rcd tripping after smoke alarm fitted.

[DC-backfrom the past]

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]

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]

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]

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]

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]

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]

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.

 

[DC-backfrom the past]

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]

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]

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]

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]

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

 

[Octopus]

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

 

[DC-backfrom the past]

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]

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

 

[DC-backfrom the past]

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

I tried it with brand new base and new alarm and it still trips. I stripped back the circuit to the original cable and new base /alarm and it still trips (ie back to original state). To say I am demented is an understatement. I appreciate that its hard to advise without being there.
I just wondered if I was missing something glaringly obvious

 

[Wilko]

I tried it with brand new base and new alarm and it still trips. I stripped back the circuit to the original cable and new base /alarm ... To say I am demented is an understatement ... I just wondered if I was missing something glaringly obvious

Glass of favourite and the installation instructions, who knows? I've had domestic blindness more than once

 

[Pete999]

I tried it with brand new base and new alarm and it still trips. I stripped back the circuit to the original cable and new base /alarm and it still trips (ie back to original state). To say I am demented is an understatement. I appreciate that its hard to advise without being there.
I just wondered if I was missing something glaringly obvious

Swap the N over to the other Nbar

 

[DC-backfrom the past]

Swap the N over to the other Nbar

to the one covered by the other rcd ?

 

[Pete999]

to the one covered by the other rcd ?

Yep