Bathroom extractor fans and lights

14 Mar 2007
Reaction score
United Kingdom
I will be having two (inline) extractor fans in the bathroom (actually positioned in the loft) , one for the shower and one for the rest of the bathroom. The power consumption for them will be 28 and 38 watts respectively.

The shower fan will also come on with its own Zone 1 light (50w). The bathroom fan will also come on with Zone 2 bathroom lights (Max 300w) but each fan will have their own isolation switch.

I seem to think that I have read that these circuits should be protected by RCD. The slight problem being that the present bathroom light circuit is on the non RCD side of the CPU. Connecting to the CPU would not be favourable due to logistics.

I do have a ring main in the loft that could easily be connected to. Would it be feasible to install two RCD FCU's for each fan circuit or even have just one for both fans and lights?

Or is there another way (that does not involve routing cable all the way to the CPU)?

Thank you
Sponsored Links
take the wiring to the bathroom lights from the normal lighting circuit, but route it through an RCD FCU with a 3A or 5A fuse in it.

Preferably place this above the bathroom door, outside the bathroom, so that it will not easily be switched off by mistake, but is visible and easily accessible when required for maintenance.
Under the 17th edition of the wiring regs, all circuits in a bathroom have to be RCD protected.

You're not obliged to RCD protect any existing fittings etc in the bathroom, but anything new you add must be. You have two ways of doing this, either as you say put an FCU on the ring main (an RCD protected one if the circuit is not already RCD protected), or just put an RCD FCU in to protect the lights in the bathroom, which is probably the easiest solution for the situation you describe...
or depending on age and type of your CU, you could have an RCBO fitted in place of the MCB for the upstairs lights. Then all the lights on that circuit will be RCD protected.

RCBOs are great!
Sponsored Links
No obvious downsides - it's less risk if you drill through a cable / touch a conductor etc, as the RCD 'should' cut the circuit out before enough current runs through you to electrocute you etc.

The only potential issue is if you have a slightly dodgy fitting anywhere with a bit of earth leakage, the RCD may trip. Generally this only happens with old appliances (washing machines etc), it's unlikely a light fitting would have leakage (at least not the sort of fittings used in domestic properties)...
yes, something like that.

The one shown might or might not be suitable for your CU depending on how old it is and if the design has changed.

The one shown is a "C" curve which is slower to trip on overload than the "B" curve ones normally used in domestic installations. For some reason some manufacturers do not offer "B" curve RCBOs yet. The work is notifiable and a suitably qualified electrician would be able to test the circuit and calculate if a "C" curve is permitted in your case.
Thanks for all the advice. Presumably if I take a spare MCB down to a local electrical suppliers they can get the right RCBO for me.

Also am I right in thinking that the fans don't have to be RCD protected because they are in the loft?

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links