RCD tripping with EV charger..Question.

[Red One]

Im not sure an electrician is left having to do so much and to be honest, if he couldn't get to the fault reasonably quickly, given that its clearly either the EV charger, or the cable from the charger to the garage CU thats at fault, Im not sure I would want to pay him to work on the issue in the first place. The only thing to me that seems non compliant is the EV charger connection to the garage CU if as it happens it should have its own dedicated RCD . The rest of the CU is as was when the house was built ie, several MCBs ranging from 6a to 32a protected by an RCD. I dont see any problem there, and it has worked without issue for 20 odd years. So if a spark cant arrange to have this EV charger or its replacement to be wired via a dedicated RCD hes not really up to much as I would expect thats elementary to any half decent electrician.
If I wanted to bring it up to current spec, then changing out the original plastic CU to a metal one would be prudent, but the EV connection aside, theres nothing wrong with the garage CU as it is.

 

[Red One]

Thing is it’s not clear from the description how the sub main to the garage is protected

You need to read it again, I stated on the description. "I then went to the garage, as I suspected the issue might be in the CU thats installed there. The garage CU is covered by the RCD in the house, so only has a mains isolator at the garage CU". Again, this is how it always has been from the house and garage were built. My understanding from posts here and reading elsewhere, is that if the garage CU is protected at the main house CU, then there is no need for a further RCD in the garage CU. The garage sub CU is supplied from the house via an underground armoured cable.

 

[endecotp]

its clearly either the EV charger, or the cable from the charger to the garage CU thats at fault

I’m not sure that’s proven, is it? Have you excluded N-E faults on other circuits? As noted by someone else above, remember that turning off an MCB does not eliminate any N-E leakage on that circuit.

 

[Murdochcat]

You need to read it again, I stated on the description. "I then went to the garage, as I suspected the issue might be in the CU thats installed there. The garage CU is covered by the RCD in the house, so only has a mains isolator at the garage CU". Again, this is how it always has been from the house and garage were built. My understanding from posts here and reading elsewhere, is that if the garage CU is protected at the main house CU, then there is no need for a further RCD in the garage CU. The garage sub CU is supplied from the house via an underground armoured cable.

So it’s abundantly clear then the original install of the EV circuit is not compliant. EV circuits need to have dedicated OCPD and dedicated RCD protection

AND you mention the house RCD - how many RCDs does the house CU have?

 

[Red One]

I’m not sure that’s proven, is it? Have you excluded N-E faults on other circuits? As noted by someone else above, remember that turning off an MCB does not eliminate any N-E leakage on that circuit.

yes, I disconnected all wiring, including all the live wires from the MCBs, and all the neutral and earth wires from the bus bars. I then tested the EV supply cable in compete isolation from all other circuits on the CU. With the EV cable out of the equation, all the garage MCBs via the RCD are working properly with no tripping. When the EV cable is connected to the main supply on its own from the house supply, it trips the RCD.

So it’s abundantly clear then the original install of the EV circuit is not compliant. EV circuits need to have dedicated OCPD and dedicated RCD protection

AND you mention the house RCD - how many RCDs does the house CU have?

I am aware that the EV circuit install is non compliant, and thats twice you have stated it. I also stated earlier that the house has 2 RCDS in 2 separate CUs, one covering lights, , appliances, cooker etc, the second in box 2 covering various house side sockets and garage. The house RCD in CU2 covers the garage supply. I am aware that the EV now needs a separate RCD by itself. But that is not the cause of my initial tripping query. Due to a process of isolation, its either the EV cable to garage CU, or the EV charger itself that is causing the trip. When tested , all other MCBs, earth and neutral cables to garage sockets and lights etc were disconnected completely from the garage CU. From a suggestion above I will now disconnect the supply cable from the EV charger while still connected to the garage CU and see if that trips the RCD. If it does, then the cable is at least one of the fault causes. On replacement of the cable, if the RCD is still tripping, then its obvious that the EV charger is at fault, and I will replace it. With the EV charger disconnected from the garage CU currently, everything supplied by the garage CU is functioning fine.

My initial query was simply curiosity as to why the EV charger is functioning completely normally when the RCD is temporarily bypassed, yet tripping when the electric supply is via an RCD. On inspecting the insides of the charger, there is no obvious stress situations on the think supply cables, nor the lead to the car charger. The PCB is completely clean like new, and there are no signs of water ingress. I can only suspect that it must be some malfunction in the circuitry as there is no physical cable damage. There is only about 3 ft of supply cable from the garage CU to the charger so its easily inspected.

 

[EFLImpudence]

My initial query was simply curiosity as to why the EV charger is functioning completely normally when the RCD is temporarily bypassed, yet tripping when the electric supply is via an RCD.

Do you think possibly the RCD is doing what it is designed to do - namely detect earth leakage and disconnect the supply - yet when you by-pass it it doesn't do that?

 

[flameport]

There are only a few options:

EVSE has excessive current leakage
Cable CU-EVSE has excessive leakage due to physical damage or cable degradation/moisture absorption
EVSE / cable / both always had excessive current leakage, but it only shows up now as the ancient RCD in the consumer unit was physically jammed and due to some unrelated trip or someone pressing the test button is now no longer jammed and it's working as intended.
Or that RCD now trips at a smaller current than it did before.

The solution:
Determine what fault(s) exist using appropriate test equipment.
Replace whatever is defective, and reconfigure the installation so the EVSE has it's own separate RCD.

 

[Red One]

Do you think possibly the RCD is doing what it is designed to do - namely detect earth leakage and disconnect the supply - yet when you by-pass it it doesn't do that?

Stop being a smartarse. I am full aware of what the RCD is doing and why. My query is how it seems to function normally with this earth leakage when the RCD is bypassed. Should there not be some other manifestation of a fault? I didnt suffer shock when testing it or doing a test charge on the car, and there was no malfunction either of the unit, its charging capability, or its connection to the internet and app. All are working as normal.
I emphasise yet again, I am NOT going to run this charger without RCD protection due to the risk. My question was simply academic.

 

[Red One]

There are only a few options:

EVSE has excessive current leakage
Cable CU-EVSE has excessive leakage due to physical damage or cable degradation/moisture absorption
EVSE / cable / both always had excessive current leakage, but it only shows up now as the ancient RCD in the consumer unit was physically jammed and due to some unrelated trip or someone pressing the test button is now no longer jammed and it's working as intended.
Or that RCD now trips at a smaller current than it did before.

The solution:
Determine what fault(s) exist using appropriate test equipment.
Replace whatever is defective, and reconfigure the installation so the EVSE has it's own separate RCD.

Excellent. thats a straightforward and clear response, thank you. I know its not a faulty RCD in the CU as I bought a new one and replaced it with the same result. That was the first thing I checked. I will now check the supply cable from the garage CU with the EV charger disconnected and see if it still trips. If not, I will likely just replace the charger and arrange for it to have its own RCD separate to the Garage CU.

 

[EFLImpudence]

I am full aware of what the RCD is doing and why.

Apparently you are not.

My query is how it seems to function normally with this earth leakage when the RCD is bypassed.

That's how it works.

Should there not be some other manifestation of a fault?

Not necessarily.

 

[Harry Bloomfield]

Should there not be some other manifestation of a fault?

Not necessarily - all it needs is something able to cause a leakage of 30mA, between L and E, or N & E.

I wonder - The plug, that plugs into the car, might that have got some moisture in it?

 

[Red One]

Not necessarily - all it needs is something able to cause a leakage of 30mA, between L and E, or N & E.

I wonder - The plug, that plugs into the car, might that have got some moisture in it?

good call, never thought of that, I will check it. Its easy to test by removing the pug and its cable from the charger and seeing if the charger then trips the RCD.

 

[ericmark]

I have decided to return to the first post, in case I had made an error reading it, as I am dyslexic.

I have 2 CUs in my house, box one covering lights/ cooker/ machine etc. The other box 2 is for sockets, garage and a few other things. several days ago, the RCD for box 2 tripped. After spending quite a time checking all the cabling in the box I tried to isolate which MCB the issue might be coming from, but with all MCBs off and the RCD on, any MCD I switched on tripped the RCD so I couldnt isolate the issue. I bought a new identical Wylex RCD, but same issue.

At this point it would seem a neutral to earth fault, as the fault exists with MCB’s off. With no test equipment, my next test would be to drop the neutrals for each circuit, with test equipment similar test, with isolator off test each neutral to earth.

I then went to the garage, as I suspected the issue might be in the CU thats installed there. The is covered by the RCD in the house, so only has a mains isolator at the garage CU. Again any MCD that was switched on in isolation tripped the RCD in the house.

With a suspected neutral earth fault, this was pointless, as all neutrals still connected.

SO I stripped all the wiring back from the 5 MCD's and the mains isolator, presuming that the problem electrical item was somehow "polluting" the whole CU causing an issue when any MCD was turned on. One by one, I connected back the MCDs for lights, sockets and EV charger.

Not sure if with this you are disconnecting a neutral or not?

Ultimately I isolated the problem to the cable from the EV charger . I again disconnected all the MCBs and all the negative and earth cables from the CU, and just connected the EV charger to the Mains Isolator, earth and negative. Again the RCD in the house CU tripped. The EV Charger has been running flawlessly for 3 years with no issues until now. I opened the EV charger, disconnected and reconnected the mains in wiring, the wiring to the charger cable, and all LED connectors etc. It was still tripping the RCD in the house.

OK so far.

I then bypassed the RCD in the house with the EV charger connected directly to supply. It started up as normal, was fully functional and on connection to the car, charged it as normal for 4 hours whilst I watched closely for any issues and checked the cabling periodically.

Rather naughty, but I can see the thought process, and would assume you did ensure no one could touch the car?

I know RCDs detect various faults like earth leakage etc, but the charger seems to be working quite normal without the RCD. Now, before the inevitable comments, I am not going to run the charger without the RCD in place as there is an obvious fault. I cant figure it out so will be getting a spark in. But given the information, and just for my curiosity, what could be causing this and why does the charger function normally when it receives a direct electric supply with no obvious ill effects? Many thanks.

OK, @flameport has listed the like causes, but as to the cure, it depends on the cable used house to garage, as can’t really use the house RCD, so if the cable house to garage does not really need a RCD, and the consumer unit is the high integrity type, (three neutral bars) then move the RCD protection into the garage, using two RCD’s one for the EV and one for the rest.

If the consumer unit is not high integrity type, and the cable to the garage does not need RCD protection, then replace all but garage MCB’s with RCBO’s, and have just a MCB feed the garage. Then again, two RCD’s in the garage.

If the cable house to garage does need RCD protection, then no option, it has to be renewed.

The rest of garage only needs standard RCD protection, but the EV will need a bi-direction type, as to if type A or type B depends on the EV unit, some EV units already have a RCD, 6 mA DC detection and loss of PEN built in, but not all, so what the EV point requires, can’t really say, but it can’t share a RCD with anything else. And if charging the EV in the garage, it may not need loss of PEN detection.