Hi all, head scratcher here

[Nick81]

Hi all

I am looking for help on a strange rcd issue.

I had a client saying there was something in there kitchen causing an rcd to trip. This was an intermittent fault and would only occur when the kitchen ring was on, prior to this there were no issues and no recent changes in the kitchen area. The MCB does not trip. The fault then changed from intermittent to continuos so unable to set rcd when the circuit is on.
I disconnected all conductors at the cu and tested continuity between them and ir tested them, this showed no faults.
Took the circuit apart and identified the first socket on the ring and last socket before the return, i.e identufuid both legs in the circuit
Connected one leg to the board and put a socket on the load, switched on and no trip, put a load in the socket and trips straight away. Did the same with the other leg and sane thing.

Took both legs out and put a leg into the board about two meters long, put socket on the end and plugged a load in, trips straight away.
This all points to a neutral problem within the board, however it was only tripping when a specific circuit was on, I removed this circuit and wired a temporary radial and it still trips.
I also took the kitchen ring to a spare breaker on the second rcd and again it tripped.
No ir faults and no continuity between conductors where there shouldn't be.

Sorry for long winded post but the symptoms have got me stumped.

Thanks for any help guys

 

[telectrix]

sounds like a N fault. are you sure the N is in the correct bar?

 

[Octopus]

Have you got an earth leakage clamp meter?

 

[Bob Geldoff1234]

Double check your RCD neutrals are in the correct bars first.Then remove all the neutrals on that bar and wire in your 2 metre length with socket.If it still trips then it could be a faulty RCD.
Also check that polarity it correct from the mains terminals.They might have had a new meter fitted and the polarity has been reversed at the meter,although I don't know how that would affect the RCD's.
Ramp test the RCD's as well.Both RCD's could be faulty due to a surge so try a brand new one to confirm

 

[Octopus]

Could be a loose connection on the service head ...

 

[Dillb]

Have you ramp tested the RCD?

 

[Midwest]

I'm waiting for @Richard Burns to post his pictorial of a fault on another circuit, tripping RCD when load is connected to another circuit (if you see what I'm saying). Another possibility?

 

[Wilko]

Hi - I'm not clear if the tripping changed to the other RCD when you moved the kitchen RFC over to the spare MCB under it?

 

[Bob Geldoff1234]

Also make sure you leave the earths connected to the earth terminal while you do your insulation resistance tests as it might show clear L+N-E but could be going down to pipe work in the kitchen.

 

[Deleted account]

Could be a loose connection on the service head ...

Totally agree.
I've had this and it stumped me for quite a while.

Eventually realised when I heard crackling in the head everytime I did a Ze test at board.

Try that if your cu is near head.

 

[Octopus]

Try that if your cu is near head.

Hum .... just try and "wiggle" the DNO cables coming out of the head and into and out of the meter..

 

[Richard Burns]

I'm waiting for @Richard Burns to post his pictorial of a fault on another circuit, tripping RCD when load is connected to another circuit (if you see what I'm saying). Another possibility?

Unless another heavy load such as a cooker or electric shower is also tripping the RCD then I doubt if it is a Neutral fault on a separate circuit that is causing this problem.

If all the conductors from the kitchen ring were removed when the temporary radial was installed then I would expect a faulty RCD or inconsistent supply, though slightly strange that it is only the kitchen circuit.
If all conductors were not removed, just the line, then a NE fault on the kitchen ring could still cause the tripping. The fault could be from neutral to an unrelated earth such as a water pipe or screw through the cable touching a wet wall since the IR test was conducted with all conductors removed from the board.
It might also be useful to measure the end to end continuity to see if there is a higher resistance in neutral from damage to the core.