Settle this Argument.

[telectrix]

metal faceplate 1363 socket. obviously needs to be earthed. argument is whether the back box should be earthed just because it's a metal faceplate. ( i know it's considered good practice to fit a fly lead anyway, but that's not the argument. the argument is with the faceplate being metal, does that make any difference. my argument is No, other party says Yes. Who is right, going by BS7671?)

 

[Ian1981]

I would agree with you.
Perhaps if the back box was exposed such as surface clad metal boxes then I would fly lead to the back box as well, only because the back box is more accessible to touch than in a wall if the socket face plate was ever removed for testing etc the back box is still earthed.
You can argue it's the same thing I suppose.

 

[Andy78]

No, it makes no difference regs wise. The regs ask for earthing of exposed conductive parts. That's been done already.

 

[kingeri]

I can't see what difference it makes if the faceplate is metal or plastic myself. So I agree with you.

Incidentally, I have noticed that the practice of earthing metal backboxes seems to be dying out, along with doubling over smaller conductors (especially CPCs).

 

[polo1]

If the backbox has one fixed lug, not required ( but I'd do it anyway). Two adjustable lugs, fly lead required, IMHO irrespective of plastic or metal accessories.

 

[Andy78]

I can't see what difference it makes if the faceplate is metal or plastic myself. So I agree with you.

Incidentally, I have noticed that the practice of earthing metal backboxes seems to be dying out, along with doubling over smaller conductors (especially CPCs).

I was on a facebook sparkies group and doubling over was brought up. All the younger guys chimed in "You don't have to do it with modern terminals" Clearly some garbage they are repeating in training centres. This was about an 80% consensus.

 

[Wilko]

My 20p - both need earth, from reg 411.4.2 which in part says "each exposed conductive part". But is a recessed metal back box an exposed conductive part, or is maybe deemed to be ?

 

[Ian1981]

Well hager specifically say in their consumer unit instructions that wires 1mm and below require doubling over into the terminals.
That's their guidance anyhow.

 

[Ian1981]

My 20p - both need earth, from reg 411.4.2 which in part says "each exposed conductive part". But is a recessed metal back box an exposed conductive part, or is maybe deemed to be ?

GN 1&8 suggests that it's an exposed conductive part and is part of the enclosure for the wiring accessory so should be earthed

 

[David M]

GN 1&8 suggests that it's an exposed conductive part and is part of the enclosure for the wiring accessory so should be earthed

Though I don't disagree with bonding the box, I cant see how a buried boxed is classed as exposed? I think its a grey area, which is simply covered by over kill bonding that is simple to install & unobtrusive any how, so why not fit it.

 

[telectrix]

the back box is earthed anyway by the 3.5mm faceplate screws until or unless the faceplate is removed. in which case, the circuit should be isolated first.

 

[Octopus]

I very much doubt that 7671 states this clearly either way!

Like many other regs.

.....

 

[David M]

the back box is earthed anyway by the 3.5mm faceplate screws until or unless the faceplate is removed. in which case, the circuit should be isolated first.

I mentioned this way way back during conversation with an inspector. He said though this is true they cannot be relied on for bonding purposes therefore the back boxes should have additional bonding.

 

[Ian1981]

Yeah the text book answer is that the socket would be isolated before removal but we all live in the real world and sometimes you need access to the terminals for any live testing or for fault finding etc.
Plug in testers are not a way in proving dead as far as I'm aware tho we all use them I'm sure.

 

[Strima]

Not forgetting DIY decorating when the faceplate is pulled away from the wall for papering or painting.

 

[telectrix]

Not forgetting DIY decorating when the faceplate is pulled away from the wall for papering or painting.

true, but we'renot talking about what may or may not be desirable. we're talking about what the regs. stipulate. was around 2003 i think, in an amendment to 16th. where the stipulation for not earthing a back box was changed from 2 fixed lugs to single fixed lug.

 

[Risteard]

I mentioned this way way back during conversation with an inspector. He said though this is true they cannot be relied on for bonding purposes therefore the back boxes should have additional bonding.

But you're not bonding it - it's not an extraneous conductive part. You are earthing an exposed conductive part. Although a separate conductor is not required with one or more fixed lugs I personally would always do it.

 

[The Ghost]

543.2.7 Where the protective conductor is formed by metal conduit, trunking or ducting or the metal sheath and/or armour of a cable, the earthing terminal of each accessory shall be connected by a separate protective conductor to an earthing terminal incorporated in the associated box or other enclosure.

 

[Ian1981]

That regulation ,is if say you used metal conduit as the cpc.
A tail Earth from the back box is needed connecting to the socket faceplate or to whatever the accessory serves as.

 

[The Ghost]

Would you have a metal surface box on anything else? i.e. galv etc.

 

[Ian1981]

Possibly yes but if you used singles within the conduit with a cpc as a separate conductor and not the containment, that regulation isn't applicable.
With a separate cpc you are mearly earthing the conduit through the fixing screws inserted into the back box fixing lugs.

 

[The Ghost]

For flush metal back boxes with two fixed accessory-fixing lugs, as shown in Figure 9.6, the box can be considered adequately earthed through the earthing straps and eyelets of the accessory and the fixing lugs on the box. An earthing tail is not therefore essential although for best practice it is highly desirable. GN8

 

[Ian1981]

Agree but not sure why you quoted that specific regulation earlier?

Wires crossed (pun intended)

 

[The Ghost]

It's the only reference in the regs I can find on the subject thought I would just put it there. I am assuming metal clad socket is surface with surface box, and would be with galv. Of course the OP may be referring to any metal back box that is not entirely clear but I think it highlights that there are specific items that do and some situations that don't require an earth hence no definitive answer.

 

[suffolkspark]

with regards to doubling over I'm afraid I'm one of those that doesn't always......
It depends on the accessories, hager, mk and crabtree have square terminals so you have to, but some brands have round terminals, click, eaton, and the cable, even 1mm centers itself nicely under the centre of the screw and I never have any problems, definitely depends on the accessory brand.
agree with most people that have said if theres 1 fixed 3.5mm screw lug it doesn't need a fly lead to the back box, that is 100%.

 

[ashg285]

I don't fit fly lead unless surface metal boxes.

 

[ashg285]

And as for doubling over I always do this on 1mm or 1.5mm cable

 

[littlespark]

Regulations are built on worst-case-scenarios... I would earth faceplate AND backbox, surface or not.
Imagine a case where the live AND the earth wires are not tight in their connections and drop out. Live touches back box, creating a danger.
The only protection now is the earth wire to the back box.

Doubling over conductors - Any screw termination must be secure. A single core cannot be deemed secure.
I still cannot believe there are older sparks out there still twisting solid conductors together.

 

[ipf]

Regulations are built on worst-case-scenarios... I would earth faceplate AND backbox, surface or not.
Imagine a case where the live AND the earth wires are not tight in their connections and drop out. Live touches back box, creating a danger.
The only protection now is the earth wire to the back box.

Doubling over conductors - Any screw termination must be secure. A single core cannot be deemed secure.
I still cannot believe there are older sparks out there still twisting solid conductors together.

Where'd you get that one from?

As regards 'older sparks', that certainly doesn't apply to those with a bit about them. I'm damn sure there's a lot more common sense used, in general, than the younger end.

 

[sparksburnout]

"Live touches back box, creating a danger."
How??? Kindly explain.

 

[sparksburnout]

If the backbox has one fixed lug, not required ( but I'd do it anyway). Two adjustable lugs, fly lead required, IMHO irrespective of plastic or metal accessories.

I don't get this. Whats the difference between fixed and adjustable lugs, as regards earthing of the back-box via the accessory? If it's securely fixed, then it is earthed. If it's not securely fixed, then it shouldn't be live. They don't just become insecure in the night do they??Anyway the back-box doesn't need earthing as it shouldn't be accessible if the socket is live, should it???

 

[littlespark]

"Live touches back box, creating a danger."
How??? Kindly explain.

A live conductor, touching a metal box, which isn't earthed because the cpc is also disconnected. Sounds dangerous to me

 

[Andy78]

A live conductor, touching a metal box, which isn't earthed because the cpc is also disconnected. Sounds dangerous to me

It's also dangerous even with the backbox separately earthed because in this imaginary scenario where conductors fall from terminals, that one fell out too.

 

[polo1]

I don't get this. Whats the difference between fixed and adjustable lugs, as regards earthing of the back-box via the accessory? .......

By its very nature, an adjustable lug does not provide a reliable path to earth (via cpc, accessory earth and accessory screws), whereas a fixed lug does.

 

[sparksburnout]

A live conductor, touching a metal box, which isn't earthed because the cpc is also disconnected. Sounds dangerous to me

Why? How can this imaginary scenario exist unless someone has tunnelled through from the other side of the wall???

 

[sparksburnout]

By its very nature, an adjustable lug does not provide a reliable path to earth (via cpc, accessory earth and accessory screws), whereas a fixed lug does.

Eh? So the accessory is fixed via 2 adjustable lugs (???) and they have both come free, very unlikely and in which case said accessory is then hanging off the wall, AND the live has ALSO become disconnected and is touching the back-box? Come on FFS.
Has anybody got a picture of these back-boxes with 2 adjustable lugs cos I can't remember seeing one???

 

[MJPD29]

Back box does not need earthed. Earthed by screws from faceplate, If its not secured properly or opened to work at it, it should be dead anyway and locked off .

 

[polo1]

Eh? So the accessory is fixed via 2 adjustable lugs (???) and they have both come free, very unlikely and in which case said accessory is then hanging off the wall, AND the live has ALSO become disconnected and is touching the back-box? Come on FFS.
Has anybody got a picture of these back-boxes with 2 adjustable lugs cos I can't remember seeing one???

I wasn't commenting on the likelihood of a particular set of circumstances occurring. The question posed was about the need to earth a metal back box viz. run an earth from the b/box to the accessory. My understanding is that, so long as the back box has one of the two lugs fixed, a separate earth is not essential as earthing is achieved via the accessory screw. Others may have a different opinion. Agree/don't agree, I won't loose any sleep either way ;>)

 

[littlespark]

Back box becomes live, therefore screws and faceplate (if metal) becomes live. No tunnelling involved.
If a backbox is designed with an earthing terminal, shouldn’t it be used?

 

[MJPD29]

Back box becomes live, therefore screws and faceplate (if metal) becomes live. No tunnelling involved.
If a backbox is designed with an earthing terminal, shouldn’t it be used?

how is this possible? if its a metal socket, it is earthed through the earth terminal on the faceplate which is connected to back box through terminal screw to fixed lug, if it is a plastic or any other type of socket the screws are attached to the earth bar on the back of the socket, therefore again earthing the back box secured by terminal screws to the fixed lug of the box. If the socket is opened and the earth link from screw to lug is broken, the socket should be dead anyway. your not supposed to be working live.