rcd tripping after smoke alarm fitted.

DC-backfrom the past · Nov 13, 2017

Murdoch said:
I am trying to help here!

So there was originally 1 smoke alarm, fed by T&E from the fuseboard.

You've added another smoke and a heat alarm to the existing smoke.

Now either 1 or the other RCD will trip.....

You've used 3 core cable for the new smoke & heat?

Or have I missed something?

apologies Murdoch if I seemed ungrateful I didn't intend to come across that way.
correct the supply is t&E from board then three core thereon
the third core is used for the interlink facility. if one alarm sounds they all sound together
I have drawn a very rough diagram I have left out the earth for clarity.

[ElectriciansForums.net] rcd tripping after smoke alarm fitted.

Octopus · Nov 13, 2017

No offence taken!

Are you 100% sure you have the neutrals in the correct places in the smoke alarm bases

L
IC
N

DC-backfrom the past · Nov 13, 2017

Murdoch said:
No offence taken!

Are you 100% sure you have the neutrals in the correct places in the smoke alarm bases

L
IC
N

yes mate I'm sure ...I checked three times or possibly four .That's why I took it back to the original circuit (T&E) to try and ascertain if it was a faulty unit to blame.
I checked with two base units and two detectors.
I couldn't understand why the other rcd tripped on two occasions though.
there was a lot of junk in the loft and I had to move some of it
I can only presume that somewhere I have maybe damaged another circuit ...but cant think if that's the case why it only trips when this circuit is made live and connected to the alarm..

Octopus · Nov 13, 2017

What is the "new" cable run like? all clipped?

Still think you need to dis the new part and IR the new bit - and you must IR between ALL cores to make 100% sure.

DC-backfrom the past · Nov 13, 2017

Murdoch said:
What is the "new" cable run like? all clipped?

Still think you need to dis the new part and IR the new bit - and you must IR between ALL cores to make 100% sure.

Its all clipped in the loft area...
I appreciate what your saying. but I've disconnected the new part completely and the original cable, which was ok, is now the only part connected and its tripping the rcd !!!!

I disconnected it and IR tested that T&E as well

hence my headache !!!!

Octopus · Nov 13, 2017

Next step, which seems a bit odd, but I think you should run the smoke from a new piece of t&e direct from the board at cu level. Do this to test the bases and heads you have.

You need to do this to rule them out of the problem ....

Toneyz · Nov 13, 2017

Sorry if I've missed something here but what is that other cable in the MCB? if the other RCD is tripping sounds like the crossed neutral. Just a thought but have you checked the two neutral bars are doing the corresponding MCB bank.

westward10 · Nov 13, 2017

He has yet to clarify how it is connected and which parts are new and what is existing.

DC-backfrom the past · Nov 13, 2017

Thanks I've resigned myself to replacing the initial cable.
Or hoping the rcd fixing fairy has visited during the night

Thanks to all for your help
Fresh eyes and clear head may help

DC-backfrom the past · Nov 13, 2017

anthonybragg said:
Sorry if I've missed something here but what is that other cable in the MCB? if the other RCD is tripping sounds like the crossed neutral. Just a thought but have you checked the two neutral bars are doing the corresponding MCB bank.

The other cable is lighting circuit for hall.
However I have tried the smoke alarm cicuit in the adjacent mcb on it's own.
As stated by you and others I will double check the neutral bar in case there is a crossover or borrowed neutral.
Thanks

DC-backfrom the past · Nov 13, 2017

westward10 said:
He has yet to clarify how it is connected and which parts are new and what is existing.

Sorry I thought it was clarified
T&E was existing cable to 1st smoke
New circuit from there is 3 core
L
N
IC
This allows interlinking .
After the fault occurred and rechecking via visual and ir test .I disconnected the new circuit and reverted back to original, T&E and first alarm
The rcd stills trips

Octopus · Nov 13, 2017

DC-backfrom the past said:
However I have tried the smoke alarm cicuit in the adjacent mcb on it's own.
Thanks

That's not what I meant, just run a meter of new cable from the CU and test the smokes and bases....

Ian1981 · Nov 14, 2017

Have you solely just powered the smoke detectors and nothing else on that rcd or even the house and if so does it still trip?

Midwest · Nov 14, 2017

So to recap, everything was functioning correctly before addition.

Property had one smoke alarm fed via one LOSH (?) cable from CU.

Additional 3c & e cable installed. Tested. Put on smoke heads which trips 'either' RCD.

Addition disconnected, now original circuit with smoke head on, trips RCD when energised.

The only thing that has changed, is OP working in loft space.

My bit of input, I wonder what global IR test would reveal if anything?

ruston · Nov 14, 2017

I have to confess I have not digested the thread properly , but have you tried the circuit intact but with the alarms removed?

rcd tripping after smoke alarm fitted.

DC-backfrom the past

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Octopus

DC-backfrom the past

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Octopus

DC-backfrom the past

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Octopus

Toneyz

westward10

DC-backfrom the past

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DC-backfrom the past

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DC-backfrom the past

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Octopus

Ian1981

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Midwest

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ruston

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