RCD keeps tripping

[alanwheeldon]

I have a problem if someone can point me in the right direction that would be great

When I turn the kitchen light on and off it trips all the kitchen sockets off at the consumer unit, the lights remain working??

There are 2 RCD's in the consumer unit, the light circuit is connected to one and the kitchen sockets connected to the other. The MCB doesnt trip on the kitchen socket circuit but the RCD does.

There has not been any new electrical work done in the house and it has been like this since I moved in. It seems to me that the 2 circuits could be connected together somewhere?? Any help would be great

 

[BS3036]

The neutral of one circuit is probably connected to the wrong RCD. This could either be in the consumer unit, or be caused by a 'borrowed neutral' somewhere in the house, for example on 2-way stair lighting.

 

[alanwheeldon]

Its all wired up correctly in the counsmer unit, so what can I check next?

 

[BS3036]

The next step really depends on how knowledgable and competent you are, and what test equipment you have.

The safe advice is to call in an electrician, if you really don't know how to proceed. Investigating this can involve serious risks.

One thing you could do is to post a picture of the CU.

 

[alanwheeldon]

I know bits but im not a qualified electrician. I was going to do a dead test of Insulation Resistance and a Polarity test next, I have the equipment to do this.

Like you said, the 2 circuits could be connected together? this test should find out weather any short circuits exist.

Would that be what I need to do next or is there something more simple?

Thanks for the help

 

[BS3036]

Well, I'm not an electrician, so take with caution!

I would (safely) isolate both live and neutral of both circuits from the CU. Then I would look for conductance between them. There should be a very high resistance. If there isn't then you have to track down why.

But it is more likely to be a lighting circuit problem. Are there two lighting circuits, one on each RCD? If so I'd be doing the above test on these two circuits first.

Can you post a picture of the consumer unit?

 

[alanwheeldon]

Im away from home and wont be back till Saturday so no photo im afraid

Yes there are 2 lighting circuits, one on both RCD's but the other light circuit is ok. I will have a go at the test this weekend when Im home and take it from there

 

[ColJack]

you say it's all wired right in the CU, but it sounds distinctly like a neutral mix up in the CU to me.. we want photo's of the insides of it to confirm or disprove this.. then we'll advise further...