Replace Existing Bath Fan with Timer fan

[lordwoody]

I have an old basic extractor fan in my bathroom which I would like to replace with a timer fan that needs a switched live feed.

The problem I have is that the current wiring is just 3 core L N E.

Would this set up work (see below) if I just took the single switched live wire from the ceiling rose and added to my existing wiring?

 

[EFLImpudence]

Your present fan has a switched live. Does it work with the light or independently?
The timer one will need a permanent live.

Same difference but if you can supply a new single cable to the fan position then you can run a four-core cable.
Your diagram likely does not represent the present set-up - no switch.

 

[Taylortwocities]

The isolator is meant so you can completely switch off (isolate) the fan. If you do as you propose then there will still be a potential live connection (the switched live) even when the "isolator" is off. May need a different arrangement.

A couple of questions..

Is the fused isolator outside the bathroom on the same circuit as the light?
What is the junction box for, why is it even there?

 

[lordwoody]

The diagram is what I am proposing with a new timer fan.

The present fan does not have a Switched Live and currently works independently from the light which is why I want to replace with a timer fan to reduce condensation.

Dont know why there is a juction box, I am guessing it was for a previous wall mounted heater and that someone added the fan later on and removed the heater and used the box for the fan!

No the fused isolator is not connected to the light unfortunately.

The isolator is meant so you can completely switch off (isolate) the fan. If you do as you propose then there will still be a potential live connection (the switched live) even when the "isolator" is off.

But the switched live is only live if the light is on, would that be illegal in a rented property?

 

[Taylortwocities]

So, you cannot do what you propose.

the fused isolator is not connected to the light

If the fused isolator originates from some other circuit then it will

1. Will not work - the safety breaker will trip every time the light is switched on
2. Be exceedingly dangerous for any unsuspecting future fan maintenance person who will turn off the isolator, turn the light on (so they can see what they are doing) and then put their fingers on the live switched live conductor.

All off the conductors for the fan must come from the same origin and through the same isolator. For a fan, the islotaor is normally a three-pole switch that isolates the permanent live, switched live and the neutral.

EDIT
It needs to be wired as shown in the WIKI
//www.diynot.com/wiki/Electrics:fan

 

[EFLImpudence]

The present fan does not have a Switched Live

Of course it does otherwise it would never stop.

I want to replace with a timer fan to reduce condensation.

Fans do not reduce condensation.

 

[JohnD]

Fans do not reduce condensation.

eh?

 

[Taylortwocities]

The present fan does not have a Switched Live

Of course it does otherwise it would never stop.

I THINK what he has is a non-timer fan that is switch on and off from the fused isolator that is outside the bathroom. That would tie up with the JB inside where (perhaps) a wall heater used to be.


So the fan has no connection to the lighting circuit whatsoever.

The whole thing needs wiring properly, or left as it is.

 

[EFLImpudence]

The present fan does not have a Switched Live

Of course it does otherwise it would never stop.

I THINK what he has is a non-timer fan that is switch on and off from the fused isolator that is outside the bathroom.

Yes, I know - therefore the fan has a switched live.
The problem is he needs a permanent live as well.

The whole thing needs wiring properly, or left as it is.

It does.

 

[EFLImpudence]

Fans do not reduce condensation.

eh?

If you have a bath with the fan OFF does condensation form on the walls and mirror?

If you have a bath with the fan ON does condensation form on the walls and mirror?

 

[JohnD]

yes, no.

And the window and cistern as well.

 

[lordwoody]

//www.diynot.com/wiki/Electrics:fan

This make it a lot clearer.

I can do this method but instead of a Isolator switch outside I could use a pull chord inside.

Thanks everyone

 

[EFLImpudence]

yes, no.
And the window and cistern as well.

So, you get NO condensation with the fan on?

And you have a window.

Sounds like you don't need a fan at all.

 

[JohnW2]

The present fan does not have a Switched Live

Of course it does otherwise it would never stop.

That's obviously correct, but I think one can understand the confusion. Whilst timer fans usually have terminals marked L, S/L & N, non-timer ones are very often only marked L & N (even though, as you say, the L must be 'switched' somewhere, otherwise the fan would be always on). In other words, they use 'S/L' to refer to a feed which is switched by the light switch.

Kind Regards, John

 

[EFLImpudence]

I refer the honourable gentleman to the OP's diagram.