Is a separate CPC required ?

muckyduct · Oct 24, 2022

Hi Guys,

I've just been looking at a job that has been installed by another company.
One thing I've noticed are the feeds to 2 BMS / Plant panels. They have run in 2 x 150mm 4C and doubled up on the main switch in both panels. No separate CPC has been installed and the banjos aren't earthed either.
If this had been myself I'd have run in a separate CPC and bonded the Banjos.
Thoughts please is this to regs or does it need a separate CPC ?

davesparks · Oct 24, 2022

It is unlikely to need a seperate CPC, you need to do the calculation to confirm that though, it is impossible to tell from looking at it. The armour of SWA, especially with 2 in parallel is likely to be suitable as the CPC.

The connection to the banjo doesn't look too good however, they should have at least cleaned the paint off the metal where the bolt connects to it.
What is on the outside of the enclosure? Is the gland and banjo fitted to clean metal on that side?

timhoward · Oct 24, 2022

Is the wire armour earthed the other end?
Might they have used the adiabatic equation (as the armour of 150 sq mm 4c SWA is only 73 sq mm equivalent copper)?
Is the body of the cabinet being used?
What are the earthing requirements of the load?

muckyduct · Oct 24, 2022

davesparks said:
It is unlikely to need a seperate CPC, you need to do the calculation to confirm that though, it is impossible to tell from looking at it. The armour of SWA, especially with 2 in parallel is likely to be suitable as the CPC.

The connection to the banjo doesn't look too good however, they should have at least cleaned the paint off the metal where the bolt connects to it.
What is on the outside of the enclosure? Is the gland and banjo fitted to clean metal on that side?

Hi, the outside is the same as the inside, fully painted. They've just drilled the plate and bolted it down.

muckyduct · Oct 24, 2022

timhoward said:
Is the wire armour earthed the other end?
Might they have used the adiabatic equation (as the armour of 150 sq mm 4c SWA is only 73 sq mm equivalent copper)?
Is the body of the cabinet being used?
What are the earthing requirements of the load?

Not that I'm aware of.
The cabinet is being used as the earth for outgoing Services connected to din mounted earth terminals.

davesparks · Oct 24, 2022

muckyduct said:
Hi, the outside is the same as the inside, fully painted. They've just drilled the plate and bolted it down.

Then I'd say it definately needs a suitably sized conductor linking the two banjo bolts and connected to whatever is provided as an earthing terminal.