Dave Plowman (News) wrote:

In my case the transformer is only powered up when the lights are on.
However, I'd not fancy using a PP3 and a standard relay - it won't last
long. You need a specialised motorised type which needs no holding
current. Like the type used on battery programmable thermostats etc.

No - in mine the primary side of the transformer would be on all the
time, and the battery is only used (and relay energised) while the
button is depressed. The idea is that pressing the button looks to the
fan like someone flicked the light on and off, and it then runs for the
duration of its timer.

The regs don't cover every eventuality word for word, but operating mains
via an ultra low voltage relay is standard practice where safety matters.

Thanks. I was just concerned that this might be outlawed on the grounds
that a stray wire in the relay box could make the ultra-low-voltage side
live. Though the fact that the switch is actually mains-rated in this
case means you'd still need a second fault (or a lot of water) to get a
shock.

Pete