Would all bathroom light circuits have a live and a switched live?

R.O.S.S.I

R.O.S.S.I

R.O.S.S.I

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At some point this week I need to tackle installing an extractor fan in our bathroom as it currently doesn't have one.

The directions state it needs a live, neutral and a switched live feed as it has a timer, from the lighting ring.

I've not had chance to go into the loft and have a poke around the lights yet but just wondering if it will be a straight forward thing to wire in from one of the existing light fittings?
 
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Yup switching live is just a permanently live live, and one live with a switch, then neutral, so 3 wires.

But live wires can come from any live.

You need to put an isolator after your switch and between the device, one that breaks the connection of all 3 wires, otherwise the device will be permanently live even if it's switched off.
 
(personally never click on anonymous tinyurl links)

R.O.S.S.I said:
The directions state it needs a live, neutral and a switched live feed as it has a timer, from the lighting ring.
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exactly - is the switched live circuit in the fan completely (opto) isolated from the fan circuit ... maybe that is mandated in the fan BS conformity ?
otherwise you could compromise earth leakage across two circuits,
if you replaced existing bathroom light switch with a double pole you could create another isolated circuit I guess.
 
Blueball said:
Not the biggest of images but it shows you how to wire things in to create a switched live (because it won't exist in the current wiring unless you have two switches controlling the bathroom light).

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Sad times
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@OP, basically the fan needs a live and neutral (take them from anywhere e.g. yes spur off the existing light fitting as closest). Then the switched live is the "return" live wire from the light switch. The one which also goes to feed the existing bulb.

Think of it as the "signal" wire so the fan knows when the light is turned on or off. But the fan needs a permanent live of its own so it can continue to run on after turning off the light.
 
LuckyBenski said:
Sad times

@OP, basically the fan needs a live and neutral (take them from anywhere e.g. yes spur off the existing light fitting as closest). Then the switched live is the "return" live wire from the light switch. The one which also goes to feed the existing bulb.

Think of it as the "signal" wire so the fan knows when the light is turned on or off. But the fan needs a permanent live of its own so it can continue to run on after turning off the light.
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Link works perfectly!
 
200sols said:
Even though the fan doesn't require an earth you should still run an earth and terminate it in a block at the fan. 3 core and earth cable will be good.
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Yup now you mentioned it mine have an earth wure that terminates I to nothing.

Never quite understood why, I'm guessing maybe it add protection if the wire gets damaged?
 
Thanks for the replies guys.

I'm assuming if i had means to wire it to its own dedicated switch that it would be an even simpler install? I think I may be able to run another cable down from the loft to the existing light switch (and just swap it for a 3 gang switch).
 
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R.O.S.S.I said:
between the fan and light switch
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That! - assuming you have wired it to the light switch and not it's own switch. If you wire to it's own switch then between the fan and that one. All of the ones in our house have the top of the isolator at about the top of the door frame for reasons unknown to me :) Maybe a safety thing?
 
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I think i'll probably wire it to the existing light switch and run it off the timer that way, annoyingly where the cables run down to the existing light switch arent easy to access to run a new cable so will have to make do with the timer.

Just need to go grab some 3 core and earth cable one afternoon and have a bash at it.
 
I found this video a while back which might give you some ideas. I think I might give it a go at some point. Am planning to use the new PIR sensor to turn my dumb bathroom extractor, into one with a timer.

www.youtube.com

How to Change a Bathroom Pull cord for a PIR Sensor | Bathroom PIR Install

In this DIY electrical guide i will show you an easy way to install a PIR sensor in your bathroom. I will show you exactly how to replace a bathroom pullcord...
www.youtube.com www.youtube.com
 
The permanent live and neutral will either be in the light switch or the light fitting. As others have said, you can’t just take a live directly to the fan, it all needs to go through the 3 pole isolator. It’s also not a good idea to take lives from random places, you can make a right mess for the next person. You should really take it from the bathroom light or switch where it’s already wired.

If the permanent live and neutral are in the light switch, you have two sensible options. Disconnect the switched leg and use to to pull through the new 3 core and earth or try and fish up a single double insulated core.

You can probably carefully cut in the back box needed for the 3 pole isolator above the existing switch near the ceiling, that will make the wiring easier.
 
You have no reason to go anywhere near the existing switch, take the Switch live, live and neutral + earth from the existing light fitting and run to new triple pole with 3core and earth, then run to extractor. You can do all this in the loft, you can install the triple pole next to the extractor fan in the loft if you wish.
 
200sols said:
You have no reason to go anywhere near the existing switch, take the Switch live, live and neutral + earth from the existing light fitting and run to new triple pole with 3core and earth, then run to extractor. You can do all this in the loft, you can install the triple pole next to the extractor fan in the loft if you wish.
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If i wanted to run it on its own dedicated on/off switch I would. I was going to replace the 2 gang light switch on the landing with a 3 gang so that I could switch the fan on and off from the landing rather than rely on the timer and existing light switch.

But seeing as access to the existing light switch isn't possible from the loft i'm reverting back to running it as you say, by taking a feed off the existing light in the loft.
 
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