Safety of EV charging points, TT, TN-S and TN-C-S.

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John Ward has done a video,
however there seems to be some errors, having a reference electrode at a distance is not a problem, but as a TT supply you want the vehicle at same potential as the ground it is standing on, so if a metal water pipe with a broken PEN has lifted the ground to 200 volt above true earth, you also want the car to be 200 volt above true earth, so earth system needs to be local to where the car is parked.

As to earth mesh with 2Ω resistance the earth wire needs to be able to take 400/2 = 200 amp, since the supply is often only using 16 mm cable, this is clearly a problem, remember there is no fuse on the earth, so bonding a TN-C-S supply to an earth better than 20Ω is a problem due to current that can flow, where it is done commercially there is a large resistor between the DNO earth and site earth to limit the current in the earth wire.

EV charging in a garage is OK, and using three phase one can monitor the three phase voltages and auto disconnect if more than 10 volt for example, but single phase 253 - 207 = 46 volt before the unit trips, or more between phases, so can't even be sure no more than 70 volt, and unless fenced in to stop quadrupeds 25 volt can kill a cow.

It would seem a TT supply is reasonably safe, as long as all are on a TT supply, but not when some houses in a street are TT and some are TN-C-S specially if there are buried metal pipes.

Public access is different to private access, so back of my house no one should be there without my permission, front of the house however, postman, milkman and many others have good reason to walk down my drive, so any car in the drive needs to be safe to touch. I can have an isolator to remove power before I touch a car, but not visitors.

I was first aware of the problem with the guy across the road when in old house, the installation was the first I had seen, and it seemed as if a simple connection to the TN-C-S supply using a MCB, this was around 2012 when Renault Kangoo long wheel base first released, it was used for a milk round.

Next was at work, three phase supply, a pair of 22 kW charge points, told TT and RCD protected, but building is TN-C-S, and there is a metal roller shutter door very near to charge points. Not installed in house, so don't have full details. No one even thought about it to start with, but they are getting used more and more, getting to the point where two is not enough.

As EV cars are becoming more popular we have a problem is the public safe? Reading Wiring matters it states
ESQCR prevents distributors from providing a PME earth terminal for certain installations, such as the metalwork in a caravan or boat and fuel filling stations.
well clearly an EV charge point is the fuel filling station for an EV car, so is it permitted to have a TN-C-S supply?

So are the EV charging points safe, or specially with TN-C-S are they potentially dangerous, and should they get a code C2 with an EICR?
 
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Mine is the safest on earth.
I put diesel in the tank and let the engine worry about letting it explode in the combustion chambers...
 
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Could an isolation transformer be used to provide a 230 V supply to the charger that is isolated from any conditions that a faulty network would create ?

A 7 kW transformer would be less cost than a new driveway.
 
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Could an isolation transformer be used to provide a 230 V supply to the charger that is isolated from any conditions that a faulty network would create ? A 7 kW transformer would be less cost than a new driveway.
Apaert from anything else, I would imagine that it would be pretty bulky (and heavy) - where would you envisage it being housed?

Kind Regards, John
 
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Obviously an isolation transformer would be impractical, as is the idea of electric vehicles for people living in areas of medium to high population density with no chance of having a fixed parking place for charging.
 
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Could an isolation transformer be used to provide a 230 V supply to the charger that is isolated from any conditions that a faulty network would create ?

A 7 kW transformer would be less cost than a new driveway.
I suggested this some time back when someone touched an EV on charge and an earthed roller shutter frame (by description it could have been Erics :)) and got a belt, the comments I received came up with all sorts of reasons why it was inappropriate. Several were based on the bulk but IMO that is not a consideration for regulation.
The big problem As I see it is the selection of likely different earth voltages around a car parked near a building.
 
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My problem is I don't know if the charge point is safe or not. It was installed by outside contractors, and one guy has the key to reset the RCD if required, it has never been required, so never looked inside. As said since close to the transformer and unlikely to be any road works to cause loss of PEN, it is very unlikely to have a problem.

However it has been known for the PEN to fail, google tells me
According to HSE statistics (table 1), each year there are around 400 reported incidents of broken Protective Earth and Neutral (PEN) conductors on TN-C-S (PME) earthed electrical installations with around 10% of these causing an electric shock.
which considering it normally causes equipment in the house to fail, so don't want it to happen too often.

So for the PEN to break supplying an EV charger is going to be rare. We have seen reports of PEN failure, but head lines tend to be copper theft caused house fire, not the PEN system caused house fire, there are times when caused by road works, but it seems no one wants to blame it on using the PEN system.

I have come across it only once, so yes it is rare. The problem was turning off the whole supply to house did not help, it still melted the earth wire, how do you remove a wire which is close to melting, only way would have been a pair of snips, and cutting an earth wire goes against the grain. So it was allowed to auto disconnect when it melted.

So even if all EV charging points to date were on TN-C-S supplies with no auto disconnection of earth wire, it is still likely no one has yet had a shock as a result.

However I would say an EV charging point should come under same rules as caravans and motor caravans and that TN-C-S should be banned for EV charging.

With the narrow boat the shore supply only fed the stage charger for the batteries, which was class II, so the shore earth so not connected, the transformer inside the charger isolated the boat from the shore supply, the same could clearly be done with EV charging, both my E-bikes are re-charged using class II chargers, since charged in doors it would not really matter anyway, but the problem is the charger is built into the car, not static.

But as with my E-bike you can get car chargers which simply plug into a handy 13 amp socket. Even the charger points
ae235
have a type AC curve B RCBO, it says
For the installation to conform to IET requirements, the appropriate RCD should be selected by the electrician and fitted at the incoming source.
so why fit a RCBO next to socket? And nothing about not being suitable for use with a TN-C-S supply, there is clearly something in the cable
ae235
I tried to find a data sheet for Masterplug MASEVCP1135SLMP but failed, it may disconnect the earth under fault conditions but there is no info to say what is inside the box.

But as EV's become more popular it is bound to happen sooner or latter, be it 2.3kW, 7kW or 22kW at some point some one will touch a live car, and possibly not the owner, but some one brushing past the car.
 
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The big problem As I see it is the selection of likely different earth voltages around a car parked near a building.
Yes, If you use the TN earth then you have a risk of shocks from voltage differences between the TN earth an "real earth". If you TT the chargepoint but don't TT the rest of the installation then you introduce a risk from any potential differences between the chargepoint earth and the house earth.

You could TT the whole installation of course but that brings risks of it's own.

I believe this is why the EV charger industry is trending away from TT earths and towards PEN fault detection devices.
 
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Yes, If you use the TN earth then you have a risk of shocks from voltage differences between the TN earth an "real earth". If you TT the chargepoint but don't TT the rest of the installation then you introduce a risk from any potential differences between the chargepoint earth and the house earth.
It's a little worse; you have the TN earth, real earth and TT earth which being relatively high resistance could be above real earth potential. Then there's the water tap which could be importing a potential from a distant bonded system.

All sounds a little hairy fairy but there are effectively 4 different earth paths which could be at different potentials
 
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All sounds a little hairy fairy but there are effectively 4 different earth paths which could be at different potentials

People living near electrified railway lines have a 5th source of potential gradients across the ground around their house.
 

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hurrah for rubber-soled boots.
 

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