Switched live for bathroom extractor fan

[drives]

Hi all,

Just wanted to check I understand the above correctly before potentially diy ing.

I currently have a bathroom extractor fan connected to an isolator switch. No switched live, so the current model I have is permanently on (If the isolator switch is on obviously). It’s a DMEV one with a pir sensor.

This is my second fan I’ve tried; first one was a humidistat which didn’t really work correctly and the pir one is also problematic. Thus I’m now thinking just a straightforward timer model with switched live is probably best- so boost mode being triggered by the light switch.

To create a switched live do I simply connect some single core (?) cable to the bathroom ceiling light, and run this to the switched live terminal on the fan? Above is some eaves space so this should be relatively straightforward.

Thanks

 

[Sureitsoff?]

Better to replace the twin and earth with three core and eartn

 

[drives]

Better to replace the twin and earth with three core and eartn

Thanks. What would the benefits of that be versus above?

 

[EFLImpudence]

Well, you would have to run the single core ideally from light to isolator to fan, so you might as well redo it all properly with 3c+E.

 

[Murdochcat]

Thanks. What would the benefits of that be versus above?

Doing it properly.

Your suggestion needs a neutral and earth ideally

 

[SFK]

create a switched live do I simply connect some single core (?) cable to the bathroom ceiling light, and run this to the switched live terminal on the fan?

Talking as a diyer...

The negative of this is that when you (or next owner) uses isolation switch, they will isolate the permanent live but not the switched live. Using isolation switch might lead to expectation that all powered off when not, and this might shock you/them if they do not properly test.

Thanks. What would the benefits of that be versus above?

The advantage of using a three core and earth from light switch to fan is that all wires from one source, and easier to see route of wires, making it generally safer.

Also in my opinion better to put three core and earth wire through a fan isolator switch if possible, but not essential regulation wise to do this.

SFK

 

[drives]

Thanks all for your help. That makes sense. I will see if I can access the wiring to run it all through the isolator switch as suggested.

 

[ebee]

Depending upon location siting, it might be easier to run a T & E from fan to the switch. That is wire your perm L the Existing permanent L in the fan to one pole of that switch and the switched L to the other pole.
That way any L to the fan is controlled by the isolator and the switch merely connects the SW L to L to get the fan to run initially.
Providing of course that the run is easy and safe and compliant, you could even put it on the fan housing itself , yet again if it would be safe and compliant.

 

[drives]

Depending upon location siting, it might be easier to run a T & E from fan to the switch. That is wire your perm L the Existing permanent L in the fan to one pole of that switch and the switched L to the other pole.
That way any L to the fan is controlled by the isolator and the switch merely connects the SW L to L to get the fan to run initially.
Providing of course that the run is easy and safe and compliant, you could even put it on the fan housing itself , yet again if it would be safe and compliant.

Might be missing something but how would the switched live be triggered by the light switch? Basically the fan I intend to use is a dmev that trickles constantly (when isolator switch is on) but boosts when light is turned on, then over runs for a set period of time.

 

[ebee]

the light switch would become the switched live if that was possible

 

[SFK]

The ceiling rose in the bathroom typically (but not always) has a Live, Neutral and Switched Live.

it does the switched live by having a 2 core and earth wire that goes from the ceiling rose to the light switch carrying the live and the returning switched live.

Lighting Ceiling Rose Wiring

Diagram of a UK lighting circuit using a ceiling rose and wiring explanation

flameport.com

Sfk

 

[drives]

This is what I have currently. Two gang light switch controlling shower room ceiling light and hallway- door is the shower room.

Isolator switch in shower room above door (this is more than 60cm away from cubicle), and fan directly above shower (over 225cm from floor level. It is a 240v one).

The last photo shows cables running directly above, which is a loft room currently being redecorated so can easily access. The white cable is the foreground will be running to the isolator switch (the hole where this goes down, is directly above the switch. Not sure where this will likely be running from where it disappears out of view to the right?) and I can just about see the cable going to the extractor fan- this is all twin and earth cable.

Happy to call an electrician if I need to but equally if something is easily do-able I would like to tackle it myself

 

[drives]

Taking on board all the above advice (or trying to), if I leave the permanent live wiring in place but then run switched live cabling from the ceiling rose, to isolator switch (it's a three pole one, with LI and L2 in and out), then run triple and earth to the fan?

 

[EFLImpudence]

Taking on board all the above advice (or trying to), if I leave the permanent live wiring in place but then run switched live cabling from the ceiling rose, to isolator switch (it's a three pole one, with LI and L2 in and out), then run triple and earth to the fan?

Yes, but if you are able to do that then why not replace the rose to isolator cable with 3c+E as well?

 

[333rocky333]

Taking on board all the above advice (or trying to), if I leave the permanent live wiring in place but then run switched live cabling from the ceiling rose, to isolator switch (it's a three pole one, with LI and L2 in and out), then run triple and earth to the fan?

What cable was you planning to use for that