On Sat, 16 Feb 2013 01:21:13 -0800 (PST), 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.


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?

Very often the earth lug on the back box isn't large enough to take
three 2.5mm wires.

--
Frank Erskine