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.
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A 76mm steel conductor would equate to around 8.9mm copper conductive equivalentThis 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. "
Yep a 16mm 2 core armour isn’t going to cut itMany 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.