Bathroom Light



Could someone please put me out of my misery......... I've just changed a bathroom light from a loop in/out system to a jb feeding a class 2 lamp.
Everything was working well and looking good. On leaving I noticed the rcd protecting the circuit had tripped. I closed the mcb to the bathroom light and opened the rcd...all ok. When i opened the mcb and switched on the light, the rcd tripped. I've checked my wiring in the jb and all ok. Everytime I switch on the light with bulb in situ, rcd trips. Changed the lampholder, still trips. What's happened?? I suppose it could be a twitchy rcd but, it's on a new board and trips at 34ms (x1) and 18ms (x5) so it would appear ok.

Any ideas please?


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I'm a bit confused - you close the MCB and the RCD, then when you operate the bathroom light it trips the RCD?
When you have the MCB open and operate the light, does the RCD trip then?
No I opened both the rcd and the mcb and all ok until i switch on the light then the rcd trips
Open generally means off btw ;)
Have you checked the wiring of the switch and anything else which is connected to it?
Have you tested the insulation resistance? Is there more than one circuit neutral present?
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Sorry yes your right my heads gone...........rcd and mcb closed and switching on the light trips the rcd
The switch wasn't touched so it's as it was before i changed the lamp. The only other circuit, apart from the power, is a shaving socket. I checked my wiring and all ok. Insulation resistance test was fine.....????
Did you have the lamp in place and switch open when you carried out the IR test or switch closed and lamp out?

It is quite normal to use the lighting circuit to supply the shaving socket in a bathroom.
Any link to another circuit?

If you disconnect the cable to the light does the RCD hold in?
The rcd is ok until i put a bulb in. It holds with the switch open or with the bulb out. As soon as i complete the circuit through the bulb it trips
If you disconnect it does it still trip? Has any work been done at the consumer unit? Is the neutral in the correct rail?
Oh s**t I think you've cracked it. When i did the IR test I think i've put the netural back in the wrong rail. What a **** :oops:

Thank you very much for your help. I'll try correcting it tomorrow and let you know...


You were spot on with the netural in the wrong rail.....thanks again! :D

Just one more question if I may.......

Having changed a CU I did a IR test before the CU was energised. Got a reading from the whole board of >200 M ohms.

Now the CU has been energised, I deceided to do a final IR test on the whole board this morning. With the power off I tested from the main switch (load side) and got a reading of 0.00 Mohms. When i opened the 32a ring mcb and tested the whole board again from the main switch I got a reading of >200 Mohms. This is suggesting a problem with the ring circuit but a reading of 0.00 Mohms???? Could it be the mcb?
Just to add everything is working ok and all the sockets are testing ok :confused:



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