Electrics - 12v lights regularily tripping RCB

dgladst

We recently had fitted an RCD mains box. We now have the problem that when the lights are switched on in one particular room only it trips the box approximately 20% of the time. It can be forced to happen by flicking the switch slowly and not making “a clean” on or off. The lights in the room are 12v spots operating thru’ a transformer incorporated within the fitting and are connected thru’ a 5amp link in the mains box.
The problem still occurs when all the bulbs are removed. The switch has been replaced and all connections throughout seem ok.
This seems to suggest that the problem is linked in some way with the transformer. Does anyone know of such a problem and how to resolve it?
Thanks, Dave

espresso

dgladst wrote: »

We recently had fitted an RCD mains box. We now have the problem that when the lights are switched on in one particular room only it trips the box approximately 20% of the time. It can be forced to happen by flicking the switch slowly and not making “a clean” on or off. The lights in the room are 12v spots operating thru’ a transformer incorporated within the fitting and are connected thru’ a 5amp link in the mains box.
The problem still occurs when all the bulbs are removed. The switch has been replaced and all connections throughout seem ok.
This seems to suggest that the problem is linked in some way with the transformer. Does anyone know of such a problem and how to resolve it?
Thanks, Dave

Lighting circuits should be on the non protected side of a split load consumer unit for safety. More info at the bottom of this page here.

Alias_Omega

does it trip the RCD, or is the the MCB.

Can you take a picture of the consumer unit for us?

Regards,

AO

dgladst

Thanks very much for your responses.
I've had an electrician in and he explained that moving the lights to the other side of the RCB wouldn't solve the problem as its not the RCB which trips but the MCB. I therefore explained the problem wrongly in my posting - sorry. He suggests that there must be a surge which exceeds the 6 amp rating of the MCB and shuffled the wiring around so that this MCB now only supplies the upstairs lights. Unfortunately the problem still occurs. Thanks, Dave

shandypants5

Hi..
are you absoloutly sure its the Circuit Breaker thats tripping, and not the RCD,?
Usually the RCD will shut off power to the whole consumer unit ,not just one circuit.
The CB on the other hand just protects the one circuit that it is conected to (lights or sockets)
These links explain in more detail.
http://en.wikipedia.org/wiki/Circuit_breaker

http://en.wikipedia.org/wiki/Residual-current_device

If the CB is tripping then that cicuit must be pulling too much current momentarily.. (pressing the switch slowly will do this too, and burn the switch contacts, so dont do it too often..;) )

The transformer is probrably causing a surge when it is switched on from cold,can you see it? does it have an Amp rating written on it?

Loose connections and old faulty switches can add to the current draw too,
allso long cable runs or too small(thin) cable used.

Your "electrician" should have checked all that out though..
sometimes an old Circuit Breaker can trip too early so I would be tempted to replace this 1st, after checking that the wiring is all ok.

spark1

dgladst wrote: »

Thanks very much for your responses.
I've had an electrician in and he explained that moving the lights to the other side of the RCB wouldn't solve the problem as its not the RCB which trips but the MCB. I therefore explained the problem wrongly in my posting - sorry. He suggests that there must be a surge which exceeds the 6 amp rating of the MCB and shuffled the wiring around so that this MCB now only supplies the upstairs lights. Unfortunately the problem still occurs. Thanks, Dave

Get the electrician back, and get him to load test the circuit ? or get the electrician back who fitted the new dis/board.

baldelectrician

Me thinks you have one on those 12V fittings with a massive torroidal (big round, heavy) transformer.

I am surprised your spark didn't realise this.

You get different types of circuit breakers, you can get 6A mcb's in type B,C,D amongst others.

The standard [newer] domestic MCB is a BS 60898 type B, which is suitable for most applications. The electricain will need to verify if the circuit is compliant, but if all tests are OK it may be possible to change the circuit breaker from a type B to a type C.

To explain a C type will take more instant surge than a B, and a D will let through more than a C, but ill still be rated at
6A, or whatever the rating

This is not a DIY job and things will need to be checked and if appropriate the MCB ordered.

You should use a competent person for the work, links below
In Scotland:
Individuals regitered;
http://www.sbsa.gov.uk/register/ListAC.asp
Companies
http://www.sbsa.gov.uk/register/SearchCo.asp?T=Construction&ID=2
In England and Wales:
http://www.competentperson.co.uk