Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 52 replies
  • Subscribers 30 subscribers
  • Views 10941 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

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 ?
  • 0
    I would say no.


    In the event of a fault the cable could see the full mains potential. Therefore is not ELV at all but LV just like any other 'mains' conductor.
  • 0
    543.3.201 is interesting in requiring insulation of protective conductors up to 6.0mm2 to have an insulation Voltage rating of at least 450/750 V with some exceptions. Metal containment like conduit or trunking need to be electrically continuous, and can be used as protective conductors,  but of course are not electrically insulated to touch, as of course are many metallic structural parts of buildings and other extraneous-conductive-parts.


    Z.
  • Former Community Member
    0 Former Community Member

    AdrianWint:

    I would say no.


    In the event of a fault the cable could see the full mains potential. Therefore is not ELV at all but LV just like any other 'mains' conductor.




    By your logic, let's say the structural steel is located inside a high voltage switchroom. Do you now deem the equipotential bonding cable as a HV conductor ?

     

  • 0
    If the structural steel is intended as a cpc or bonding conductor then it must be considered to be a HV conductor but otherwise not I would think
  • Former Community Member
    0 Former Community Member

    ebee:

    If the structural steel is intended as a cpc or bonding conductor then it must be considered to be a HV conductor but otherwise not I would think




    Thanks Ebee. 


    I am talking about and equipotential bonding conductor bonding some structural steel.


    So if your saying it must be considered HV in your above scenario then BS7671:2018 would seem not to apply as that standard has scope for alternating current voltage sources up to 1000 V AC.


    BS7671:2018 sure does talk about equipotential bonding conductors quite a bit so it must apply, so are you saying BS7671:2018 applies HV conductors ?

  • 0

    Mike M:

    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 ?




    No, green-and-yellow cables are protective conductors.


    As others have said, protective conductors can carry hazardous voltages and currents.


    Under normal circumstances, when connected properly in the electrical installation, they are considered safe to touch, at least in dry conditions, as they are connected to exposed-conductive-parts or extraneous-conductive-parts.


    However, once a protective conductor is disconnected at one end, it must be considered as hazardous to touch, and may in fact be carrying low voltage (LV) hazardous voltages and currents, and is therefore definitely never ELV.


    In HV installations, a different set of criteria exists, and in fact under fault conditions, earth conductors may even when connected be LV (or occasionally higher for short periods).

  • Former Community Member
    0 Former Community Member

    gkenyon:




    Mike M:

    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 ?




    No, green-and-yellow cables are protective conductors.


    As others have said, protective conductors can carry hazardous voltages and currents.


    Under normal circumstances, when connected properly in the electrical installation, they are considered safe to touch, at least in dry conditions, as they are connected to exposed-conductive-parts or extraneous-conductive-parts.


    However, once a protective conductor is disconnected at one end, it must be considered as hazardous to touch, and may in fact be carrying low voltage (LV) hazardous voltages and currents, and is therefore definitely never ELV.


    In HV installations, a different set of criteria exists, and in fact under fault conditions, earth conductors may even when connected be LV (or occasionally higher for short periods).


     




    I would say the single core green/yellow insulated equipotential bonding cables are generally considered safe to tough if disconnected at one end as they still provide basic protection as they are insulated but we are getting a bit side tracked here.


    To apply your logic you are saying that if a protective conductor can carry mains LV voltage then it is definitely never ELV. I would use a PELV circuit as an example, as you are aware PELV circuits can be connected to earth. Under fault conditions mains LV voltage could be present on that earth, but the PELV circuit is still an ELV circuit right ? 

     

  • 0
    What are you ultimately trying to prove Mike?


    Z.
  • Former Community Member
    0 Former Community Member

    Zoomup:

    What are you ultimately trying to prove Mike?


    Z.




    BS7671:2018 mandates different criteria in relation to the voltage category of a cable be it LV, RLV, SELV, PELV, FELV. Before we can review against the relevant criteria we must establish which of these categories a cable belongs to. I am wanting to establish the correct category under BS7671:2018 in relation to a single core green/yellow insulated equipotential bonding cables originating from an earth bar and bonding some structural steel work. 

  • 0
    Mike, we normally use green and yellow insulated 6491X cables for main and supplementary bonding purposes. It meets all normal requirements for that use to comply with B.S. 7671. In other colours it can be used in metal conduit and trunking, and sometimes in plastic containment as well as live conductors.

    https://www.ukcables.co.uk/cables/6491x



    Z.

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines