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6mm vs 10mm cable for electric shower

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gst300

from United Kingdom

Joined: 28 Mar 2009
Posts: 8
Location: United Kingdom

PostPosted: Wed Mar 16, 2011 10:36 pm Reply with quote

I am replacing a 9kw electric shower with a 10.8kw - or I was until I was told I need to replace the existing 6mm cable with 10mm cable. Is this necessary? What are the consequences if I don't? If it is necessary then it is beyond my capabilities so should I then pay someone to do it or buy another 9kw shower?

All advise greatly appreciated

PS: I am a single mum on a tight budget so the cheapest solution is the best one for me
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onlyfitidealboilers

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PostPosted: Wed Mar 16, 2011 10:43 pm Reply with quote

the shower could draw a lot of electric and the cable may
burn out due to lenth of run etc will req 10mm tho
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gst300 (17 Mar 2011)
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seco services

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PostPosted: Wed Mar 16, 2011 10:53 pm Reply with quote

gst300 wrote:

PS: I am a single mum on a tight budget so the cheapest solution is the best one for me


is it in my eyes the safest solution is the best one.
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1john

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PostPosted: Thu Mar 17, 2011 8:35 am Reply with quote

The 10,8kw shower wont work on the circuit as it is, if it's constucted safely. It will blow the fuse every time you switch it on. You need to replace like for like if you want to keep the job price to a minimum.

Seco services comment is very very true. You need a safe competent job by a tradesman who will test this work is electrically safe. Not a cheap job. Pop in the electricial forum and read the 'so sad' thread icon_sad.gif
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gst300 (17 Mar 2011)
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gst300

from United Kingdom

Joined: 28 Mar 2009
Posts: 8
Location: United Kingdom

PostPosted: Thu Mar 17, 2011 2:30 pm Reply with quote

Thanks guys. I suppos that's pretty much what I expected to hear icon_sad.gif. Think my cheapest option is to buy another 9kw shower, and avoid the rewiring bit.

Thanks again for the advice
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JohnD

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PostPosted: Thu Mar 17, 2011 2:59 pm Reply with quote

You haven't got a combi boiler have you? if you have a cylinder, where is it, and the cold tank (distance and height) in relation to the shower?
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gst300

from United Kingdom

Joined: 28 Mar 2009
Posts: 8
Location: United Kingdom

PostPosted: Thu Mar 17, 2011 3:10 pm Reply with quote

No combi boiler. Cold tank in loft - above shower about 6-7metres away. Have had no probs since I moved in (4 years ish) until 2 months ago when shower stopped working and is leaking water. Have now been given a brand new 10.8kw shower - same make, so minimal fuss regarding installation (or so I thought!)

What am I losing by buying a smaller (and cheaper) 7 or 8 kw shower?
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JohnD

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PostPosted: Thu Mar 17, 2011 3:19 pm Reply with quote

less hot water from a less powerful shower (or the same amount of water but not as hot)

electric showers are quite weedy, especially in winter when the incoming water is colder.
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ajrobb

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PostPosted: Thu Mar 17, 2011 3:28 pm Reply with quote

I suggest you check the rating of the fuse or circuit breaker for the shower in your consumer unit (fuse box).
Assuming winter water temperature of 5C and shower temperature of 38C:
32 A = 7.6 kW (3.4 litre/min)
40 A = 9.6 kW (4.2 litre/min)
45 A = 10.8 kW (4.8 litre/min)


Last edited by ajrobb on Thu Mar 17, 2011 3:32 pm, edited 1 time in total
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gst300

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PostPosted: Thu Mar 17, 2011 3:32 pm Reply with quote

Thanks for that. Think I will get new 9kw - can live with weedy I suppose, but maybe not weedier icon_smile.gif
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1john

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PostPosted: Thu Mar 17, 2011 5:05 pm Reply with quote

The pressure releive valve may have gone on the shower and you may be able to get a replacment from the shower doctor website which will be cheaper than buying a new shower.
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PrenticeBoyofDerry

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PostPosted: Thu Mar 17, 2011 5:07 pm Reply with quote

This will depend on the length of run to calculate voltage drop and the method it is installed.
6mm Twin and earth can carry 47A if clipped direct (ref method C)
if the the length of the run is less than 33.5 Metres, the voltaged dropped is within the permitted range.
10.8Kw/230V
=46.96A
It's borderline but you don't need to upgrade your cable, providing it's clipped direct, no thermal insulation, run is less than 33.5M


Last edited by PrenticeBoyofDerry on Thu Mar 17, 2011 8:57 pm, edited 1 time in total
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simond

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PostPosted: Thu Mar 17, 2011 7:38 pm Reply with quote

But the 10.8Kw shower should be fused/protected at 50A.

And then the protection is beyond the current capacity of the cable, and that is without any external factors applied.

I agree it is borderline, but in the wrong direction. Strictly speaking, the job can''t be done.
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PrenticeBoyofDerry

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PostPosted: Thu Mar 17, 2011 8:59 pm Reply with quote

Again borderline but by putting a 45A protective device on the circuit, it would be possible.
I don't think the overload that will be applied for the period of a shower would be too, disruptive.
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PEDANTICVINDICTIVEMAN

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PostPosted: Thu Mar 17, 2011 10:30 pm Reply with quote

I "once" ran a 6mm cable 21 meters, which I was told by an electrician who worked it out on his calculator was the max for an 8.5Kw shower and ok, never again, the cable got shiny and rather hot after 20 minutes of use icon_cry.gif
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