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Discuss copper equivalent of steel in the Electrical Forum area at ElectrciansForums.co.uk.

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  1. wirepuller
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    wirepuller Forum Mentor

    Location:
    south uk
    Does anyone have the copper equivalent of a two core 16mm SWA to hand? Or the minimum SWA 2 core CSA in which the steel would be equivalent to a 10mm copper conductor? Don't have the info to hand.
    Thanks.....
     
  2. Leesparkykent
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    Leesparkykent Super Moderator Staff Member Super Moderator

    Location:
    Kent
    In conductivity or as in CSA?
     
  3. westward10
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    westward10 In echoed steps I walk across an empty dream. Staff Member Moderator

    Location:
    Northamptonshire
    For conductivity off the top of my head as no books to hand 95.0 or above.
     
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  4. Ian1981
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    Ian1981 Forum Mentor

    Location:
    North east
    The ratio in gn8 for copper to steel is 8.5.
    So a 85 mm steel conductor -equivalent conductive copper conductor is 10 mm
    85/8.5=10
     
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  5. happyhippydad
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    happyhippydad Member Electrician's Arms

    Location:
    Gloucestershire
    This really isn't my area as it's rarely used in domestics.

    However, I've found from one table on the net (https://www.dungannonelectrical.co.uk/dun1-shop/pdf/cable/SWA.pdf) that 2 core 16mm will have a 42mm CSA of steel.

    I am then not sure if you divide by 8.8 or 2.75.

    AJJewsbury explains it below: (IET Forums - SWA Size of steel armour for CPC - https://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=47544)

    "If the armour is only being used as a c.p.c. (and not as PME bonding conductor) then you're not really interested in its actual resistance (either absolute or copper equivalence) - just its ability to survive an earth fault current for the required time - i.e. it's "k" value (tables 54.2 and following). E.g. if the cable runs at max 70 degrees in normal service with a maximum ambient of 30 degrees, then k for copper is 143 and steel 52 - making copper just 2.75 times "better" than steel for the same c.s.a.

    So if the cable had 76mm2 of steel that would be the equivalent of 27.6mm2 of copper - easily satisfying table 54.7. "
     
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  6. spinlondon
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    spinlondon Forum Mentor

    Location:
    Harlow Essex
    I believe the minimum CSA for the armour to have the equivalent conductivity of a 10mm2 copper conductor is 95mm2.
    I think it would be cheaper to run in a 3core.
     
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  7. wirepuller
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    wirepuller Forum Mentor

    Location:
    south uk
    Many thanks for the replies.
    Just to clarify an EICR on a recent build (new <5yrs ago,) steel framed outbuilding has a 2core 16.0mm SWA feeding from a TNCS supply in the main building. No main bonding has been installed to the steel frame, the supply head is a TPN 100a so a minimum 10mm copper equivalent is required to serve as main bonding and cpc. Just to complicate matters a supply back from the outbuilding serves a pump installation in the main building so converting to TT would result in two separate earthing systems in the main building.
    Why the original installer put in a 2 core is beyond me, but it is what it is now.
     
    Last edited: Jan 9, 2019
  8. Ian1981
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    Ian1981 Forum Mentor

    Location:
    North east
    A 76mm steel conductor would equate to around 8.9mm copper conductive equivalent
     
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  9. Ian1981
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    Ian1981 Forum Mentor

    Location:
    North east
    Yep a 16mm 2 core armour isn’t going to cut it
     
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  10. buzzlightyear
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    buzzlightyear please let me back in to the prison cell.

    Location:
    star command
    where's Pete with the information he mostly on the ball .stop taking his job. ;)
     
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