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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


  • Former Community Member
    0 Former Community Member
    Have you seen the cost of those? Eight will cost a small fortune. The thinking is that pay a little more now with wiring etc which is still far less than the radio linked and when they need replacing every 10 years it's not going to cost another small fortune. 


    This has been brought in Scotland thanks to Grenfel towers and our esteemed leadership up here bringing in a law for interlinked alarms. The irony is that we are in a solid brick build with internal render then plastered. MDF skirting, and laminated MDF flooring. There is very little that can actually contribute towards proper fuel for a fire and we checked the labels of items such as the soft, bed covers etc, all made of fire resistant materials, so how a serious fire would occur is a bit questionable. To start a fire we would literally need to take a blow torch to most items to get them ignited. Only the electrics could be a source of ignition, but I did all the re -wiring and had it checked and certified by my qualified electrician. 


    Still it's not as stupid as the council representative who insisted that the communal hallway be painted in fire proof paint. The walls are again brick and render. Even if you were to deliberately pile up wood and start a fire, I wouldn't be too worried.
  • 0
    Sounds like the real risk is cooking. Heat alarms rather than smokes are the way forward to avoid false alarms.

    Anything more than 2 or 3 flats, or more than one set of stairs  is the sort of situation to use red FP type cable, and a panel system (type A) either 4 core or 2 depending if sounders and sensors share wires or have separated loops.


    Are you sure that a type D is enough -  as if not,   you will need call points all possible fire exit doors as well ?

    please, and I'm not trying to be funny, before you start, do check exactly what you are supposed to be installing or you may end up doing it twice.

    (I do realise Scottish rules are not the same as English, but I think it is similar.)


    mike

    For reference.

     

    Grade A: Fire alarm system with detectors and a central control panel. Usually with call-points (break glass units) near exits and on each landing



    Grade D: System of (usually interlinked) mains-powered smoke or heat alarms with backup batteries. The interlink can be achieved with cable or radio-interlink. In low risk properties the mains power supply for smoke alarms might be replaced with a requirement for ten year sealed battery supply (usually combined with radio-interlink).



    Note: in the 2019 update to BS 5839-6, Grade D was split into D1 (tamper-proof backup battery) and D2 (user-replaceable backup battery).



    The coverage within the building by the detection system is described with the following codes:



    LD1: Covers all circulation spaces that form part of escape routes plus all rooms in which a fire could start








  • 0
    I think you're underestimating the risks of a fire. There are many possible sources of ignition even in a well-maintained house: unattended pans on a stove; faulty electrical appliances; etc. Most houses are brick/render/plaster, yet still regularly burn down. A few years ago there was a fire in a Victorian terrace house a few minutes walk from my house which killed the whole family. It was started by a faulty battery charger.
  • 0
    I am not an expert on fire alarms, but this sounds as though the legislation is new and therefore not well known. If flats with communal entrance halls and stairs you will need an expert, because there will be reams of small print. Are you being asked by the Council employee to fit smoke detectors in every room, hall and stairwell? It sounds as though this legislation was invented by the fire alarm industry, you need to get the inside story. It will not be cheap, but at least should be fully compliant, as Mike says you only want to do it once and you undoubtedly will need the certificates, which you cannot do yourself.
  • 0
    Calm down Wally, house fires are rare, complete loss is unusual because there are usually alarms. For a battery charger to start a fire would be very difficult unless it is placed on inflammable furniture, not fire rated, or somewhere similar. One cannot believe many reports, few fires are "properly" investigated, because it is very expensive and time consuming so not worthwhile. Even that rarely produces a certain result, unless arson, because there are so many variables to consider.


    I just saw your pans on the stove remark Wally. It is only deep frying which is significantly dangerous, All those pans of water will not do much, even if your vegitables come out black! As I have said before, it takes a lot more heat to start a fire than most people realise, but add a suitable volatile accelerant, say petrol and you have everything you need! Don't try it, accelerants added deliberately can be spotted almost immediately and the forensics will get you locked up pronto!
  • Former Community Member
    0 Former Community Member
    You're right the legislation is new and I suspect it will evolve over time to include push button activation on the stairwell but not at present. The problem is that we're in an old build, there are no fire exits just the one communal stair. 


    Whilst I'm on this I also need to run an Earth bond cable from a gas pipe in the attic to the MET, there currently isn't any! Can I put 10mm earth cable in the same conduit as 1.5mm three core and earth or is there a regulation against this?


    Thanks

  • 0
    Does the gas pipe enter the building in the attic??
  • Former Community Member
    0 Former Community Member
    No it doesn't, I should have said, this is the outlet pipe 22mm from the meter in the flat, the pipe then runs up into the attic, all the way along the attic and back down into the flat to the boiler. No bonding that I can see on the entry pipework. I was thinking that I could run an earth bond on the outlet into the attic and bring it back down into the flat using the same conduit for the 3 core and earth to the MET next to the consumer unit.
  • 0
    Which simultaneously touchable objects are you bonding here - flat gas pipes and flat wiring, of whole building gas pipes, and whole building MET. ?

    Main bonding should be building incomers (gas and electric) Flat bonding needs to be local to the flat.


    A 22mm pipe has more copper cross-section than a 10mm cable, so if it runs the right way, get it nearer  the ends,

    Regs do not prohibit earthing sharing a duct, but  the laws of physics might - I think it will be hard to thread unless it is a very easy route.

    mike.
  • Former Community Member
    0 Former Community Member
    I took another look and there is definitely no bonding at all on the incoming gas supply which is old fashioned low carbon steel covered in paint. A communal supply pipe enters the building and runs up the wall in the hallway branching off on each floor to the relevant flat. The visible pipe where it emerges from the ground floor all the way up to our meter has no bonding anywhere. I do not know if there is bonding below the ground floor subfloor - guess I'll be taking a look tomorrow.  


    As for the output side of our meter, the gas copper pipe has been propped up on timber along the joists. All other electrical supplies are in old steel conduit so there is no chance of any of those supplies coming into contact with the gas pipe. There is however a 10mm earth cable that originates from the same cavity that the gas pipe runs down, into the boiler. I'm going to have to check that this end of that cable is actually connected to something near the boiler because the opposite end of that 10mm earth runs parallel to the gas pipe back to the gas meter but terminates in an earth block in the attic which itself is not connected to anything.


    If running an earth in the same conduit is not against regulations then I'll utilize the earth block and connect an earth cable to it, run this back down the conduit next to the consumer unit and MET and get it connected up.

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