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Mains smoke and heat detectors

Discussion in 'Electrics UK' started by foxhole, 15 Dec 2015.

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  1. foxhole

    foxhole

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    About to run some wiring, what cable/size is required for the detectors.
     
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  3. Echo the husky

    Echo the husky

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    It depends on the alarms you choose. For normal mains alarms 1.0mm² 2 core and earth between the consumer unit and first detector, then 1.0mm² 3 core and earth to all the other detectors. Don't forget to wire CO alarms as well if they are required. www.aico.co.uk has a huge amount of information on what detectors to use and where to fit them.
     
  4. Risteard

    Risteard

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    You could only do this if you feed them from a lighting circuit, otherwise 1.5mm^2 is required.

    Also, CO detectors if interlinked with smoke detection will require an alarm controller to indicate cause of alarm (smoke/CO).
     
  5. PrenticeBoyofDerry

    PrenticeBoyofDerry

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    That is interesting, can you not go 1.0mm on 6A device? As that is exactly what you would be doing if you connected up to most domestic lighting circuits!
     
  6. Echo the husky

    Echo the husky

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    What reg number is that? I thought they ditched the bit about only lights on 1.0mm²

    Oops I missed that bit. :notworthy:

    I never saw sense in it, we used to put the alarms on 3A MCBs when we used MK boards. I've never seen domestic smoke alarms installed with 1.5.
     
  7. PrenticeBoyofDerry

    PrenticeBoyofDerry

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    Well 3A mcbs are not a common device, so not an issue or concern for me. I have in the past installed smokes with 1.5mm, but that was because I had reels of it at the time, other than that I am not aware of any regulation stating smoke alarms circuit are not allowed on 1.00mm. I have done plenty of EICR/PIR on housing assoc. properties and never flagged up a 1.00mm circuit and never been told to!
     
  8. Echo the husky

    Echo the husky

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    It was a big thing a while ago and there were arguments with people insisting that bathroom fans needed to be wired with 1.5mm² as they wern't lights, the same with central heating controls. I can't find the regulation in the book, though I havn't looked very hard.
     
  9. PrenticeBoyofDerry

    PrenticeBoyofDerry

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    As far as I am aware, if the cable can deal with deratings and the rating of the protective device? It is fine, but I shall wait on that one.
    I am sure it will be interesting bedtime reading?
     
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  11. Risteard

    Risteard

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    Nothing wrong with fans or smoke detectors being wired in 1mm^2 if they are connected to a lighting circuit.

    If it is a dedicated circuit then the minimum csa is 1.5mm^2 and has been for some time now.
     
  12. RF Lighting

    RF Lighting

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    Can you cite the regulation which requires this please.
     
  13. EFLImpudence

    EFLImpudence

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    He's thinking of Table 52.3 - a particularly good example of nonsense.

    Having said that, it does state "For a specific appliance - as specified in the product standard".
     
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  14. PBC_1966

    PBC_1966

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    What does table 52.3 actually say?
     
  15. Iggifer

    Iggifer

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    It's easy, just fit smokes with those little green LEDs :D That's a lighting circuit in my book!
     
  16. EFLImpudence

    EFLImpudence

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    The relevant parts are:

    Minimum csa of conductors

    Non-sheathed and sheathed cables............Lighting circuits....................................Copper I.0mm²
    .............................................................Power circuits.................................................1.5
    .............................................................Signalling and control circuits............................0.5 (see Note 1)

    Non-sheathed and sheathed flexible cable...For a specific appliance.....................................As specified by the product standard
    .............................................................For any other application...................................0.75*
    .............................................................ELV circuits for special applications (see Note 2)...0.75

    Note 1 In information technology, signalling and control circuits intended for electronic equipment, a minimum csa of 0.1mm² is permitted.
    Note 2 For special requirements for ELV lighting see 715.
    * In multicore flexible cables containing seven or more cores, Note 1 applies.

     
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  17. PBC_1966

    PBC_1966

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    Interesting. If one wanted to be pedantic, one could ask how it's possible to get lights to work without supplying them with power......

    But assuming they intended "power" to mean anything except lighting, what happens if you have a circuit supplying lights and other devices, such as fans? Which takes precedence for determining whether that's a "lighting circuit" or a "power circuit" in such a case?

    What on earth is the point of this? So long as the cable is suitably sized for the current and any voltage-drop concerns related to its length, and suitably protected by the appropriate fuse, what does it matter?
     
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