Correct use of the oscilloscope when probing circuits connected to mains
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- เผยแพร่เมื่อ 9 มิ.ย. 2024
- Using the oscilloscope to take measurements on circuits directly connected to mains is a risky task that should be performed with some precautions. Not recommended for asbolute beginners, not much interesting for skilled people in electronics and electrical engineering.
Starting from understanding earthing systems this video go through the wrong and the correct way of taking measurements on electronic circuits connected to mains. This video is primarily based on earthing systems in use in Europe, and somewhere in North America, however care should be taken for those that are served by electric utilities arranged with different ground systems than TT or TN-x (i.e. those served by Single Wire Earth Return (SWER) systems) the operating conditions are pretty different than the one shown in the video may not apply in those cases. regardless of this caveat, the solution proposed and in particular the use of specialized probes is valid for every earthing system.
*VERY IMPORTANT - DISCLAIMER*: THIS VIDEO PROVIDES INFORMATION ABOUT A NARROW TOPIC TARGETED TO UNDERSTAND WIRINGS AND CURRENT PATHS. WORKING WITH CIRCUITS AT MAINS VOLTAGE GOES BEYOND THE SCOPE OF THE VIDEO. OPERATING ON MAINS VOLTAGE REQUIRES SPECIFIC TRAINING AND THE ADOPTION OF SAFETY PROCEDURES AND PROTECTIVE GEAR. - วิทยาศาสตร์และเทคโนโลยี
Congratulations, best explanation I have seen so far on TH-cam.
Excellent video on a very important topic for technicians. Thanks.
Late comment but anyway...I've just watched your video and I must say, that besides your good explanation off the subject, I can really appreciate a good drawing like you did. Nice preparation🙂
Excellent video and explanation, especially with the sketches indicating load/neutral/pe. Thank you for making & posting this video.
*VERY IMPORTANT - DISCLAIMER*: THIS VIDEO PROVIDES INFORMATION ABOUT A NARROW TOPIC TARGETED TO UNDERSTAND WIRINGS AND CURRENT PATHS. WORKING WITH CIRCUITS AT MAINS VOLTAGE GOES BEYOND THE SCOPE OF THE VIDEO.
OPERATING ON MAINS VOLTAGE REQUIRES SPECIFIC TRAINING AND THE ADOPTION OF SAFETY PROCEDURES AND PROTECTIVE GEAR.
excellent explanation..nobody concern this type of things..good job
Great video! I was always wondering about the probe shield and protective earth, and this video really helped me understand those topic. Thanks a lot!!!
Ideally , the Professional OScope being properly grounded, and the device under examination has to be on an Isolation Transformer, which would allow one to take precise measures of the values.
Thank you, Accidental Science!
This is a really nice overview of this isolation topic.
Love the beauty figure of power lines distribution in the start of video 2:30. Nice work man!
thank you.. very interesting and well explained (I like the schematics that are very explicit and well drawn. take care
This was very informative. Thank you!
What a GREAT video. Thank you, sir!
Glad you enjoyed it.
Thanks for the clear explanation !
As you indicated at the end, it is best to use a handheld scope powered by batteries.
Thank you very much. Life saving info.
Great video thank you .
I live in the uk .
so could you connect the shield to the mains earth pin and touch the probe on live or neutral?
Thanks for your explanation.
Nice explanation. Thank you
What a Wonderful Video. Thank you so much. I UNDERSTAND NOW. How can i learn more about the system in North America - taught in such a clear manner?
Thanks, great video. I missed one option: Connect only the hot of the probe to the mains power as there is no need to connect the ground of the probe as it is already going to earth via the mains of the scope itself. This should make it possible to measure the 230V safely by the scope or am I mistaken?
Thanks. About your option: 1) you actually don't know how internally the scope is wired so you can't predict the exacth current path. Very likely the input amplifier won't like this 😉 .
2) there are many occasions where you need a measurement that is realative to some point in your circuit under test and not in reference to earth. 3) neutral is not the same as earth (or PE). Also this definitely wouldn't work wth double live (non neutral) mains (ie 120+120).
4) often oscilloscope inputs can cope no more than 300Vpp, your probe wouldn't work attenuated without the return path.
5) shielding wouldn't work.
Conclusion. I think those are enough reasons to reject this option.
Happy new year 🍻
And second i am writing about the effort to test a relative large UPS when replaced its dead batteries with a laptop power supply connected in series with the bench power supply which is fully isolated from the mains.UPS batteries and their charging circuit was isolated,but laptops minus is connected to the mains grounging exactly as the oscilloscope minus does.The result was to end with a blown cpu and the UPS finally took its own way to the recycling simply from nothing.And still i cant believe it,it brings me bad memories.The same thing occurs also for AT PC power supplies,metal casing and minus output are connected to mains ground.
i like the graphics :)
Good information thank you. My solution for using scope with mains circuits is to isolate the scope by plugging it into a "portable power station" which is basically a battery and inverter. I use a Jackery 1000 (which is overkill) but any unit with a pure sine wave output should work.
That's an interesting idea. Just be cautious with the exposed contacts such as the metal of uncovered BNCs.
the only way its possible to use an earthed instrument to work on mains is to galvanically isolate with an isolation transformer. You can make one for your scope using 2 x 120v to 240v transformers.
Trained users only.
Main ac should be avoided. What of measuring indirectly through step down isolation transformer(120/240 v to 6v)? The oscilloscope probe would be connected to 6v output. All safety measures must still be observed
What if the power supply gets the spurce from main similar to scope? Its confusing. Power supply also have ground which you use in circuits. Im glad i bought a battery operated scope
Got the oscilloscope question answered. Now I have a new earthing question have to search that one. Ahh it never ends.
Can I ask sir, how about in our country where we have no ground in our outlet and only live and neutral?
I suppose you mean unearthed neutral (otherwise it is similar to what is showcased in the video). In that case the situation is similar to the one with an isolation transformer. However a question arises: where the oscilloscope's ground is connected? To arrange a laboratory the best practice is to have an independent ground and ideally the circuit should be a TT (see Terre-Terre grounding systems).
Excuse me Sr, What happen if I connect a Transformer to feed My osciloscope instead of feed the circuit that is going to be test ?
In that case the oscilloscope is isolated so no risk to blow it up, yet the circuit under test is stll connected to mains and you risk to be electrocuted or cause other accidents if you touch thè body of the oscilloscope or it touches other earthed things, e.g. a nearby instrument. This is why the isolation of the oscilloscope is not recommend. There are special oscilloscopes that are fully insulated in a way that the body, knobs etc are safe to touch even when (internally) the scope is connected to mains. Powering the scope through an isolation transformer is not enough to convert a common oscilloscope into such a special kind of oscilloscope.
What about using osciloscope with more probes ?
I needed a recap and this was good, BUT i do not have a differential probe or isolating transformer any more and need to see waveforms on the mains side, I did think of disconnecting the earth from the DSO, but thought there might be another option hence looked it up. But it looks like I am going to have to disconnect the earth as I am not spending a lot of money for something I may never do again, how about I connect the earth from the DSO to a 1Meg down to ground just so I can test?
I've uploaded a short video right now to answer your question, and a more detailed full-length video will follow next week. Hope you'll like and share. Greetings from the Alps.
@@AccidentalScience Thanks, I will be interested, but in the meantime I have disconnected the earth all together, enabling me to test the live voltages with success, look forward to the video!
Why does the scope have a socket in the back? Is that power out?
That's the plug holder, it is not connected!
Have you heard of RCD / GFCI,,, if so, why don't you mention it and use one ? by the way I like your demonstrations,,, keep going mate.
Of course I have, but that's not the point.
A RCD or GFCI won't protect your circuit and your scope.
Thank you for commenting.
What if I disconnect the earth from the plug of my oscilloscope completely?
As said in the video while it could work it is also quite dangerous cause you could get electrocuted! Absolutely a deprecable practice. Also beware of the max voltage supported by both the input of the oscilloscope and the probe.
It's called the Napolean effect. You have heard of Napolean Blown Apart, haven't you?
I just scape from electro boom sparks and finde you video but... 😂😂
😂
Great, you look very much like my wife. She too always shows me the back of her hands when she try to show me something :-)
LoL not that easy to show something while your hands are in the middle.
Yes there is a risk of short circuit because the grounding clip of the oscilloscope probe is connected directly to the earth of the mains voltage socket plug and there is 50% chance to contact the phase wiring of the device being tested.A such an accident i had in the past while trying to repair crt power supply and connect ground clip to the minus of the mains capacitor followed by a short circuit,fuses blown till the companys counter box and the tv had 4 rectifications diodes blown and a fuse.The solution is to connect either the tested device to the mains through an isolation transformer or to connect the ocilloscope to a plug without having the groung pin connected to the mains socket.The conclusion is that earthing the oscilloscope protects only from leakage malfunction of the oscilloscope itself and has nothing to do in no circumstance with the device which is being under measuring.Battery operated oscilloscopes or other testers dont have this issue because they dont use mains earth grounding.
Thank you for having commented and told your experience.
I'm sorry to say that isolating the oscilloscope through a plug without ground prong is not a good idea. Besides the risk involved in the case you touch the chassis and get electrocuted, the parasitic capacitance developed between the chassis of the oscilloscope and ground (not the ground wire, but the actual Earth) introduces a lot of noise and makes the transients ringing.
Battery powered oscilloscopes that are meant to work with no grounding are designed to minimize this parasitic capacitance, and they are fully insulated to prevent shock hazards.
If you are working often on those kind of circuits consider to purchase an isolated differential probe, or just a battery powered scope (that will likely cost as much as a differential probe).
Cheers.
The scope should always be connected to ground earth as I understand it.
@@northgork If a scope connected to ground then an isolation transformer must supply the tested device,for example a welder machine while scoping pulses on output mosfets.
Is the test circuit connected to earth ground? It does not look like it is from your diagram.
No, it is not. It hasn't, because PE *must* be connected to the chassis *only*.
@@AccidentalScience so is the test circuit powered from an isolation tansformer?
@@northgork no! What would be the point of the whole video otherwise?
An other point: that is not a test circuit but it is the circuit *under test*.
@@AccidentalScience So you show a scope that is not earthed, how does that help the point? Your scope power cable does not have an earth ground. Thats bad. Your explantion is quite excellent however there is a short coming. You should make it clear that if both circuits are wired to the same earth ground and you touch the ground probe to a power rail of the circuit being tested then current will travel from the ground probe to the scope ground, then from the scope ground to earth ground then from earth ground back to the ground of the circuit under test, then zap! You have a short circuit. You did not explain how current can travel when the probe ground clip is connected to a power rail on the circuit under test. I know that is what you meant, you just fell short of a clearer explanation.
😃 i jumped back twice
The power cable does not have an earth pin. This is bad.
So you are saying there are countries with the systems where ground is NOT bound to neutral? Really.
I don't remember exactly what is said in the video, but yes there is a system named TT where the ground (at consumer) is not bound to neutral: en.wikipedia.org/wiki/Earthing_system#TT_network
When you say impedance it sounds like impotence :)
Even that one could be seen as a form of impedance after all :)
@@AccidentalScience lol
PE means protective earth, not positive earth.
For a moment I thought I've gotten senile so I watched again the entire video, but no, I never said "positive earth"!
Sorry, me misunderstanding your accent....!
@@anthonykinrade8642 oh no problem. Indeed my accent was worsened by the effects of the bad flu I had at the time ...in hindsight I also think it was very similar to Covid19 for the symptoms I had (and my entire family had).
Long story short: He never measures the mains voltage with the oscilloscope. There, I just save you 17 minutes.
but you could if you had it hooked up to an isolation transformer right? 🤔
The grounding EU idiots got to ground no only scopes but soldering irons too. Remove SMPS from scope and get transformer instead. Your DMM is floating for a reason. Another "smart" youtube influencer tells tales how floating scope can kill it with static discharge, really funny. If 400/600Eur scope can die from electric static then company will have big hole in their pocket. That is all I can say. Try to kill DMM on milivolt range for skeptics.
I did never say the scope would be killed by electrostatic discharges. Here the problem is YOUR OWN safety AND to avoid to fry the scope/probe and or your circuit under test. The grounding rules didn't come from the "EU idiots" (I suppose you are referring to politicians) but from a committee for standardization composed by electrical engineers, that I think are all but "idiots".