Earthing Metal Accessories

[Piratepete]

Hi Guys
A simple question.
For metal light switches on metal back boxes does the cpc have to be connected directly to the terminal provided on the front plate or can the cpc stay in the terminal in the back box (provided, of course, that there is continuity between the two via the fixing screws)?
While doing an EICR, I've come across the cpc connected in the back box only. Um?

Instructions supplied with metal fittings suggest that the CPC should be taken to the accessory terminal - but then they would say that to cover for the use of plastic back boxes.:sailor:

Pete

 

[RISElectrical]

If the back box has a fixed lug the it isn't necessary, however it's always good practice to do so, and it takes 2 minutes to take a flying cpc from the backbox so do that

 

[Top Cat]

I would say, loop between back box and switch plate. If anyone takes off switch without the switch plate being earthed you run the risk of a fault happening that makes the switch plate live.

 

[telectrix]

agree with TC. the cpc must be terminated to the switchplate . connecting to the box is an optional extra with a fly lead.

 

[Deleted member 26818]

This is one of those questions that boils down to personal opinion.
My opinion is that either the CPC should be connected directly to the accessry front, or via a fly lead from the back box terminal.
If the manufactuer's instructions indicate the CPC should be connected directly to the accessory front, then those instructions should be taken acount of as per the requirements of Regulation 510.3.
To my mind, the reliability of continuty between the CPC terminal in the accessory and the earthing terminal in the back box, cannot be guaranteed.

 

[telectrix]

cpc to the switchplate and a fly lead to the box ( you'd do it for randolph scott )

 

[Deleted member 26818]

I would prefer the CPC connected directly to the accessory front, but there is no requirement in BS7671 for such.
In some instances, it is physically impossible to do so, such as when the containment is used as a CPC, or when the terminal in the accessory is too small to allow three or in some cases four conductors to be connected.

 

[telectrix]

know what you mean. some of these switches have ridiculously small earth terminals. i have occasionallt terminated the cpc's into a choc block, then a bit of 2.5mm single to the terminal.

 

[GLENNSPARK]

what i do is take the CPC to the wallplate/front first.....but double it back on itself (thus keeping it continous)...and then into the terminal in the box.....just a way i do it ....thats all.....

 

[Piratepete]

I totally agree with it being best practice to connect to the front plate, (which is what I do) but generally it sounds as if you think that the mechanical link to the box terminal complies.
Will someone please point me to the clause in the regs that permits this. I've read it before but can't seem to find it right now. Need to read it again!
Cheers
Pete

 

[Guitarist]

I always take the cpc to the plate first then 1.5mm tri-rated, ferruled earth cable to the back-box. It's a bit more flexible and makes pushing the accessory back easier.

 

[mickys86]

what i do is take the CPC to the wallplate/front first.....but double it back on itself (thus keeping it continous)...and then into the terminal in the box.....just a way i do it ....thats all.....

That's the way I do it except I go to the terminal in the box first

 

[Strima]

That's the way I do it except I go to the terminal in the box first

This is the way I do it, my logic being if someone in the future fits a class 2 at least I know the CPC will reach the back box.

 

[Ponty Massive]

I would say, loop between back box and switch plate. If anyone takes off switch without the switch plate being earthed you run the risk of a fault happening that makes the switch plate live.

....ah but you shouldn't be taking the switch plate off live.

 

[malcolmsanford]

Reg 411.4.2 seems to indicate that the faceplate must be connected to earth via a protective conductor, and so should not rely on earth via the continuity of the screws through a back box lug.

 

[wildgoose]

If it's a metal fitting then yes I normally fit the fly lead but if it's a plastic fitting, I don't bother because it's not a reg's requirement.

HOWEVER, if it one of those sockets boxes that's already stuffed full of wires then you make the call - is it value added to shoe horn yet another cable in there?

 

[mickys86]

Reg 411.4.2 seems to indicate that the faceplate must be connected to earth via a protective conductor, and so should not rely on earth via the continuity of the screws through a back box lug.

But Malcolm the cpc isn't cut, it's doubled over going from the back box to the faceplate in a continuous run. Would that not comply?

 

[malcolmsanford]

Hi Guys
A simple question.
For metal light switches on metal back boxes does the cpc have to be connected directly to the terminal provided on the front plate or can the cpc stay in the terminal in the back box (provided, of course, that there is continuity between the two via the fixing screws)?

But Malcolm the cpc isn't cut, it's doubled over going from the back box to the faceplate in a continuous run. Would that not comply?

Micky I was responding to the OP.

That Regs tells us that All exposed conductive parts must have an earthing conductor, and so as Pete asked, you can't technically take the CPC to the back box and then pick up the earth to the face plate continuity of the screws, regardless of fixed lugs or not

 

[Top Cat]

....ah but you shouldn't be taking the switch plate off live.

Just trying to make it fool proof!

Mind you a fool proof system doesn't take into account the ingenuity of fools!

 

[mickys86]

[/I]



Micky I was responding to the OP.

That Regs tells us that All exposed conductive parts must have an earthing conductor, and so as Pete asked, you can't technically take the CPC to the back box and then pick up the earth to the face plate continuity of the screws, regardless of fixed lugs or not

That's going to give me some firepower to fire at a guy at work tomorrow