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Discuss rcd tripping after smoke alarm fitted. in the Periodic Inspection Reporting & Certification area at ElectrciansForums.co.uk.

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  1. DC-backfrom the past
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    DC-backfrom the past EF Member

    Location:
    Glasgow
    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.
     
  2. Pete999
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    Pete999 Trusted Advisor

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    Location:
    Northampton
    Borrowed Neutral may be??
     
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  3. DC-backfrom the past
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    DC-backfrom the past EF Member

    Location:
    Glasgow
    The original smoke alarm is on its cable directly from the consumer unit.
    If the fault is a borrowed neutral its on another circuit.
     
  4. Pete999
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    Pete999 Trusted Advisor

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    Northampton
    Where have you taken the L from and which side of the CU have you taken the N from?
     
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  5. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
    Business Name:
    Wilko Electrics
    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?
     
  6. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    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.
     
  7. DC-backfrom the past
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    DC-backfrom the past EF Member

    Location:
    Glasgow
    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.

    View attachment 20171113_122321.jpg
     
  8. DC-backfrom the past
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    DC-backfrom the past EF Member

    Location:
    Glasgow
    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.
     
  9. DC-backfrom the past
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    DC-backfrom the past EF Member

    Location:
    Glasgow
    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 .
     
  10. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
    Business Name:
    Wilko Electrics
    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.
     
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  11. DC-backfrom the past
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    DC-backfrom the past EF Member

    Location:
    Glasgow
    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.
     
  12. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    So is the original circuit still in place and your new circuit is paralleled at the mcb?
     
  13. Murdoch
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    Murdoch Electrician's Arms

    Location:
    Woking
    You need an earth leakage clamp meter ......
     
  14. DC-backfrom the past
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    DC-backfrom the past EF Member

    Location:
    Glasgow
    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
     
  15. Murdoch
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    Murdoch Electrician's Arms

    Location:
    Woking
    EDIT: If it trips when you attach the smoke alarm - did you use the existing bases or fit new ones?
     
  16. DC-backfrom the past
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    DC-backfrom the past EF Member

    Location:
    Glasgow
    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
     
  17. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
    Business Name:
    Wilko Electrics
    Glass of favourite and the installation instructions, who knows? I've had domestic blindness more than once :)
     
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  18. Pete999
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    Pete999 Trusted Advisor

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    Location:
    Northampton
    Swap the N over to the other Nbar
     
  19. DC-backfrom the past
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    DC-backfrom the past EF Member

    Location:
    Glasgow
    to the one covered by the other rcd ?
     
  20. Pete999
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    Pete999 Trusted Advisor

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    Location:
    Northampton
    Yep
     
  21. DC-backfrom the past
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    DC-backfrom the past EF Member

    Location:
    Glasgow
    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 ?
     
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  22. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    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?
     
  23. Pete999
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    Pete999 Trusted Advisor

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    Location:
    Northampton
    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
     
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  24. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    Is your cable supplying the smoke detectors the white 2.5 LSOH cable?
     
  25. Murdoch
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    Murdoch Electrician's Arms

    Location:
    Woking
    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.
     
  26. Pete999
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    Pete999 Trusted Advisor

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    Location:
    Northampton
    I understood you supplied the new detector straight from the CU
     
  27. DC-backfrom the past
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    DC-backfrom the past EF Member

    Location:
    Glasgow
    That's the original cable that was connected to the first smoke alarm. I took the photograph prior to removing any cables for testing
     
  28. DC-backfrom the past
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    DC-backfrom the past EF Member

    Location:
    Glasgow
    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).
     
  29. DC-backfrom the past
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    DC-backfrom the past EF Member

    Location:
    Glasgow
    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.
     
  30. Murdoch
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    Murdoch Electrician's Arms

    Location:
    Woking
    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?
     
  31. DC-backfrom the past
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    DC-backfrom the past EF Member

    Location:
    Glasgow
    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.

    rough diagram].JPG
     
  32. Murdoch
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    Murdoch Electrician's Arms

    Location:
    Woking
    No offence taken!

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

    L
    IC
    N
     
  33. DC-backfrom the past
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    DC-backfrom the past EF Member

    Location:
    Glasgow
    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..
     
  34. Murdoch
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    Murdoch Electrician's Arms

    Location:
    Woking
    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.
     
  35. DC-backfrom the past
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    DC-backfrom the past EF Member

    Location:
    Glasgow
    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 !!!!
     
  36. Murdoch
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    Murdoch Electrician's Arms

    Location:
    Woking
    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 ....
     
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  37. anthonybragg
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    anthonybragg Electrician's Arms

    Location:
    NORTHAMPTON
    Business Name:
    CHARLTEC ELECTRICAL LTD
    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.
     
  38. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    He has yet to clarify how it is connected and which parts are new and what is existing.
     
  39. DC-backfrom the past
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    DC-backfrom the past EF Member

    Location:
    Glasgow
    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
     
  40. DC-backfrom the past
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    DC-backfrom the past EF Member

    Location:
    Glasgow
    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
     
  41. DC-backfrom the past
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    DC-backfrom the past EF Member

    Location:
    Glasgow
    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
     
  42. Murdoch
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    Murdoch Electrician's Arms

    Location:
    Woking
    That's not what I meant, just run a meter of new cable from the CU and test the smokes and bases....
     
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  43. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    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?
     
  44. Midwest
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    Midwest Electrician's Arms

    Location:
    Oxfordshire
    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?
     
  45. ruston
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    ruston Trusted Advisor

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