Earthing and Bonding sizing.

[fatboyslim]

Morning All,

Think I'm having a brain fart but I have a 70mm2 4 core SWA with a separate 35mm2 CPC.
Earthing is TNS with main bonding requirements being 25mm2.
Using table 54.7 - CPC is half of line conductor so 35mm2.

Am I correct in thinking the 35mm2 conductor is adequate for both CPC and bonding requirements?

Cheers guys.

 

[Shaun-]

Morning All,

Think I'm having a brain fart but I have a 70mm2 4 core SWA with a separate 35mm2 CPC.
Earthing is TNS with main bonding requirements being 25mm2.
Using table 54.7 - CPC is half of line conductor so 35mm2.

Am I correct in thinking the 35mm2 conductor is adequate for both CPC and bonding requirements?

Cheers guys.

Good morning,

That’s looking good, could probably manage smaller if you did Adiabatic but that’s on the safe side I guess.

So for 70mm² line if you select from the book it has to be (S / 2) so that’s your 35mm² main protective conductor. Then main bonding should be no less than half the main earth but need not exceed 25mm².

If I’ve missed anything let me know but all looks good to me.

 

[bill01803]

SWA equivalent to 61mm of copper from 54G

 

[davesparks]

SWA equivalent to 61mm of copper from 54G

Errrrm, what? Could you explain what you mean here?

 

[bill01803]

The SWA of 4 core 70mm is 138mm² the equilalent in copper is 61mm², therefore the armour is big enough on its own.

 

[davesparks]

The SWA of 4 core 70mm is 138mm² the equilalent in copper is 61mm², therefore the armour is big enough on its own.

Copper has a conductivity 8 times that of steel, so 138mm steel is equivalent to 17mm copper. So no, the armour is not sufficient to meet the requirements for bonding.

I think you may he confusing the calculation for suitable size of steel CPC with that for working out the 'copper equivalent' for the purposes of bonding.