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Conduit requirements and cable type

Former Community Member
Former Community Member

I’m in the process of installing seven hard wired fire alarms into our property all of which have to be interlinked.



I intend to re use a now empty steel conduit that runs from right beside our consumer unit up into the loft space. The steel conduit at its point of entry into the loft terminates there presumably the rest was removed in the past. I want to run a cable from there which will have to do an up and over brickwork in the loft.



My first question, is it acceptable in compliance with electrical regulations to simply clip the cable to the brick at the mortar joints or do I have to or even if strictly not necessary should I, put the cable in PVC conduit? This area is not trafficked.



Once I have crossed the brick work and come down to the first alarm, from there I intend to run a cable down the near center of the loft adjacent to the walkway in pvc conduit parallel to the 2 existing lighting circuit conduits located above the joists. I am not going to drill through the joists. At points along the conduit there will be junctions to allow clipped cable not in conduit to be ran parallel to the joists to the relevant alarm. The conduit is going to be a straight run, so my question is having consulted a few sources that state 1.5mm flexible cable not twin and earth must be used in conduit, does it? I understand the reason for flexible cable in conduit with a lot of turns and junctions but this is a straight run.


Thanks


  • 0
    Here are some questions for you to consider.

    What type of property are you proposing to install into?

    I would suggest that you do not use solid core singles even in straight runs as it is likely to kink up even when drawing through from a .supported drum..

    What happens when your proposed 1.5mm2 single cables leave the steel conduit?

    Have you considered earthing the steel conduit?

    Have you considered using proprietry fire alarm cables such as FP or Pyro?

    Legh
  • 0
    If you use a cable with sheathing  like T and E or FP you can leave it clipped direct when it emerges, , but you may have fun getting it in to the conduit unless it is a straight drop.

    mike
  • Former Community Member
    0 Former Community Member
    Hi Legh


    Block of flats circa 1950 build. The plan is to not put the cables tee ing off  the junction boxes to the individual alarms in conduit but clip them to the joists. The conduit is to protect the cable as it runs above the joists right next to the main traffic walkway from gable end to gable end. 


    I can earth bond the steel conduit since the MET is right next to the base of the conduit.


    I think the FP cables are a little overkill we have double layer plasterboard on ceilings that was skimmed, I'd hope the alarms would have long gone off before worrying about ordinary cable failing due to fire.


    Neil
  • 0
    What happens if the fire starts in the loft space?
  • Former Community Member
    0 Former Community Member
    Fair point, having had a look can't find anything less than 100m of FP 3 core and earth cable and nothing flexible. 


    I think I'll put a heat detector in the attic too then.
  • 0
    CEF for one sell FP200 by the metre.
  • 0
    Rubia30:

    I’m in the process of installing seven hard wired fire alarms into our property all of which have to be interlinked.



     




    Can't these have radio link bases, more expense but look no wires!


    Jaymack


  • 0
    It is normal to use red FP200 for fire alarms, andit  is reasonably priced and well mechanically protected, even rats don't like it much, and fireproof! If these are just the detectors (and just single dwelling domestic) you may be happy with something less, but singles in conduit cost more than FP200 and are far less tidy. I suspect you are in an HMO because the double board is for fire protection, so you will need all the bits and pieces including an alarm panel and fire buttons, to give firemen a guide to the fire zones and 7 smoke alarms are quite a lot!. If so you will need some professional advice.
  • 0
    For those wondering what you get for your extra money with FP200, there is rather a nice   John Ward youtube demo with blow torch   For those in a hurry skip past the chat about what it is for and 8 or 9  minutes of flame waving, to about 11 mins in, where he pulls the cores out of the charred remains of the  bit he has been cooking, and the inner insulation is perfectly intact.

    you cannot do that with PVC.

    Of course if you join it in a plastic box with plastic choc blok, it rather defeats the point.

    If only consumer units could have the same sort of additives in the plastic...


    Mike
  • 0
    It is the construction Mike.

    The outer sheath is almost unplasticised PVC with lots of flame retardant, then an aluminium foil, and the cores are silicone rubber insulated, with a composition that basically turns to silicon dioxide bound together under extreme heat. The foil keeps the oxygen out and the PVC to itself, and the cores are pretty inert as a result. JW didn't really heat it enough to show the worst-case state, still servicable though.

    I rather like the stuff for clipped direct applications, it can be very neat, does not need trunking, the clips are small and tidy and very firm and it bends nicely around corners of woodwork or whatever. It is nearly as fireproof as pyro, although does not look too good afterwards unlike bare pyro, better than PVC coated stuff though! Insulation tests after fire exposure are excellent, even if you get the sheath bright red hot.

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