wiring an extractor fan

Hi all,     I bought an extractor fan and have since build it into the wall and now I must wire it up to the light. Is there any pitfalls/ advice to look out for? It's the type that comes on when the light is switched on.
Thanks
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igloo wrote:

It will need a 4 core cable. Earth, live, switched-live and neutral wired to the ceiling rose. Strictly speaking you should wire it through a double pole fused connection unit but many people do not seem to bother with this...
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BillR scribbled :

I always use a triple pole switch which is specifically for fans. You need to isolate the L, N and SL. If you use a double pole fused connection unit then the outgoing load should also feed the light in the same room as the fan so when you isolate it the light cannot be switched on causing the Switched Live to become live at the fan.
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Gary
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Gary wrote:

You're right, it should be a triple pole switch. Big ugly things they are too and they don't seem to match normal light switches...
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BillR wrote:

Oh? I found nice brass ones with fuses that EXACtLY match the light switches.

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The Natural Philosopher wrote:

Fine if you've got brass light switches...
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They're usually a triple light switch, but with a large rocker jammed onto all the actuators.
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Andrew Gabriel

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Andrew Gabriel scribbled :

And normally mounted at high level so an exact match with a light switch will not become an issue.
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I been on few new housing estates round my area and noticed how these installations had been done on new builds.
The light switch and TP fan isolator were mounted adjacent to each other outside the bathroom/ensuite. Some estates also included a 3 amp FCU adjacent to these. If the FCU was fitted, the bathroom light and fan were all wired behind the 3 amp fuse. (The FCU should be fitted if the fan manufactuter's instructions call for it).
Disadvantages of wiring the fan to the light are... You always have to operate the light to get the fan to run, even during the day. At night you always put the light on, so the fan runs, whether you need it to or not.
Mounting the TP isolator in a convenient position gives the option of silencing the fan if it is not required.
BillP.
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Gulp. I'll get an electrician!
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"igloo" wrote | Gulp. I'll get an electrician!
No, you get (assuming it's a timer over run fan) a length of triple-and-earth cable and a triple-pole fan isolator switch (which are readily available in the sheds). (Switch off at the mains first, usual disclaimers etc.)
Take the cable from the light to the isolator switch location and then from the switch to the fan. The switch needs to be out of reach of the bath or shower - google Bathroom Zones for more info.
At the light, terminate red on the Permanent Live (this will probably already have 3 reds on it, 2 for the lighting loop and 1 for the switch feed). Terminate yellow on the Switched Live (this may be a single red for the switch return, or a black with a red sleeve, or just a black, but will connect to one side of the bulb). Treminate the blue on the Neutral (this will probably already have 2 blacks on it for the lighting loop, and connect to the other side of the bulb).
At the switch, just match up the red yellow blue on the supply side of the switch to red yellow blue on the load side.
At the fan, terminate red on L, blue on N, and yellow on the teminal probably marked Trigger.
All earths need green/yellow sleeving and to be connected up even if the fan is double insulated.
Owain
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