extractor fan wiring

[urchaidh]

I'm fitting a new extractor fan in my kithen. I plan to have a switched FCU to create a spur from the ring main to provide the power. The fan will be wired directly or perhaps through a fixed appliance connector, no plug/socket.

I believe (manufacturer's info) that the fan must have an isolator switch, which in my case would be the dual pole switch in FCU. However, there will be a second control switch (swicthed live) for the fan so, in terms of day to day operation, the switch on the FCU will be redundant. Is it always required? I'd guess that any permanently connected kit needs an isolator, but I though I'd ask.

Next, possibly daft question. I'll have cable (all 1.5mm2 twin & earth) running from the FCU to the fan and then, to provide the control, a second cable back from the fan to a standard single pole switch to provide control (swicthed live). The FCU and switch will be in the same double wall box so a single run of three core and earth would do the same job with a single cable run. I can't imagine that it would be allowed, but is it?

Last question. Is there any good reason why I shouldn't use the spur, on the fused side of the FCU, to power a new wall light while I'm in there?

Thanks for the help.

I used to be interested in all forms of agricultural machinery but I just lost interest, I guess I'm now an...

[Owain]

OK

Why not just use the switch on the FCU?

Yes, for mechanical maintenance.

'dual' wall box will mount two single accessories

I don't know why it wouldn't be allowed, but why do you need an FCU and a switch? Can't you just use the switch on the FCU to turn the fan on and off? Or do you need a timer over-run like on a bathroom fan?

You can if you want, although obviously not if your'e using the FCU switch for the fan operation.

You could use a gridswitch with a fuse and two switches, which might be neater than two separate single accessories.

Owain

[urchaidh]

Fair point. The main reason would be so as not to have to switch the whole spur to control the fan, perhaps to use it to run some lights as well. I tend to think too far a head and see feel the spur *might* be useful in the future and I thought a wall light would be good, easpecially since I'm running new cable anyway.

Sorry, meant dual rather than double. One S/FCU and one single pole switch.

Well I can see that it would be perfectly safe (for me), but so much about the wiring regulations is about sticking to conventions so the the next poor sucker who looks at the wiring will know what's going on. I couldn't find a reference to any convention on using 3C/E for live, neutral and switched live.

Live is straightforward. Would you then chose one conductor (which?) for switched earth and label with red tape, and use the third, unmarked, for neutral? Or label the neutral with black? (Still on old colours).

Sorry if I'm being over cautious or pedantic, the previous owner was a very bad bodger and sorting out the electrics has been a bit of a challenge. I've been trying to do it 'by the book', but the book is hard going.

That looks neat. Do you know, are the mounting boxes the same size as the 'standard' metal wall boxes? Can these be retrofitted?

Thanks for the reply, very helpful.

[Martin Angove]

Plenty of uses of this, particularly for fans where you'll often take the supply from (say) a bathroom light and have L/SL/N/E, not forgetting to run the L/SL/N through a 3-pole switch.

^^^^^

I'm a little confused why your kitchen fan needs both live *and* switched live. Unless you are making use of an overrun facility, forget the permanent live and just use switched, in which case you can use T&E.

If you do need both L and SL then, silly as it seems, I believe you must run it through a 3-pole isolator as otherwise you'd have to remember to switch both the SFU switch and the single-pole switch off.

As for using 3&E RYB cable, yes you'd normally use R=permanent live, Y=switched live (sleeved red) and B=neutral (sleeved black).

HTH

Hwyl!

M.

[Owain]

Up to 3 or 4 'modules', same as a standard box. You can get them up to

16 or 20 modules. You have to order the box, frame to hold the switches, switches, and faceplate separately. I think MK will have the widest range. Most electrical wholesalers will probably know somewhere locally you can get the faceplates engraved.

Owain