Earthing metal back boxes

[ebee]

Agreed John

 

[Notch7]

the low level of risk is commensurate with the small amount of work to do it.

Especially as pro electricians no doubt carry a reel of earth single cable and will chop up a load of 6” bits and bare the cable both ends

Even for a DIYer pulling out a bit of Earth and pushing on some sheath isn’t that much of a pain.




One quick question: is it acceptable practice to terminate the earth from the ring cables in the back box lug and then fit a fly lead? I’ve done it once or twice when the cables have been too short.

 

[Adam_151]

One quick question: is it acceptable practice to terminate the earth from the ring cables in the back box lug and then fit a fly lead? I’ve done it once or twice when the cables have been too short.

I would say that provided the box terminal is a proper brass terminal that has been attached to the box, then yes it would be acceptable (but somewhat un-prefered*), I wouldn't want to use one of those that are pressed out of the box themselves with another bit of galv for this purpose, they just don't seem secure. The flylead is of course estential, the screws can provide the earth to the box when the cpcs go to the socket under some situations but not vice versa.

You could also put the two CPCs in a 5 way wago and run a lead off to the socket and the box if you wanted

*Yes, I know, bad english, but it conveys my meaning!

 

[JohnW2]

the low level of risk is commensurate with the small amount of work to do it.

Yes (well, the other way around), which I suppose is the main reason why I personally always do it.

One quick question: is it acceptable practice to terminate the earth from the ring cables in the back box lug and then fit a fly lead? I’ve done it once or twice when the cables have been too short.

It's not an uncommon practice and, provided only that the connections are all 'secure', it is obviously electrically no different from doing it the other way around.

Whilst is is preferable to take the CPC to the socket, with a fly lead from there to the back box (since the 'earthing' of the socket is ''more important' than is the earthing of the back box), I certainly wouldn't personally say that the other approach was 'not acceptable'. However,opinions may vary!

Kind Regards, John

 

[ebee]

Yes I would agree that it is my non-preferred method to earth the box then a fly lead from box to socket. The "prime " earth being the socket and then secondary the box . Having said that, on rings I do tend not to use fly leads anyway so one leg to the socket E and the other leg to the box first then doubled at the box and continued to the socket. This ends up as both ends terminating at the socket E but one leg visits the box terminal first, to do that you need strip say 2.5 T & E about twice as long on one leg to begin with. This results with both box and socket being on the ring proper and if the box terminal pulls out it continues as one conductor to the socket unless it breaks. I do it really for ease of not using a reel of earthwire really more than any other reason. Actually not only on a ring but also on radials, Just my quirk really.

 

[JohnW2]

Yes I would agree that it is my non-preferred method to earth the box then a fly lead from box to socket. The "prime " earth being the socket and then secondary the box .

Quite so. As I said, despite all these discussions about earth back boxes, it is the provision of an adequate earth to the socket which is thee most important thing.

Having said that, on rings I do tend not to use fly leads anyway so one leg to the socket E and the other leg to the box first then doubled at the box and continued to the socket. This ends up as both ends terminating at the socket E but one leg visits the box terminal first,

I've also done that - and, in fact, have sometimes taken the CPCs of both legs via the back box to to the socket (unbroken).

Kind Regards, John