PE from metal back box to socket

[Paul228]

Have things changed and I missed the memo.
Let's start by saying I'm a fossil. I was trained the old way, were u went with a mate and went to night school and day release. Anyway, was on a domestic fault for a mate of a mate. I rocked up, kitchen ring tripping. Asked any recent works, holes drilled etc, non was the reply ( which was a fib, but no matter). Took both legs out of the board, circuit breaker tests ok, ring has 48k short. Went to split the ring mid point and noticed no earth strap from the box to the socket ( in my day this was mandatory). Found fault, someone had fitted an outside socket, full of water. Anyway back to the internal metal back box. The ring was in a new extension, one year old. So I advised them to get the sparks back to fix it. A few days later, customer rang me and said the sparks said it's not a requirement anymore. My question..since when

 

[Upton Sparks]

Apologies for the late arrival to the conversation,

So, does anyone know where in the regulations (BS7671) it says, you can use the lug hole of the metal box as an earthing point?

I think the regulation 411.3.1.1 applies, As does 132.1

The only question is. Are the metal back boxes classed as an exposed conductive part when buried in the wall?????.... I would agree when it’s fitted into the wall it may not be an exposed conductive part, but again if it’s not stated within the regulations, it’s all about interpretation.

Then again, it’s all about the idiots who live in the house, if they take of the socket of the wall then the back box is an exposed conductive part. Agree they would deserve an electric shock for being stupid in doing it live, (but these are the same people who put 30 amp fuse wiring into a 5 amp fuse carrier because the 5 amp kept blowing) … therefore its incumbent on the designer to take into account the layman and woman who will be living in the installation afterwards. hence 132.1

I don’t know if I agree its not good practice to earth the metal box. I think it is, and makes a statement about the standards the electrician is aiming for.

but I am on the fence now about it being a bad practice in not doing it… possibly it’s just lazy….

OK Tin Hat on …..

And

Merry Christmas and happy new Year to everyone.

 

[ipf]

NOBODY is using one of my lug holes as an earth connection point....

 

[richy3333]

Just as an addition/clarification GN8 Amd3 states at 9.7
'For flush metal back boxes with one fixed lug and one adjustable accessory fixing lug, as shown in figure 9.8, it is always desirable to provide and earthing tail.'

 

[Flanders]

The only question is. Are the metal back boxes classed as an exposed conductive part when buried in the wall?????.... I would agree when it’s fitted into the wall it may not be an exposed conductive part, but again if it’s not stated within the regulations, it’s all about interpretation.

The metal screws holding the switch to the back box would be an exposed conductive part though , so I would say that a metal box would have to be earthed even if the accessory did not need an earth, unless of course they where nylon screws.

 

[chris gray]

Over 50mm2 to be classed as exposed conductive part

 

[Silly Sausage]

The metal screws holding the switch to the back box would be an exposed conductive part though , so I would say that a metal box would have to be earthed even if the accessory did not need an earth, unless of course they where nylon screws.

Indeed, but if you look at the construction of a BS1363 socket outlet, the screws become Earthed when fully tightened up, and thereby, Earthing the backbox via 1 or 2 of the fixed lugs.

 

[Flanders]

Indeed, but if you look at the construction of a BS1363 socket outlet, the screws become Earthed when fully tightened up, and thereby, Earthing the backbox via 1 or 2 of the fixed lugs.

Yes I know That's why I said an accessories that does not need an earth for example a plastic lights switch

 

[SJD]

I have found on sockets (on several occasions) on an RFC, where the two incoming earths are terminated in the metal back box. And the installer has relied upon the screws to earth the socket, with no strap fitted!

Measuring a somewhat higher than expected Zs at the socket, and giving the screws a quick tighten (when Zs drops) usually gives the game away.

 

[chris gray]

I have found on sockets (on several occasions) on an RFC, where the two incoming earths are terminated in the metal back box. And the installer has relied upon the screws to earth the socket, with no strap fitted!

Measuring a somewhat higher than expected Zs at the socket, and giving the screws a quick tighten (when Zs drops) usually gives the game away.

I’ve honestly never seen this done?

 

[johnduffell]

Over 50mm2 to be classed as exposed conductive part

Maybe truet, but in terms of IP ratings that's not good. To be effectively class II it would need double or reinforced insulation, neither of which a socket has.
Wagobox or even surface mount back box yes, but metal socket box even though it's not an appliance i would still treat the back box as the enclosure as the wall is not part of the electrical installation.

 

[Upton Sparks]

I was also thinking of Reg 526.1 as well to why you should earth the back boxes with a lead.

I don't believe the screw achieves that ....

So your not confused, my position is;
I'm with putting the fly lead in, I think that is the right way. I am also on the opinion the back boxes is an exposed conductive part. regardless of it being buried in the wall.

But I am now starting think about it, but I have taken on board the thoughts and option of everyone on here and there information from and GN8. this is leave me with a question.
how would you code this on a EICR. C3 or not bother ?...

Anyway enough for today. Happy new year everyone we'll pick this up next year

 

[westward10]

GN8 does not quote a Regulation for its statement.

 

[pirate]

Pirate peeks above parapet...
Question:

If you have a metal back box, whether with a fixed and moveable lug or not, the faceplate screws earth the cpc to the box, so the only danger is if a live comes loose and touches the back box, maybe when you are removing it for inspection, at which time it really ought to be isolated, but might not be if for testing?
Maybe a live comes loose and touches the back box due to poor installation...
I don't know, I'm only asking...
but what is the problem with just taking a cpc from the faceplate earth terminal to the back box? I mean, it's just 6" of wire, and takes less than a minute to do?
If installing surface mounted metal boxes with metal faceplates, you would take an earth from the faceplate to the box, wouldn't you?
Is there a downside I'm not seeing?

 

[Deleted member 26818]

I imagine, the downside would be that it would increase the time taken to install each point.

 

[pirate]

Yes, Spin...that is the downside, but as my post said, it takes less than a minute...
I know, 200 sockets in an industrial unit = a lot of extra time, but for most folks it's maybe 20 or 30 sockets at a minute each...
My analogy is putting on a lifevest when I go out boating...it takes a minute...