Neutrals from transformers and in electrical circuits
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- เผยแพร่เมื่อ 27 ก.ย. 2024
- What a neutral wire is and how it is derived at the transformer.
Also how part of a circuit is a neutral, how it isn't once disconnected and possible dangers of disconnecting wires which have apparently no voltage on them.
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Other videos on transformers and electrical systems:
Isolating transformers: • Mains Isolation Transf...
Why normal supplies are not isolated: • Isolated Electricity S...
Earth connections: • Transformers & Earth C...
Many other electrical basics: • Mains Electrical
+John Ward
I think the impedance of the earth-rod itself is worthy of mention... In your video, your early comment that connecting ground-rod to neutral brings neutral to ground-voltage can (sometimes) be misleading.... I think I read somewhere that distribution transformers are supposed to be grounded with
A neutral wire only carries the operational current. The PE (protective earth) carries only fault currents. The PEN conductor is a combination of the PE and the neutral, it carries operational current and in addition in case of a fault it would carry the fault current too.
And in case of a broken PEN the same thing would happen as shown in the video with the broken neutral. But in addition metal housings of class 1 appliances would become live. That's the reason why PENs are only permitted if you use larger wires (at least 10mm² copper or 16mm² aluminium).
Here in Germany the most common system is TN-C-S. You get three phases and a PEN from the supplier, the PEN is splitted into a separate neutral and PE inside of the service entrance box. In some older installations the PEN is splitted in the fuse box, and in installations made before 1973 the PEN was actually splitted on the outlet. The PEN was connected to the earth terminal, and from there a wire bridge was installed to the terminal for the neutral of the outlet.
The N is actually an operational earthing, the PE is a protective earthing.
You can actually calculate the voltage between the line conductors if you know the voltage between one line and the neutral. You multiply the voltage with sqrt of 3 (~1,73):
230 V * 1,73 = 398 V
240 V * 1,73 = 415 V
In Germany kitchen cookers are connected to three phases, two heating plates on one line and the third one for the oven. The circuit is fused with three B16A MCBs:
400V * 16A * 1,73 = ~11kW
If your neutral breaks in a three-phase system this will cause some major issues. For example imagine you've got a 20W soldering iron connected to L1 and a 3680W electric heater connected to L2 and the neutral breaks inside of your fuse box then this would happen: You'll get a voltage divider, the soldering iron would "see" 397.8V and the heater will "see" 2.2V.
Thats a good point. Ignoring any resistance issues with the ground rod, the ground rod impedance is something to think about. Since power stations almost always run as a wye configuration (from the station transformer at least) with a neutral conductor to handle unbalanced loads and provide a common return, the earth is connected to the neutral conductor at the power station. The earth being a rather good conductor as far as organic material goes, means when you put a ground rod into the ground from your house (this depends on the setup in your country as some will use the neutral from the pole) if it has to handle a fault, it will have to travel all the way through the earth possibly hundreds of miles to find the nearest transformer ground to complete the circuit, this results in high loop impedance, with can be almost as deadly as not having a ground at all.
I'm interested in the different systems in use around the world. Some run separate ground and neutral from the transformer, some run combined ground/neutral from the transformer, some have no ground or neutral. In modern US installations (extreme rural installs excluded) we run the two lives from the split phase, and a combined neutral/ground that is grounded at the pole, then once it reaches the house another ground spike is used and the neutral and grounds are separate from there on.
Transformer station is 100m (~300 ft) from my home. And there's another one nearby for another grid segment. These transformer stations are small, they're only 15 to 20m² (150-160ft²) and are inside of a pre-manufactured concrete housing:
www.hildesheimer-allgemeine.de/typo3temp/_processed_/4/b/csm_ecad01a400-70a35c98-4b90-11e7-aba0-377d83391380-710f3470-4b88-11e7-aba0-377d83391380_9c87ee5356.jpg
The cables are laying below the sidewalk. In most cities and towns here overhead wiring was replaced by this system. The cables are laying inside of conduits, so they can be replaced easily.
And here in Germany houses have an additional grounding system, even if the utility company provides a TN-system. The ground rod is implemented in the concrete foundation of the house. In older houses, built before the 1970s, the incoming water pipe was used. That was the reason they made these pipes of thick cast iron.
In Europe these systems are common:
-TN-S:
The utility supplies you with the lines, a neutral and a ground wire.
-TN-C:
The utility supplies you with the lines and a PEN. The PEN is a combinated neutral and ground wire. In most cases this wire is splitted into two wires, a separate neutral and the ground inside of the house. This is changing the TN-C into a TN-C-S grid.
-TT:
The utility supplies you with the lines and a neutral. Ground must be provided locally by a ground rod. In addition to achieve the cut-off time in case of a short-circuit RCDs (residual current device, in america called GFCI) must be installed. The cut-off time in case of a short-circuit must be less than 0.4s for a circuit which is fused with less than 32A. In a TT grid you can only reach this time if you use RCDs/GFCIs, as you already mentioned the resistance is too high. Especially when the ground is dry. With the RCD you can achieve a cut-off time of less than 0.2s. In most cases we're talking about 0.02s.
en.wikipedia.org/wiki/Earthing_system#Low-voltage_systems
That's the reason why we have RCDs which are completely separate, not integrated into an outlet or a circuit breaker. But you can also get them integrated into these devices. When it's integrated into a circuit breaker it's called RCBO (residual current circuit breaker with overcurrent protection).
There are RCDs available where you can install a single one to cover the whole house. They are rated for 3x40 or 3x63A. But that's no longer state of the art to use a single RCD for a whole house, because if a problem occurs the whole house is without power. And in addition every class 1 appliance produces a small leakage current, and these sum up.
Marcel, You live in Germany? I learned a little while back that many residences in germany have an incoming 3phase supply instead of a single phase supply as we get here in the US. How does that work for you guys? I imagine it makes high power appliances like stoves and large motors easy to install and handle with small amounts of copper. But is there ever a concern with having two outlets on different phases and having equipment connected between them? We have enough problems with that on our split phase in America when residential AV equipment is hooked up, say a TV or projector on the wall on one phase and a home theater or computer or similar device on a separate phase connected by cables which join the chassis grounds. It manifests here with a 60hz hum between devices and on some with particularly high leakage, small tingles from electric shock between the two phases (240V between the two). More modern electronics for this reason have gone to double insulated with only live and neutral with no ground connection, but many devices simply must have a ground because of exposed metalwork for the AV connections. Does that cause problems with high leakage devices between your 400V legs in a 3 phase system?
Yes, I live in Germany. Three-phase supply is common here in Germany.
The connection is comparable to the split-phase system you use in the US, but instead of two-pole breakers we use three-pole breakers for three-phase appliances. All the other appliances are connected single phase, but you must take care that you distribute them evenly on all three phases.
And I suppose AV-equipment is double insulated everywhere, the reason for this is that you can otherwise create a ground-loop which makes humming noises. The shielding of antenna cables is always grounded, that would be the first grounding point. The second one would be the grounding of a housing of a class 1(grounded) appliance. That's the reason why these appliances are all class 2 (double insulated). In most cases the hum would be 50, or in your case 60Hz. Sometimes it can be double the mains frequency, coming from the rectifier (pulsating current before it is smoothed with capacitors).
AFAIK there are no problems if the system is according to the regulations and fully ok. In case of a damage of the neutral wire inside of the panel it can become ugly....the appliances connected there would be roasted propably. But in most cases one room is only connected to one phase.
Kitchen cookers and stoves are connected three-phase, but they are 230V appliances in most cases so you need the neutral. The four plates are divided onto the two phases inside of the cooker, always one large and a small plate on one phase. The third phase L3 is for the baking oven. Actually this wiring is inside of the appliance, you just need to put the five wires (L1, L2, L3, N and ground) into the correct terminals. The stoves are always hardwired here. And you could wire them for single phase use, then you must insert bridges between the correct terminals. In this case here the terminal of a cooking field, the oven is a separate appliance:
www.elektrikforen.de/attachments/img_3514-jpg.13051/
It's connected two-phase, the oven as a separate appliance would be connected to L3 directly in the box were the transition is from the installation of the house to the appliance cable. Cover removed:
www.xavax.eu/bilder/00110/awx/00110828awx2.jpg
brown is L1, black L2, grey L3, blue is neutral and green/yellow is the ground. The strain relief is for the cable to the stove. But you can also connect the stoves single phase. The manufacturers deliver bridges with the stove which then must be implemented:
forum.teamhack.de/attachment/4898-anschluss-jpg/
1, 2 and 3 are for the line conductors, next to it are the two neutrals (oven and cooking fields). Don't ask me why someone made a connection between the neutrals and the ground. That's not compliant to the regulations.
It's like being back at school, but with a good teacher who's actually interested in what he's teaching.
I've had this explained to me 100s of times, but never fully understood it until this video. Fantastic teaching. One of the best channels on TH-cam. Thanks JW.
An excellent description of mains supply principles, a very simple and clear explanation of a usually poorly addressed electrical question asked by so many. Great job JW.
You have no idea how long I've waited for somebody to finally be able to explain this to me. Electricians and other people on the internet I've talked to pretty much have different explanations for this. None which made sense. Like nobody knew what they were talking about. I find it so mind blowing how getting this information was so hard for me to obtain. So thank you very much! You are awesome. *subscribed*
I needed a quick transformer refresher and this ticked all the boxes 👍🏼 I love the mild comical / sarcasm that John does so well. If my college tutoring had been like this, I would have understood it better. Great delivery
That’s the bit that’s hard to get your head around, if you touch the neutral terminal in that heater circuit you don’t get a shock coz there’s no voltage there but if you disconnect the neutral at the same point and touch the wire and the neutral terminal, thus completing the circuit, then you will get a pretty nasty shock
Brilliant thanks John. Its so good to get someone that explains it in easy terms instead of all the fluff and rubbish. you remind me of my old Physics teacher who was a very great man. He could make Quantum Physics understandable!
I lived in the UK for around 15 years and have since moved to Ecuador, which is more the US style approach. It is extremely common here to not have earth connections, to use inappropriate (typically thinner than required) wiring and have very poor safety in mind. Although I have now lived here for 10+ years and the electrical systems are quite distinct, it is always a pleasure to watch your content and see if it can be applied in a manner that improves the safety of the circuits we have in our property. Thanks for your dedication over all this time.
I've had this explained to me a number of times.. finally I think I understand it a lot better! Thanks!
Fantastic! Thanks John
Thank you John for this useful video!
Hi JW
Thanks for another great explanation. Everything seems so simple when its explained by you Sir.
Many thanks! Best explanation I've seen on a neutral!
Exelent! Thank you so much for taking the time!
Another very well presented blog John, thanks. A full explanation of the various ways 3 phrase is supplied and used is would be very much appreciated. You made me smile thinking of my Physics teacher who also left us hanging in mid air for an explanation of items to be conveyed in forthcoming seminars... watch this space as we say - well done!
Hi John great videos. I have been following you for a few years now but may I say I would love to see you smile just once you always look so serious.
Of course, in the stuff you didn't go into here, it turns out that *if* the 3-phase load is perfectly balanced then the neutral remains neutral even if you disconnect it back at the transformer. That doesn't mean it's safe to touch the neutral in a 3-phase system when it's disconnected because the load might not be balanced, or may become unbalanced.
I'll leave explaining why this is so to you. :)
If you draw a symetric load from all three phases there's no current flowing on the neutral. And in case of an unbalanced load only the difference between the load of all three phases will flow on the neutral. For example:
L1: 15A, L2: 15A and L3: 16A would mean that there's only 1A flowing through the neutral.
Your situation is purely theoretical, because you always have an imbalance in such a system. There are only a few appliances which don't require a neutral. In residentials a type of typical appliances which don't require a neutral are flow-type water heaters. They only require a cable with 4 wires, the three phases and the protective earth.
If the neutral is connected you can touch it, even if you have an unbalanced load between the three phases. But the system would loose it's zero point or better you would have a floating zero if you disconnect the neutral, for example in your fusebox. That means all connected loads in these fusebox would act as a voltage divider. As a simple example you got a 20W soldering iron (~2645 Ohms) connected between a circuit connected to L1 and the neutral. On a different circuit, connected between L2 and neutral, you have an electric heater with a demand of 3680W (~14.4 Ohms). If you would disconnect the neutral in the fusebox the soldering iron will get a voltage of 398.8V and the heater will get 2.2V. Meaning your soldering iron would be roasted. And in case of a PEN wire in a TN-C or TN-C-S system you would loose your protective earth. This would, in addition to what I already said, cause that the housings of class 1 appliances would become live. Quite undesirable....
Execellent teaching👍👍 thank you JW for all your Effort and for enlightening us who wants to learn
Very useful. I also learn't the other day why neutral isn't needed on motors - its simply because in a 3ph motor, the current draw on each of the phases is equal, whereas in other applications where 3 phase power is used, such as one of my dimmer racks for dimming stage lighting, the power draw on each phase can vary, and thus a neutral is required to act as a 'drain', though im not sure if my terminology here is correct.
Your video also explains why a string of old style fairy lights can run on 240v without a transformer and yet uses low voltage bulbs, since the voltage is divided up between them all, providing of course that the bulbs are wired in series or 2x pairs of series. Meanwhile a 240v festoon has 240v bulbs because the bulbs are all wired in parallel.
Have you ever done a video on building site 110v electrics where there are 2x 55v lives and the neutral and earth are combined with (i believe) a centre tapped earth?
Best regards,
Jonathan
Jonathan Cook Building site 110V supplies are fed from isolating transformers. The secondary (output) windings are two identical windings with the ends joined, at this "mid-point" or join, a connection is made to earth. Another way of describing the winding, is a centre tapped secondary. Hence you will see the term CTE for Centre Tapped Earth. The reason for this arrangement is if either conductor in the cable, or tool, or whatever becomes exposed, the voltage to earth will only be about 55V. So the risk to a human is considerably less compared to normal 230V system. And on a building site, there is a far greater risk of damage to the cables, tools etc. compared to day, a home or office environment.
th-cam.com/video/fRhofcMyAyk/w-d-xo.html
Thanks Mark, I do understand this, but Im sure there is more to learn.
The neutral basically carries current that allows the voltages to be balanced. (That is, the neutral to phase voltage.)
It's worth noting that with harmonic currents, the neutral current can be many times higher the current on any one phase at a given time. If not kept it check, it can cause electrical system failure. (Burnt wires, connections, arc flashes, etc...)
Great video John. It’s always a pleasure to learn from your videos.
Superb explanation, John.
Thank you John for this explanation!
Good explanation.
Great video. I look forward to some material on three-phase systems.
I would point out for anybody watching but at 10:16 the voltage across the 20 Ohm resistor (heater) is zero because you only get a volt drop when a current flows. The potential difference across the 20 Ohm resistor is 0 volts so no current flows. The left hand side of the circuit has a path through the secondary of the transformer for current to flow and the voltage (potential difference) is 230 volts .
Thanks for the explanation. It really helped me.
So , John when you get to 60K subs are you gunna bust out a tune on the organ in the background??
Or will he smile for once and stop looking so serious
Love your videos john, im learning the things ive always wanted to
Why does the lagest part of the voltage appears where you got the largest resistance? And if the neutral and hot wire are connected in series why isn't the hot grounded? And also how will the circuit be closed if the neutral is grounded so the electrons can flow to earth? Also in AC I understand current goes back and forth because of polarity change, so does that mean that phase will become neutral and neutral will become phase?
you are genius....well described in simplified way.
Hmm pretty straight forward, but lets discuss how to check the floating AC transformer of say about 24VAC for which cable is which. How do i identify which is common and which is phase? Although in many cases its not important at all.
Hey JW great video as always. About 20 years ago at work, half of our 2 storey office PCs and monitors literally went POP and smoke poured out of 100's of devices as the line connector floated up to dangerous voltages (normally say 230V ish). The fault at the time due I think to a faulty Neutral connector going open circuit after some contractors had previously been in connecting some Air Con equipment up etc. Rumour has it they had not tightened the Neutral back up correctly in the distribution panel which subsequently burnt out. Anyway about 200 PC power supplies were toasted and also hundreds of computer monitors went Bang! I'm still struggling to see how an open circuit on the N. side causes the line side to raise up to much higher potential. Between phase and N is circa 230V, so why does open circuit on the N give > 400V?
Brilliantly explained.
And the mystery of neutral remains!
more lift videos please.
+Tangobaldy
Go watch/subscribe to Beno's channel:-
th-cam.com/users/benobvevideos
+Tangobaldy
Go watch 'beno lifts' channel instead =). th-cam.com/users/benobve
Wrong channel. You want mrmattandmrchay
The neutral is only introduced at the final distribution substation 11kv/400 and 230v transformer.On transmission (400,275 and 132kv) and Hv distribution typically 33 and 11kv there is no neutral, they work using the 3 phases only, there is earthing on the high voltage system,but as earthing suggests it is only there for safety and also to provide safe isolation on disconnected conductors to prevent induction from other nearby energized circuits during maintenance or replacement. Just for anyone who is interested.
Here in the UK one often sees single phase 11kv circuits
@@greenpedal370 Gawd, shut ye gob!
@@kimballscarr OK Mr External Plant man But it took you 3 years to come up with that. Good work.
@@greenpedal370 That would be a rare example of an ultra relativistic correction... at low velocity
Nicely explained
Very useful information. Thanks so much
A few mentions are made of receiving shocks by touching the phase line while standing on the ground. That doesn't necessarily happen if the connection a person makes to earth is only by standing on the ground, and is unlikely to be near as high magnitude as direct contact between phase and neutral with hands. Dry shoes on dry ground/floor, and there may be no shock perceived by touching a phase only.
robbie77300 Hmm, except it does not really work like that. It only takes a relatively small current to give you an electric shock, and such leakage currents have a way of finding a route from the line (live) conductor to ground/earth via you, and then back to the supply. And yes, it has happened to me, while dry, and stood in a dry room.
Yes, 30ma for example, the threshold imbalance of tripping an RCD, gives quite a nasty shock. However, the impedance for 30ma to flow is around 7600 ohms. Standing in your living room with shoes on will be a far higher resistance/impedance than that. It wont just find a way if there is none. Anyone getting a shock from 230v in such circumstances will be almost certainly in contact with another flow route, not just a phase and nothing else. Enough current to give a shock, does not automatically happen unless there is a path capable of conducting such current available. Most assume contact with a phase means a shock occurs. This is not always true. Stand knee deep in wet cement, and it is going to be nasty. Stand in dry shoes in your living room, or even out on the path outside, and there will not be low enough impedance/resistance to the ground for perceivable current to flow if that route is the only path. Anyway, a demo, which shows it does indeed work that way....... th-cam.com/video/xZyEX2NE3Lc/w-d-xo.html
dear mr Ward, at the power station does this mean that one side of the power station is connected to the live or line and the other side of the power genarators are connected to the earth in order to complete a circuit. have you by any chance done a posting that may help me to understand this better? love the channel, please keep up the good work....
My question is what if we add potentio on neutral end, will effect load end?
a big Like for this information
is there a practical reason for the neutral to be connected to earth, if so would a high resistance connection still be practical as opposed to the low resistance connection currently in use. Meant purely as a thought exercise obviously electrical codes wouldn't allow it
+Brendan Randle
Yes you are describing "IT" electrical system (isolated from ground), as opposed to TN or TT supplies. Specialist-only (e.g. operating theatres) and, as you say, not normally used.
Johns' video also explains why Isolation not normally used for everything in:-
th-cam.com/video/Wx_v1-T1gE4/w-d-xo.html
thank you!!
Great information professor. I have a question though…there is something I’ve always struggled with that I can’t get an answer for though. Being that AC is alternating back and forth, how does your ground rod not have 120v on it.
AC means the line conductor moves between +230V and -230V relative to the neutral.
The neutral is connected to the mass of Earth at the transformer, so is always the same voltage as the neutral, so any measurement of voltage between the Earth and neutral will be zero.
There is no 120V in the UK.
In places such as North America, the two line conductors (hot conductors) are between +120V and -120V relative to the neutral and Earth (ground), and are at 240V relative to each other - when one of them is +120V, the other one is -120V. That gives 240V between them for higher powered appliances such as dryers, or 120V between one of them and the neutral for smaller items.
+john ward I have a question on earthing and neutrals. Basically at work we had a machine with a transformer that was stepping down 400V 3 phase to 230V single phase. It then passed through an RCBO, then to sockets. If the neutral of the transformer is not earthed then no current coming from the output of that transformer can flow to ground because there is no path to complete the loop. Even though the machine and the earth pin are grounded they will not work. But anything connected to it will still be at ground potential. If this was true then the MCB would not work in a short circuit condition and the RCD wOuld not work either.
Am I correct? I was told at work the neutral does not need to be earthed for current to flow to ground. Also if there was no RCD on the output but there was an RCD on the primary side of the transformer. There would be no RCD protection as they are now different circuits?
Thank you!
In the US you would need a system bonding jumper to bond the secondary neutral to the equipment grounding conductor of the primary system.
Current doesn't magically disappear into the earth. The only way current would leak to ground is if it's able to use the ground as a path back to the source (the star-point of the transformer secondary, where the neutral wire is connected).
A great video to watch is this by Mike Holt, it will explain everything about earthing, a must watch in my opinion: th-cam.com/video/mpgAVE4UwFw/w-d-xo.html
Hi John great video,any chance you can do a video on if you have any experience on using a generator on house wiring using a changeover switch,and the earthing arrangement,I am getting a lot of conflicting information over the net regarding this
biggest lesson I learned in the caribbean, is that all the supplementary grounding, for extra ground rods, generators, solar panels, even cb and ham radios, needs pulled back to your main ground point with at least a 10 mm but preferably a 16 mm wire, to make them all one grounding point... otherwise, the lightning strikes can actually do more damage to them.I think the new 2017 International wiring codes addressed this as well. Thus, if you are running a line out to an outbuilding, or a generator, or a shed, and you are planning a ground spike there, you still want to find a way of connecting that ground spike back to the first ground spike or ground position in your home. I believe there is an excellent video showing this under the 2017 NEC videos.
Why do they connect the neutral to ground, if it wasn't connected, then you'd only get a shock if you touched two-wires at the same time? That would reduce the chance of getting a shock & reduce deaths. In your 3K heater example, if you touch the two open ends of the cables, (Complete the circuit) you would get the current flow of the circuit go through you I assume.
Thanks John
How come there's potential difference between neutral and Live wire, how does that come about, what makes neutral different in potential to live? That's my questions. GREAT VIDEO INDEED Sir
Because neutral is on one side of the coil and live wire is on the other side, so potential difference exist.
السلام عليكم..
أعتقد أن خط المحايد سمي بهذا الإسم لانه لا يكمل الدائره الكهربائية لطور دون غيره في محولات الثلاثية الاطوار بل لجميع تلك الاطوار فهو لذلك السبب محايد.
اما بالنسبه للامان من الصدمه الكهربائية فاعتقد أن الأمر لايتعلق بالمقاومه الكهربائيه الموضوعه بالدائره بالدرجه الأولى لانها تستخدم من زاويه الحماية كحمايه من الجهد الزائد لبعض الاجهزه.. الأمر بالحقيقه يتعلق بهل اكملت الدائره الكهربائية ام لا.. فلو ربطنا الخط الساخن بالأرض بدلا من الخط المحايد و امسكنا الخط المحايد لتعرضنا لصدمه كهربائية لان الدائرة ستكتمل مرورا باجسامنا من الارض و من ثم إلى الخط المحايد و من ثم إلى المصدر.
ارجوك صحح لي اذا كنت على خطأ.
شكرا لمجهودك الرائع ..
متابعك من العراق.
Can you explain a split phase supply please ?
That’s North American. He’s in the UK. There are many videos on the North American system.
Great video. thanks
In other neutral diagrams. The neutral wire goes to the Centre of the transformer. Also is the neutral is just a continuation of the line, as seen above - why isn't it live as well has the hot line? Help.
th-cam.com/video/AgCY_d98HF8/w-d-xo.html
I think it’s a pity that you didn’t show the substation transformer as it is in real life, namely, a delta/star (11kv to 415v step down), with the star point connected to earth. And, of course, in such a device, there is a connection between the ends of the windings on the star side, but no current flow due to the 120 degree phase angle. I live in a rural area supplied by TP-N overhead lines. There was a power cut some time ago, due to a break in the neutral. It would appear from this that neutral current is monitored, and the lines are cut if the neutral current falls below a certain value (the line supplies domestic dwellings, so there will always be neutral current).
Hi John , got an old Maplin regulated DC output linner power supply 0-15v 15-30v DC . Q : On the transformer have 240v AC primery and on secoundry one pair 6v and three terminals with 0v , can you tell me why please
Why is Line and Neutral necessary instead of an isolated AC supply? I'd guess that it's to protect against a fault where any one AC conductor is connected to ground, flashover of the 11kv supply to the 240v output, lightning protection?
Isolated is safer, but it is impossible to ensure it stays that way - any inadvertent connection to ground anywhere would make it ground referenced, but with no control over which conductor was grounded.
It's safer to make it ground referenced by design, so that fuses/circuit breakers are always in the correct conductor,.
Hi John the natural wire completes the circuit and takes the current back to the source so how come it isn't live when touched? Is it that current is actually flowing but as it's connected to ground you won't get a shock?
Can you still have amps in a netural? If so why?
The current in the neutral of a single phase circuit is identical to the current in the line (unless there is a fault).
Unless its 3 phase! under certain circumstances (Computers, Inverters etc) the neutral current can be HIGHER than and individual phase current (search for "3rd harmonic" for more information)
Concept: 2 wire circuits never can have a neutral. If one of the conductors is grounded then it’s a return wire. 3 wire single phase circuits center tap is a neutral, this is a neutral because it’s neutral to the phases on each side of it. In this set up it will carry the imbalance of the two phases. 4 wire wye, the conductor attached to the point where all 3 windings connect to each other is a neutral and it will carry the imbalance of the 3 line conductors.
Nice video
Thank you 👍👍
good.
Hey great video. I have a question we have 3 phase power 120,208,120 on a cnc machine. The machine was drawing 30 amps when servos turned on. We had to install a isolation transformer and it fixed the problem. All the other machines do not need the isolation transformer. Can you explain why this one machine needs the isolation transformer?
I need to do a line diagram of a single phase auto transformer showing the earthing arrangement of such a transformer and similarly earthing arrangement for a double wound transformer can you help please.
Hello! There was such a situation - the current in the neutral of a single-phase autotransformer 500/220/10 was measured with ticks and showed 30-35A. It's the same in other phases. There are indications of currents from the 500 kV and 220 kV side, there is a tiny asymmetry. So, does anyone know how to calculate by calculation what the current in the neutral AT should be? Thank you!
John
Just watched video on transformer neutral single phase power.
My question is what happens when all of the circuit is closed but no ground. Will secondary side still work? And what is voltage?
Much appreciated John, Thanks for the information.
So if you lowered the resistance to a certain level then would you get a voltage somewhere between zero and 240v or would it just stay at zero until the point where the resistance was low enough that it would go short circuit?
If you lowered the resistance of the equipment you would blow the fuse or trip the circuit breaker but theoretically greatest loss of voltage happens where the greatest resistance is.
But why earthing/grounding one wire in the first place ?
It's there to protect the system from lightning. Basically if the grid is striked by lightning, the current will go through this grounded conductor instead of the system potentially destroying whatever that is connected to the system. Tv, computer, lights, etc...even the transformer itself. However, grounding is actually a trade off because we essentially connect the ground (earth) to the transformer and we are standing on the ground, which makes us electrically connected to the transformer also. So all it takes is for us to touch the other side of the transformer and we complete the circuit, thus, get shock.
Star & Delta 3 phase systems.. Now theres a subject. No neutral on Delta? Why is that? Discuss lol 😊 great video again JW..
You only get 3 phases from 3 corners of a delta, no reference to have a neutral. With a star you always create 4 reference points, 3 of which we get our line conductors and the center reference we get a neutral conductor.
Nice video!
What are your transmission lines like in the UK? US has three-phase delta transmission lines, which are cheaper but more susceptible to phase imbalance.
The same - 3 phase delta. 400kV and 275kV for the larger ones,
Hi +john ward what i dont get is that when you showed the broken neutral and you said if you touch it youll get the full 240 shock isnt that the same thing of a isolated transformer because theres no earth supply so you wouldnt get a shock?
The neutral at the other end of the break would still be on earth.
Why is there 230 V across the transformer when it is just wire with no resistance? Is this an example of what they call impedance?
The coil of wire of which 230 volts is across is low in resistance and high in inductive reactance. Resistance and inductive reactance = impedance, long answer to affirm your correct thinking.
Hello, please tell me ...what will be output voltage on 1∅ transformer if not grounded?
Output voltage would be the output voltage the transformer says it will be. Grounding does not change the output voltage.
What if it is floating neutral ?
why neutrals from transformer have voltage when N from home return to transformer
What will happens if the neutral line is disconnected from the transformer? Will my fan run faster or slower, or else? As the neutral is shared between homes and every phase, i wonder what's the consequences
On a 3 phase transformer, if neutral is disconnected and the loads are equally balanced, then nothing changes. If loads are not balanced between the phases (most likely), then some will get a much higher voltage and others much lower, resulting in equipment damage and fires.
@@jwflame then why some phase has lover voltage even tho the neutral line is connected. In my area, one particular phase has much lover voltage (190v) compared to the other two (220v) resulting in unstable computer and dimm lights when using that particular line. That makes me think that neutral line won't guarantee stable voltage across phases.
@@dputra If the voltage is low all the time, then it's one or more of: cables that are too long, cables too small or the system is overloaded.
@@jwflame thanks for the answers! 👍👍👍
Why do you say "Line"? I thought it was the "Live" terminal?
“Line” is an electrical term. “Live” or “hot” refers to not at ground potential.
Hi John. I've been following much of your videos, and they are all very informative and helpful.
I have have a question as follows:
For a domestic AC circuit, we say that the Neutral is connected to the ground, hence making it 0V. Now, if close a lighting swith for example, to complete the circuit, this would cause the alternating current to flow on either direction between Line and Neutral.
Under this circumstance (a closed circuit) wouldnt this make the Neutral "life" during the reverse cycle?
And if I touch the Neutral during the reverse cycle, would I then get a shock?
I think another way asking is that can I get a shock when I touch the Neutral busbar at the consumer unit while the end circuits are closed?
Hope you can give me a bit more clarity on this.
Thank you
You won't get a shock from the neutral in normal operation (although touching one isn't recommended as a fault could result in dangerous voltages appearing).
Neutral is always at 0V because it's connected to ground, and current cannot flow between ground and N because there is no voltage difference.
Line is either +230V or -230V relative to ground.
AC is not swapping L&N - it's just having L being positive or negative relative to N.
@@jwflame
Many thanks John for the explaination. Very helpful.
@@jwflame
In case of an isolated AC transfomer, without any earth connection, is it correct to say that there is voltage swapping between one conductor to the other? (Non of the conductors are connected to ground)
@@jwflame This is confusing "AC is not swapping L&N - it's just having L being positive or negative relative to N"
Please explain
A.C. 50Hz UK Transformer 11Kv to 230V AC
+ - + - +
- + - + - wire connected to Ground current flows to grown, Earth BANG/FIRE!!!!
Every 50Hz, as the Neutral on the positive cycle should sink current into Ground/Earth
OK Fuse will blow every 50Hz, as the Neutral on the positive cycle should sink current into Ground/Earth.
You portray current as always flowing from the top terminal of your transformer to the load and back to the transformer at the bottom terminal with the neutral wire (and ground) also wired there. However, during the second part of the AC cycle doesn't current flow reverse and flow from the transformer bottom terminal to the load and back to the top terminal? If this is true, then during this part of the cycle, current would flow to directly to neutral and ground and never reach the load? I've asked this question and no one provided an explanation so far
Yes, the current changes direction and flows in the opposite direction. it's either L to N, or N to L.
Current will not flow between neutral and ground in either case, as both are at the same potential / voltage.
Thank you. But current still flows to ground (or whatever you want to call it) and not to the load because its much easier to do that than to overcome the load resistance? The question was not whether current flows between neutral and ground (it doesn't because they are wired together) but does it flow directly to ground/earth from the transformer the way your diagram depicts? Please explain
@@georgerocks5191
Current does not flow to ground. Current always returns to the source. If a circuit is defective current may flow through ground but only to reach the source.
As for current always flowing out of the top terminal, instructors tend to treat simple AC circuits as if they are a strange form of DC. Don't care what the voltage polarity is. Don't care which way the current is flowing. It just doesn't matter. Instructors rarely tell you that.
Bill
bill- if ground has lower resistance than the source, how can current return to the source? preferable path is to ground
@@georgerocks5191
A battery can be a source. The secondary of a transformer can be a source. All sources have one requirement. Every electron that leaves a source must be replaced by an electron that enters the other source terminal. This accounting is very strict. The only reason current flows at all is to balance the books in the source.
Bill
UK voltage spec is 230V. But when I measure it I get 240V, is your voltage 230 or 240?
230V, +10% / -6%., or anything between 216V and 253V.
It is usually about 240V, as it was previously 240V +/- 6% and although the definition changed, reality did not.
Since 2009 the tolerance is +/- 10%. The +6 and -10% percent was during a transition period so the appliances in countries which had 220V before wouldn't get roasted.
You're talking about the electric strength of capacitors and other parts because in most cases this value for this rating is for a DC voltage. But the peak voltage in an AC-system is ~1.4 times (precisely it's the sqrt of 2) higher than the nominal 230V.
Mains voltage in Europe is 230V, and the permitted tolerance is +/- 10%. Meaning the voltage can be between 207 and 253V. If you live next to a feeding point the voltage is always higher. Here in Germany we've switched from 220 to 230 for the harmonisation in 1986. Before this some had already 230V, now they have almost 240V. Near the feeding point the voltage is always higher, so the last one gets a deicent voltage (voltage drop in the cables is the cue).
Hi
And Low
Sir, could You please provide the book "British standard for electrical installation" as PDF format in the comments section? Anyway, thank U for this great video
lol @ 1.05.
JW you have to learn to say what you mean...no more beating about the bush! 🤪😂
Hmm, you’re only discussing things in a half cycle. Everything in the video is reversed during the negative half is the cycle.
Whoops wrong video.
This guy is dangerous. You will get a shock on the neutral
As explained in the video neutral is connected to the earth at zero volts potential so no you do not get a shock from the neutral.
@@jamesm90in theory, yes. But this creates confusion for electricians, especially the new ones, because they assume neutral is always safe to touch. As a matter of fact, getting shock from a neutral is very common in the field. Is it beause the theory is wrong? No. It's because the term "neutral" is relative. It's called a neutral only because it is connected to the ground. A shared "neutral" is the evidence why neutral is relative. It's so dangerous that it is now against the code to have a shared neutral
the ground wire cannot be connected to the circuit, otherwise the path chosen will be altenative to closed circuti to the utility tranformer? the ground it's an emergency connection with very low resistance to connect, in case of a ground fault the connection will be hot? That is how i know it.
John what happens in the case the three phase power is unbalanced? A) L1 - L2 - L3 are all showing 400v differential in any combination. But B) L1 shows 270v to ground, L2 shows 242v to ground, and L3 shows 229v to ground. Now some caveats often the 400v is supplied by the power distribution system of the city, but just as often it is supplied from a transformer on the premises from a much higher voltage supplied to that premises.
Also, in some situations there really exists no ground like in the arctic, shipboard, or aircraft. I have seen helicopters at sea and in arctic land and the grounding hook basically gets a lightening bolt as it gets close to the aircraft. Sometimes in the arctic you will see salted wells 200' - 300' or more deep in attempt to create a ground. So this makes things very interesting. Particularly with rotor wing aircraft flying in snow or rain, where static charge production builds up to immense proportion. Though you see few of these problems in houses... remember where the ground is frozen there exists no possible ground.
Those voltages suggest the neutral connection at the transformer is missing or damaged.
@@jwflame Thanks... that never occurred to me, brilliant! If I may borrow my god-daughter's favored exclamation. The building was constructed in 1950 by a famous engineer, inventor, and industrialist credited with the first step to the automatic car... it had well over a million lavished on it in that days money 9000 sq.ft./900sq.m.. Electrically it is perfect, even with todays standards... except for a couple installs in the last 20 years. One of those is a piston type compressor of 25 hp/19KW... which was installed without a neutral but with a substandard ground wire gauge. Installed 12 years ago, though the panel has a neutral connection from the time of the buildings construction. The closing coil went out in the motor controller with very dodgy wiring job too. No control secondary power source, meaning it being hot wired without fuse protection, off the main; no interrupter of the supply, and; everything else never seen print in a standards book, So I undertook repair... my partner thought I was crazy to do it. The town has had for as long, as long I remember a phase problem, due to a transformer issue, and that I am not knowledgeable about. I thought they may have had a bad winding or phase connection, and bypassed that. But it just never occurred it could be a neutral though that makes absolute sense... but remembering most are Delta - Wye connected, brilliant! Am afraid it is my defective French education in physics, and EE, now nearing 50 years ago.
Great explanations and help in educating those modern education has passed over. Of course, my Université Pierre-et-Marie-Curie-Paris, and you know the French they had all the great discoveries in the Age of Electrification. Don't remember Faraday even mentioned, but do François Arajo, Léon Foucault, and André-Marie Ampère, supposing; Arajo's story was more interesting; it's those Pirates... putain de merde! Of course, the French do not have any profanities existing.
@@jwflame I must admit your understanding of electricity and concepts is top notch.
John nice vid. First time I have seen it.
But, many will be thinking, *why* is the circuit (N) connected to the ground? What has this taking cable to connect to the ground, when I do not do that with my battery radio?
There is: *1)* grounding; *2)* circuit protective conductor (cpc); *3)* Equipotential bonding.
These are all _separate_ but all meet at the main grounding terminal.
All these three use the same coloured wiring creating confusion. *Different coloured cable for each would make matters easier.*
*1).* Connecting a system to the ground is for lightning strikes and static electricity. Lightning always wants to get to the ground, so if it hits electrical equipment it has a path to ground.
*2).* cpc is a parallel neutral (N) with no current running through it - if L is in contact with the cpc for any reason it runs back to the point where the cpc and N join which is _before_ the protective device in the main panel. The L & N will be out of balance _after_ the protective device so it will trip isolating the circuit.
*3).* Equipotential bonding is connecting all the metal parts of a house together (e.g., water and gas pipes) that do not carry electrical current - to the electrical _ground._ This is to ensure if a metal part becomes live all metal parts become live to reduce/eliminate electrical potential.
Thanks for the lesson. I have an isolation transofrmer when I use my oscilloscope so I don't blow my self up.
I still wonder why / how it came to be that the neutral is connected to ground. I always thought using isolated mains was safer, like an isolation transformer? Then so long as you don't touch both outputs you are safe. I guess there's a reason?
If everything worked perfectly this would be true, and then instead of Live (L) and Neutral (N) we would have two lines out of the transformer. L1 and L2. In a single fault condition there would be no earth path, so no fuse would trip and the frame of your toaster would sit there "Live" this would not be an issue if you touched it as there is no earth path. However if your faulty toaster had a fault from L1 to the frame and another appliance had a L2 fault then you would have the full 230V between them.
In reality maintaining full isolation across a network is very hard, and bits of metal, pipes etc would end up being live to one line or another. Much easier to earth one line and call it a neutral. It works best when there are multiple earths on that neutral, otherwise known as the MEN system, or multiple earth neutral
John Simpson Thanks for the answer.
John Simpson Also, 3 phase system, if isolated system was used, and one phase has a fault to ground, it will go unnoticed because of the isolated setup. But now there is a potential 400v from the other phases to ground. Where as with neutral connected to earth, there is reference which means phase to earth faults should show, or operate tripping devices.
+James Searle
John did a video on EXACTLY this -- th-cam.com/video/Wx_v1-T1gE4/w-d-xo.html
John Simpson In North America, 240 volt circuits have no neutral; both conductors are active. The line to neutral voltage is 120 volts,,and there are 2 active lines, 180 degrees out of phase.
Now the weather is improving, do you have plans for another lift video?
Hi John, loving your videos...got a quick question.
UK nominal 230v with +10% and -6%.
What is the 400v, is it the same +10% and -6%?
Yes, the statutory voltage envelope in the UK for low voltage supplies (230V single-phase, 400V three-phase) is -6% to +10%.
I Like watching all your tutorials, thanks
Now, how does this all apply if you have a delta primary and star secondary isolated transformer and you do not connect N together with PE. Then N still is 0v, but not a part of earth. How does this apply to the safety of the system?
In this way there would never be any way for the current to pass through you an back to the source should you be so unlucky and touch one of the phases?
I see now how everything around you potentially can turn into one of the phases if there is a fault and that will dramatically increase your chances of completing the circuit with your body.
This was incredibly interesting, thank you John, this was very well explained now I have a better understanding of 3 phase and single phase. Cheers.
In Europe single phase systems are uncommon. The system that is used in most cases is three-phase. Even if you don't have a three-phase system in your house, there are always three phases below the street and the houses are equally distributed to the houses. Meaning first house is on L1, the next one on L2, the next one on L3, the next one on L1 again and so on.
Marcel Germann For most applications this is true. But some industrial systems do use three-phase to single-phase transformers. For example, where a limited supply is required, or as the mains supply element that is backed up by a standby emergency generator.
All industries that I know use the three-phase system here in Germany, because that's the standard here. And even if you don't need the three phases, you can always pick one of the three phases and a neutral and you've got 230V. Three-phase is common even in residentials. And there are three-phase generators available which generate 3x230/400 VAC. In Germany the kitchen cookers are connected to all three phases. The heating plates use L1 and L2, the baking oven is connected to L3. That requires a 5x2.5mm² cable (L1, L2, L3, N and PE) and it's fused with 3xB16A MCBs. That are round about 11 kW, but in most cases you could upgrade to 3x20A (~14 kW, depending on the length of the cable and heat dissipation) if that's not sufficient. In single phase systems the kitchen cooker is fused with 25 or 30A in most cases and the wiring is 4 or 6mm².