I'd like to wire the shower room extractor fan from the shower pull-switch so that it goes on with the shower and not the light. I found some info where one person said it's a no-no under current wiring regs but could be done via a contactor, and another says it can be done without a contactor as long as it goes via a fused spur from the shower switch.
Any electricians here can tell me which is the legal way to do it as I'd like to do it through a fused spur from the shower pull switch for simplicity.
You can do it with a fused spur from the shower isolator switch it you
want. You should label it at the consumer unit to avoid surprises for
later maintainers. Also since you would be removing all power from the
fan when you turn the switch off, you would lose any ability to have a
an automatically timed run on after the shower.
If you wanted to power and trigger the fan from the lighting circuit,
but also trigger it from the shower circuit, then you get into the
realms of needing contactors/relays etc to keep the circuits
electrically isolated from each other.
or even wire the fan into the shower itself, so picking up the permanent
live before the controls and the switched live after the controls?
Thus removing the risk of confusion if wired into the the shower
@John Rumm, not sure I understand what you're saying. What I intended was to run some three core and earth from the shower pull switch so that I'd have a permanent live and neutral and a switched live all going to the fan via a fused fan isolating switch. So the fan will still run on when the shower pull switch is turned off after using the shower. None of that would go near the consumer unit of course. Does that sound ok?
Yup, that would be fine - your OP made it sound like you just wanted to
pickup just from the switched live from the shower isolator.
The only slight practical difficulty you may have is getting a good
termination on the smaller fan cable at the same time as the (sometimes
significantly) larger shower supply cable, bearing in mind shower
connections need to be 'kin tight!
You will also need to check that whatever cable you use to connect the
fan is offered adequate fault current protection by the shower MCB. This
is not likely to be a problem with say a B32 MCB and 1.5mm^2 3&E. But
you start getting more marginal on larger MCBs and shorter cable lengths
(as the prospective fault current rises). Having the fuse close to the
main shower isolator helps reduce the risks.
What about if I feed the permanent fan supply from a light fitting as normal with 1.5mm twin and earth cable and then run a 1mm twin and earth cable from the shower pull switch just for the switched live feed? That way the fan goes on with the shower pull switch but is not fed permanently by the shower circuit. Not sure where to fuse though if it is ok?
Your fan should not be fed from more than one circuit.
If you want it to come on when the shower is on, you would need a relay,
preferably a changeover one (SPDT) that won't put the bathroom light on
at the same time as the fan.
Really *really* bad idea - that would be powering one appliance from two
separate circuits (which might not even share a RCD!)
(not to mention feeding a lighting circuit wired in 1 or 1.5mm^2 T&E
from combined nominal current rating on a pair of MCBs that could be
If you want to do something like that, then you would be better with an