Smoke Alarm Cable question?

Discussion in 'Electricians' Talk' started by jonny_d, Apr 3, 2010.

  1. jonny_d

    jonny_d New Member

    Hi guys,

    I have just conveted my loft into another room etc. And i know i will need mains powererd smoke alarms fitted. My questions are

    1. What cable should i use IE 1.5 twin and earth
    2. Should they be linked
    3. And can i run them from a lighting ring or a new run to the board.

    Thanks for any help with this

    Regards john D
  2. fast

    fast New Member

    jonny i would run a twin from the board on a 6a breaker then 3core and earth to the next one and next one 1mm or 1.5mm, using the grey in the 3 core as a link. also sleve the black if your using it as a neutral
  3. Removed 4

    Removed 4 New Member

    1mm 3core&E for the linking cable(s) would be better, jonny. It's far easier to terminate than 1.5mm.

    It isn't necessary to run a dedicated circuit, in fact, it's no longer considered sensible or desirable to do so.

    Provided that the detectors have a battery back-up, then the best thing is to power them from a principal lighting circuit. It's also the easiest way to do it, in most cases.

  4. Removed 4

    Removed 4 New Member

    Not so fast, fast.

    The black should be used as the signal core and the grey oversleeved blue as a the neutral. This is the convention accepted by the electrical industry.

  5. fast

    fast New Member

    oh ok i stand corrected, i like what you say about using 1mm instead of 1.5 and taking it from a prim lighting circuit. although i see no arm in using any coulor and im sure that a lot of electricians are still sleving there back to blue.
  6. jonny_d

    jonny_d New Member

    just to let you know i the property now has 3 floors. I will use that cable you suggested but i have been told that i should run this direct from the board. I will need a test on this so i really need the regs on this.

    regards jonny
  7. fast

    fast New Member

    do as i say in my first post then. but use 1mm. and there are 2 types of smoke alarms optical and ionizing you should use them both but im not sure where, look it up man
  8. JP.

    JP. Screwfix Select

    My advice Jonny..take Lucia's advice M8, you wont go wrong.
  9. Removed 4

    Removed 4 New Member

    but i have been told that i should run this direct from the board.

    Well, now you've been told otherwise, jonny, haven't you?

    It's certainly true that when mains detectors started to be installed, that they were usually on a dedicated circuit. But current thinking led by most Local Authorities now recognises the flaw in doing so.

    You're familiar, I supppose, with the age-old snag with battery-powered devices, when the householder would remove the battery because of the 'annoying' low-battery 'chirp'. He would then get around to replacing the battery 'sometime' - or not.......

    Mains-powered devices with battery back-up, also have this low-battery warning. So if you were to connect the detectors to a dedicated circuit, the user could then remove the battery and also switch off the circuit.

    This wouldn't be the case, if the detectors were wired to a principal lighting circuit, because the user wouldn't want to be without light, would he?

  10. Removed 4

    Removed 4 New Member

    'fast' dear, I don't know where on earth you come from, but I wish that you'd stop handing out dodgy advice here.

    I don't doubt that you have a helpful nature, but I'm not impressed with your opinions on harmonised cable colours here, and less encouraged by your obvious lack of knowledge on a neighbouring PME thread.

    Please, stop it, and try to confine yourself to those subjects that you do know about. Thank you.

  11. Krog

    Krog New Member

    Jonny, as Lucia says, there is no need to use a dedicated circuit, and indeed, a regularly used lighting circuit is preferable. If the linking of the smokes over 3 floors proves problematic, you could power each from the lights for each floor, and link them using remote bases which allow the units to 'talk to each other' without the need for a three core cable to be run between floors.
  12. fast

    fast New Member

    my advice to you jonny is to go to a popper forum, like ITE forum register on there and ask your question again. you will get the popper answer there it is monitored a lot better than this.
  13. Smokey

    Smokey Member

    Look at recent letter from Electrium's Mike Cash re a quiz on smoke alarms in January issue of Professional Electrician, and where they disagree with the answer given by a certain manufacturer of alarms.

    In fact they agree with other poster re always putting on a dedicated circuit under 17th edition/not sharing with anything other than other smoke & heat alarms.

    Same point made by them in March Elect Contracting News article confirming that you should not install where other pieces of equipment share the one RCD.
    BS5839 Pt 6, is quite clear on this matter: (Code of Practice re Fire & Smoke alarm installation).

    Can't see an online version of it currently.
  14. JP.

    JP. Screwfix Select

    Logic dictates that smokes and heat rises detectors are better on a principle lighting circuit surely. People take batterys out etc but they do not defeat lighting..its a matter of fact. So can you say in a definite way why smokes and the like cannot go on a principle lighting circuit Smokey..and the reasons why not. Please avoid the use of reg numbers if at all possible.
  15. Guest

    according to the building regs , document B Fire Safety ,
    you can connect the smokes to the lighting supply so long
    as the lighting circuit does not share a rcd with a socket circuit.
    something to consider.
  16. JP.

    JP. Screwfix Select

    What is the reasoning behind that Professor Biff?
  17. Guest

    so that the supply to the smokes isn't affected by for example , repeated nuisance tripping from a kitchen appliance.
  18. JP.

    JP. Screwfix Select

    Don't really understand that, but thanks anyway Professor Biff.
  19. Guest

    you're welcome.
    its basically to ensure continiuty of supply to a "safety service" within a dwelling.
  20. oliver1234

    oliver1234 New Member

    I'm with Biffo on this.

    I spent many years installing fire and intruder alarm systems and it was always considered bad practice to use an RCD protected supply if it was also feeding other circuits.

    Imagine a scenario whereby a cleaner tripped an RCD one evening by using a dodgy vaccumn cleaner, the batteries in the larm would go flat resulting in a false alrm usually hours later.

    Lighting circuit is a good call IMO, if the mcb trips it's going to be noticed and rectified pretty quickly, if the smokes are on their own circuit it might never get sorted.

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