Borrowed neutral on split load board

[Penguin]

I have a client with what appears to be an intermitent fault on the lighting, but trips the power.

The installation has a 16th edition board with sockets on the RCD side, and lighting on the other side as usual.

Occasionally when the landing light is switched the RCD trips on the socket side. Would a borrowed neutral cause this. The lighting circuit itself has RCBO on it that doesn't trip; does the RCBO have anything to do with it.

I haven't checked for a borrowed neutral on the lighting yet, but even if there was one I can't see why that would affect the other RCD side.

Many thanks in advance

How old is the wiring (not the DB).?
Is the landing light on a 2way switch set up.?

Is there only one single module RCBO for the light or 2. ? ( upstairs & downstairs) ?

Let me know

 

[Brightonbill]

My guess is that the wiring is late 60s early 70s.

The landing is 2 way, and the hall is 2 way. Both are on the same RCBO which never trips, only the RCD on the socket side of the board.

As I’ve combined all the circuits into one and put them on the RCD side I thought that would eliminate any possible cross connection/borrowed neutral.

So I’m looking at a fault rather than a cross connection I think.

 

[timhoward]

It may the the photo....but double check the count of live conductors vs neutral conductors on the RCD side.

Both are on the same RCBO which never trips,

Side thought - does that RCBO actually work?

Have you tried turning everything off and checking continuity between the N bars, and continuity between the top of each breaker ( in the off position) and the top of every other breaker?

Normally if there's a N-E fault on the RCD side and another unknown load driving current through the fault, the load in question would have to be connected 'somehow' to downstream of the RCD.

But a minor N-E fault on the RCD side, and a N-E fault on the non-RCD side can cause fun, e.g. a cooker element, or even that lighting circuit if the RCBO doesn't work.

Being honest as it's a Protek CU with a Volex RCD and a Niglon RCBO, it might be quicker to start again with a DP RCBO board fully testing each circuit and checking for interconnections as you go. Even if you miss the fault the DP RCBO's will show you where the problem is. I understand that budget may not allow this though.

 

[Brightonbill]

Thanks. I’ll be back again to have a discussion with the client about a new board. As always they just want it fixed NOW, and for nothing.

 

[MJPD29]

Thanks. I’ll be back again to have a discussion with the client about a new board. As always they just want it fixed NOW, and for nothing.

Have you tested the current earth leakage and/or ramp tested the rcd?

 

[Penguin]

My guess is that the wiring is late 60s early 70s.

The landing is 2 way, and the hall is 2 way. Both are on the same RCBO which never trips, only the RCD on the socket side of the board.

As I’ve combined all the circuits into one and put them on the RCD side I thought that would eliminate any possible cross connection/borrowed neutral.

So I’m looking at a fault rather than a cross connection I think.

Why are there so many different Manufacturers Breakers in the DB.??

 

[Brightonbill]

Why are there so many different Manufacturers Breakers in the DB.??

Why are there so many different Manufacturers Breakers in the DB.??

Can’t really answer that one. I have a feeling that the RCBO was part of an en-suite installation.

As for the Volex I don’t know. Possibly a fault?

 

[Brightonbill]

Have you tested the current earth leakage and/or ramp tested the rcd?

No. I did a standard auto test which was fine. I’ll give it a ramp rest tomorrow and check the earth leakage.