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Fire alarm panel supply

Apostolos
Good morning.

I have a question that may sound silly so excuse my ignorance in advance

I have a Fire Alarm Panel

This is going to be fed through FP200.

However the installation of the FP200 would need an RCD because it is chased within a stud wall less than 50mm from the surface.

Can I omit the RCD on the grounds that it is a critical system for the safety of people?

Is there anything like that in BS7671?

It seems really counter intuitive to use an RCD on a Fire Alarm Panel...

Thanks
  • 0
    Extract below from BS 5839-1:2017 [my emphasis], clause 25.2 Recommendations for mains power supplies:


    " i)  The circuit supplying the fire detection and fire alarm system should not be protected by a residual current device unless this is necessary to conform to BS 7671. "


    Unless using a fire rated BS 8436 compliant cable, running the non-BS 8436 fire rated cable in metallic conduit or running it surface mounted - RCD protection would be required unless the buried depth can somehow be increased to greater than 50mm (double sheet that wall?).


    Happy to be corrected but personally I can't see that there's all that much wiggle room on the above.


    I would state that I too would try and keep the circuit RCD-free, but to do so I'd be using one of the above methods - preference being concealed galvanised conduit drop from above.


    P

  • Former Community Member
    0 Former Community Member
    The fire alarm panel should be on a dedicated supply, in fire resistant cable and terminated in a double pole fcu needing a special tool. BS5839 overrides BS7671 (in this instance) and the recommendation is that a non RCD circuit should be used since this is a life safety system. Will most definitely be a L1 cat system with a minimum of 24hrs standby capacity. 

    Regards

    TS
  • 0
    An ariticle about fire alarm cables for use in thin walls or partitions - www.voltimum.co.uk/.../fire-alarm-cables-use-thin-walls-or-partitions-0 - needs you to sign away your soul to read it, Basically because it meets the nail penetration test  BS8436 cable can be installed without additional protection if buried in a wall<50mm etc but olnlly on a low current  type b breaker/RCBO  - or the foil may blow out first.

    www.napitonline.com/.../CP 3 08 P 11-12 BS 8436 Cables.pdf here  also suggests BS8436 cable as a get out of RCD option.


    Or you could  use a length of thin SWA for the vertical drop, and have a joint at ceiling.

  • 0
    MICC isn't an option? It'd be more expensive but would solve this issue and used to be the done thing for fire alarms, at least where I was trained (a university maintenance dept)
  • 0

    OMS:




    Apostolos Kasinalis:

    OMS, sorry I am not so advanced in my knowledge around the regulations.

    As I understand there is no provision in BS7671 to omit an RCD in case of a safety or a critical system. Am i right?

     




     

    It depends on what it's wired in, and how as discussed and described in several posts above.


    Personally speaking, I would use all of the available mechanisms to omit the RCD protection from a life safety system


    Regards


    OMS 

     




    I solved my issue temporarily bu adding on the drawing a note to the installers that says "Cable to FAP should be surface mounted or chashed in an earthed steel conduit"

    In this way the RCD is not needed by definition.

    However I am still looking at the answers to get a better understanding about the RCD (which ME TOO .... doesn't want to use on a FAP feeder) and a possible chased cable in a plastic conduit of dropped in a stud wall void behind the FAP....

    I remember seeing somewhere in the BS7671 that in hospitals for critical systems the RCD can be ommitted (don't remember where and what paragraph...) so I assumed that the same would apply to a FAP.

    And to be completely honest I will apply the same to a Refuge Alarm Panel which usually goes side by side with a FAP

  • 0

    OMS:

    This sounds like a commercial job to me - so why do you specifically thing an RCD is required for the circuit ?




    I am no expert on fire alarms, but a large dwelling (at least one floor of 200 m2) of three storeys requires Grade A Category LD2. As I understand it, that means a panel. So either we have an RCD, or surface mounted (which won't do in a grand home, save perhaps below stairs), or screened/metal conduit, etc. Not an ideal situation!

  • 0
    Agree with OMS. Scrub the RCD!
  • Former Community Member
    0 Former Community Member

    Apostolos Kasinalis:

    OMS, sorry I am not so advanced in my knowledge around the regulations.

    As I understand there is no provision in BS7671 to omit an RCD in case of a safety or a critical system. Am i right?

     




     

    It depends on what it's wired in, and how as discussed and described in several posts above.


    Personally speaking, I would use all of the available mechanisms to omit the RCD protection from a life safety system


    Regards


    OMS
  • Former Community Member
    0 Former Community Member
    OK - agreed, that there is no mention now of skilled and instructed persons - I was just trying to get the OP to think about the risk hierarchy that he is trying to address with the design given the supply is a part of a life safety system


    If the fire alarm supply cable is buried in zone, then is there a very real, credible risk of a "strike" to that cable in this environment - I suspect not


    It may well be that the selected cable is already compliant in terms of an earthed metallic screen or sheath - it may take some calculations to prove that


    It is a requirement for a lockable isolation position so it seems entirely credible to me that the 230V supply cable would easily be installed in a length of earthed conduit from the ceiling void to the lockable isolator and then to the panel, as a flush installation


    Personally, I would try to avoid at all cost the provision of RCD protection to this circuit from a life safety safety perspective.


    BS 7671 excludes fire alarm systems compliant with BS 5839-1 - is the 230V feed to the panel actually a 230V fire alarm circuit ? -  and not covered by BS 7671 anyway.


    Regards


    OMS





  • 0
    wiring to sensors, call points and sounders will be ELV, so can route anywhere.

    Only the mains wiring needs consideration, and that is very similar to the rules for a lightswitch.


    Namely that

    If the route  is not concealed, RCD protection is not needed for any cable.

    If the cable has a built in earthed screen or armour and the cable is of a type listed for that purpose, RCD protection is not required.

    If the cable is protected by an earthed enclosure, conduit / trunking etc , RCD protection is not required.


    Or it must be in rhe 'safe zones' and have RCD protection.


    the former exception for wiring

    ‘under the supervision of a skilled or instructed person’  went in one of the amendments to the 17th, in 2015 -ish

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