I wish to install an extractor fan in our bathroom.

The lighting circuit is switched by a pull cord dimmer switch so i can’t just wire the fan directly into that circuit.

I bought a 240v relay from maplins and my plan is to wire the lighting circuit through the coil side and the fan form an existing supply (for an un-used TV distribution amp) in the loft via a pull cord isolation switch to the ‘open normal’ side of the relay.

will this be ok or am i going to blow the house up?

the supply has it’s own 5 Amp breaker on the fuse board.

I know that i could just wire the fan to the lighting circuit but despite being a non inductive load i’d rather avoid it as i don’t know how the (somewhat expensive) dimmer switch will react

No, you should not run it off a lighting circuit. You plan sounds too complicated – why the need for a relay on a mains supply?
Presumably, you are talking about a dedicated extractor fan, rather than one enclosed in a spotlight?
You should run it off either a spur from a ring main, or, preferably, a direct run, dedicated line from the fusebox/consumer unit. All new fitments in bathrooms should now be RCD protected.
It is Part P certifiable, but I’m not getting into that bollocks – some will say you need a certificate for taking a dump soon.
Alan.

Erm, why a relay exactly ?

circuit but despite being a non inductive load

A fan has a motor in it, a motor is inductive….

Sounds like you need to pay a sparky to do it to me, you are going down the wrong route with it at the moment, you dont want to be sticking relays into your loft space for no good reason.

Ive no idea why it shouldnt be run of a lighting circuit??

What you are intending to do does sound a bit complicated tho. What about a humidity activated fan? or one with a pir sensor to activate it? there may be a good reason why not??

Living north of the border I have no real knowledge of the part P overkill but one way to get round it and still comply with the building regs would be to install an in-line fan with only the vent being in the bathroom. That would need you to have an attic or void, but it would let you install a local means of isolation with ease.

mrmichaelwright, just a thought making these kind of chanches to a ringmain in you house and either not getting it installed by or certified by a part P acredited electrician can invalidate your house insurance should you have an accident, do you really want to take that chance?

i want it to switch automatically, so i can’t just run it off a spur, the relay gets round the fact that as mr tragically states i can’t run the motor off the dimmer switch (i confused myself there), hence the relay.

It’s an in line fan in the loft and there is a light in the internal fixture which will be run off the lighting circuit

i’ve already bought the fan so don’t want to buy a humidity/pir one

Part P surely applies to installations requiring a new supply, this utilises an existing one

I’m not paying a sparky to come and inspect/install the wiring for a £20 fan.

We have one that runs directly off the lighting circuit (so it comes on automatically when the light is switched on). Doesn’t have separate fuse or anything and wouldn’t pass regs I am sure.

But I fitted it before the regs came in.

No, honest, I did. Like the day before. Probably.

(And it was a doddle to fit – the hardest bit was routing the ducting out of the room, through the cavity and under the eaves – ripped my hands to shreds).

no part p applies to any changes to a ringmain

and either not getting it installed by or certified by a part P acredited electrician can invalidate your house insurance should you have an accident, do you really want to take that chance?

But work done before the regs came in doesn’t need to be retrospectively passed.

OH and MF the i fitted it b4 wont work now a days as modern cable is date stamped with manufacture date

mastiles – luckily we’ve just had our soffits done so the nice workmen did that for me as they had to lift the first two rows of tiles anyway, that’s why it’s taken so long for me to install it (i bought the fan years ago), didn’t fancy that part of the process. there be spiders in them there rafters 😕

I think if its an inline fan in the loft its outside of any special areas that normally complicate things in the bathroom.

You dont and shouldnt need a relay, you are barking up the wrong tree with that one, its all a bit too vague to comment in any detail TBH, and for that reason i am out….

hustler – where does the ring main end? The fan will use a standard plug with a 3A fuse into an existing supply, the lighting part will just be another connection into the junction box already installed, i’m not really worried about regs, our lighing circuits are un-earthed anyway an i doubt the current wiring is up to code

i’m sorry, what is vague? you want me too draw a flippin circuit diagram? I want to switch on a fan using a lighting supply from a dimmer switch, what other way is there to do this without using a relay?

correct me if Im wrong MrM, but are you wanting the fan to come on when the lights come on (possibly with an over run after the lights go out?) and you dont want to use the dimmed output from the existing light switch which is a dimmer?

OH and MF the i fitted it b4 wont work now a days as modern cable is date stamped with manufacture date

But if the cable isn’t stamped (mine wasn’t as it had been sat in my dad’s garage for years) it’s not a problem. Granted it could be if you buy it new.

Then again, if dodgy wiring has burnt your house down….

sorry just saw your reply

that’s it turin

If your wanting to use the kit you have already bought I dont think that there is any other way, what your proposing should work. It might be a good idea to install a double pole switch or switched spur unit in the loft beside the realy, so you can make sure that the fan can be isolated if yo have to work on it or the realy

what your proposing should work

🙄 Brilliant, internet electrician quote of the century that one….

that’s the idea of the isolating pull switch (pretty sure that the type used for shower isolation is double pole) with a short cord hidden away in the corner, also means i can switch the fan off manually if i want a nice quiet relaxing bath (hence the dimmer switch in the first place, it plays Barry White CDs when it reaches minimum dimmage 😉 )

tragically – you have failed to provide adequate reason as to why this won’t work other than waving a Part P document in my face. If i was a fool and did a shitty job of the installation using bell wire twisted together with paper clips and selotape for insulation then i’d pretty much deserve for my house to catch fire, that’s what darwin awards are for. I am not however (that much) of a fool, i work with electricity every day and short of actually wiring it up (although i used to) am competent enough to spot when i won’t be plugging my stuff into a dodgy 3 phase supply and test it with a meter. I’ve yet to blow anybody up or electrocute anybody* in 10 years. I know my limits and a 150W fan in a loft connected to a 5A supply is within them.

*well maybe a little bit, we did give the american women’s softball pitcher a bit of a tingle in Beijing but i maintain that it is not my fault that the Chinese have yet to discover the ‘Earth’

I thought there’s usually a permanent live to the fan which is independent of the dimmer. The switch live is potentially dimmed but since its only a momentary switch maybe the fan wont mind?

Stoner – it’s a very basic fan with no switch live, hence the relay

tightwad. get a nice silent, switched one with a run off timer 😉 Ive just put one in.

where’s the fun in that 🙂

MrM

The only thing I would be concerned about having the isolation pull cord is in the unlikely event you are working on it in the loft and somebody “de-isolates” the circuit then it could get a bit tingly. ideally there should be some means of mechanically locking the isolating switch in the safe position, unless its close enough to the load that it can be watched. They get round that on the shower circuit by assuming that the circuit only supplies the one piece of equipment, plus it should be in view. Maybe install teh switch in the loft as well as the pull switch?

i can isolate the supply in the loft by unplugging it from the socket (supplied for the TV distro)

plus if the wife wants to kill me i’m sure she’d be more inventive than that 😉

Fair point but could the input side to the relay be energised?

I might have picked you up wrong, but if you are going to install another pull cord switch (the isolator) then would it not be easier to come of the live side of the light switch to the new pull cord switch and control the fan directly from that switch?

That would mean that you would have to use 2 pull cords to have the fan and the light on and may not be what you wanting. It would let you have the fan on without the light?

not trying to confuse matters but it woudl mean no need for the relay

I read I see I say nothing.
Actually
I’m probably wrong but don’t you need an Isolator outside the bathroom if you are going to install a fan? From which I gather you can get your permanent live and neutral.
A timed fan for £18* (here you need a three core cable)
A pull cord fan for £12 (here you don’t need a three core cable)
Your lighting circuits have no earth, that might warrant a moment of consideration and getting it properly done. Just saying. Well you did ask.
*here

other than waving a Part P

Do keep up old chap, i do believe that was someone else that waved part P, not me.

i work with electricity every day and short of actually wiring it up (although i used to) am competent enough to spot when i won’t be plugging my stuff into a dodgy 3 phase supply and test it with a meter. I’ve yet to blow anybody up or electrocute anybody* in 10 years. I know my limits and a 150W fan in a loft connected to a 5A supply is within them.

I bow to your superior knowledge in all matters electrical, best get in the loft and sort it then rather than asking strangers for advice that “should work”….

well basic knowledge mr MW the ring main starts at your fuse board and surprisingly enough ends at the fuse board, the word ‘ring’ is supposed to give this away, if you dont even know this you really shouldn’t be touching the electrics…..