Lights tripping Sockets RCD

[willbewill]

I've recently had a new consumer unit fitted - the old 'fuse' one gone and a RCD one installed (Clickit with 2 sets of RCDs) - however I now get an intermittent problem:

A couple of nights ago when I switched a light on the 'other' set of RCDs tripped i.e. not the set that the lights are on - this light switch controlled a couple of Fluorescent units (the fault was repeatable) and I found that if one of these was isolated the problem ceased.

But tonight when another light was switched on the same thing happened but the fault couldn't be repeated.

It might be worth mentioning that the house was 'flooded' from a burst pipe in roof a few months ago (we've only just moved back in after major building works to correct this) and not all the switches were changes - could this be the cause?

 

[willbewill]

It just happened again but this time no lights were switched but CH was on - maybe that circuit as the controller was changed a few days ago?

 

[BS3036]

This is usually caused by the neutral of a circuit which has its line conductor connected to one RCD, being connected to the other RCD. This causes an imbalance in the live conductor currents at both RCDs, but presumably only enough to trip one of them in your case.

In other words the new CU is wired wrong.

 

[willbewill]

Thanks for the quick reply - could it be that the wiring 'shares' a neutral somewhere in the house and that the new CU has 'highlighted' this?

Should this have been picked up in the commissioning tests?

 

[BS3036]

Thanks for the quick reply - could it be that the wiring 'shares' a neutral somewhere in the house and that the new CU has 'highlighted' this?

Yes, often caused by 2-way hall lighting, I understand.

Should this have been picked up in the commissioning tests?

I'm not an electrician, but I don't believe that the standard tests for an Electrical Installation Certificate would pick this up. You'd have to be specifically looking for it.

 

[willbewill]

Thanks again - looks like I need to get an electrician in again to help find the problem wires

 

[ColJack]

for a complete CU change, this should have been picked up..

any electrician worth his salt will check for borrowed neutrals on lightling circuits..

 

[Taylortwocities]

Indeed, get the electrician back who did the consumer unit change.
Its his problem.

Hey, Will. Are you in England & Wales - or one of the dependant territories??

 

[willbewill]

Indeed, get the electrician back who did the consumer unit change.
Its his problem.

Hey, Will. Are you in England & Wales - or one of the dependant territories??

Thanks again - I'm in Wales

 

[vintagegt]

Sounds like a borrowed neutral to me. This should definetely have been picked up on a test and sorted as this can lead to problems when isolating one circuit, ie lights, you think its dead but it still has the potential to carry current down the neutral that connects it to the sockets, or wherever its borrowed from.
Any Inspection council, like the NIC would pull that immediately and have you repair it as it can lead to electric shock.
My advice, get the sparky back who is meant to have tested it and get him to repair it, these can be a lenghty and tricky repair as the neutrals could be connected anywhere in the house and can be hard to find, this will be why its been 'overlooked'.
Get it repaired or it will be a constant fault that won't just go away on its own and can be dangerous.

 

[rebuke]

Also, watch out for the sparky trying to cut corners, by e.g. just moving the lighting circuit to the other RCD - while that will fix the current symptom (RCDs tripping), the borrowed neutral still exists, and as others have said means you can have issues as a circuit may not be fully isolated etc...

 

[willbewill]

Thanks everybody - spoke to electrician today, is due to return to check this week. He did say that the problem evidenced itself when the unit was fitted but he thought he had tracked and sorted the problem - looks like there was more than one.

 

[willbewill]

Update:

Electrician came back - twice! But although he gave lots of suggestions and did loads of testing he didn't cure the fault - but...

last Saturday my wife said she noticed some water under dishwasher (which is next to Washing mc in kitchen under work surface). I investigated and found a small leak on Washing mc pipe behind it which was dripping onto wall etc. - this must have been happening for weeks as it had soaked all the wall behind the units before finally getting to the floor - and lo and behold in the wall is a pair of sockets for the appliances which is switched from above the work surface. I isolated them and changed the switch above the surface for a socket...the problem seems to be solved...no more tripping since then!

Lessons learned - expect the unexpected and look everywhere!

 

[vintagegt]

Update:

Electrician came back - twice! But although he gave lots of suggestions and did loads of testing he didn't cure the fault - but...

last Saturday my wife said she noticed some water under dishwasher (which is next to Washing mc in kitchen under work surface). I investigated and found a small leak on Washing mc pipe behind it which was dripping onto wall etc. - this must have been happening for weeks as it had soaked all the wall behind the units before finally getting to the floor - and lo and behold in the wall is a pair of sockets for the appliances which is switched from above the work surface. I isolated them and changed the switch above the surface for a socket...the problem seems to be solved...no more tripping since then!

Lessons learned - expect the unexpected and look everywhere!

Still seems odd to me. How come the lights were tripping the RCD before? Hmm, who knows, hope it solves your problems.

 

[willbewill]

Update:

Electrician came back - twice! But although he gave lots of suggestions and did loads of testing he didn't cure the fault - but...

last Saturday my wife said she noticed some water under dishwasher (which is next to Washing mc in kitchen under work surface). I investigated and found a small leak on Washing mc pipe behind it which was dripping onto wall etc. - this must have been happening for weeks as it had soaked all the wall behind the units before finally getting to the floor - and lo and behold in the wall is a pair of sockets for the appliances which is switched from above the work surface. I isolated them and changed the switch above the surface for a socket...the problem seems to be solved...no more tripping since then!

Lessons learned - expect the unexpected and look everywhere!

Still seems odd to me. How come the lights were tripping the RCD before? Hmm, who knows, hope it solves your problems.

I think the damp sockets must have been causing a certain amount of leakage to earth and then the 'shock' of certain other things eg fluorescent lights caused the trip (there may also be a borrowed neutral with those lights from that ring main)- other times the trip happening just with the socket.