Lights Causing Sockets Breaker Tripping

[Doug99]

Hi All
Today I replaced like for like x2 garden wall lights.
I opened the lights breaker and confirmed by MM no 240v at the light fitting.
Light fitting had twin live, twin neutral and single earth to a choc block.
I disconnected everything as the original choc block was dirty so replaced with new.
It was during this block change that the sockets breaker opened.
The new light was fitted, both light and socket breakers closed and the light worked ok.

For info, the second light only has a single live/neutral.

What caused the sockets breaker to open?
Would the twin live/neutral have something to do with it?

Cheers
Doug

 

[Jackrae]

Your breaker probably only opens the live lead. If you accidentaly touched the neutral lead to the earth lead that would trip any system RCD

 

[ericmark]

All these can turn off the supply line. The RCBO may be single or double pole, the Isolator and RCD are double pole and the MCB only single pole, neutral and line are both considered as live, so to isolate you can't use the MCB, however since neutral unless under fault conditions is normally at earth polarity it is common to work on systems when only the MCB has been turned off, however we know the neutral is still live so we are careful not to allow it to touch earth with older RCD systems or it will trip the RCD, however it should not trip the MCB on another circuit. So what do you mean by "socket breakers"?

 

[Doug99]

View attachment 341163All these can turn off the supply line. The RCBO may be single or double pole, the Isolator and RCD are double pole and the MCB only single pole, neutral and line are both considered as live, so to isolate you can't use the MCB, however since neutral unless under fault conditions is normally at earth polarity it is common to work on systems when only the MCB has been turned off, however we know the neutral is still live so we are careful not to allow it to touch earth with older RCD systems or it will trip the RCD, however it should not trip the MCB on another circuit. So what do you mean by "socket breakers"?

It was my daughters house and from memory I opened the lights MCB and when rewiring the choc block, the RCD opened. I called it the sockets breaker as it was only the socket feeding my drill that I noticed wasn't working.

From what you said, I can assume everything worked as expected - Cheers

 

[ebee]

Yes it does fox some people when they switch a breaker off and Line is disconnected but N is not.
If the N is still connected then a N to E short (brief touching for example) can still trip an RCD .
Most RCBOs are single pole (L) switching but you can get them that are double pole (L & N) switching.

 

[JohnW2]

Most RCBOs are single pole (L) switching but you can get them that are double pole (L & N) switching.

True, but for completeness, perhaps one should also say:

Most MCBs are single pole (L) switching but you can get them that are double pole (L & N) switching.

In terms of domestic installations, I would think that DP RCBOs are probably as rare (both virtually unknown) as DP MCBs, except when present for 'specialist' reasons.

 

[ebee]

Yes Absolutely John, my very small way of commentating minimally to avoid a ramble (Me Ramble? yes it has been known! .

Often an RCCB (Known as an RCD because it does contain an RCD and often not much else) are usually DP (or 4P) and MCBs/RCBOs are often single pole (but not always)

I am trying to master the art of giving the OP enough info but not too much to swamp them or put them off but with enough info but avoiding a ramble - often not an easy task because it is so easy to get it wrong one way or tother.

 

[JohnW2]

I am trying to master the art of giving the OP enough info but not too much to swamp them or put them off but with enough info but avoiding a ramble - often not an easy task because it is so easy to get it wrong one way or tother.

That's a laudable approach, but you worded your statement about SP (as opposed to DP) switching in terms of RCBOs (rather than MCBs), even though I don't think we have any reason to believe/know that the OP has RCBOs, do we? ... so I'm not convinced that you were giving the OP the most relevant 'concise information', were you?

Kind Regards, John

 

[ebee]

That's a laudable approach, but you worded your statement about SP (as opposed to DP) switching in terms of RCBOs (rather than MCBs), even though I don't think we have any reason to believe/know that the OP has RCBOs, do we? ... so I'm not convinced that you were giving the OP the most relevant 'concise information', were you?

Kind Regards, John

|Go on then. I`ll agree with you, I did slant it a bit but I hope it`s clear now that both RCBOs and MCBs are most often Single pole switching but there are Double Pole versions too (for single phase - more poles are available in 3 phase variety's) Phew! I feel like I`ve been told off!

 

[JohnW2]

|Go on then. I`ll agree with you, I did slant it a bit but I hope it`s clear now that both RCBOs and MCBs are most often Single pole switching but there are Double Pole versions too (for single phase ...

Yes, it should be clear to everyone now

Kind Regards, John

 

[Doug99]

Thanks Ebee for your succinct response to my OP. You answered my query without being too technical.