A friend asked me to have a look at a Superswitch 2304 timer which
stopped working when the bulb which it was switching blew, and replacing
the bulb didn't fix it.

The answer, of course, was that when the bulb blew, so did an internal
3A fuse in the timer.

But, having had a look at the thing, I don't understand how it works. It
replaces a conventional wall switch and only has 2 connections - live
and switched live. Yet the thing itself needs power to operate the
display/logic/relay, etc. - and it doesn't have a neutral connection. My
first thought was that maybe it gets a connection from an earthed
backbox - but the holding screws go through insulated sleeves, and don't
connect to the circuit board.

My next thought was that it could get a neutral connection through the
bulb (it apparently only works with tungsten bulbs). But surely, that
would only work when the light was off. Once it had switched the light
on, the live and switched live would be at the same voltage and wouldn't
be able to power it to do any further timing/displaying/switching.

Clearly, I must be missing something! Anybody know what?
--
Cheers,
Roger
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