Main RCCB tripping on r1+r2

[Bacon]

Was with a chap doing a PIR today all was ok when doing r1+r2 on all circuits bar the lighting circuit,

When he did this the main breaker tripped any ideas why this would happen.

Was ok when disconnected the live out of the breaker,The breaker for the light was ok open when off closed when on.

No emergency lights in the lighting circuit.

All IR readings ok Zs all ok RCD trip times all ok.

 

[sellers]

borrowed neutral would be my hunch.

 

[ADS]

Was with a chap doing a PIR today all was ok when doing r1+r2 on all circuits bar the lighting circuit,When he did this the main breaker tripped any ideas why this would happen.

Was ok when disconnected the live out of the breaker,The breaker for the light was ok open when off closed when on.

No emergency lights in the lighting circuit.

All IR readings ok Zs all ok RCD trip times all ok.

I think you'll have to explain what you were doing in a bit more detail.

If you were doing a standard R1 + R2 test on a lighting circuit, then the whole board should be isolated and the L & CPC are connected together at the CU, and the test performed at the furtherest point - how on earth would this trip the 'main breaker'....whatever that might be?

 

[Bacon]

But all the others breakers were open i believe may be wrong.

Thanks for reply Sellers

 

[sellers]

sorry my reply was a bit short, i was in the middle of a quote.

if you imagine you have the live from that lighting circuit and a neutral from another circuit still connected in the board. When you short r1+r2 on your isolated circuit your creating a N-E short on the circuit that is still connected through the load on the circuit you have isolated.

I hope it makes some sense.

 

[Sidewinder]

Sellers,

This would be anyones gut feeling, but there is no N related to an r1+r2 test.

 

[ADS]

I hope it makes some sense.

I'm hoping the whole thread is going to make some sense, soon.

 

[sellers]

Sellers,This would be anyones gut feeling, but there is no N related to an r1+r2 test.

If you see my theory above that could produce whats occuring, I beleive?

 

[ADS]

I'm not getting how the 'main' RCCB is tripping when it should be off anyway.

 

[Sidewinder]

ADS,

Why should it be off?

They are undertaking a PIR.

 

[sellers]

Main RCCB's are a laugh a minute. You can't even get your megger out of the van without it tripping!

 

[ADS]

ADS,Why should it be off?

They are undertaking a PIR.

So it's standard practise to poke around in a 'Live' DB/CU now - disconnecting 'Line' conductors, croc clipping or whatever method they were using.....I'm still trying to find out.

OK, fine - if you say so......I'm fed up of arguing on this forum.....you win, R1 + R2 in a 'Live' board.

EAWR Springs to mind.

 

[Sidewinder]

ADS,

The DB may need to be isolated whilst making the disconnections & reconnections, however it could then be re-energised whislt that test is undertaken, remember, it could take 1/2 an hour to get from the DB to the test point, as long as the work is done safely then there is no reason not to do this.

You don't have to test at the board remember.

I have not sid it is standard practice to poke around in a 'live' db.

I probably have worked woth EAWR a considerable amount more than you have mate!

You please need to understand that not everyone on here is an installation spark.

Also do you actually understand the wording of eawr89?

I have personally discussed live working with the head of electrical safety within HSE in my geographic area.

We both funnily enough as far as you are concerned it seems, agreed.

 

[Doc Hudson]

Are there not numerous instances where it is impractical to isolate a whole installation just to test one circuit?

Doc H.

 

[sellers]

yes doc!

No spark can call themselves a spark if they seriously think they will never work in a live board.

Why can't we help the OP out instead of being total hypocrites!

 

[ADS]

Are there not numerous instances where it is impractical to isolate a whole installation just to test one circuit?Doc H.

Then you would risk assess and decide whether you really need to R1 + R2 at all......Zs at the end of the lighting circuit would probably be a better option - It is a PIR after all.

 

[sellers]

Then you would risk assess and decide whether you really need to R1 + R2 at all......Zs at the end of the lighting circuit would probably be a better option - It is a PIR after all.

so you're going to open up the last light while live? can't do that.

 

[ADS]

so you're going to open up the last light while live? can't do that.

Well, it's a 'live' test, sellers - it's not quite the same as doing a 'dead' test with most of the installation left 'live', is it.

I've had enough, now, I'm off......... it's been an interesting week.

Ive learnt that it's OK to 'dead test' in a 'live' board, and we only have to follow the 'Regs' that we agree with.

:coat

 

[Bacon]

Ok this what the situation was Main RCCB on all circuit breakers in open position i.e OFF, Lighting circuit left on to see what were doing.

All circuits bar lighting r1+r2 tested IR tested Zs tested RCBO'S tested all fine.

All circuits now in open position i.e (OFF) execpt main RCCB.

Get portable light out the van to be able to see what were doing when carrying out the test on lighting circuit carry out r1+r2 on lighting circuit trips main RCCB.

All other tests carried out on lighting circuit all ok IR Zs

I'd like to meet the Spark you has never done any work or testing on a live circuit

 

[sellers]

as far as I'm aware connecting onto a dead circuit with your probes is safer than connecting onto a live circuit, but I'm not going to argue because I do both and see no problem with it. I do work in live boards and I have worked with live cables. I guess I was in the wrong and will isolate DB's from now on before entering. There goes my livelyhood.

Anyway back to you bacon. I beleive my below post to be correct unless anyone can tell me any different or any other ideas?

sorry my reply was a bit short, i was in the middle of a quote.if you imagine you have the live from that lighting circuit and a neutral from another circuit still connected in the board. When you short r1+r2 on your isolated circuit your creating a N-E short on the circuit that is still connected through the load on the circuit you have isolated.

I hope it makes some sense.