On Thu, 11 Oct 2007 09:46:58 +0100 someone who may be "TMC"
wrote this:-

Some 30 years ago I was taught to wire the earths to the socket (sheathed)
and a single piece of insulated earth wire to the connector on the metal
box.

That is sensible.

The reason given for this was that without the connection to the back
box the only way the box was earthed was through the screws holding the
socket and needed to be 'bonded' in case the socket was unscrewed whilst it
was live.

The Wiring Regulations don't require this except, if as has already
been mentioned, conduit is providing the CPC.

A better reason for doing it this way is that failure of the single
conductor leaves just the back box unearthed (or to be precise
subject to the vagaries of any screws).

Mind you this was at the time when councils were specifying earth
bonding to metal window frames.

Why councils should specify such things is beyond me. They know
little about electricity and it wasn't required in the Wiring
Regulations. What seemed to be common was a misreading of the
wording. There were several tests about whether an item should be
bonded and it was only if ALL of them were met that it should be
bonded. Almost any bit of metal would meet one or two of the tests,
but that didn't mean it should have been bonded.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54