16mm twin and earth

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now i may be wrong but i thought the CPC had the be half the size of the live conductors..

So if you where using a 16mm T &E for a sub main, that wouldn;t be right would it?

am i missing the point?

 
now i may be wrong but i thought the CPC had the be half the size of the live conductors..So if you where using a 16mm T &E for a sub main, that wouldn;t be right would it?

am i missing the point?
A 6mm twin and earth has only 2.5mm cpc and a 10mm twin and earth only a 4mm cpc.

I thought the rule you mentioned applied only to choosing the size of earthing conductors rather than cpc's.

 
why is that out of interest... just to cover your ass?
Well, for example, if I was in a block of flats and I was running a 63A SP&N supply to each one of those properties then I would class the CPC as an earthing conductor, in which case it would need to satisfy 4.1 OSG which says 16mm tails should have a 16mm earthing conductor.

 
Hi Danny7299

If you are not sure if cpc is large enough for your install, then you can use adiabatic equation to check this

S= square root of I2 * t divided by k

s=nominal cross sectional area of cpc mm2

I = fault current needed to operate protective device

t= time in seconds for protective device to operate

K = factor of 115 for copper.

If you dont have regs book, let me know what protective device is (type and rating) and I will try and do calculation.

 
It is common practice now to run a seperate 16mm earth to each DB.

I think Revved up sparky gave a good answer.

 
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