UK Borrowing a CPC?

[mat_coley]

I have been asked to wire up a new extension for a customer and during testing prior to starting I have found that both upstairs and downstairs lighting circuits have no cpc's. However, upon further investigation it appears that the downstairs lighting circuit has managed to "borrow" a cpc from the downstairs socket circuit.
I've never come across this before and am inclined to say it isn't right. The CU is supposed to be upgraded to an RCBO board as part of the ongoing work and I'm not sure if this may flag up problems. Upstairs lighting circuit is being rewired as part of the project already but most of the downstairs has been done already by previous contractors.
Any advice for how to best proceed much appreciated, Thanks in advance

 

[telectrix]

if the down stairs lights have recently been rewired, they should have a cpc, even if bob the builder hasn't connected it. check the new cabling.

 

[mat_coley]

if the down stairs lights have recently been rewired, they should have a cpc, even if bob the builder hasn't connected it. check the new cabling.

The cable coming out of the cu is old colours and 2 core. I was visually checking at lights to cpc's connected then when took the cover off the board noticed there wasn't a cpc at that end. Did some testing and got an R1+R2 readin when clamped to earth bar, then managed to narrowed down to one of the ring main cpc's. Board was a total mess as are connections at lights so appears to have been done by someone not overly bothered about the standard of their work I'd say.
I maybe should have explained a little better

 

[loz2754]

It is technically allowed for more than one circuit to share the same CPC. Just think about systems using the metal trunking as a CPC for multiple circuits for example.
Having said that, it may well lead to problems in your case, because who's to say that someone comes along and makes an alteration to the socket circuit that happens to be sharing it's CPC with the lights, and disconnects the CPC because it seems not to be doing anything. Then you have no CPC at the lights again!!
It's also possible to run a separate (minimum 4mm2) to each point on the lighting circuit and back to the board. But then you may find it just as easy to rewire the lights.

 

[Wilko]

Like what they say about umbrellas, I have one roll of 4mm g/y just so I’ll never need it .

 

[mat_coley]

I am inclined to suggest a rewire of downstairs lighting as well as the upstairs, although that'll be a much more difficult job. Here's hoping there is capping on the switch drops to the nicely decorated rooms!

 

[HappyHippyDad]

I have been asked to wire up a new extension for a customer and during testing prior to starting I have found that both upstairs and downstairs lighting circuits have no cpc's. However, upon further investigation it appears that the downstairs lighting circuit has managed to "borrow" a cpc from the downstairs socket circuit.
I've never come across this before and am inclined to say it isn't right. The CU is supposed to be upgraded to an RCBO board as part of the ongoing work and I'm not sure if this may flag up problems. Upstairs lighting circuit is being rewired as part of the project already but most of the downstairs has been done already by previous contractors.
Any advice for how to best proceed much appreciated, Thanks in advance

Regulation 543.1.2 does show that it is acceptable to use a cpc common to 2 or more circuits, although it does seem a bit of a cheat and I'd much rather each circuit has it's own CPC.

I'm not sure what you mean by the downstairs lights have 'no cpc' then you say they are earthed by the socket circuit? Can you see an earth cable at each of the lights and switches?

 

[mat_coley]

Regulation 543.1.2 does show that it is acceptable to use a cpc common to 2 or more circuits, although it does seem a bit of a cheat and I'd much rather each circuit has it's own CPC.

I'm not sure what you mean by the downstairs lights have 'no cpc' then you say they are earthed by the socket circuit? Can you see an earth cable at each of the lights and switches?

There is a cpc connected at the lights of 3 of the rooms and also at 2 of the switches which are all class 1 fittings, leaving just 1 class 2 switch with no cpc. I just want to make the most informed decision with the client as early as possible while there is other mess being made and they are away from the property. Don't really want to have to attack this issue after plastering etc at the end

 

[Welchyboy1]

This usually happens when there is no CPC at the lighting circuits then a customer deciedes they want to put a few chrome light fittings up in the lounge and wont have the circuit rewired

I have done it myself, use a 4mm link from ring circuit to light points

not the most ideal situation but its much better than if i turn down the job and the next guy just connects them with no earth at all