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

 

[DC-backfrom the past]

to the one covered by the other rcd ?

Yep

Apologies I'm missing the point to doing this... apart from thinking the rcd might be too sensitive or to check it trips the other one ?

 

[Ian1981]

How have you installed the 3 core and earth cable. Could you have possibly damaged(drilled/screwed) an existing cable located in the fabric of the property such as the wall?

 

[Pete999]

Apologies I'm missing the point to doing this... apart from thinking the rcd might be too sensitive or to check it trips the other one ?

It could be you have the L and N across 2 different RCDS I'm clutching at straws but worth proving a point, hence borrowed N

 

[Ian1981]

Is your cable supplying the smoke detectors the white 2.5 LSOH cable?

 

[Octopus]

Are you 100% sure you used the same cores in the interconnecting cable the same in each leg?

If you did IR at the board this wouldn't include the interconnecting cable so I suggest that you dis the smoke base and do IR across all 4 cores and see what comes back - and at the same time double check the colours and consistency.

 

[Pete999]

It could be you have the L and N across 2 different RCDS I'm clutching at straws but worth proving a point, hence borrowed N

I understood you supplied the new detector straight from the CU

 

[DC-backfrom the past]

Is your cable the white 2.5 LSOH cable?

That's the original cable that was connected to the first smoke alarm. I took the photograph prior to removing any cables for testing

 

[DC-backfrom the past]

Are you 100% sure you used the same cores in the interconnecting cable the same in each leg?

If you did IR at the board this wouldn't include the interconnecting cable so I suggest that you dis the smoke base and do IR across all 4 cores and see what comes back - and at the same time double check the colours and consistency.

yes Murdoch I had checked using a wander lead for each cable at the different areas.
This was before connecting to any equipment.
I also visually checked the cable and connections as well in case of loose connection,... although any faults should have been picked up in the initial IR / test.
I cant understand how even reverting it back to the original circuit it now still trips.

All the new cabling can be seen as there are no cable drops for the new circuit and the only part that is hidden is the drop to the consumer unit (this is the original cable which was operating beforehand).

 

[DC-backfrom the past]

I understood you supplied the new detector straight from the CU

I used the original cable and used that as a supply for the original smoke alarm then linked the other two via three core and earth cable.

 

[Octopus]

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?

 

[DC-backfrom the past]

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.

 

[Octopus]

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]

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]

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]

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]

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]

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]

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

 

[DC-backfrom the past]

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]

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]

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]

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]

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]

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]

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

 

[Octopus]

That's a nice new shiny board. Do you have access to the EIC?

 

[Midwest]

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

Don't think he has, but he's tried using new base & head; still trips. As the alarms are class 2, does seem peculiar?

Wonder what would happen, if he connected a different load. Hardly scientific, just curious?

 

[ruston]

@Midwest . Yes , I was wondering , never had a faulty one ; but one of the units may be duff , or as has been alluded to -damaged.
Obvously looks like a borrowed neutral or earth fault in the feed , or the feed is supplying something else too if it is not dedicated.
First suspicion always goes to two way switching on up landing and down hall , but I think that is ruled out here .
Not a sneaky loft light is it?

 

[Midwest]

@Midwest . Yes , I was wondering , never had a faulty one ; but one of the units may be duff , or as has been alluded to -damaged.
Obvously looks like a borrowed neutral or earth fault in the feed , or the feed is supplying something else too if it is not dedicated.
First suspicion always goes to two way switching on up landing and down hall , but I think that is ruled out here .
Not a sneaky loft light is it?

Possiblier, think I would also do that global IR.

 

[DC-backfrom the past]

ok so I went back today with fresh eyes and clear head.
I checked the circuit again all good, visually and ir test.
amongst other things,I decided to give the board a good look over
it had only been fitted last year.
long story short ... I found a fault the bus bar where it should connect the live side of rcd to mcb it wasn't connected properly. In the MCB it was touching the outside of the screw clamp
ie the cable entry clamp was closed and it wasn't securely holding the bus bar .
Thus the only thing that was securely holding the bus bar in place were the screws/cable clamp of the rcd. As I was switching on the mcb switching up the way there was slight movement of the mcb .
I checked the other side and it was the same
it was as though whoever fitted the board had connected the bus bar outside on the rcd and thereafter placed the mcb

I sorted this and then tried again and success all working properly
what I did notice as well was when the cover was on its a tight fight due to the metal so there is no movement/play at all when switching on or off any mcb or rcd . sometimes the plastic boxes had a bit of play due to being flimsy.
When the other side was tripping I think I had been switching on and off via main switch, so may explain the other rcd tripping with the slight movement.
I cant find anything else that's wrong anymore and its working now
thanks to all that helped and replied last night.
I was particularly thankful for the support here, as other forums I've seen people ridiculed asking for help.