Lighting fault

[nrwilliams]

Hi,

My parents house recently developed a lighting fault. Split load cu and the rcd tripped on one side, the only way we could get the rcd to stay on was to switch off the upstairs lights mcb. Switching on the mcb causes the rcd to trip.

So we went and checked everything obvious and no luck.

Bear in Mind the cu was changed 3 months ago and the electrician tested all the circuits and no issues.

So they got another electrician in this week, he was there for fifteen minutes and says he earth is incomplete on the circuit and this is causing the rcd to trip. The only option he gave was a complete rewire of the lighting circuit.

Can an incomplete earth cause an rcd to trip? I thought it would need a L or N to earth fault?

Just looking to understand and see if a re wire is completely necessary.

Many thanks

Neil

 

[AdrianUK]

I think you need to find yourself another 'electrician'. One who knows what he is talking about - since the one who visited you clearly does not!

An RCD cannot detect an incomplete earth nor can it detect a L to N fault. It can only 'see' a current imbalance between L & N which is most likley caused by a fault between L & E or N & E. (Although, given your description of the problem & given that the RCD holds with the relevent MCB switched off, my money is on a L to E fault)

A common problem with retro fitting a RCD board is the case of a borrowed neutral with the staircase light, although, if this board change was 3 months ago, one would expect that this would have shown itself by now ..... try closing the MCB again with the lamp removed from the stairs light.......

 

[ricicle]

Does the fault occur when you turn on a particular light or is it random if no lights are on ?
Are there any external lights on the circuit that might have water ingress ?

 

[nrwilliams]

The fault occurs all the time, lights on or lights off. No external lights.

 

[pjcomp]

Any recent work done around the house, even something as simple as putting up a picture? As the upstairs lighting circuit starts downstairs the wiring has to get upstairs, so a nail in the wall could be downstairs. Check the light fittings - I recently had a similar symptom, which turned out to be the brass light fitting in the hallway - been there years but something inside it went rogue (probably a terminal/connection overheating which led to the N-E short)

pj