Metal electrical mounting box

[Janice]

Well, this is easy only if you know the answer! I have created a ring circuit and am now ready to wire in my sockets. Can anyone tell me what the little screw in the back corner of the metal box is for - is this for earthing? If so, do I assume one of my earth wires goes in the socket and the other one in the little screw in back box? Can anyone advise please?

 

[securespark]

The best bet is to terminate the earth conductors in the socket earth terminal, and run a third from there to the box terminal. Don't forget to use green/yellow sleeving.

 

[ban-all-sheds]

Best bet? Only bet! If you put one earth to the box and one to the socket, then the only thing which gives your circuit earth continuity is the connection between the edge of the box and the strap across the back of the socket....

 

[securespark]

Well, there is a school of thought in the IEE Ban that says if your boxes have at least one fixed lug, there is no longer a need for an earth strap, but I disagree.

Hence the wording best bet.

Sorry, re-read Bans post. Yes, you MUST put the earths from the circuit cables into the socket earth term. Whether you fit an earth strap to the box is debatable, but strongly advised.

 

[Gerbil]

Whether you fit an earth strap to the box is debatable, but strongly advised.

Hi securespark

Are you saying that as far as the regs are concerned a metal back box doesn't have to be earthed?

I've replaced a couple of sockets in the house I've just moved into, mainly because they were covered in paint and it was easier to fit new sockets than try and clean them. Neither of the sockets had their metal back boxes earthed so I rectified this at the same time as I assumed it was unsafe not to have it earthed and whoever wired it ten years ago was just lazy.

I was planning on opening all the other sockets eventually just to check they were earthed, but if its not a requirement and not considered unsafe then I guess I may as well save myself a job.[/quote]

 

[ban-all-sheds]

There's no regulation to say they should be earthed, but it is a Good Idea™. It's not a big job to put it right.

Not much danger if they're not - did you notice if Mr Slapdash used grommets?

 

[Gerbil]

Now I'm confused...

Grommets where?

 

[ban-all-sheds]

Around the holes in the boxes where the cables run in and out....

 

[Gerbil]

Thanks for that. I don't remember seeing any...

I'll double check next time I have a socket off the wall.

 

[ChrisRogers]

Not much danger if they're not - did you notice if Mr Slapdash used grommets?

Is there a regulation to use grommets?

 

[Studders]

Not much danger if they're not - did you notice if Mr Slapdash used grommets?

Is there a regulation to use grommets?

Only if Wallace says so.

 

[Janice]

The best bet is to terminate the earth conductors in the socket earth terminal, and run a third from there to the box terminal. Don't forget to use green/yellow sleeving.

Thank you so much for for all your replies - I am new to all this but am determined to do it myself and to get it right (safe)! Can you please tell me how/where I get a third earth from since I only have the two cables?

 

[ban-all-sheds]

From a bit of 2.5mm² T&E, strip back the outer sheath, cut off a few inches of earth wire, slip some green/yellow sleeving over it, and screw one end into the earth terminal of the socket, and the other into the earth terminal of the box.

It would be wise to have the supply to the circuit turned off while you do this.

 

[plugwash]

while it does mean an extra item to keep around some sparkys find it easier to use 1.5mm single earth (which is the same size as the earth in 2.5mm twin and earth) than mess around with sleeving offcuts of bare earth wire

 

[dingbat]

Yeah, I always use a bit of 2.5 sq mm yellow/green X-grade (6491X), as I always have a reel handy for those (mechanically protected) supplementary bonding jobbies.