Mains smoke alarms

Discussion in 'Electricians' Talk' started by DIYaster, May 17, 2004.

  1. DIYaster

    DIYaster New Member

    I have two mains smoke alarms installed in my house. They have both recently started going off for no reason.
    The only way I seem to be able to reset them is to flick the CU off the back on again.
    Where would these be wired into? Would they be wired in the lighting ring main or from the sockets?
    Any idea why they would be going off?
    I have an extractor fan in the bathroom that as recently stopped working. i.e. no power st ceiling switch. Could this have something to do with it?
     
  2. sparky Si-Fi

    sparky Si-Fi Well-Known Member

    I have two mains smoke alarms installed in my house.
    They have both recently started going off for no
    reason.
    The only way I seem to be able to reset them is to
    flick the CU off the back on again.
    Where would these be wired into? Would they be wired
    in the lighting ring main or from the sockets?

    If they are Mains operated,they should have small green LED's to indicate a healthy supply and a red LED which flashes at intervels to indicate a battery check.

    Flick off each individual circuit breaker at the board,when the correct breaker is open,the LED will go out.
    Any idea why they would be going off?

    Could be any number of reasons,usual one is they are located in the wrong place ie. close to a scource of smoke or steam,may require further investigation

    I have an extractor fan in the bathroom that as
    recently stopped working. i.e. no power st ceiling
    switch. Could this have something to do with it?

    mmm,not sure there,further inspection needed.

    If you feel unsure,get a spark in

    SF
     
  3. sparks

    sparks New Member

    I have two mains smoke alarms installed in my house.
    They have both recently started going off for no
    reason.
    The only way I seem to be able to reset them is to
    flick the CU off the back on again.
    Where would these be wired into? Would they be wired
    in the lighting ring main or from the sockets?
    Any idea why they would be going off?
    I have an extractor fan in the bathroom that as
    recently stopped working. i.e. no power st ceiling
    switch. Could this have something to do with it?

    If the alarms are installed as per the regs they should be supplied from thier own dedicated circuit and the circuit should have a warning label at the CU. Some people wire them from the local lights, test that you have a 230volt supply at the fittings and if back-up batteries are fitted then make sure they are servicable, if in doult ask a sparky to have a look, also depending what type of smoke detector you've got dust with set them off.
     
  4. Fused

    Fused New Member

    Have you cleared the problem? Was it just the batteries? Trust you realise that the batteries are completely concealed on these mains-powered alarms, such that you have to completely disconnect the mains connection to access the battery compartment.
     
  5. DIYaster

    DIYaster New Member

    Hi, thanks all for your replies.
    .
    I have confirmed they are mains as they have green LEDs flashing.

    They have stopped going off for some reason so at least its quiet for the time being.

    I have checked CU but not labelled. They were installed when the house was built in 1998 so would of thought they'd comply with regs.

    I'll not have the time to look at them proper until the weekend but have taken on all the points stated.

    thanks again
     
  6. foxey

    foxey New Member

    I believe building regs require smoke alarms to be fed off a regularly used cct. eg lighting.
    A dedicated fuse/mcb could trip and be out of action for long oeriods without the consumer knowing.
     
  7. pyrotenax

    pyrotenax New Member

    [/quote]I have two mains smoke alarms installed in my house. They have both recently started going off for no reason.
    The only way I seem to be able to reset them is to flick the CU off the back on again.[/quote]

    sounds like you got a faulty smaoke alarm unit/head . If it was just a flat battery you would probably be hearing a small chirp every 30secs-1min

    without further testing or tracing you will not find out , but they most probably will be wired back to the dis board on their own circuit or failing that , wired to a local lighting ceiling rose with possibly a spur nearby

    yes , faulty head

    i doubt very much this has anything to do with it . The fan prob is no doubt a failure on the 12v side of the transformer ( usually in the loft and you may find a tripole pole isolator switch for it nearby so it can be safely isolated and worked on or swapped out.

    hope that helps
     
  8. pyrotenax

    pyrotenax New Member

    i think your talkin about emergency lighting there
     
  9. pyrotenax

    pyrotenax New Member

    ok , i just checked , appologies


    The new British Standard 5834: Part 6 recommends that mains-powered smoke alarms in domestic buildings without a standby supply should be connected to an independent circuit at the distribution board. Smoke alarms with a standby supply can be connected to a lighting circuit, providing the standby supply (battery back-up) has a minimum duration of 72 hours and a low power warning signal to warn when the standby supply is exhausted.
     
  10. DIYaster

    DIYaster New Member

    Just to update on this.

    The damm things went off again last night.

    I had a check last night and the smoke alarms are wired into the upstairs lightning circuit. Although I havent been up in the loft yet to see where they are wired.

    After I reset them, one beeped every 30sec-1min before settling down after a while
    From the above does this mean the battery has gone?

    They have a green LED and a red LED flashs every min or so when on normal operation.
     
  11. jonnyb

    jonnyb New Member

    I'm about half the way through my rewire. I'm putting in 2 mains powered some alarms with BB on their own 6amp MCB (no RCD protected.

    Will that be ok - as you said earlier if the mains goes for a long period of time it will start churping as the batt. runs low
     
  12. pyrotenax

    pyrotenax New Member

    @johnyb , yes mate that will be fine . I take it one upstairs and one down ?
    also the type of smaoke alarm downstairs would be an optical type , whilst the smoke alarm upstairs would be an ionization type ( they will look different because of the different types , even if they are from the same manufacturer ).

    simply ...... optical type work by the alarm being sounded once the optical eye inside is blocked with smoke and the ionization type work by having some radioactive isotope inside wich reacts with certain particles in the smoke

    i would say , in general , that the ionization ones are less prone to false alarms and are more acurate (sensitive even) and tend to be installed upstairs and depending on layout and length of landing even 2 or three.

    hope that helps
     
  13. pyrotenax

    pyrotenax New Member

    no doubt they will be class II equipment ( double insulated ) [​IMG] , make sure you dont cut off the cpc . Connect it together in a connector block , 6amp one will do
     
  14. Paddypat

    Paddypat New Member

    I have the same problem. I have mains ionization type. I got this as I thought it wouldn't go off so often as the optical battery one we have. It's been fine for 5 months and then went off at about 3am for about a minute. It then went off about 4 weeks later during the day both for no apparent reason. It's been fine since. I was wondering if dust or a very small spider could get in it and set it off
     
  15. Gopher

    Gopher New Member

    have the same problem. cause - leaving the bathroom door open and steam crossing the alarm.
     
  16. plugwash

    plugwash New Member

    you should use three and earth between alarms so you can link them
     
  17. pyrotenax

    pyrotenax New Member

    @Gopher , solution : keep the door shut and install an extract fan in the bathroom that is upto the job.
    The correct size, type and number of fan unit(s) required for any area is determined by three factors: the room size, its use and location.
    First, work out the volume of the room by multiplying length x width x height. This volume is then multiplied by the required number of air changes per hour (ACH) to provide the total number of air movements required per hour. Select the number of fans necessary to achieve the desired volume.
    Bathrooms:
    an extract rate of no less than 54m3/h 15 l/sec. For calculation purposes its recommended an air change rate of 6 per hour
     
  18. DIYaster

    DIYaster New Member

    yep. The alarms i beleive are working fine.

    I think my problem is as the extractor fan in the bathroom is broken as one of the alarms is on the landing outside the door.
    I never used to have this problem before i installed the shower. Hopefully fixing the fan will cure the problem. I would of thought that they wouldn't be that sensitive to steam tho, esp the ionisation type i have.
     
  19. pyrotenax

    pyrotenax New Member

    Intermittent alarming can be caused by ....

    loose connections can intermittently disconnect power to the smoke alarm. The effect is the same as a power failure. When power is restored, the units may alarm briefly.

    Cover or sensor chamber is covered by dust or dirt.
    Alarms may look clean, but dust can accumulate inside the cover, even in newly built homes. Gently vacuum smoke alarms regularly using the soft brush attachment.


    Smoke alarm may need to be relocated...

    Install smoke alarms at least 20 feet from appliances like furnaces and ovens, which produce combustion particles. Alarms should be at least 10 feet from high humidity areas like showers and laundry rooms, and at least 3 feet from heat/AC vents whenever possible.
     
  20. ban-all-sheds

    ban-all-sheds New Member

    have the same problem. cause - leaving the bathroom door open and steam crossing the alarm.

    That happened to me once. I was staying in a hotel where the bathroom could also be used as a sauna. "I'll give that a go", I thought, so I read the instructions, set the controls, and as instructed left the bathroom door closed for 15 minutes for the steam to build up before going in there. After the 15 minutes was up, I opened the door, and a vast cloud of steam surged out and enveloped the smoke detector in the room, setting off the fire alarm. It was very loud.

    So there was I, b*llock naked, having just set off the fire alarm in a hotel...

    I immediately phoned reception to explain, hoping that they could cancel it, stop evacuation, tell the fire brigade not to come.

    It was with mixed emotions that I heard the person on reception say "what fire alarm?"
     

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