere in a or other device? Or where can you find them?
I bought the the one I have way back when I worked in the business from the electronic parts supplier (now closed after the owner passed), it was about 125.00 as it is a big one. Will handle 500 watts easily
12voltvids Thank you, for the quick response. Is there any other way to keep yourself safe? Or is the only way this transformer? Yes itself very well pay attention, but that's normal. We have 220 volt in Netherlands.
@@Repair5700
Remember you can still receive a jolt with an isolation transformer if you contact a ground on the chassis and hot on the chassis, but an isolation transformer will protect you from receiving a shock from any energized part on the device under repair and earth ground. Without an isolation transformer you can get a nasty shock. It also protects your expensive test equipment like oscilloscope. The scope must also be floating though, so no connection to earth on the scope. I plug my scope into the same transformer so it is isolated as well.
An isolation transformer is a key piece of safety equipment that everyone working on electronics should invest in. It could save your life. It has certainly saved me from countless shocks or damage to test equipment.
12voltvids Thank you very much for your help. Also thank you for my questions answered. I'm going to be sure search ons.
Where can I get one from?
Mouser and digikey sell them.
What if we install an inline fuse of maybe 500 mah on the crocodile clip of the scope like those that comes on car stereos to help causing an accident to those who don't own a isolation transformer or simply forger to use it on a determinate moment.
Not that I am recommending this but...and if you do it, you do so at your own risk. The very first shop I worked for was run by a very smart, ex military electrical engineer. He didn't believe in isolation transformers. He cut the ground off his scope (that would be that big old 1963 HP that I now have) so the scope chassis was not directly connected to earth. He then wired up a small red light bulb, a little 5 watt xmas type bulb between the scope chassis and earth ground. This way, if the scope ground probe inadvertently made contact with an energized hot ground, there would be no sparks, no blown equipment, the little red light would light up. The red light was a warning that the scope chassis was HOT and not to touch it. Now that was him, for me, once I finished my training with him, and got into the next shop (Sony Canada) and the next one after that where I stayed for 20 years, I had an isolation transformer and would not service without it. I have an isolation transformer on my bench now, my variac is plugged into the isolated output, and that feeds my test power bar.
Isolation is the safest, but cutting the ground prong will prevent you from blowing up your test gear or melting your scope probe. Just if you do that, and I am not telling you to, I am telling you not to, but if you do, remember the light bulb trick and you will know if the ground is clipped onto a hot point without sparks and the subsequent cursing that follows.
12voltvids No no, i never intended or tried to said the fuse thing was the solution or the way to get rid of the transformer ,but i do know it would help a lot to mitigate fire hazards or equipment damaged like you just said, i know the isolation transformer its important but i just was making a point in those cases when you don't have one at hand or taking meaurements out of the shop etc, also some or all commercial transformers come with the ground atached to the one lead of the secundary making it a neutral since they are intended for power conditioning purposes and some folks don't modify then to make it truly isolated or don't know so still i think the fuse thing or even better the lightbul trick should even be part of the osciloscope and be buil in already, heck should even be a code regulation i think.
That was great thanks mate. I'm a 3rd year apprentice electrician and am constantly trying to understand electricity. So current always wants to go back to the original transformer that it came from?
Electricity always goes back yo it's source. That is a closed circuit. It can't go back to another source.
Regardrless if you are talking batteries or mains.
In a battery you have a + and - terminal. Electrons flow from the - terminal, go through the circuit, and return to the + terminal.
In mains you have your generator and load. Transformers are just a way to step the voltage up and down. The power company steps the voltage up to a high voltage for long distance transmission for 2 reasons. A higher voltage requires less current, therefore the conductor can be smaller, and there are always losses in the transmission line. These losses are less when dealing with higher voltages. The transformer that feeds your house is the last step in the transmission line from the generator.
On the secondary winding one side is grounded in single phase 240V countries. In north america we have split phase 120V, so the center tap is grounded and there is an A and B phase. These are 180' out of phase with each other. If you connect across the 2 hot lines you have 240V. This is what ranges, HVAC, Dryer, hot water and heat uses.
The danger comes from that neutral line, the center tap being tied to ground.
Now either conductor, if it is grounded will complete the circuit, and becomes a potential risk for anyone servicing electronics connected to the mains.
A proper isolation transformer has NO GROUND REFERENCE in the secondary winding. The primary side will have one side of the winding tied to ground through the grounded neutral, and of course the hit wire, but the secondary is floating. You can touch one wire and be grounded, and nothing will happen, because there is no complete circuit. No complete circuit no shock.
Yes if you were to grab both the secondary wires then you will get a shock, bt not from touching a single wire and ground because the load is balanced.
Now, if you were to ground one side of the transformer, well then the other one would be just as dangerous, because the hot side is no longer isolated.
The real reason to use isolation transformer is to protect your scope and other grounded equipment. On non polarized old radios for example one of the power wires is connected to the chassis. If you happened to plug that radio in directly, and the side that was connected to the hot was the chassis connected wire, now the chassis is floating at line potential. Touch your grounded scope probe and sparks will fly, and at a minimum you will be buying a new scope probe, and possible a new scope.
Plug that same radio into an isolation transformer and it is safe to connect your scope, just remember that as long as your scope is connected you are removing the safety factor for you. If you are grounded and touch a hot wire you will be the path to ground.
I not only have my bench isolated, but I also don't have my scope grounded.
I just found an old isolation transformer in my storage unit, so perhaps a tear down video of that one is in order.
Alot of what you just said I've heard before at trade school and from other tradies but each time I hear it it sinks in a bit deeper so thanks for that I appreciate it!
Joshua Caldwell
Work safe around electricity and give it the respect it requires as it can kill you in an instant. I work at my day job around utility wires as I have to climb utility poles to hook up phone lines and fiber optic drops. I see contractors doing really dumb things that leaves me shaking my head at times. Like using metal ladders in the close vicinity of power. HELLO! Wood or fibreglass only for safety sake.
12voltvids thanks Mate yeah I did my first 2 years of my apprenticeship changing the overhead services from the open power lines to the point of attachment at the house end so I know exactly what you mean. I was either on a fiberglass ladder with insulated gloves or I was in an insulated bucket cherry picker. Our overhead open LV mains have 3 phases and a neutral (in Aus)
Just one more question if I may but you said on the big trasmition HV lines that it carries a small amount of current because it's very high voltage but my question is that ohms law says if you increase the voltage doesn't the current increase? Its got something to do with power or something doesn't it?
No the opposite. For the given load as you increase the voltage the current goes down.
So if you are drawing 100 watts at 100 volts it would take 1 amp. At 200 volts it would only dray .5 amps to provide that same 100 watts of power.
Ohm's Law:
States the relationships between current (amps), resistance (ohms) and voltage.
Volts = Amps x Ohms
Amps = Volts / Ohms
Ohms = Volts / Amps
Watt's Law:
States the relationships between power (watts), current (amps) and voltage.
Watts = Volts x Amps
Volts = Watts / Amps
Amps = Watts / Volts
My isolation transformer is isolated between primary and secondary but gives me 120v between secondary and house neutral. I’m in a 220v environment by the way. Isn’t this enough to get electrocuted or destroy the scope I wonder? I thought it was safe enough but after those measurements I’m getting worried. Is there also a faston connector on the transformer body and the maker suggested me to connect it to primary hot ground in order to shunt to ground parassital current... even with the ground connected to the primary it doesn’t change a lot and I still getting 120v between secondary phase and house heart. Ohmmeter still reporting hight isolation between chassy ground and the rest of the secondary output. That’s weird to me at this point... can you explain what’s the reason I’m getting those results?
Your transformer is not isolated. There is probably a center tap that is groinded. This needs to go. You should see 0 volts between either side of the secondary and ground, neutral or hot. You should only see voltage between the 2 secondary terminals.
Anything else is not isolated and you can still get a nasty shock and blow up your scope.
I asked about the center tap to the maker and he told me that there’s just a sort of shield that need to be connected to ground... I give a try and isolate the cable that is connected to the chassis and that seems to come from an internal winding (don’t know if is the center tap or whatever...) thank you for the suggestions.
12voltvids here is the answer I just got from the maker: ...Two positive voltages to earth in an isolation transformer are absolutely normal, indeed it proves that the winding is isolated, therefore it does not have a neutral reference to earth.
You will see that if you put one pole of the secondary to ground it is with that pole (obviously) at 0V to earth and the other pole at (about) 230Vac, but this turns out to be in practice a "first fault" that increases the risk for the user and therefore must be practiced only if a neutral reference is required on the secondary and only if adequate protections are arranged for the user who is no longer isolated following an earth fault.
@@ictrepairs6963
Huh? An isolation transformer will have no reference to any earth or neutral on the secondary. Therefore, if your secondary winding is not connected to anything there will be no voltage measured whatsoever on the output as the secondary is floating.
If you tape your meter in ohms mode, you will see resistance when measuring the primary coil, and secondary coil. You will see infinite resistance between primary and secondary, and between secondary and ground, or neutral.
If either of the secondary wires has ANY resistance at all to any terminal other than the other end of the secondary then the transformer is NOT an isolation transformers. Many so called isolation transformers are NOT because they pass the earth terminal through, which incidentally removes isolation. A real isolation transformer will have no connection on the earth terminal. Mine does not even have an earth terminal period. It has a 2 prong cord on the primary, and a 2 prong receptical on the output. I had to cut the 3rd prong off to my Variac, which is what is plugged into the transformer.
100% isolation. I have demonstrated this.
@@ictrepairs6963
I I have previously demonstrated, if t here is an earth connection, that is passed to the output then it is not fully isolated. There are many medical isolation transformers on the market that pass the ground through, and have one side of the secondary tied to earth ground. This defeats the purpose. and these need to be modified to restore isolation. A service technician, or engineers grade transformer has no electrical connection between primary and secondary.
Use of isolation transformer?
please make a video about what will happen if took any wire from the output and connected it to the nutrial of your power socket
I can tell you what will happen. You will loose your isolation. Neutral is strapped to earth ground. so tying one side of the secondary to ground, or neutral will effectively remove the isolation transformer from a safety perspective.
You need that floating neutral, so that if you make contact with an energized conductor, that conductor will be pulled to ground and become the ground reference.
Thanks
sir whether one should connect crt tv to isolation transformer and connect oscilloscope directly on main 220 v line and carry out the test or vice versa .which way is the better
My scope is connected directly to mains however my scope had had the ground (earth) prong removed from the cord. My scope floats. If you don't want to remove the earth pin then plug it into the isolation transformer as well. The whole point if using isolation transformer is safety while servicing and that means no equipment under test can be earth referenced. It has to float so that an accidental touch to live circuit will not result in you becoming the complete path to ground. Even if you are grounded the unit under test is isolated.
Yes man, thank you
Did people really told you that you get no protection using an isolation transformer?, man, what kind of moron would say that?
Great explanation as always.
There are those that will argue that connecting your grounded scope removes protection. It doesn't remove protection. You can still get a shock with an isolation transformer if you contact 2 different potentials on the circuit.What an isolation transformer protects you from is a direct line shock with a return to earth from touching an earth and live circuit, because the reference to earth is removed by an isolation transformer. The argument is that if your scope is grounded you restore that ground, and then you can be shocked.Partially true, yes you restore the ground reference if your scope is bonded to earth, and that is why it is safest to unbond the scope from earth as well.What it does, if your scope is bonded to earth is remove the dead short line to ground if your ground lead gets connected to hot, because the hot and neutral is floating, so the hot will be pulled to ground potential, and no sparks.If you remove the ground pin on the scope then the scope will not provide a ground reference, and you are as safe as you can be. Never remove the ground pin on a scope without using an isolation transformer though, because if you do, and the scope ground lead comes in contact with a hot circuit the entire scope chassis will become hot, and if you were to touch the scope chassis, you could become the path to ground :(That could ruin your day.So, to recap the lesson, for safety. No earth ground on the scope, and all equipment under repair plugged into isolation transformer.FYI I plugged my scope into a grounded cord specifically for this demo, because if I didn't, when I connected the light bulb between hot and the scope ground it would not have lit up, but my scope chassis would have become live. I never have my scope grounded.
this is also an issue if you use your scope analyze your mains if you want to do this without an isolation transformer use an inverted that is not grounded same result no ground the grounding works great when our hands are not inside the device when our hands are inside a device the ground is a threat but even standing on concrete floor with shoes on you can still get a nice a zap if you have any amount of oil on your shoes or if the concrete is wet
My bench plug is isolated from ground, and neutral, as is my scope.
It is the safest way to work on equipment. I would never work on any equipment with isolating it, and I still practice safe operating procedures, and that includes keeping one hand in my pocket, and wearing CSA certified footwear at all times when working in the shop.
What is a 1:1 grounded transformer used for?
A grounded 1:1 is not isolated. You can remove the bond to ground and float the secondary winding to make it an isolation transformer. These type are usually used in medical devices where they what to isolate from mains connection but need to remain earthed. They are not a serviceman isolation transformer until the earth bond is completely isolated.
it would be useful to show a schematic of what you are doing
Somebody is skipping ahead because the very first thing that shows up after the intro is guess what? A schematic showing what an isolation transformer and an explanation on how it works and why you need one.
@@12voltvids Sorry, I did see that schematic... I do see what you were trying to illustrate by using the light bulb and isolation transformer but got a a bit lost trying to follow what you were connecting to what
Hang on, so everything would be safer if our utility transformers and houses weren't grounded???
No, but when you are working on a hot chassis you don't want to be that path to ground. With an isolation transformer you allow your equipment under test to float isolated from both earth and the live wires so a short to ground either through s scope probe or you won't harm you or your test equipment.
@@12voltvids But why is is only safer when working on electronics? Why not for all appliances?
Say for instance you have one of those dodgy Chinese rechargeable camping lights (that Big Clive has featured), where the USB outlet becomes live at mains voltage whilst the unit is charging. From my understanding of your explanation in this video, if you plugged the light into an isolation transformer and touched the USB port, you wouldn't get zapped, but if you plugged it into a regular socket instead you certainly would.
@@man_eating_monkey
Yeah you could plug one of those dodgy camping lights with no isolation into an isolation transformer and it would be safe. That camping light should have had a transformer inside. They went for a capacitor dropper.
is the variac isolated? what isolation transformer u used?
Raj Dann
yes there is a big 500 VA transformer under the bench.
Iom i saw u got a vaiac too
You forgot to mention... In america.
Why? Same thing applies anywhere.
Can you recommend an isolation transformer for my first bench?
Mine is a Hammond if I remember. Allison manufacturing also makes them. Just be sure you get one that does not have a pass through ground. 2 prong cord only. If it has a ground prong on the cord it must be cut off so there is no bond to ground whatsoever. This is very important. If there is any bond to ground then the safety provided by an isolation transformer are lost.
@@12voltvids I got a TrippLite IS-1000 I would like to plug in front of all of my pro audio recording gear. Can I just use a couple of cheater plugs (one on each side) to make it truly isolated? I see some people doing modifications to remove the secondary ground to neutral, which I what I was going to try until I saw this video. Thanks in advance!
@@crossdynamix7176 got exact same situation and query as CrossDynamix. did the mod,removing grnd from secondary neutral, but am stuck in the same place as CrossD. If the secondary hot and neutral wires are floating then how would passing ground from mains counteract the separation of ground from neutral on the output? Furthermore, would severing connection to output ground be enough to float the output entirely, without disconnecting chassis ground from primary? Thanks
wish you would be careful with those live alligator clips
Well it isn't like I didn't know they were live.You don't see me touching them, and there are no animals, or small children around. Nothing wrong with my handling of them, you do notice that I am making sure they don't touch anything.
where we can get the transformer
You should be able to find them at most electronics distributers or search online.
I could heat that tv turn on
U mean hot as in Negative and Neutral as Positive?🤔
No negative and positive on AC.
Neutral is the return (grounded) side, and hot is the supply. On the output transformer there is no neutral as the secondary is not connected or referenced to earth ground. Both sides float, so either side could be grounded and not cause a short to ground because it is totally isolated from the supply.
@@12voltvids ahh ok thank u when u say hot supply what do u mean by that and thanks for replying larrning about isolation transformers before hooking up to crt arcade cabinet
@@gamingo_gguyverx6812
The mains supply at the wall plug will have 1 "hot" wire and a neutral which is at ground potential, but not ground. It is the return wire that runs back to the transformer. The ground wire is just that, earth. Now the neutral is also earthed at the transformer as well, but there will be currents on the neutral wire and not normally on the ground wire.. If you take your meter in AC mode and put one probe in the ground port on the plug and then measure the other 2, you will see one measuring 0 and the other showing the line voltage, 120 in north america, 240 in europe. In north america the 2 blades for the plug are different size. The larger blade is neurtal, and the smaller one is the hot side.
great vid now clean your shop I'm seeing spots
The maid quit.. Volunteers?
@@12voltvids haha my maid won't even clean up my shop