Wiring a bathroom fan with shower cable.

[martii]

I am hoping to commission an electrician to install an extractor fan (operated by humidistat sensor only, I don't want it to come on with the lights) and a mirror with lights in our bathroom.

As we are going to change from the existing electric shower to a shower run off a combi boiler I will be asking them to decommission the electric shower as well.

The existing electric shower was installed by an electrician about 15 tears ago.
It has its own 45 amp fuse in the consumer unit and a very thick grey cable runs from the consumer unit to an isolation switch outside the bathroom door then under the floor to the shower.

Will they be able to use that cable/isolation switch for wiring either the extractor fan or mirror with lights or both.
If yes then I could crack on with replacing floor boards over the bank holiday (hurray!), I would like not to have to remove them again if the existing cable has to go and new ones put in.
Thanks in advance for any help.

 

[endecotp]

Normally those items would be connected to the lighting circuit. Is that difficult in your case?
In principle the shower circuit could be repurposed, if necessary, but that would be less conventional.

 

[martii]

Thanks for your response endecotp. It would be difficult to use the light circuit as the loft space above is extremely tight and although I have stripped the wall back to brick I have, so far, managed to keep the ceiling intact and would like to keep it that way. I'm fairly handy with pipework, carpentry etc but know very little about electricity and have a couple of days off work so would like to get some other things done. I did get a number for a spark from a friend but can't contact him until Tuesday. Do you think it would be expensive to repurpose the shower circuit?

 

[kai]

One way is to get a small two way consumer unit with a 63amp RCD, install that outside the bathroom door, and run the fan and mirror from that instead, Fit a B6 breaker for both the fan and mirrors.

 

[endecotp]

One way is to get a small two way consumer unit with a 63amp RCD, install that outside the bathroom door, and run the fan and mirror from that instead, Fit a B6 breaker for both the fan and mirrors.

Why would he do that rather than just replace the current shower MCB with a 6A one?

 

[ban-all-sheds]

I will be asking them to decommission the electric shower as well.

I would advise keeping it as a backup. If your combi should break you'll have no hot water anywhere, and if it breaks at a busy time of year you might have none for several days.

 

[Taylortwocities]

Why would he do that rather than just replace the current shower MCB with a 6A one?

Maybe because kai has spotted they have a special offer for Wylex ones in Wickes this weekend

Martii, the new electrical items in the bathroom should be RCD protected. Does the old shower circuit have RCD protection? If so, endecotp's suggestion to replace the 45A MCB with a 6amp one is fine. If not, you could use a 6amp RCBO.

 

[EFLImpudence]

It would be difficult to use the light circuit as the loft space above is extremely tight and although I have stripped the wall back to brick I have, so far, managed to keep the ceiling intact and would like to keep it that way.

I am having trouble seeing the difference, as far as the ceiling is concerned, between either method.

 

[martii]

Thanks for all the advice everybody.

TTC, with regards to an existing RCD I really couldn't say. The only type of RCD I'm familiar with is a plug in one for when I'm using power tools. Would that be located locally to the bathroom or be a part of the consumer unit? Would the spark who installed the shower not have included that as part of the job?

Ban all sheds, would love to have the space to keep the Leci shower as backup but no can do. Will just have to keep fingers crossed re the boiler and I have it serviced once a year.

EFL, does that mean the cable has to come from above through the ceiling from the loft space to conform to regulations? Presently it comes up from the floor and up the wall.

 

[EFLImpudence]

EFL, does that mean the cable has to come from above through the ceiling from the loft space to conform to regulations? Presently it comes up from the floor and up the wall.

The lighting circuit connection would come down the wall from above but it does not have to affect the ceiling.

 

[sparkwright]

Usually it's easier just to wire into the lighting circuit.

Most electricians may find a way to fish a cable in place despite the tight loft space.

 

[endecotp]

with regards to an existing RCD I really couldn't say

Post a photo of your consumer unit ("fuse box").

 

[martii]

sparkwright, The way the roof timbers have been formed mean that you can only physically get to within about 4 feet of the wall I want the fan and mirror to go on, the wall opposite the door, and the ceiling curves down so even if somebody could squeeze through the gaps in the timbers they would only have lath and plaster to support them.
If it does go on the lighting circuit where would isolation switch be? There are two outside bathroom door already, one of which is for the current shower but the other just seems to be dormant. If lighting circuit is used I am guessing cable would have to be run down the wall outside the bathroom and go into one of the existing isolation switches as I don't suppose it could be in a bathroom 2.5mtrs square?
Would really love to avoid having any cable runs visible outside the bathroom and certainly don't want anyone else chasing walls. I'm making enough mess here on my own without anybody else starting

 

[martii]

 

[endecotp]

You don't seem to have any RCD protection. This will need to be resolved, irrespective of how the wiring is done.
The most obvious solution will be to replace the entire consumer unit. Someone else might know more about that particular box and if/how it can be upgraded.