Sharing a CPC

[Adam Smith]

Hello all, I have been ask to run power to a couple of AC units in armoured cable clipped along the outside of a new building.

It is going to require 2 separate 20amp circuits so was wondering whether I could run a 4 core armoured cable, giving me 2 lives and 2 neutrals then using the armour as a CPC for both circuits? Or maybe running a supplementary CPC if the armour isn't up to it.

I do get the over whelming feeling this might not fly, but as always I'm having a bit of trouble coming up a conclusive answer from the big green book.

Thoughts?

 

[davesparks]

There is no problem using 1 CPC for multiple circuits, if you couldn't then you'd be a bit screwed for running multiple circuits down one conduit wouldn't you!

If you do decide to run multiple circuits through the same cable don't forget the grouping factor in your calculation.

 

[Geordie Spark]

There is no problem using 1 CPC for multiple circuits, if you couldn't then you'd be a bit screwed for running multiple circuits down one conduit wouldn't you!

If you do decide to run multiple circuits through the same cable don't forget the grouping factor in your calculation.

Sod sharing a CPC ....... share this -----> :sifone: - and :chillpill:

 

[Adam Smith]

Thank you for the input :icon14:

 

[uksparks]

My god all these times I have ran multiple CPC in conduit...

 

[shanky887614]

Hello all, I have been ask to run power to a couple of AC units in armoured cable clipped along the outside of a new building.

It is going to require 2 separate 20amp circuits so was wondering whether I could run a 4 core armoured cable, giving me 2 lives and 2 neutrals then using the armour as a CPC for both circuits? Or maybe running a supplementary CPC if the armour isn't up to it.

I do get the over whelming feeling this might not fly, but as always I'm having a bit of trouble coming up a conclusive answer from the big green book.

Thoughts?

why not ask the wholesaler about 5c.

 

[trev]

I think you'll struggle to find a reg which will prevent you doing this mate. After all, it's very little different from running 2 circuits in metal containment and using that as the CPC is it?

 

[Darkwood]

Your means of isolation will have additional requirements also marking up and your earthing requires to meet the criteria for supplying multiple circuits. Others have noted a conduit with common earth here but it slightly differs in that the cores are within 1 cable - it needs to be clear that someone thinking they have isolated 1 unit is not in any confusion that the cable is dead.

Edit... You will require a point of isolation at the source that can de-energise the whole cable safely usually a lock of isolator or an MBC that is DP and shuts of all power - consideration needs to be taken about regulations where a fault on one circuit does not affect others so the DP option is questionable to the inconvenience caused.

All the additional costing to conform to the above usually means it might as well be run in 2 swa's

 

[Andy78]

Nowt wrong with the CPC issue that I can see.
However as regards isolation you will need to make sure that warning notices are attached to any enclosure that requires more than one point of isolation, as you are running two separate circuits down one multicore cable. See 537.2.1.3
I would mark this label with the circuit and DB refs.

EDIT: lol DW beat me to it

 

[Farmelectrics]

do it right run 2 seperate supplys

 

[Guest77]

do it right run 2 seperate supplys

YUP my thoughts exactly.

 

[davesparks]

My god all these times I have ran multiple CPC in conduit...

Why run a cpc in conduit at all, the conduit will offer a path of much lower resistance.

 

[Pete999]

Why run a cpc in conduit at all, the conduit will offer a path of much lower resistance.

Could be PVC conduit. or steel conduit that has a poor continuity test either way, I would personally run separate cpcs.

 

[davesparks]

Could be PVC conduit. or steel conduit that has a poor continuity test either way, I would personally run separate cpcs.

He didn't say PVC though did he.

Steel conduit with poor continuity is not compliant with the regulations to start with so you shouldn't be installing anything in it.

Every part of a steel conduit system must be earthed if it is to have LV cables in it. Therefore every joint must be electrically and mechanically sound the same as any other joint in an earth, unless you earth every box and length of tube separately that is.

 

[Guest77]

The job stinks, run a seperate armoured to each unit and do the job right.