sub main cpc size?

[chrisreid186]

how do you work out the size of cpc supplying a sub main? and is it the same method for working out the main earthing conductor size?

cheers in advance

 

[chrisreid186]

so all G/Y cables to the electrode should be 16 mm as it ends up being buried?

 

[pushrod]

so all G/Y cables to the electrode should be 16 mm as it ends up being buried?

Not necessarily depends on your earth pit, but if it does have to go underground/ be buried , with the price of copper, it is cheaper to give it some mechanical protection

 

[chrisreid186]

just seems odd that if the cable was burried it would need to be 16mm but if you run it on top of the ground then 4mm will do even though it ends up getting burried anyway

 

[chrisreid186]

whats an earth pit and how will it effect it? i thought you just banged in a rod ?

 

[pushrod]

Think it is to do with physical strength- if it is visible it shouldn't be accidentally damaged (like surface mounted T&E) 4mm run above surface but clipped to something sensible should be relatively safe. I don't think anyone is advocating trailing it over the soil ;-)

 

[pushrod]

google earth pit images and you will see some -price from about £7 to £25 IME

 

[pushrod]

A CHEAP ONE

 

[chrisreid186]

think i'll go with 6mm G/Y buried, as long as pefc works out ok i cant see i problem,

 

[chrisreid186]

sorry never knew they were called earth pits

 

[pushrod]

think i'll go with 6mm G/Y buried, as long as pefc works out ok i cant see i problem,

6mm is sensible but it will need mechanical protection eg conduit, where it goes underground

edit -

sorry never knew they were called earth pits​

or earth rod enclosure.

 

[chrisreid186]

changing the subject slightly when bonding plastic services where there is a metal installation within the premises
how do you confirm that any metal pipework is not at earth potential ?????

 

[chrisreid186]

test continuity between met and said pipework ?

 

[pushrod]

test continuity between met and said pipework ?

Yes can also confirm that metalwork is not an extraneous-conductive-part by IR testing between it and MET. If result is > 22MΩ then it is not extraneous and does not need bonding - mind if it was water pipe i would bond it anyway

 

[chrisreid186]

thanks for the advice thats made it lot clearer