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Extra Low Voltage (ELV)

Former Community Member
Former Community Member
Guys,


BS7671:2018 is classing cables extra low voltage (ELV) as an operating voltage not exceeding 50Vac or 120V ripple-free dc.


BS7671 goes on to further categorize ELV cables into SELV, PELV, FELV.


For single core green/yellow insulated equipotential bonding cables lets say originating from an earth bar and bonding some structural steel work, are these classed as FELV under BS7671:2018 ?
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    SELV circuits don’t require a CPC because the insulation within the transformer and other equipment  is good enough to provide complete separation between the ELV and SELV circuits, so you will not be at risk due to there being 240 volts on the SELV circuit.


    FELV circuits may require a CPC because the insulation within the transformer and other equipment  is not good enough to provide complete separation between the ELV and SELV circuits and there may be 240 volts on the FELV circuit and you are relying on the ELV circuit CPD to provide ADS and the RCD to provide supplementary protection, if there is one, for the FELV circuit.


    So the circuit protective conductor or any other protective conductor has to be capable of withstanding the voltage and current that may be placed on it, which in the case of a FELV circuit is generally 240 volts, even though the circuit is rated at say 24 Vdc.


    I am failing to see how you have strung this topic out for so long, this is stuff we learnt in the second year of  C&G 2360 course.


     Andy Betteridge 

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    Diagrams and explanation below 

    https://www.tlc-direct.co.uk/Book/7.16.3.htm
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    Highest voltage and current it has to withstand after a failure of the FELV transformer has put the primary circuit voltage onto the secondary circuit along the the primary circuit fault current.


    The secondary circuit could have 240 volts and several hundred amps to deal with if the transformer insulation breaks down livening up all the earthed metalwork.


    Andy
  • Former Community Member
    0 Former Community Member

    Sparkingchip:

    Highest voltage and current it has to withstand after a failure of the FELV transformer has put the primary circuit voltage onto the secondary circuit along the the primary circuit fault current.


    The secondary circuit could have 240 volts and several hundred amps to deal with if the transformer insulation breaks down livening up all the earthed metalwork.


    Andy 




    Andy the question was for single core green/yellow insulated equipotential bonding cables lets say originating from an earth bar and bonding some structural steel work, are these classed as FELV under BS7671:2018.


    In regards to your above statement this structural steel work may be located inside an HV switchroom where the highest voltage to withstand may be thousands of volts however this has no bearing in regards to the conclusion that we arrive at as we summized that the equipotential bonding cable did not meet the criteria to be classed as SELV, PELV, FELV, RLV, LV, MV on that basis that the equipotential bonding cable did not form part of a system that had a designated voltage.

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    Mike M (aka Jim?) I am throwing the towel in on this one. Reading the whole topic again from the start I am sure that there were posts that have been deleted and there are answers and comments to points raised in posts that no longer exist.


  • Former Community Member
    0 Former Community Member

    Sparkingchip:

    Mike M (aka Jim?) I am throwing the towel in on this one. Reading the whole topic again from the start I am sure that there were posts that have been deleted and there are answers and comments to points raised in posts that no longer exist.


     




    Andy I have not deleted anybody's answers. I posted one of my comments twice and removed the duplication as it came in under a different account name but I have not deleted anybody's answers. The content has not been modified. I'm not sure there was anything to resolve in the first place the thread had already been answered sufficiently and was marked as closed/answered. If you have an issue with the conclusion that was made then detail why if not then I accept your towel.

  • 0

    So the circuit protective conductor or any other protective conductor has to be capable of withstanding the voltage and current that may be placed on it, which in the case of a FELV circuit is generally 240 volts, even though the circuit is rated at say 24 Vdc.



    I'm not sure I understand the concept of a protective conductor being able to "withstand" a certain voltage - given that generally there's no requirement for protective conductors (or they parts they connect) to be insulated. Live conductors need insulation of course (including from the protective conductor or exposed-conductive-parts) - and in the case of FELV that might need to be according to the voltage of the primary circuit rather than the secondary - but I'm not aware of any similar requirement for FELV c.p.c.s.


       - Andy,
  • Former Community Member
    0 Former Community Member

    AJJewsbury:




    So the circuit protective conductor or any other protective conductor has to be capable of withstanding the voltage and current that may be placed on it, which in the case of a FELV circuit is generally 240 volts, even though the circuit is rated at say 24 Vdc.



    I'm not sure I understand the concept of a protective conductor being able to "withstand" a certain voltage - given that generally there's no requirement for protective conductors (or they parts they connect) to be insulated. Live conductors need insulation of course (including from the protective conductor or exposed-conductive-parts) - and in the case of FELV that might need to be according to the voltage of the primary circuit rather than the secondary - but I'm not aware of any similar requirement for FELV c.p.c.s.


       - Andy,

     




    Andy in my opinion I would agree and I would say the current is the relevant factor. For example we frequently use a 10mm2 bare un-insulated aluminium cable/tape under BS EN/IEC 62305 to conduct millions of volts safely to ground during a strike.

  • Former Community Member
    0 Former Community Member

    Mike



    Andy in my opinion I would agree and I would say the current is the relevant factor. For example we frequently use a 10mm2 bare un-insulated aluminium cable/tape under BS EN/IEC 62305 to conduct millions of volts safely to ground during a strike.



     

    I thought BS EN 62305 indicated that aluminium components of a LPS should be a minimum of 50mm2 if solid round or stranded round and 70mm2 if tape.


    Did you mean 10mm diameter (allowable as a reduction for short air terminations) or exceeding the nominal 8mm diameter of circular aluminium of 50mm2 CSA 


    Regards


    OMS
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    Mike M:




    Sparkingchip:

    Mike M (aka Jim?) I am throwing the towel in on this one. Reading the whole topic again from the start I am sure that there were posts that have been deleted and there are answers and comments to points raised in posts that no longer exist.


     




    Andy I have not deleted anybody's answers. I posted one of my comments twice and removed the duplication as it came in under a different account name but I have not deleted anybody's answers. The content has not been modified. I'm not sure there was anything to resolve in the first place the thread had already been answered sufficiently and was marked as closed/answered. If you have an issue with the conclusion that was made then detail why if not then I accept your towel.


     




     

    I read a comment that it is possible to have earthed SELV, which is not possible as it ceases to be SELV and becomes FELV.


    The original post asked if a main equipotential bonding conductor between extraneous steel work and the main earth terminal can be classified as FELV without any apparent comprehension of what FELV is.


    So hence the need to go back to basics. I am questioning if you are actually located outside of the UK and not used to the terms used in BS7671?


    Andy Betteridge 


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