# Earthing of Metal Back Boxes???



## Trimix-leccy

Mmmmmmmm!
It has always been classed as 'good practice'. However it is required if
CPC is MICC
CPC is Metal conduit
CPC is SWA
If accessory backbox has the accessory attached by 2 adjustable lugs. If one lug is fixed then it is not required. HOWEVER NIC bloke tried to knock me one year....egatube to metal socket, cpc run to E term on socket. He said it should have a CPC 'link' to box [my lad had forgotten it]. When I asked to see the appropriate REg he said it was 'his preference'. I mentioned that he was inspecting our work in accordance with the published standards and NOT his personal whims.I get a tad confrontational in these situations:laughing: 

Having said all that...what does it take to fit a link? 125mm of 2.5 g/y and about 20 secs? We fit them all the time now [ish, sort of style:whistling2: ]


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## RePhase277

I am lost on the acronyms, because I'm in the States, but are you saying you are not required to bond the grounding (earthing) conductor to a metal enclosure as well as the device?

Here, it is still legal to use a metal conduit as the sole "equipment grounding conductor", as we call it. All good electricians pull a green wire in every conduit anyway. But, if we use a metal conduit along with an EGC, we are required to bond them together. Our boxes have a tapped hole in the back so that we can insert a 10-32 machine screw and connect a "bond jumper" to it. The idea is that if the pipe and wire aren't bonded, a large fault current on the EGC may cause the conduit to act like choke and limit the magnitude of the current, which is bad for the operation of a circuit breaker.

InPhase277


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## Trimix-leccy

Here the fixing screw is counted as an earthing conductor IF one of the box lugs is fixed and NOT adjustable
MICC copper sheathed cable [aka Pyro]
CPC earthing conductor
SWA steel wire armoured cable
NIC abbrv. For National Inspection Council or Electrical Installation Contractors
Egatube plastic conduit


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## cornishsparks

Always put earth link to the back box even though NICIEC inspector told me not to bother.Guess its a habbit but i dont think it takes extra time, most of the time i just make one of the ring ends longer and go to the socket double over and then to box.


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## supasparx

Trimix-leccy said:


> Here the fixing screw is counted as an earthing conductor IF one of the box lugs is fixed and NOT adjustable
> MICC copper sheathed cable [aka Pyro]
> CPC earthing conductor
> SWA steel wire armoured cable
> NIC abbrv. For National Inspection Council or Electrical Installation Contractors
> Egatube plastic conduit


 
Thanks for clearing that up, unable to find my copy of the regs. (going to purchase 17th).

Fixed lug or not, I always thought that if a socket/switch is unscrewed form the box it isn't earthed. Therefore introducing the potential for it to become live under fault circumstances.

I think I will continue to bond all metal back boxes, regardless of the personal preference of whoever I'm doing the job for.


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## Trimix-leccy

supasparx said:


> Thanks for clearing that up, unable to find my copy of the regs. (going to purchase 17th). Got mine in the car, not even oened it yet:whistling2:
> Fixed lug or not, I always thought that if a socket/switch is unscrewed form the box it isn't earthed. Correct, my point exactly. But it does not seem to matter. I still go for the good practice angle though. Therefore introducing the potential for it to become live under fault circumstances.
> I think I will continue to bond all metal back boxes, regardless of the personal preference of whoever I'm doing the job for.


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