many factors have to be taken into consideratiom when selecting the correct cable size.

First thing to consider is that the circuit within the bathroom must be protected by a residual current device at the consumer unit end.

It's unlikely, given that the original shower being only 5kw will have a cable of suitable size to accomodate a modern shower, being typicall around 8.4 Kw

A correct calculation has to made by an electrician, or other person with the kowledge. Factors effecting cable size are :

Method of installation, eg buried in wall, clipped to surface, enclosed in trunking

Type of protective device, (however this has to be RCD or MCBO)

Whether the cable is covered in any thermal insulation, eg firba glass insulation.

Volt drop also must be considerd, eg the longer the run from supply to appliance and the smaller the cable, the higher the volt drop will be. Thos has to be calculated and fall within certain limits.

As to the cost and disturbance, I am sure any competent electiican will do a nice clean job for you at a reasonable rate.

Try posting job on this site.

Only accept quotes from part P registered installers who can self certify the work, otherwise you will have to inform building control yourself and pay for the job to be inspected.

Good luck

Kind regards,

Adrian Hagger

you could have a 10.5kw shower installed but not on the same supply cable this would need to be uprated to a 10.0mm supply protected by a 50a mcb also rcd protected. Ideally should also look into suplimentary bonding.The mess depends on the route to be taken from distribution board to shower and/or whether you are happy to run cable in trunking or totally concealed. As to cost this also depends on distance between distribution board and shower/ ease of route/your exsisting distribution board (can it facilitate mcb to supply shower and is it rcd protected). You really need someone to look at what you already have installed to put a price on what needs to be fitted. A lot to take in but hope it helps, kevinkan. P.S dont forget the bathroom/shower room is covered by part p regulations and a certificate is required for these works.

Hi there,
It really all depends on the current installation you have.
It all depends on cable length from the consumer unit, what type of walls you have and if there is any type of insulation involved. You also require and RCD unit which will trip out in at least 30ms which you may already have if you have a new type of consumer unit.
Going off the old installations then you are probably running 6mm cable.
This will need to be upgraded to at least 10mm cable if you would like a more powerful electric shower, which will take it up to 11kw.
Then you will have to upgrade the fuse rating in the consumer unit to at least 45amp from your 32amp.

The rating of the fuse can be changed,but the deciding factor is the cable size, to install a higher rated shower the cable would have to be a 6mm twin+earth this would support a 8.5kw depending how far this is from the fuse box, a 10mm twin+earth would have to be installed for anything higher.To replace the cable depends on the route the cable takes ,it is likely that floorboards will have to be lifted-walls chased or cable surface mounted in plastic trunking . which ever method is employed some degree of mess/disturbance would be encountered.A true cost for this can only be given by an electrician after a site visit,hope this helps,Terry