David Robinson explained :
The idea is to ensure both socket and both are properly earthed, even when the screws are taken out and the accessory hanging on its wires.
I always have, because I've always seen it done, but I wondered about this when reading...
Is a socket an "accessory"? Does the fixing screw count as making contact between the eyelet and the box?
If so, I can't see why people bother with running an earth wire to the back box (all the sockets I've ever bought connect the earth to the eyelet) so why is this common practice? Have I misunderstood the above, or is this covered elsewhere in the regs?
(Obviously you have to earth a light switch back box, because there's no earth on a switch - this is specifically about sockets)
Cheers, David.
David Robinson :
I'm no expert but my understanding is...
Yes.
Yes but eyelets aren't generally earthed so that doesn't count.
No. Not enough pressure for a reliable contact.
Yes the fixing screw makes the earth between the eyelet and the backbox if it is a fixed lug.
People like to make too much work for themselves or follow old regs (such as bonding a kitchen sink)
The sockets in our 2007 new-build house are all wired like that i.e. no seperate earth to the back box, only that obtained via the fixing screw to the earthed socket wiring plate. I would be surprised if this wiring was non regs-compliant.
It is my understanding that if the back box has at least one fixed lug, and the socket earth is present at both screw positions (they usually are these days), then this is perfectly acceptable.
Mathew
Have a read of
Mathew
Do all boxes have one fixed lug these days? My favourites had both adjustable.
I've always fitted this extra earth wire. And grommets. ;-)
That is so 1960's.
Next you will bragging about fitting earth sleeving to the cpc:-)
Not fitting the earth tail is allowed (a minimum standard). That does not stop a good DIYer fitting the earth lead if they feel happier doing so.
Yup. To go with a '60s spirit level. A proper sparks one - if it read wrong just turn it round...
I can understand someone fitting thousands for a living keeping things as simple and fast as possible.
What do the regs say about Metalclad sockets mounted on a surface, particularly where a row of them are joined together with conduit nipples. Obviously one has to be earthed with a tail, as do the sockets themselves, but do all the back boxes have to be tailed individually, or is their interconnection through the conduit nipples seen as adequate?
If metal conduit is acting as the CPC it would be sufficient, regs-wise, simply to have a tail between the earth terminal of each box and its socket. Good workmanship is of course required to ensure earth continuity between the boxes, as for the rest of the conduit system.
If the primary CPC is a wire in the conduit the regs don't have anything specific to say, other that all exposed-conductive-parts must be earthed, including the conduit itself. I would daisy chain the CPC between the socket earth terminals (as for L & N) and add a separate box-earthing tail in each box.
+1.
I might add some anyway where the plasterer has gunked the eyelets up, but otherwise this has put my mind at rest.
Cheers, David.
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