RCD tripping. Not appliance

e5c3d4 · Nov 29, 2023

An RCD keeps tripping.

Please see attached photo of the board (2 photos attached). I’ll call the breakers:

MCB (1) marked ‘Upstairs lighting’
MCB (2) marked ‘Sockets’
MCB (3) marked ‘Water heater’
MCB (4) marked ‘Sockets’
RCD (5) for MCBs (1-4)
MCB (6) marked ‘Kitchen sockets’
MCB (7) marked ‘Downstairs lighting’
MCB (8) marked ‘Garage’
MCB (9) marked ‘Cooker’
RCD (10) for MCBs (6-9)

No appliances are plugged in to any sockets and all sockets are turned off.

Turning on MCB (4) trips RCD (5) every time.

It is possible to have all MCBs other than (4) on and not trip RCD (5). However, it will trip eventually, around every 30 mins.

Even with all of MCBs (1-4) off, RCD (5) occasionally trips.

Kitchen sockets are on a different circuit MCB (6) and RCD (10). Using high powered appliances in the kitchen (e.g. kettle) will also trip RCD (5). However, the appliance, MCBs (6-9) and RCD (10) all stay on.

RCD (5) is not faulty: it has been replaced.

I can’t use a socket tester other than in the kitchen as as turning on MCB (4) will trip RCD (5).

Any ideas much appreciated.

Tom

Taylortwocities · Nov 29, 2023

Why on earth did you shoehorn a BG RCD into a Wylex board?
There’s a fault, the RCD is telling you that. It’s not the RCD. Put the right one back.

You need an Insulation Resistance tester and someone who knows how to use it.
A competent electrician is your best bet.

Just changing things isn’t gonna fix anything. Sorry.

timhoward · Nov 30, 2023

e5c3d4 said:
Turning on MCB (4) trips RCD (5) every time.

e5c3d4 said:
Kitchen sockets are on a different circuit MCB (6) and RCD (10). Using high powered appliances in the kitchen (e.g. kettle) will also trip RCD (5)

These two together suggest a rather complicated specific fault scenario (a large load driving current through a fault on a different circuit).
As already said, there is no hope of finding this fault without testing every circuit with specialised (expensive) gear that only electricians are likely to have.
It won't take long for an electrician to do this (usually around an hour).
I normally tell people that if the fault is persistent I can usually find the reason within two hours. (Intermittent faults are a different kettle of fish but this doesn't sound like that)

pc1966 · Nov 30, 2023

It has all the hallmarks of a N-E fault somewhere, but finding it needs a systematic approach and the correct test gear (insulation tester) to disconnect each circuit in turn and check for a fault, then when you identified the circuit(s) with a fault, to further divide-and-conquer it until the fault location (cable, accessory, junction box, etc) has been located.

richy3333 · Nov 30, 2023

timhoward said:
These two together suggest a rather complicated specific fault scenario (a large load driving current through a fault on a different circuit).
As already said, there is no hope of finding this fault without testing every circuit with specialised (expensive) gear that only electricians are likely to have.
It won't take long for an electrician to do this (usually around an hour).
I normally tell people that if the fault is persistent I can usually find the reason within two hours. (Intermittent faults are a different kettle of fish but this doesn't sound like that)

A kettle boiling fish - thats your fault right there... or is it a red herring?