On 16/02/2013 09:21, mike wrote:
On Feb 15, 10:29 pm, John Rumm wrote:
On 15/02/2013 20:15, mike wrote:

But if someone made the earth connection to the back box on
the Toolstation version, any connected appliance (double insulation
and plastic earth prongs aside) wouldn't be earthed. Is that right?

No, because the circuit earth wires will always be connected to the
earth terminal on the socket face plate. You would not simply terminate
the circuit earth wires on the backbox and rely on that to make an earth
connection to the backbox.

So "no" in theory but "yes" in practice because there will inevitably
be cases where people connect it to the back box earth.

Excluding cases conduit/sheath/armour earthing is in use it seems
relatively unlikely - its not as if its any easier to connect two wires
to the box and four to the socket... I have seen countless examples of
no flying lead betwixt socket and box, but don't recall ever seeing the
being being used at a primary connection point.

With a "normal" socket that has earthed screw holes the reverse
situation is allowable - i.e. you can re;y on them to earth the backbox
(assuming it has at least one fixed tag), however good practice would
suggest adding a separate fly lead between circuit terminal and the
earth terminal on the back box.


If everything is reliably earthed via the socket screw in the
situation you describe, how would it be any less reliable if the earth
were connected to the back box rather than the face plate?

Because in reality its a less reliable connection...

While not desirable, an unearthed backbox is unlikely to kill you, but
an unearthed socket might.

Imagine a situation where some one is decorating and has release socket
screws to get paper etc behind the faceplate. Anything plugged into that
socket *must* still be earthed, but whether the box still is in those
circumstances is less important.


--
Cheers,

John.

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