Exactor fan advice much appreciated...

abone · Aug 3, 2014

Hi sorry posting this here as DIY thread is locked..

I am installing a new extractor fan in our bathroom (in Scotland).

It is a timer and humidistat fan and ideally I would like the fan to be able to run on even when the light is off, so it needs a live, a switched live and a neutral.

The light wiring is quite old and only has three wires at the fitting, switched live, neutral and earth.

It is not possible to get access to the permanent live of the lighting circuit without major demolition.

My question is, can I wire up the extractor fan using a live and neutral from a socket ring circuit (which is easily accessible in the loft space) and take the switched live from the lighting circuit?

I have set it up this way and it works, but not sure if this would be frowned on or is unsafe. If it is unsafe would love to understand why.

Many thanks!

Richard Burns · Aug 3, 2014

It will work but in the case of a fault then current can flow down either circuit reducing the chance of a circuit disconnecting and saving your life.
Also if someone were to isolate the sockets and expect them to be dead then someone switching on the light would power the socket circuit and could kill the person working on the sockets.
Also if you have RCD protection and the circuits are on different RCDs then the RCD would trip instantly.

It is very common for there to be a permanent line for the lighting in the loft space, the cable that is going to your light switch in you bathroom has a permanent line and switched line, it would be far better to take the supply from there.

Darkwood · Aug 3, 2014

Can we also ensure you have selected the correct fan for the location ie its is in the correct zone for 230v use?

The instructions may specify a 3amp fuse for protection so the lighting may need to be fused down at the bathroom.

RCD protection?... as you are making an addition to an existing circuit and it needs to comply to modern regulations regardless of the existing install you are linking it to so can we clarify you have factored this in too?

All of a sudden a simple fan install may becomes an expensive job because you were unaware of regulations to meet if this is the case.