Fitting new electric shower

[Joolz89]

Hello,

I am after some advice if possible from those in the know. My current shower has just died (Only supplies cold) I would like to replace it but with a higher power unit. The current one is a 7kW unit. The shower is fed from the houses main CU which has a main trip fuse of 100A and the shower feed is connected to a 32A MCB on the RCD side of the CU. The cable runs from the CU through the wall and then runs up the outside wall of the house wall into the attic. It then goes to the ceiling mounted switch in the bathroom and then through the wall and exits into the back of the shower. The cable used throughout is 10mm in width (measured from the one side of the grey sheath to the other) Total length of the cable from CU to shower is approx 9m. Having read the various posts of questions of this nature if I want to fit a 9.5kW unit am I going to have to have the circuit upgraded? Can this be just the change of the MCB in the CU to a 45a rated one and then replace the shower or am I going to need a separate RCBO ? Also is the cable the correct size for a 9.5kW unit or is this going to have to be replaced as well?


Thanks in advance for any advice given.

 

[mikeyd]

If your cable is 6mm2 then it is borderline for a 9KW load (38Amps) even before you start to add in the factors for length and installation method.

So for a 9.5KW shower you need at least 10mm2 cable

Do you really mean it runs up the outside wall of your house? Is it flat (oval) grey twin & earth. If so this shouldn't be used outside.

Just measured a bit of 10mm2 flat T&E and it's 17mm across, so your cable certainly isn't 10mm2. So new cable needed unfortunately.

You have a split load consumer unit so with the new 10mm2 cable you can probably upgrade the MCB. It's a job for a qualified electrician though I'm afraid. You need to check the rating of the ceiling switch too.

 

[Joolz89]

Thanks for the speedy reply appreciated,

Yes the cable runs from the CU which is downstairs in the kitchen cupboard through the wall and up the side of the house and back through the wall to the attic. It is clipped to the outside wall with cable tacks. Next door neighbour has the same setup it was in situ when I moved in. The cable is flat with oval edges, grey in colour twin and earth.

So I need to get a new feed cable fitted of the right capacity and routing and also upgrade the MCB in the CU.

I take it this is all outside of DIY in regards to legalities and part P?

 

[mikeyd]

Grey twin and earth doesn't like been out in the weather. For one thing It's not UV protected so our fierce English sunshine will destroy it.

So I need to get a new feed cable fitted of the right capacity and routing and also upgrade the MCB in the CU.

I take it this is all outside of DIY in regards to legalities and part P?

It's a yes to all There are plenty of electricians out there who would be willing for you to chase the walls and make good after.

 

[Joolz89]

mikeyd,

Thanks for the reply again. I can see why it was routed up the side of the house as internally would require a lot of work chasing walls.

Is there any cable, or anything that it could run in that would allow it to go up the outside wall or am going to have to get cutting grooves lol!

Best starting getting some quotes in, and as you suggest speak to the guy and see if I can do the donkey work then he comes and lays the cable and wires up.

Cheers

Joolz

 

[Steve]

You have a couple of options. If the cable is not susceptible to damage in its current location, then you can run it in plastic conduit which will protect it from UV light.

If you want to go a bit more belt-and-braces, you can use SWA cable, which will provide an earthed metallic layer and is a lot tougher than plastic conduit.

 

[Joolz89]

Steve,

The cable exits the house onto the outside of the wall at about a foot above head height and then runs up the wall vertically, then back into the attic. I can't see how it would get damaged in this location, other than by the elements. The current one must have been there for quite a few years and is fine.

 

[Taylortwocities]

Yes I know it looks fine but electrical installations can stay in place for several decades. Installations have to be designed with this in mind.
As stated above, PVC twin and earth cable is not UV stabilised and is not deisgned for extremes of hot sun and/or freezing conditions. Sooner or later the insulation will break down and the cable will fail.

There's pics on this forum of cables that have suffered this fate.
Its up to you if you decide to ignore the advice given, I think you will not as you have already noted issues re "DIY in regards to legalities and part P?"

 

[Joolz89]

Taylor,

The reason I am posting on here is for advice, and I am not going to ignore it, break the law or invalidate my house insurance.

I would just like to gather together the options available to me for this job so that when I do get an electrician in I am not going to get things done that are not really required. Not saying that all tradesmen are like this but there are the odd one or two, as I found out when I needed my garage roof replacing!

So my final question is, is it possible to route the cable on the exterior wall if it is protected in a condiut and fastened to the wall? Or is this still a no go?

regards

Joolz

 

[DESL]

Just a thought have you thought how your upstairs lighting circuit cable gets to the loft space from the CU?

Bet it's not run on the outside wall.

A competent electrician will be able find the best route for a cable to a shower without resorting to running outside and back in again..

 

[Taylortwocities]

is it possible to route the cable on the exterior wall if it is protected in a condiut and fastened to the wall? Or is this still a no go?

Joolz

Yes, the 10mm cable can be run in the correct sized conduit and fixed to the wall, or a length of 10mm armoured cable could be used similarly fixed.

This is notifiable work, if you do it yourself, or use a registered spark.
Look here: www.competentperson.co.uk for one near you. Good luck!

 

[Joolz89]

Thanks for all the advice, will get an electrician in and see what he suggests and take it from there. Thanks for the link for the competent register the nearest electrician to me came up on the site so will give him a call.

Regards

Joolz