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16mm twin and earth


danny7299

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As far as I know, 6mm.

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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?

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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?

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.

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But if I did use 16mm T&E as a submain feed I would run a separate 16mm earth.

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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.

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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.

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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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