In message ,
Mark Evans wrote:

Lobster wrote:
PoP wrote in message . ..

The fan should be a spur from the upstairs ring main, not the lighting
circuit. And upstairs ring mains tend to come up from the floor rather
than down from the loft. Note the word "tend", you can't count on it.

Why not from the lighting circuit? Isn't that the way to wire them if

Because Murphy's says that if it is going to fail it will do so at
night

you want them to switch on automatically with the light switch (eg as
in the case of an internal bathroom/toilet)?

In this case the fan has two live connectors. One to power the fan
and electronics and one connected to the switched live feeding the
lamp(s).

I would have thought that your idea is bloomin' dangerous - by
connecting the "permanent live" to the sockets and the "switched
live" to the lights the fan is in effect connected across two separately
fused circuits and a fault at the fan may not cause enough current to
flow to blow both fuses. Also consider the case where the fan actually
connects "SL" to "PL" internally, perhaps in a fault condition (who
knows what the electronics do?). In this case you have created a huge
circuit, partly wired in (usually) 2.5mm cable, partly in (usually) 1mm
cable and protected by what amounts to probably a 38A MCB (32A+6A). Not
only that, but you have bridged the two neutrals too and this could
cause big problems if, as is often the case these days even upstairs,
your sockets are wired via an RCD but your lights are not.

The only instance where I would consider spuring a typical run-on fan
from a sockets circuit would be where the fan is controlled in some way
*other* than via the light switch. It may have its own pullcord, or a
door switch, or it may be controlled by a humidity sensor or even a PIR.

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Don't fight technology, live with it: http://www.livtech.co.uk/
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