Bit quick advice please

[davesparks]

Cheers guys. I've just had a read of the relevant section of GN8 but it didn't offer any reasoning behind the 8.5 factor and the difference between a CPC and bonding conductor in terms of copper equivalency.

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A CPC's size is based on the temperature rise in the time it takes the ocpd to operate when a particular fault current flow. So this is looking at the ability of the conductor to survive a high current for a short length of time.

Bonding is sized considering its ability to safely handle a sustained flow of current.

Also it's worth noting that the table you linked to above is incorrect and has been for many many years.

 

[Leesparkykent]

They are for situations where you need to know the copper equivalent CSA, this is not used for bonding.

For bonding you need equivalent conductance, this is a different physical property. A factor of 8.5 is generally accepted as being the ratio of conductance of copper versus steel. So for a 10mm copper bond you need 85mm steel.

Theres an echo in here .......

 

[Ian1981]

Gn8 also gives warning to using the armour as a combined cpc/protective conductor as with tncs diverted neutral currents can raise the temperature of the cable meaning a increased sized conductors maybe needed for your ccc.
It's up to the designer whether this may happen or not.

 

[Ian1981]

Gn8 also gives warning to using the armour as a combined cpc/protective conductor as with tncs diverted neutral currents can raise the temperature of the cable meaning a increased sized conductors maybe needed for your ccc.
It's up to the designer whether this may happen or not.

Or rather raise the temp of the armour I should say