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Fire Alarm Panel Electrical Isolation.

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Is single pole electrical isolation suggested here even if we are going to prod and poke about inside the fire alarm panel? And, what are the two fuses removed mentioned all about? Is the lecturer confused?


Please see 41.12 onwards.

https://www.bing.com/videos/search?q=youtube+bs+5839+part+1&&view=detail&mid=92E9069FDA874942E42A92E9069FDA874942E42A&rvsmid=7BBC139314220094A9417BBC139314220094A941&FORM=VDQVAP


Z.
  • 0
    The pulling 2 fuses thing is not right as he describes it - that is not what we mean by 'double pole' isolation (i.e. breaking L and N together ), what he seems to mean is isolating in 2 places. (a variation on double fault to danger - you have to break the wrong circuit, in 2 places to reach a dangerous condition - bit like cascade RCDs)

    I presume single pole isolation, from the sparks perspective, is only OK when you have a solidly earthed neutral, and or a 3 phase system where you would not want a switched neutral.

    Mike.



  • Former Community Member
    0 Former Community Member
    Not watching that too long ? here's what you need to know as far as I'm aware, the OCPD should be on the main board, with relevant markings.  The OCPD should not be of the RCBO/RCD type. 


    At the fire alarm panel you need a double pole FCU with fish tail key or similar, with relevant markings. 


    Regards
    Ts

  • 0
    I'd agree, but the presenter is suggesting the need for DP isolation has gone from the new version. (of the fire standard, BS7671 may still need it....)

    Mike.
  • Former Community Member
    0 Former Community Member
    mapj1:

    I'd agree, but the presenter is suggesting the need for DP isolation has gone from the new version. (of the fire standard, BS7671 may still need it....)

    Mike.


    Pretty sure it's still there, maybe I'll check tomorrow, if I'm feeling better had covid jab Monday, not been well since!


  • 0
    I presume single pole isolation, from the sparks perspective, is only OK when you have a solidly earthed neutral

    Perhaps better thought of as a solidly neutraled earth?


    N is earthed the same at the source on both TN-S and TT systems - yet we require DP isolation for TT but not TN - the distinction is rather whether PE is connected to N or not.


      - Andy.
  • 0
    What is 537.2.6 all about then? 


    Switched fused connection units are double pole switched, as are 45 Amp cooker switches and shower switches, and consumer unit main switches, but extractor fan switches are triple pole. All used as isolators. I think that the presenter believes that neutrals are fused, that is why he is referring to two fuses being removed for fire alarm panel isolation, L & N. Still, hopefully the P.S.U. bits inside the panel are well insulated and the 24 Volts won't be too deadly.


    Z.
  • 0
    What is 537.2.6 all about then?

    I think that's just saying that where you need to open several poles of the same circuit to achieve isolation, it should preferably be done by a multipole device rather than several single pole devices.


    461.2 is what decided whether the N needs to be isolated or not (where BS 7671 applies) - although the new wording isn't anything like as clear as the previous version (to me at least).


       - Andy.
  • 0
    Interestingly an unswitched FCU is permitted for isolation purposes (by removing the fuse link) - unless on a TT or IT system.....Table 537.4.
  • Former Community Member
    0 Former Community Member
    Timeserved:
    mapj1:

    I'd agree, but the presenter is suggesting the need for DP isolation has gone from the new version. (of the fire standard, BS7671 may still need it....)

    Mike.


    Pretty sure it's still there, maybe I'll check tomorrow, if I'm feeling better had covid jab Monday, not been well since!




    Well had a look at bs5839:1:2017 and it seems that the mention of a double pole isolator has indeed disappeared!


  • 0
    Well had a look at bs5839:1:2017 and it seems that the mention of a double pole isolator has indeed disappeared!

    Which presumably stops it contradicting BS 7671 - where generally N doesn't need isolating on TN systems.


    I'd guess that where BS 5839 doesn't override something then normal BS 7671 rules would apply to the supply - so you'd still need DP isolation on a TT system.


       - Andy.

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