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V2L Earthing - how?

The circuit is working because you use the V2L adaptor, plug a kettle in and the kettle boils. This means the live and neutral magnetic fields are cancelling each other out and the circuit is balanced. The kettle faults and you touch it making a circuit through you as an earth. The rcd now senses the magnetic field imbalance because the neutral and live magnetic fields are not cancelling each other out and either a live to earth fault or a neutral to earth fault is causing this imbalance because you are now the earth.
 
The circuit is working because you use the V2L adaptor, plug a kettle in and the kettle boils. This means the live and neutral magnetic fields are cancelling each other out and the circuit is balanced. The kettle faults and you touch it making a circuit through you as an earth. The rcd now senses the magnetic field imbalance because the neutral and live magnetic fields are not cancelling each other out and either a live to earth fault or a neutral to earth fault is causing this imbalance because you are now the earth.
But why in a V2L would the circuit travel to earth if the neutral conductor itself is not earthed? Please, remember, the reason in a MEN grid system that electricity travels to earth is because the neutral is earthed at multiple points. In a V2L, IT system; the neutral is never earthed. Electricity will not flow to earth under a fault condition in V2L because earth does not complete the circuit.
 
No, but electricity will flow any way to complete its circuit. Do you know why your home electrical system will flow to ‘earth’ if you touch it? It’s because the neutral conductor, which completes the circuit, is earthed at multiple points in the grid, including probably your earth stake at home; but also at multiple points along the poles and wires from the source to your house. This is why when you touch a live conductor, the electricity will ‘want’ to flow through you to earth. When this occurs, the RCD detects an imbalance between the home neutral and live, and disconnects. In an isolated system, such as V2L or a generator, where there is no earthed neutral, touching the live conductor will not cause electricity to flow through you as the earth does not complete the circuit back to the source (the V2L source or generator), so a RCD won’t work because there will be no imbalance. So. How would a RCD work in this case if electricity won’t flow through you to earth?
I totally agree with you, RCD's in a home rely on detecting an imbalance between L & N, that imbalance occurs when there is a current flow to earth, for example the circuit becomes.... L > Fault point > Earth

On a V2L
  • the ground that we stand on is not earthed to the car
  • If you touched the L you wouldn't (shouldn't) get a shock unless you are also touching the N, in this case you wouldn't trip an RCD, as there wouldn't be an imbalance
  • If the you touched the L and a metal point body of the car (AND assuming that this is classed as Earth) then that could trip an RCD
 
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I totally agree with you, RCD's in a home rely on detecting an imbalance between L & N, that imbalance occurs when there is a current flow to earth, for example the circuit becomes.... L > Fault point > Earth

On a V2L
  • the ground that we stand on is not earthed to the car
  • If you touched the L you wouldn't (shouldn't) get a shock unless you are also touching the N, in this case you wouldn't trip an RCD, as there would be an imbalance
  • If the you touched the L and a metal point body of the car (AND assuming that this is classed as Earth) then that could trip an RCD
THANK YOU 🙏

I totally agree with you, RCD's in a home rely on detecting an imbalance between L & N, that imbalance occurs when there is a current flow to earth, for example the circuit becomes.... L > Fault point > Earth

On a V2L
  • the ground that we stand on is not earthed to the car
  • If you touched the L you wouldn't (shouldn't) get a shock unless you are also touching the N, in this case you wouldn't trip an RCD, as there would be an imbalance
  • If the you touched the L and a metal point body of the car (AND assuming that this is classed as Earth) then that could trip an RCD
I do wonder though if you touched L and N and completed the circuit (and of course, had current flow through you), will the RCD ‘see’ it, as wouldn’t the current in and out of you be equal?
 
I think the answer is is PE and N Are linked at source?

The car cannot detect any earth fault, as it's not got any sort of earth reference, as to all intents and purposes the tyres are insulators. This means that earth leakage devices cannot work, as there is no earth for any current to leak to that would create an imbalance between the two live conductors from the car. The V2L supply is IT, so neither line nor neutral are referenced to earth at all, AFAIK, although it's possible that there may be a neutral to PE link for UK specs (not sure about this, TBH).

Nothing wrong with IT for V2L, as long as the user is aware of the reduced safety and understands the limitations of an IT system, and that an IT system must be kept separate from any other form of electrical installation that may have a different type of earthing system. Lots of small generators are IT, some with an optional N to PE link, some with a separate earth electrode connection to make them TT. We rarely ever use IT in the UK, it's pretty much only used for some medical and other specialised installations.
 
I think the answer is is PE and N Are linked at source?

The car cannot detect any earth fault, as it's not got any sort of earth reference, as to all intents and purposes the tyres are insulators. This means that earth leakage devices cannot work, as there is no earth for any current to leak to that would create an imbalance between the two live conductors from the car. The V2L supply is IT, so neither line nor neutral are referenced to earth at all, AFAIK, although it's possible that there may be a neutral to PE link for UK specs (not sure about this, TBH).

Nothing wrong with IT for V2L, as long as the user is aware of the reduced safety and understands the limitations of an IT system, and that an IT system must be kept separate from any other form of electrical installation that may have a different type of earthing system. Lots of small generators are IT, some with an optional N to PE link, some with a separate earth electrode connection to make them TT. We rarely ever use IT in the UK, it's pretty much only used for some medical and other specialised installations.
I agree. And really I wonder if it truly is less safe, because if you touching a single conductor won’t cause a traditional ‘flow to earth’ as the neutral isn’t truly ‘earthed’ then is it really less safe? The dangerous fault condition in V2L is you somehow touching both conductors
 
I do wonder though if you touched L and N and completed the circuit (and of course, had current flow through you), will the RCD ‘see’ it, as wouldn’t the current in and out of you be equal?
Sorry, typo now corrected, I meant to say "wouldn't be an imbalance"
I have a nasty habit of missing off the "n't" which totally changes the meaning :)
 
Sorry, typo now corrected, I meant to say "wouldn't be an imbalance"
I have a nasty habit of missing off the "n't" which totally changes the meaning :)
Gotcha! Thought so

Sorry, typo now corrected, I meant to say "wouldn't be an imbalance"
I have a nasty habit of missing off the "n't" which totally changes the meaning :)
So in which case I would think, your safety mechanisms in a V2L system are the RCD detecting a fault between the neutral/live and body of the vehicle (if the earth pin is attached to the vehicle body), or the good old circuit breaker under a short circuit fault through your body 💀
 
So in which case I would think, your safety mechanisms in a V2L system are the RCD detecting a fault between the neutral/live and body of the vehicle (if the earth pin is attached to the vehicle body), or the good old circuit breaker under a short circuit fault through your body 💀
Simply answer is that I'd be guessing, I don't understand how there could be a RCD without test and reset buttons
As we've discussed, the risk is relatively low, you'd have to be touching 2 conductors, rather than 1 and standing on earth
Even if the body of the car was earthed, there's not many conductive surfaces to touch
 
Well gentlemen I have been asking this same question about earth on V2L. I have to be honest and say I don’t understand a lot of what as been posted in this thread so I have 2 further questions which are
1 when I purchased our MG4 I all so purchased an official genuine accessory an MG V2L cables as in this picture From my MG dealership.
39FF5192-62B3-4665-A335-26CF220DF513.jpeg

So some will say I was mad to pay that price when there are much cheaper ones on the market now I know, but at the time there was not really, but there was a bit of method in my madness, you see this was all new and I didn’t want any future issues if something went wrong and the electrical systems in the car might get damage then MG could turn away a warranty claim because we had used an unapproved cable, so I decided to buy the genuine MG approved item which I did.so this MG approved V2L cable is fitted with a double 13amp switched socket which as an RCB inbuilt, I assume that’s to avoid anyone getting an electric shock.

2 Is it safe to uses or not yes or no ?
Thank you
Les



2
 
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That's interesting that they supply it with a resettable RCD when some have said it is built into the car...
Now is there, I remember a few years ago I had been using a plug in RCB breaker for my electric lawn mower for a long time without issue, and when we had solar PV installed we had a new consumer unit fitted at the same time which had a RCB inbuilt which protected several circuits including the sockets everywhere in the house, the electrician who fitted the unit advise me not to use my plug in breaker for my mower anymore and said it is bad practice to use to RCDs on the same outlet, so in effect that is what this is doing if there is one in the car and one on the approved V2L cable plus I don’t see anyway to reset a RCD in the car if it has one and it tripped I don’t know to be honest.
Les.
 
An RCD (residual current detector) measures the current passing through the Live and Neutral Wires. As long as the current is the same it will function. If there is an imbalance between the live and neutral (measured in milliamps) the RCD will trip and stop the flow. This difference can be caused by many things, for instance by some current running through you to earth, (not recommended). Because the trip current is so small and the trip time so quick it gives good protection, double pole is better than single pole as it protects both the live and neutral wires.
An electrician would be able to tell you more about it than I.

RCDs Explained | Electrical Safety First
 
As others have stated, it makes sense that the V2L source would be isolated from the vehicle chassis, and it makes sense that the earth pin on the outlet(s) is connected to the vehicle chassis. That way, there can be no potential between any appliance metal and the vehicle metal; it would be easy to touch both at once.

EVs are an especially well isolated source, because they actually perform insulation monitoring at start-up (part of that set of muted clicks you hear when the car goes to ready or prepares for charging). So you can be fairly well assured that there is no leakage to the metal chassis from the battery. Unless you get an electrical leakage while driving, are forced off the road in turtle mode, and as you wait for a tow, you think "while I'm waiting I might as well use V2L and have a cup of tea!" :oops: Even then, you'd have to have a fault with the jug, be touching the jug's metalwork, and also be touching some metal in the car to complete the circuit.

So it makes no sense to me to make a connection from the generated neutral to the earth pin of the outlet(s). But with the official cable including a Residual Current Device, it looks like they do make that connection. In my mind, the biggest use case for V2L is outside the vehicle, where the tyres effectively insulate the car chassis from earth, rendering the RCD pointless. But there are at least some use cases for using V2L inside the vehicle, and there you would often be insulated from the chassis by the seats and carpet, but there would still be plenty opportunity to make contact with the chassis of the vehicle. So for when you are inside the vehicle, I guess that the occupants are either floating, or at or near chassis potential. So inside the vehicle, or outside but touching the metalwork, the RCD does make some sense, and will protect you from faulty appliances that have conductivity from the live output to the metalwork. As noted earlier, if they didn't make that connection from neutral to chassis, there would have been effectively no danger, and no need for the RCD. Although I suppose it's possible that the vehicle's battery insulation monitoring might be conducted before every part of the vehicle's inverter is active, so there may be some potential risk due to a faulty inverter. It seems possible to me that a leak to chassis might not impair normal vehicle operation, and thus go undetected.

Outside the vehicle, everything is effectively isolated unless you have contact with the metalwork. But with that contact, it's the same situation as being inside the vehicle: you are protected by the RCD. I can't see how the neutral to chassis connection would alter safety when outside the vehicle. The RCD won't trip if you make contact with a live conductor, but you won't get a shock either. Any shock current, unless live to neutral, would register as an imbalance, so it would trip the RCD in case you did manage to get a connection through earth (perhaps it's pouring rain or heavy snow or there is an animal touching the metalwork).

But to me that raises a safety issue: if you opt for a cheaper option that doesn't have an RCD built in, then if as I assume the neutral output is connected to vehicle chassis, then it seems to me that you really should use an RCD to protect yourself while inside the vehicle, or one of the cases where something earths the vehicle chassis. Fortunately, it's easy enough to add one, but unless it's part of the cable, there is the chance that you'll skip using it when you actually need it.

Now it would be great to check that my assumption that the neutral and earth pins of the V2L cable are at the same potential when running. Obviously, this is non-trivial to do safely, so if you're not totally sure of what you are doing, don't attempt this. Testing for conductivity between neutral and earth when the V2L is not running is not relevant; there must be relays to connect neutral to the earth pin only when V2L is running. Otherwise, when charging, there would be a second connection from neutral to earth (the first being at the distribution/switch board), and this is not allowed, and can lead to nuisance tripping of RCDs as earth conductors share part of the neutral current.
 
Had I further look at this today as I found a mains socket tester in my garage and I hope you can see from my picture there is no earth light on in the V2L outlet when I plug it into a socket on the house ring main all three lights are on.not sure what this means
Les
DABBDF86-AF4C-4CA0-A5A3-00422C2A3311.jpeg
 
Very interesting discussion. As originally suggested by Tsch, if the battery system can be regarded as fully floating, then touching either pole when outside the vehicle should not produce any current flow. I suppose its conceivable that neither pole is connected to the chassis either. All references to other car systems may be isolated too.
 
Had I further look at this today as I found a mains socket tester in my garage and I hope you can see from my picture there is no earth light on in the V2L outlet when I plug it into a socket on the house ring main all three lights are on.not sure what this means
LesView attachment 16012
Hi Les, out of interest have you tried the test button when it is connected to the car to see if it trips without an earth?
 
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