Running cpc with swa and not use the swa as cpc

[Steve93]

why do people run a cpc Along side the armoured that supplies the board. Why not use the metal sheathing as the earth?

 

[DavidSpark]

One reason could be that the SWA is susceptible to rust and corrosion and over the life time of the installation the integrity of the earth could become compromised.

Another reason could be that the SWA is not sufficient in terms of equivalent CSA size to carry the fault currents or meet bonding requirements.

 

[Leesparkykent]

why do people run a cpc Along side the armoured that supplies the board. Why not use the metal sheathing as the earth?

The armour may not be of an adequate CSA. The armour may not be of an adequate CSA for bonding (if bonding is required). Long runs may have a seperate earthing conductor to meet disconnection times. In areas like marinas then the armour should not be relied on due to corrosion.

Edit:@DavidSpark beat me to it

 

[Steve93]

Looking at this table it shows there all more than capeable. This is why it’s confusing me. Lol

 

[DavidSpark]

I think it all comes down to what the designer specifies most of the time. If my name is going to go onto something then I'd like to know that it's going to be rock solid.

Peace of mind is something you can't put a price on, if god forbid something went wrong and they eyes and fingers come looking for you.

 

[Pete999]

Looking at this table it shows there all more than capeable. This is why it’s confusing me. Lol

Not all of them are capable Steve look at the cables shaded in pink.

 

[Steve93]

Not all of them are capable Steve look at the cables shaded in pink.

But I’m on about a standard 3phase board now if they are 25mm (most are) then why run it? Is it due to resistance of copper rather than steel?

 

[Leesparkykent]

But I’m on about a standard 3phase board now if they are 25mm (most are) then why run it? Is it due to resistance of copper rather than steel?

The armour of a 25mm SWA would not be adequate for bonding.

 

[Pete999]

But I’m on about a standard 3phase board now if they are 25mm (most are) then why run it? Is it due to resistance of copper rather than steel?

Perhaps if you had mentioned that in the first post then there would have been less confusion, 25MM4 core SWA has a steel csa0f 70mm2 equivalent to 22.5 mm2 copper, but as others have said that wouldn't be good enough for bonding as well as a cpc, of course only if bonding is required.