Earthing of metal boxes

[John D v2.0]

This really is getting confusion with all the screws and all the Johns! Fwiw, I think we should just use special emoticons with a picture of the part we're talking about. After all this technology it should be possible!
PS surely they are bolts not screws?

 

[John D v2.0]

Edit: not to mention the double posts :s

 

[JohnD]

I heard you the first time

I heard you the first time

 

[eveares]

It's not required, so long as one of the lugs is fixed

That may be, but lets not forget some plastic sockets do not have a earth connection to the screw holes, thus leaving the back box un-earthed.

 

[DaveHerns]

Really?

 

[sparkwright]

I don't think I've seen a regular socket that didn't have an earth earth connection to the screw holes.

That said though, and this is very similar, not so long ago Tenby un-switched fused spurs only had ONE screw hole earthed, the other one wasn't. So this could be a problem on a back box with only one fixed lug.

 

[eveares]

I don't think I've seen a regular socket that didn't have an earth earth connection to the screw holes.

WS10U Socket Back

• eveares
• 3 Sep 2016

WS10U Socket Front

• eveares
• 3 Sep 2016

Will try and grab some more examples of sockets and light swicthes.

 

[eveares]

Just found this in my shed, think I may have originally obtained it at my Grandparents. May have also seen a similar socket in their shed.

Potentially a worse problem than sockets as a live un-earthed metal back box could be combined with someone operating a light switch with damp/wet hands and touching the head of the plate screw in the process.

A light switch without earthed screw holes. (1)

• eveares
• 3 Sep 2016

A light switch without earthed screw holes. (2)

• eveares
• 3 Sep 2016

 

[sparkwright]

Light switches of course do mean that a metal back box must be earthed, as plastic light switches don't have earth terminals.

Where, for example, there may be one or several earth wires, there needs to be some contact to the back box as there is no way it can get earthed.

Of course when a pattress or plastic dry-line box is used, the two fixing screws will both be unearthed.

It also worth noting, in the early 60s and before, flush metal back boxes for light switches had nylon lugs for fixing the faceplate to. There often woudn't be an earth wire present, and these metal boxes didn't have an earth terminal. Presumably this arrangement meant if the box became live the screws wouldn't or vice versa. Either way, unearthed lighting circuits was a very bad idea.

 

[JohnW2]

Light switches of course do mean that a metal back box must be earthed, as plastic light switches don't have earth terminals.

Indeed - but, if the cable(s) had CPCs they would presumably naturally/usually be connected to the backbox terminal, since there is nothing else that could be done with them.

Kind Regards, John

 

[securespark]

Either way, unearthed lighting circuits was a very bad idea.

In certain circs, yes.

But where you have plastic ceiling roses and switches along with either back boxes with nylon lugs or nylon faceplate screws (see what I did there?), it is reasonably safe.

 

[deadshort]

Thanks guys. I will fit a flylead.

And it took less time than writing your post !

DS

 

[Iggifer]

WS10U Socket Back

• eveares
• 3 Sep 2016

WS10U Socket Front

• eveares
• 3 Sep 2016

Will try and grab some more examples of sockets and light swicthes.

Well that's not a standard socket! And I doubt it conforms. What do you do when about earthing the faceplate screws when you fit that to a dryline box?

And as has been covered, plastic switches don't have earth terminals. But I suppose if you're being anal, you could apply the same logic about those screws in a dryline box

 

[JohnW2]

Well that's not a standard socket! And I doubt it conforms. What do you do when about earthing the faceplate screws when you fit that to a dryline box?

Do you mean when fitting that (plastic) accessory to a (plastic) dry-lining box? If so, the need for earthing the faceplate screws wouldn't arise, would it?

Kind Regards, John

 

[EFLImpudence]

I suppose if the plasterboard is thick enough, it would be possible for a live conductor to touch the screws.