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Discuss copper equivalent of steel in the Electrical Forum area at ElectriciansForums.net

wirepuller

Forum Mentor
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.....
 

Leesparkykent

Super Moderator
Staff member
Super Moderator
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.....
In conductivity or as in CSA?
 

westward10

In echoed steps I walk across an empty dream.
Staff member
Moderator
For conductivity off the top of my head as no books to hand 95.0 or above.
 

Ian1981

Forum Mentor
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
 

happyhippydad

Member
Electrician's Arms
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. "
 

spinlondon

Forum Mentor
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.
 

wirepuller

Forum Mentor
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:

Ian1981

Forum Mentor
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. "
A 76mm steel conductor would equate to around 8.9mm copper conductive equivalent
 

Ian1981

Forum Mentor
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.
Yep a 16mm 2 core armour isn’t going to cut it
 

buzzlightyear

please let me back in to the prison cell.
Electrician's Arms
where's Pete with the information he mostly on the ball .stop taking his job. ;)
 

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