light switch trip socket breaker

[faborson]

Hi Sparkys!

one to scratch your head with: randomly one switch light trip the rcd sockets on the board?
have a look at the pic if it helps..
thank you
Fab

 

[Richard Burns]

I am not certain what your question is, presumably you are asking why on certain occasions switching on a light switch can trip the RCD that is protecting the other half of the board.
I would say the most logical answer is that there is a neutral earth fault on one of the socket circuits and if there is enough load on the lighting then the redirected current can trip the sockets RCD.

 

[faborson]

morning Richard,
Thanks for your prompt response.
I apologise for my poor grammar, and yes that was the question. It only happen with this light switch, and not every time?
As it happen the other part of the board is only for the sockets, thats why I wrote the sockets RCD.
So you say its more a sockets problem than the lights??

 

[Richard Burns]

The circuit that has a fault will trip it's own RCD, there cannot be a normal fault on the lighting circuit that can trip an RCD that is not connected to that circuit. However if the light in question was connected to the socket circuit then it would be possible.
Therefore the faulty circuit is one of the socket circuits, (Unless that light is part of a socket circuit).

Because the fault does not occur all the time it must be due to a change in the current drawn.
For the light to cause the RCD, that it is not connected to, to trip there must be a current flowing from the neutral bar back through one of the socket circuits.
Though it might be worth testing the RCD to ensure it is working correctly.

 

[Octopus]

An earth leakage clamp meter would help indicate what's going on too

 

[Dave OCD]

I just wonder if the light in question has a 'borrowed' neutral from one of the RCD protected circuits.

 

[Richard Burns]

Then it would trip the RCD every time it was switched on.

 

[Dave OCD]

True Richard, I didn't read that bit first time round about the tripping being inconsistent. :smile5:

 

[Marvo]

Might be along shot but if the live comes from the isolator to the two 6A MCB's first then it's extended to supply the RCD then a poor termination could maybe cause enough imbalance in the RCD to trip it, especially if there's arcing. Check all CU terminations and check for any busbars that are on the wrong side of a clamp.

 

[faborson]

Thanks Marvo, I will check this tomorrow.

 

[faborson]

Thanks again Richard,
looks like I have to get a professional in! I just bought that house and didn't really want to spend money on rewiring the full house!!
when I check the CU, whoever installed it put 3 differents MCB on the sockets side-hager- I had to buy 3 wylex ones! So better check the rest of it...the worst bit its that this house used to be rented and should have follow regulations??
cheers

 

[Octopus]

Thanks again Richard,
looks like I have to get a professional in! I just bought that house and didn't really want to spend money on rewiring the full house!!
when I check the CU, whoever installed it put 3 differents MCB on the sockets side-hager- I had to buy 3 wylex ones! So better check the rest of it...the worst bit its that this house used to be rented and should have follow regulations??
cheers

If it's a Hager board why did you buy Wylex?

 

[faborson]

If it's a Hager board why did you buy Wylex?

if you look at the pic you can see its a wylex board....thanks anyway

 

[Octopus]

if you look at the pic you can see its a wylex board....thanks anyway

oops. Didn't notice that!

Back to the original question - I suspect you have a fault on the lighting circuit and a combination of "leakage" on the RCD side of the board - so when the lights are switched on it pushes the leakage over the trip level for the RCD.

You need a spark with a MFT and a earth leakage clamp meter so check this out

 

[faborson]

oops. Didn't notice that!

Back to the original question - I suspect you have a fault on the lighting circuit and a combination of "leakage" on the RCD side of the board - so when the lights are switched on it pushes the leakage over the trip level for the RCD.

You need a spark with a MFT and a earth leakage clamp meter so check this out

No worries lol!
yes I will get one, I thought there was something to do with the actual switch, something easy to sort out!
cheers, have a good week end!

 

[David M]

Then it would trip the RCD every time it was switched on.

Though it is worth noting that it is a 3 gang switch, and the op hasn't categorically stated whether its the one same switch that's operated which causes the trip each time. So it could well be a light that is less often used which when switched on trips the RCD. This could indicate a borrowed neutral problem.

To the O.P,

Is it just one of the switches on the 3 gang switch which causes the trip or does it trip randomly with any one of the 3?
The reason I ask is that to determine where the fault lies there are processes of elimination to go through. It can be sometimes difficult to pin down the cause of random tripping without eliminating the obvious first.

 

[Flanders]

It also could be a lighting cable that as rubbed againts a socket cable when they were installed ,with the neutrals almost touching together and the insulation broke down it could course the intermittent fault coursing the rcd to trip , but this is just a idea as said the only way to find out is test out the circuits