1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

Mains Smoke Alarm Wiring - Very Odd!!

Discussion in 'Electrics UK' started by MFRacing, 19 Jul 2015.

  1. MFRacing

    MFRacing

    Joined:
    10 Dec 2014
    Messages:
    178
    Thanks Received:
    2
    Location:
    West Yorkshire
    Country:
    United Kingdom
    Hi guys,

    Just been fitting some new Nest Smoke/C02 mains powered alarms to replace my current mains pawer smoke alarms. Fitted the downstairs one with no issues, wiring as expected, i.e. Brown - Live, Blue - Neutral, Grey - Interconnect (not used on the new Nest alarms, so left disconnected). 2 of each to connect the other alarms in the house (i.e. ring)

    Go upstairs to fit that one, and do it up as expected and no power to the alarm. I have 4 wires, Earth, Grey (Sleeved with Blue), Black (sleeved with Brown), and Brown. So I get my multimeter out and find:

    Grey (Sleeved with Blue)
    Brown 178v
    Earth 36v
    Black (Sleaved with Brown) - 0.55v

    Brown
    Grey (Sleeved with Blue) - 0.8V
    Earth - 1.4v
    Black (Sleeved with Brown) - 3.7v

    Earth
    Grey (Sleeved with Blue) - 36v
    Brown - 240v
    Black (Sleeved with Brown) - 0.5v

    Black (Sleeved with Brown)
    Earth - 100v
    Grey (Sleeved with Blue) 0.5v
    Brown - 128v

    What the heck? So if I connect brown and earth I get 240v, and that would power the alarm!? I didn't see how the old upstairs some alarm was wired up (taken out before i got there, it was working fine though)

    What do you think is going on? Maybe the wiring in the downstair one has affected the upstairs one? They are all connected on the same circuit (one MCB for all smoke alarms)

    Can any one help?

    Thanks
    Matt
     
  2. Sponsored Links
  3. Lectrician

    Lectrician

    Joined:
    18 Jul 2004
    Messages:
    8,473
    Thanks Received:
    399
    Location:
    Devon
    Country:
    United Kingdom
    Disconnect everything on the circuit and start from scratch. You're over complicating things. Remove everything, and start to install your new ones. You should have one that has a two core cable feeding in, and three cores between the rest. If there is not one with just a two core, you can see inside your CU (most likely) which core has been used as neutral (the grey or the black).
     
  4. Iggifer

    Iggifer

    Joined:
    8 Sep 2011
    Messages:
    4,637
    Thanks Received:
    587
    Location:
    Warwickshire
    Country:
    United Kingdom
    You've wired something up wrong if they were all working correctly before. Go back to the first smoke and start again. Check the first smoke for a T+E & 3C&E.

    This will tell you what to connect to which terminal, as you only need a live and neutral it should be super simple.
     
  5. MFRacing

    MFRacing

    Joined:
    10 Dec 2014
    Messages:
    178
    Thanks Received:
    2
    Location:
    West Yorkshire
    Country:
    United Kingdom
    That's what I'm doing. The wiring is all Installed already though. Why can I not find 240 at the upstairs point apart from brown and earth?

    Thanks for your help.
     
  6. Iggifer

    Iggifer

    Joined:
    8 Sep 2011
    Messages:
    4,637
    Thanks Received:
    587
    Location:
    Warwickshire
    Country:
    United Kingdom
    I would guess you've lost your neutral
     
  7. MFRacing

    MFRacing

    Joined:
    10 Dec 2014
    Messages:
    178
    Thanks Received:
    2
    Location:
    West Yorkshire
    Country:
    United Kingdom
    Yer that's my thinking. Gonna pull down the downstairs one now. That's working fine so not sure what could have gone wrong! Cheers
     
  8. MFRacing

    MFRacing

    Joined:
    10 Dec 2014
    Messages:
    178
    Thanks Received:
    2
    Location:
    West Yorkshire
    Country:
    United Kingdom
    I'll report back in 30min or so!
     
  9. sparkwright

    sparkwright

    Joined:
    20 Aug 2009
    Messages:
    8,422
    Thanks Received:
    1,053
    Location:
    Dorset
    Country:
    United Kingdom
    It's odd at the first one to have brown, blue, grey. If you really have those colours there, I would expect some more wires too be floating around.

    As suggested, turn off power completely, and disconnect everything and test it all out with a continuity tester.

    PIctures will help enormously.
     
  10. Sponsored Links
  11. Lectrician

    Lectrician

    Joined:
    18 Jul 2004
    Messages:
    8,473
    Thanks Received:
    399
    Location:
    Devon
    Country:
    United Kingdom
    As I said at the start - Start again. From the start. You have dropped a connection somewhere. You are over complicating things by metering everything out.
     
  12. Lectrician

    Lectrician

    Joined:
    18 Jul 2004
    Messages:
    8,473
    Thanks Received:
    399
    Location:
    Devon
    Country:
    United Kingdom
    Just to confirm. All old ones removed? There aren't some now with just wires hanging, not connected?
     
  13. MFRacing

    MFRacing

    Joined:
    10 Dec 2014
    Messages:
    178
    Thanks Received:
    2
    Location:
    West Yorkshire
    Country:
    United Kingdom
    Bang on! All fixed. A neutral had slipped out of the connection block in the downstairs alarm, re connected that and all good upstairs! Thanks again guys. I can have a beer now! :)
     
  14. ban-all-sheds

    ban-all-sheds

    Joined:
    27 Aug 2003
    Messages:
    69,783
    Thanks Received:
    2,858
    Location:
    London
    Country:
    United Kingdom
    I cannot for the life of me understand why it can be a good idea to use wireless interconnects instead of wired when the wired infrastructure is already there.
     
  15. Iggifer

    Iggifer

    Joined:
    8 Sep 2011
    Messages:
    4,637
    Thanks Received:
    587
    Location:
    Warwickshire
    Country:
    United Kingdom
    There is no good reason. More expensive and much more chance of them not all going off.

    I would have gone with Aico myself but the Nest ones do have the advantage of telling you they've gone off when you're not there.

    Let's just hope the OP doesn't have a VM Superhub or his house will burn to the ground
     
  16. MFRacing

    MFRacing

    Joined:
    10 Dec 2014
    Messages:
    178
    Thanks Received:
    2
    Location:
    West Yorkshire
    Country:
    United Kingdom
    Just so you know guys they don't use the wifi network for interconnect. They talk direct to each other.

    Loving the path light feature!
     
  17. JohnW2

    JohnW2

    Joined:
    28 Jan 2011
    Messages:
    47,636
    Thanks Received:
    3,099
    Location:
    Buckinghamshire
    Country:
    United Kingdom
    In terms of 'instead', I would agree - but, as the OP now seems to have confirmed, I thought that the Nest ones did have wired interconnect.

    However, I could see some theoretical merit in having wireless as well as wired interconnection, since it's not beyond the realms of possibility that wired interconnections could fail in the case of a major fire - but I don't know if any have that facility.

    Kind Regards, John
     
Loading...

Share This Page