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Mains powered smoke alarm

Discussion in 'Electrics UK' started by JBR, 9 Sep 2020.

  1. JBR

    JBR

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    I have a mains powered smoke alarm in our hall which, to be honest, I had forgotten about!
    I have two battery powered smoke alarms elsewhere in the house which I am about to replace, as they are at the end of their stated life. The new units I have sent for have a guaranteed life of 10 years including lithium batteries.

    I was also going to replace the mains powered unit, but it occurred to me that a similar replacement would also have a guaranteed life of at most 10 years, and would cost at least as much as the battery powered ones I have ordered, so why mess about with another mains powered one?

    Now for my question. If I remove the mains powered unit, what do I do with the trailing wires? I assume these lead from a transformer somewhere in the loft (it's a bungalow) and that is likely to be attached to the nearest light fitting. If so, the loft is boarded in that area, so I'm going to have to remove floorboards to get at it.
    I'd prefer to remove the lot: transformer and attached cables. Is there an easy way of doing that, or is it safe just to leave the lot in the loft, still attached to the mains supply?
     
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  3. AndyPRK

    AndyPRK

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    There is no transformer.

    It’s worth checking in the cu fusebox if there is a seperate circuit for smoke alarms.
     
  4. JBR

    JBR

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    Thanks.
    No, there's no separate circuit. I assume it is taken from the nearby light fitting.

    You mean they run directly on mains electricity?
    If that is the case, I suppose I could just attach chock blocks to the ends of the wires (after having turned off all the mains, or perhaps the lighting MCB) and poke them back above the ceiling?
    Would that be safe enough?
     
  5. winston1

    winston1

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    No.
     
  6. JBR

    JBR

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    OK. So what must I do?
     
  7. winston1

    winston1

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    Find the other ends of the wires and disconnect them.
     
  8. securespark

    securespark

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    Is the nearest light a ceiling rose?
    If so, turn off the lighting circuits and unscrew the cover, then post a pic here. We may be able to identify the conductors you need to disconnect.
     
  9. securespark

    securespark

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  11. Taylortwocities

    Taylortwocities

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    If the power connection is not discovered at the nearby light / ceiling rose, I would just buy a new mains alarm.

    If you really can’t do that, then you could terminate the supply ends in a proper connection box like this.
    https://www.toolstation.com/hylec-debox-connector-box/p32672

    You’ll have to make a larger hole in the ceiling to get the box through and into the ceiling. Easier to get a replacement mains alarm with battery back up.
     
    Last edited: 11 Sep 2020
  12. JBR

    JBR

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    Thank you. Some very helpful suggestions here.
    I'll have a look in the nearest ceiling light rose (I put it up a few years ago, but didn't think about the smoke alarm) and see what I can see. I should be able to identify the permanent live if I turn the light switch off, but I'll take a picture as you say SS...
    when I get round to it!
    Safelincs do battery-powered alarms with guaranteed 10 year life. If less than 10 years, they replace them. I'd prefer to get one of them to replace the mains-powered one.
     
  13. securespark

    securespark

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    :)
    If you get stuck, I'm not far away.
     
  14. JBR

    JBR

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    Thanks SS.

    I have now had a good look at this smoke alarm.
    I opened it and found that it has no trace of any mains voltage in it. Neither does it have a back-up battery. So I assume I was right in the first place that there is a transformer somewhere up the line.
    All I can assume is that it is somehow tied in to the house alarm system. I must look closely through the documents.

    I'm glad that I didn't go out and buy a replacement mains-powered smoke alarm as that wouldn't replace this directly! Smoke alarm 1.jpg Smoke alarm 2.jpg
     
  15. AndyPRK

    AndyPRK

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    Not seen one of them before !
    Does it interconnect to another smoke alarm ?
     
  16. Risteard

    Risteard

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    You're not correct. There is no transformer.
     
  17. AndyPRK

    AndyPRK

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    Well there is no battery.
    And a circuit board where the battery would normally fit.

    Maybe a master unit has a battery ?
     
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