Seperate / Integral earth CPC on 400A supply

[Ian1981]

I think there is a bit of confusion here, the thing I was trying to highlight was that the software said it was ok to use a 5c cable with an integral earth conductor, but not ok to use a 4c cable with a supplementary earth of the same size.

Did you try using a half sized cpc in the software in parallel with a 4 core swa?

 

[Andy-1960]

Did you try using a half sized cpc in the software in parallel with a 4 core swa?

Tried full size cpc in parallel with a 4 core SWA and it just would not have it. I think the software was suggesting either one 300mm 5c SWA or 2 x 150mm 5c SWA, but if I tried 4c SWA + supplementary it threw it out on earth loop value.

 

[Ian1981]

Tried full size cpc in parallel with a 4 core SWA and it just would not have it. I think the software was suggesting either one 300mm 5c SWA or 2 x 150mm 5c SWA, but if I tried 4c SWA + supplementary it threw it out on earth loop value.

Why not just use table 54.7 and use a half size cpc rather than a cpc the same size as the live conductors?
That's if you want to install the supplementary cpc

 

[Andy-1960]

Why not just use table 54.7 and use a half size cpc rather than a cpc the same size as the live conductors?
That's if you want to install the supplementary cpc

Because it will not pass - the earth loop value is too high

 

[Ian1981]

Because it will not pass - the earth loop value is too high

Sorry Andy understood
I think I'd go with the 150 x2 rather than pulling a 300mm swa in.

Maybe cable manufacturer can help with regard to cable calcs.

 

[Ian1981]

Is 0.06 ohms the max zs?
Did 300mm give you an R1+R2 of 0.04 ohms?

 

[Dave OCD]

They don't make anything easier for us as time goes by that's for sure !

 

[Leyland30]

Wow - that was almost helpful. Trimble have outdone themselves.

 

[Leyland30]

Could you post the cable calc for the two options. IMO an external Cpc would be electrically preferential but I guess the brains at IET think otherwise.

 

[westward10]

I think there is a bit of confusion here, the thing I was trying to highlight was that the software said it was ok to use a 5c cable with an integral earth conductor, but not ok to use a 4c cable with a supplementary earth of the same size.

I have been thinking about this and and the only thing that comes to mind is the programme assuming the cpc will pass through a separate hole to the line conductors which would not happen if it were a core of the cable which may under fault conditions be problematic, maybe.