Having an electric shower installed.

Postby bluenun » Sun Jan 06, 2008 10:11 am

I have recently moved into a new home and when I pull the isolation cord the red light comes on but the old electric shower is not heating up the water.
I am going to buy a new electric shower to be installed.

Currently the shower is connected to a 10mm cable and a 30 amp fuse.

Can I choose whether I want to have an 8.5 or 9.5kw shower installed?
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Joined: Sun Dec 30, 2007 7:39 pm


Simply Build It

Postby ericmark » Sun Jan 06, 2008 7:02 pm

This seems a repeat of earlier post but I will go through it quickly.
30 Amps is same as 6.9Kw so if the shower is over 6.9Kw it will blow fuse after some time.
Sometimes when a fuse blows a little current milliamps may flow enough to light a neon.
10mm cable can allow up to 57 amps but it is dependent on how long and how it is routed through insulated walls etc all which can reduce its current rating.
Some installations as a whole can't supply all that is required the supply into the house is not really good enough.
So before up-rating and fuse or MCB the whole system has to be checked to see if it can be done.
I expect you could upgrade by just changing the fuse carrier but maybe you can't and only a on site visit by an electrician could say if you can or can't upgrade.
I ripped my electric one out and fitted thermostatic valve and it now comes direct from 27Kw gas boiler give a lot better shower.

Postby kbrownie » Sun Jan 06, 2008 8:48 pm

Hi blunun,
It seems to me that you have low design current to your shower, this current would only allow you to run a maximum 6.9kw.
There are a few calculation that need to be done as regards of length of cable, ambient tempreture, whether the cable runs through insulation, if it is grouped with other cables and by what means it is clipped/fixed. For you to arrive at the correct fuse rating
If you wanted to install a 8.5 or 9.5kw rated shower you would need at least a 45amp fuse that's with all calculations being in your favour.
10mm cable okay, (I believe you can put up to 65amps through 10mm cable as long as all calculation allow)
But if you are having shower fitted it comes under part p of building regs and has to be done by an electrician quaified to that standard.
Hope that the info was of use and remember always to be safe around electrics
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Joined: Mon Mar 05, 2007 9:36 pm

Postby bluenun » Mon Jan 07, 2008 9:10 am

Thank-you both for your replies.

As always it is not as simple as I had first hoped :)

The reason I asked in the first place is because an electrician told me I could choose whatever shower I liked because he looked at the cable supplying the old shower, I asked if the 30amp fuse would restrict my choice and he said "no" I asked him again about the 30 amp fuse on his way out.

I am pleased I aksed here because I certainly want the installation to be safe and relaible (no fuses blowing or tripping out).

I need to get another electrician around and ask for his suggestions.

Last night I looked at the old shower and it is a 7KW shower.
Are 7KW showers still sold these days? The lowest I have seen is an 8.5KW in places like Argos and B&Q.
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Joined: Sun Dec 30, 2007 7:39 pm

Postby kbrownie » Mon Jan 07, 2008 12:59 pm

Hi Bluenun,
yes you can still get 7kw showers, i'm sure triton have one in their range. But don't be despondant it may only be a case of changing the fuse and fuse carrier. (Cost about 10-15 pound for one).
You have 10mm cable already so that should allow (depending on calcs) up to 10.340kw with a 45amp breaker as current protection. Your electrician should know this!
Good Luck
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Joined: Mon Mar 05, 2007 9:36 pm

Postby ericmark » Mon Jan 07, 2008 1:08 pm

If an electrician says you can have any size you like after looking then that is most likely right. When we can't see the house we have to point out what may be a problem. I expect he has realized it is very easy to change the fuse and nothing else will stop it. We as remote electricians would not tell you to change fuse in case there was something you had not told us that would cause a problem.

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