connecting CPC between socket and light circuit

[AndyPRK]

I thought I asked this a couple of years ago, but can't see it in my watched topics.

I wish to fit a dual metal back box (capable of fitting 2 single accessories(sockets)) in my bedroom.
(might actually get round to doing it!)

One accessory will be connected off the socket circuit.
The other accessory will be connected to the lighting circuit.

When the accessories are screwed in this will join the 2 circuit CPC's. (via the screw holes and back box)

This really doesn't seam right to me. Is it ok?

To prevent connection I could use a clean earth socket for one of them. This would prevent the CPC's being joined through the screw holes, but the socket CPC correctly connected.
Clean earth sockets are double the price though! It's quite cleaver though!
And I guess it would prevent an electrician in the future wondering why the CPC's are connected and where!

I could also leave the lighting circuit CPC disconnected, and use the socket circuits CPC for the socket.

The size of the CPC in 1mm and 2.5mm is different isn't it?
I guess I worry the socket circuit CPC could become disconnected one day, and it wouldn't be noticed in testing as it was using the CPC in the 1mm cable.

How you worry when you get older. I'm sure I never bothered connecting earths when I was as teenager!

What are peoples thoughts?

 

[JohnW2]

I wish to fit a dual metal back box (capable of fitting 2 single accessories(sockets)) in my bedroom. .... One accessory will be connected off the socket circuit. The other accessory will be connected to the lighting circuit. ... When the accessories are screwed in this will join the 2 circuit CPC's. (via the screw holes and back box). This really doesn't seam right to me. Is it ok?

It's no different from what might actually be required by regs in the name of supplementary bonding (if required) in some situations.

The size of the CPC in 1mm and 2.5mm is different isn't it? I guess I worry the socket circuit CPC could become disconnected one day, and it wouldn't be noticed in testing as it was using the CPC in the 1mm cable.

It would not be noticed by 'superficial testing', but proper testing should detect it. Furthermore, given that testing is only undertaken 'occasionally' (if at all!), such a fault could exist for years before being detected by testing and, quite frankly, if the socket circuit were to lose its primary CPC connection, I think I'd prefer there to be a 1mm² CPC connected to the socket (or whatever) for all those years, rather than no CPC at all!

Kind Regards, John

 

[scousespark]

Why, if you have a supply for your sockets, would you want to complicate matters in the way you are describing. Isn't a DSO suitable, as this is what they are designed for. I'm not really a fan of sockets on lighting circuits and avoid them unless they are the only option available.

 

[securespark]

Oh God.....

 

[EFLImpudence]

Yes, my son?

 

[scousespark]

Why `oh God`?

 

[JohnW2]

Why, if you have a supply for your sockets, would you want to complicate matters in the way you are describing. Isn't a DSO suitable, as this is what they are designed for. I'm not really a fan of sockets on lighting circuits and avoid them unless they are the only option available.

I also wondered that. We've been starved of information, but is it not possible that the socket 'on the lighting circuit' is a 'switched' (by light switches) outlet (quite possibly not a 13A BS1363 socket) for a lamp of some sort (old-fashioned 'lamp', not the type of lamp that one plugs into a lamp!)? Hopefully the OP will clarify.

Kind Regards, John

 

[JohnW2]

Why `oh God`?

Mention of sockets on lighting circuits is, historically, likely to result in a 10-page 'war' - but, come to think about, I don't think that I've seen the primary perpetrator around in recent times!

Kind Regards, John

 

[scousespark]

I was querying why you would make a conscious decision to join the 2 circuits in a double box. I'm not trying to say it shouldn't be done, just that it's unusual.

 

[JohnW2]

I was querying why you would make a conscious decision to join the 2 circuits in a double box. I'm not trying to say it shouldn't be done, just that it's unusual.

As I said, we will hopefully get clarification from the OP.

I find it very hard to believe that he simply wants two 'general purpose' socket outlets next to one another and has decided to feed one from a sockets circuit and the other from a lighting circuit! There must be some explanation - possibly along the lines that I mentioned.

Kind Regards, John

 

[yorkspark]

i read it as a dual mount box, with 1x single socket and 1x 5a socket fitted or something similar fed fom the lighting circuit

 

[bernardgreen]

Joining the CPC is not a problem. They are jpoined togethere at the Earth bus bar in the CU.

The only concern would be if these two faults occured at the same time :-

(1) CPC in the 2.5 mm² cable(s) feeding the socket went open circuit ( leaving only the CPC in the lighting cable to earth both the accessories ).
(2) a Live to Earth fault in the accessory on the power circuit that might overload the CPC in the lighting cable before the MCB for the power circuit tripped.

Most unlikely that the CPC in the lighting cable would fail before the MCB tripped.

 

[AndyPRK]

yes, yorks has read it correctly. Other guesses correct.

I currently have a 2 gang light switch by the door.
One of those switches controls a bedside table lamp.
There is also a 2 way switch near the bed to turn it on. It works well.


I now need to add a socket on the other side of the bed for the other table lamp to be controlled by this circuit.
And add an additional power outlet at the same time.

Assume the socket circuit is powered via a 25A or 32A MCB

 

[scousespark]

That is a bit clearer. In the first post, you said you were fitting two sockets.
What you describe now is similar to a hotel with 2 individual switches along with a master by the door. Why do you want to position the SO where you are fitting the new switch?

 

[AndyPRK]

I am fitting 2 single sockets in the same dual metal back box.

One off socket circuit
One switched off light circuit