Dual backbox cpc

[AndyPRK]

if I were to use a metal dual back box with 1 side used for a socket and the other side a light circuit; this would link the cpc's.

Is there an issue with this?
Maybe during testing ?

 

[EFLImpudence]

It may confuse someone testing - but, of course, it will be well documented.

 

[AndyPRK]

I could use a clean earth socket.

 

[JohnW2]

if I were to use a metal dual back box with 1 side used for a socket and the other side a light circuit; this would link the cpc's. Is there an issue with this? Maybe during testing ?

Do I take it that both of the accessories are metal? If not, there would presumably be no reason why the backbox would have to be connected to both CPCs - provided that it was 'earthed' by one or the other.

Kind Regards?

 

[PBC_1966]

It's no different in principle than if you run cables to a twin light switch from two different lighting circuits and they end up joined together, or if you use metallic conduit for earthing with multiple circuits inside, or if you run multiple circuits in PVC conduit with a shared earth. There's no need to keep the earths of different circuits separated, in fact in many homes there will already be parallel paths from one circuit to another anyway.

 

[AndyPRK]

Both are plastic. But they get joined through the screw holes.

I guess I was nervous that if the socket circuit cpc failed it would only be protected via the light circuit cpc and this could go unnoticed.

 

[plugwash]

Do I take it that both of the accessories are metal? If not, there would presumably be no reason why the backbox would have to be connected to both CPCs - provided that it was 'earthed' by one or the other.

IMO metal enclosures for electrical connections should always be connected to the earths of all the circuits they serve. Otherwise if one circuit is removed the enclosure would end up without an effective earth.

I guess I was nervous that if the socket circuit cpc failed it would only be protected via the light circuit cpc and this could go unnoticed.

Better that than it ending up with no earth at all.

 

[JohnW2]

Both are plastic. But they get joined through the screw holes.

Not in the case of most plastic light switches, which usually have no earth terminal.

I guess I was nervous that if the socket circuit cpc failed it would only be protected via the light circuit cpc and this could go unnoticed.

Most backboxes are connected to earth by only one CPC. However, I take plugwash's point that, theoretically, thje accessory circuit earthing the backbox might be removed one day.

As PBC has said, there can be countless 'incidental' cross-connections between CPCs of different circuits. Although that does somewhat confuse testing (and could result in misleading test results), I suppose it is a fact of life.

Kind Regards, John

 

[PBC_1966]

IMO metal enclosures for electrical connections should always be connected to the earths of all the circuits they serve.

The National Electrical Code here in the U.S. actually requires that. All ground wires running into a box must be connected together and to the box, regardless of whether they're all part of the same circuit or not.

 

[ericmark]

I would not worry connecting light and socket earth together, however if you want to keep separate use a grid switch plate and double instead of duel back box, there is no connection to earth through screws with the LAP grid switch system, the modules simple click in place.