2 x RCD's tripping

[driverman]

Hi guys, tried searching,whereby explanations have been given as to why a RCD will trip by a fault on a circuit that ISN'T electrically protected by the RCD tripping. Typically crossed neutrals or borrowed neutrals. I'm not into testing. Company I work for been called out to an EV bollard with 2 x 32 amp skts and 2 x Type A RCBO's protecting each socket within the bollard. Separate 65amp MCB SWA circuit supplying bollard. Socket 1 protected by Type A RCBO 1. Socket 2 protected by Type A RCBO 2.
However when skt 1 used RCBO 2 tripps! When socket 2 used RCBO 1 tripps! All internal wiring has been check out to ensure connected correctly ie no cross neutrals etc.
Bollard sited internally, TN-C-S earthing. On a temp basis TN-C-S removed and TT created at bollard. Made no difference. RCD's trip within about 5 mins when 1 x skt on load (about 30amps). The RCD's when tested by instruments are OK. As usual your thoughts appreciated.

 

[Farmelectrics]

throw a sicky till its sorted lol

 

[driverman]

throw a sicky till its sorted lol

Others will be dealing, not me. But I'd like to know how why etc

 

[R G]

When you say a separate 65A MCB SWA circuit to the bollard what do you mean , is it an additional supply ??
Perhaps a sketch or photos may be helpful...

 

[marconi]

Hi guys, tried searching,whereby explanations have been given as to why a RCD will trip by a fault on a circuit that ISN'T electrically protected by the RCD tripping. Typically crossed neutrals or borrowed neutrals. I'm not into testing. Company I work for been called out to an EV bollard with 2 x 32 amp skts and 2 x Type A RCBO's protecting each socket within the bollard. Separate 65amp MCB SWA circuit supplying bollard. Socket 1 protected by Type A RCBO 1. Socket 2 protected by Type A RCBO 2.
However when skt 1 used RCBO 2 tripps! When socket 2 used RCBO 1 tripps! All internal wiring has been check out to ensure connected correctly ie no cross neutrals etc.
Bollard sited internally, TN-C-S earthing. On a temp basis TN-C-S removed and TT created at bollard. Made no difference. RCD's trip within about 5 mins when 1 x skt on load (about 30amps). The RCD's when tested by instruments are OK. As usual your thoughts appreciated.

By Marconi May I ask for a little more information? Has this problem only recently arisen? Does it happen for all the EVs which are charged at the site? What size is the SWA and how long? Is there a separate CPC between the 65Amp MCB and the bollard? Are the RCBOs electronic types? Has there been any lightning recently nearby?

Some quick things to consider:

Are the SWA glands in good order and fitted correctly?

Are the RCBOs Functional Earths securely connected?

Are all connections, at both ends of SWA, especially for CPC and N, tight and good?

I am wondering whether the RCBOs are being tripped because of an effect somewhere between their input terminals and the MCB. What you describe might be due to the Functional Earth and associated internal circuitry detecting loss of N, loss of CPC, loss of supply or N-E fault upstream of the RCBOs.

Might you take some voltage readings, at the supply terminals of the RCBOs: L-N and N-CPC for off-load and on-load conditions and watch what happens to them until a trip occurs? And put them in a post for me to take a gander at and muse over?

 

[davesparks]

Classic symptoms of a N-E fault

 

[Dave OCD]

Slightly off topic and forgive me if I'm wrong but I thought TNCS wasn't acceptable for EV charging supplies ?

 

[nickblake]

Borrowed neutrals would possibly cause both RCD's to trip at the same time,however it could be a fault causing a neutral neutral fault, ie . 2 neutrals damaged and shorting together, if they trip individually then the chances are its a neutral to earth fault , but this may not be associated with the circuit connected to the socket ,as the earths and neutrals are linked together on there own bars , all earth all neutrals , the fault could be on another circuit which is causing the in balance , and the best way of finding this is to disconnect all the earths and neutrals and test each circuit until the fault is located ,so its get the tester out and start testing

 

[Leesparkykent]

Slightly off topic and forgive me if I'm wrong but I thought TNCS wasn't acceptable for EV charging supplies ?

I know If the vehicle charging point has an isolating transformer then it can be TNCS.

 

[Dave OCD]

Yes that's it Lee, thanks for clarifying .

 

[Lazlo]

N-E Fault

 

[marconi]

Hi guys, tried searching,whereby explanations have been given as to why a RCD will trip by a fault on a circuit that ISN'T electrically protected by the RCD tripping. Typically crossed neutrals or borrowed neutrals. I'm not into testing. Company I work for been called out to an EV bollard with 2 x 32 amp skts and 2 x Type A RCBO's protecting each socket within the bollard. Separate 65amp MCB SWA circuit supplying bollard. Socket 1 protected by Type A RCBO 1. Socket 2 protected by Type A RCBO 2.
However when skt 1 used RCBO 2 tripps! When socket 2 used RCBO 1 tripps! All internal wiring has been check out to ensure connected correctly ie no cross neutrals etc.
Bollard sited internally, TN-C-S earthing. On a temp basis TN-C-S removed and TT created at bollard. Made no difference. RCD's trip within about 5 mins when 1 x skt on load (about 30amps). The RCD's when tested by instruments are OK. As usual your thoughts appreciated.

By Marconi With regards to this problem and the highlighted text above I understand the description to be the off load RCBO is the one which trips after an interval of around 5 mins but the on load RCBO remains set. Perhaps driverman could clarify please? It is the feature of the problem which most intrigues me.

 

[driverman]

By Marconi With regards to this problem and the highlighted text above I understand the description to be the off load RCBO is the one which trips after an interval of around 5 mins but the on load RCBO remains set. Perhaps driverman could clarify please? It is the feature of the problem which most intrigues me.

Yes, that is exactly it. However I'm a bit of a bystander with this. At the moment the RCBO's have been changed to type A RCD's and is all working fine. The situation is being constantly monitored.

 

[marconi]

Yes, that is exactly it. However I'm a bit of a bystander with this. At the moment the RCBO's have been changed to type A RCD's and is all working fine. The situation is being constantly monitored.

By Marconi Thank you. I will look out for any further developments and chip in my tuppence-worth if I see you post on it again. It is very interesting to me.