rcd tripping after smoke alarm fitted.

DC-backfrom the past · Nov 13, 2017

I was installing a smoke and heat alarm on an existing circuit today (aico ei141 )was already in place, so I have used the same type for the install.
All insulation and resistance tests were within limits.
I interlinked the alarms and all worked then rcd tripped. Initially we thought it was a faulty hoover as the householder had just plugged in a hoover.
I reset and the rcd on the other circuit tripped.
it can cause either rcd trips they only trip when the smoke alarms are pushed into positon. I rechecked all the cables again(visual /insulation/ resistance ) and it still trips as soon as a smoke alarm is connected.
The only thing I can think of was the loft was full of stuff and I had to move some out the way to get access. It may have disturbed another circuit although, nothing trips until the smoke alarm is put into place.
I appreciate this is a shot in the dark I am going back tomorrow and would appreciate any advice.
The smoke alarms are on battery backup so the client is covered.
I also tried connecting the smoke alarms on another circuit breaker in case that was faulty.
Its still tripping even on their own circuit?
I am new to inspection and testing and wondering if there is anything else to try before going through every other circuit.
thanks in advance..... I hate getting beat.

Pete999 · Nov 13, 2017

DC-backfrom the past said:
I was installing a smoke and heat alarm on an existing circuit today (aico ei141 )was already in place, so I have used the same type for the install.
All insulation and resistance tests were within limits.
I interlinked the alarms and all worked then rcd tripped. Initially we thought it was a faulty hoover as the householder had just plugged in a hoover.
I reset and the rcd on the other circuit tripped.
it can cause either rcd trips they only trip when the smoke alarms are pushed into positon. I rechecked all the cables again(visual /insulation/ resistance ) and it still trips as soon as a smoke alarm is connected.
The only thing I can think of was the loft was full of stuff and I had to move some out the way to get access. It may have disturbed another circuit although, nothing trips until the smoke alarm is put into place.
I appreciate this is a shot in the dark I am going back tomorrow and would appreciate any advice.
The smoke alarms are on battery backup so the client is covered.
I also tried connecting the smoke alarms on another circuit breaker in case that was faulty.
Its still tripping even on their own circuit?
I am new to inspection and testing and wondering if there is anything else to try before going through every other circuit.
thanks in advance..... I hate getting beat.

Borrowed Neutral may be??

DC-backfrom the past · Nov 13, 2017

The original smoke alarm is on its cable directly from the consumer unit.
If the fault is a borrowed neutral its on another circuit.

Pete999 · Nov 13, 2017

DC-backfrom the past said:
The original smoke alarm is on its cable directly from the consumer unit.
If the fault is a borrowed neutral its on another circuit.

Where have you taken the L from and which side of the CU have you taken the N from?

Wilko · Nov 13, 2017

Interesting fault ... if it's not a borrowed N and since these units are not earthed (iirc) how can they be tripping RCD? Cable fault right at connector perhaps? Especially if you've tried the unit on its own circuit and it still trips RCD. What happens if you plug the new alarm into the original position?

westward10 · Nov 13, 2017

Am I correct in thinking there is an existing smoke detector circuit from which you have installed a further two detectors? If so where have you connected the new ones from.

DC-backfrom the past · Nov 13, 2017

Pete I had photographed the unit its the brown and blue cable to the left as you look at the screen this was taken prior to any testing.

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

DC-backfrom the past · Nov 13, 2017

westward10 said:
Am I correct in thinking there is an existing smoke detector circuit from which you have installed a further two detectors? If so where have you connected the new ones from.

They are interlinked and I have visually checked them as well as muti meter test on that circuit.
basically live and neutral supply and then three core and earth between each alarm.

DC-backfrom the past · Nov 13, 2017

Wilko said:
Interesting fault ... if it's not a borrowed N and since these units are not earthed (iirc) how can they be tripping RCD? Cable fault right at connector perhaps? Especially if you've tried the unit on its own circuit and it still trips RCD. What happens if you plug the new alarm into the original position?

I disconnected my additional circuit and reverted to the original and it is still tripping. I think I may have physically disturbed another circuit and created a fault, although I cant understand why its only when the smoke detectors are connected the rcd fault occurs .

Wilko · Nov 13, 2017

Just a reminder on IR testing - Aico installation instructions specifically warn not to do it with units connected. Likewise accidentally making the interconnecting link wire live will trash them, if I recall correctly.

DC-backfrom the past · Nov 13, 2017

Wilko said:
Just a reminder on IR testing - Aico installation instructions specifically warn not to do it with units connected. Likewise accidentally making the interconnecting link wire live will trash them, if I recall correctly.

I completed the ir testing with the cables unconnected from the smoke alarms. (the alarms were still in the box)Sad as it seems I actually tested each cable rather than link( R1-R2)as I had a new wander lead and it was a flat I was in.

westward10 · Nov 13, 2017

So is the original circuit still in place and your new circuit is paralleled at the mcb?

Octopus · Nov 13, 2017

You need an earth leakage clamp meter ......

DC-backfrom the past · Nov 13, 2017

westward10 said:
So is the original circuit still in place and your new circuit is paralleled at the mcb?

Original cable which is direct from mcb was taken out from first smoke Alarm and is used as the live/ neutral /Earth supply in the loft void.
the interconnecting cables (three core and earth) for the alarms are linked in to this feed .
I will draw a diagram as I realise this explanation might not be clear

thanks for the help folks

Octopus · Nov 13, 2017

EDIT: If it trips when you attach the smoke alarm - did you use the existing bases or fit new ones?

rcd tripping after smoke alarm fitted.

DC-backfrom the past

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Pete999

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DC-backfrom the past

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Pete999

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Wilko

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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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Wilko

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DC-backfrom the past

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westward10

Octopus

DC-backfrom the past

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Octopus

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