what power shower can I have?

[gucciman]

Our electric shower has packed up and I want to replace it, It's a 7kw unit and the power supply is 6mm cable, what is the max power of shower I can have on the existing cable i.e. can I go up to a 8.5 or 9.5kw?

[AlBags]

8Kw maximum with 6mm, if cable run short and not buried in insulation/insulated walls.
Anything higher, use 10mm cable. Sorry.

[Buenchico]

8.5kW on 6mm cable should just about be OK if
(a) the cable run is fairly short ;and
(b) the cable is not bundled with any other cables at any point on the run ; and
(c) an appropriate MCB (45A) is fitted.

Chris

[BRIGHT SPARK]

Sorry you need to stay at 7000w to comply.........7000w/230v =30.44a.
Your situation will almost certainly attract a correction factor for insulation at the least.
So.....7kw shower....6mm twe cable...32a mcb..30ma rcd...or 32a/30ma rcbo...also make sure that the appropriate sized earths are installed on the gas ...water etc
Take the plunge and install a 10mm this will give you more flexibillity.

[gucciman]

thanks for the answers, i would love to get an electrician in and uprate the cable to 10mm but unfortunately the previous householder buried the cable under the wall tiles and as we have no spare ones I dont want to risk taking them off and breaking them.

and we have the worst case scenario, the cable literally runs from the very front of the house right to the very back where the shower is situated within an extension, it passes through the hallway ceiling, through the bedroom ceiling, along the full length of the loft nder the insulation and boarding, back down to ground level and then along a passageway then under the wall tiles and plasterboard, i would estimate it's at least 20 mts in length, i bet even if the 10mm cable could be run without damaging the tiles it would cost a fortune to do so?

if i did install a 8.5kw shower and kept the fuse to 30a, would that offer protection against any possible mishaps i.e. would the fuse just blow if there was a problem?

[gucciman]

one more thing, I am in 2 minds whether to bother replacing the shower or just buy a new heater unit and repair it. this unit must be about 12 yrs old, has shower technology moved on since then so it's worth installing new ?

[scotman]

8.5 kW is approximately 34 Amps so your 30 A fuse would not last long

[terence7556]

hi gucciman the most expensive part of a new 10mm T&E cable is the labour to run it in and that is something you are more than capable of, its no different to being on your hands and knees , raising floorboards to run pipework in .then you can pay an electrician to terminate each end and test/inspect. last sunday i was in B&Q and happened to look at some 10mm T&E and it was nearly £2 a metre but im sure you can get some cheaper at trade.
it will not be cheap to do this and an awful job running the cable in but it will open up a lot of choices for your shower. .

[gucciman]

thanks terence, the real problem is how to get the cable to the shower without removing the wall tiles, the missus wont like it surface mounted i'm sure, think i will either repair it or get the triton t80z 7kw shower

[BRIGHT SPARK]

Am I right in thinking you are an heating engineer? If so why are you using an electric shower....only kidding.
If you installed an 8.5kw shower with a 32a B curve BS60898 MCB the MCB would carry 48amps all day long.As the shower would draw 37amps the MCB would not trip.You must remember that the work is in a bathroom and is notifiable under part p.
From your description of the job it sounds like several correction factors are applicable including a possible volt drop situation.To comply with regs you will have to use a 7kw...an 8.5 would work ...and stress the cable.
Whatever choice you go with use a 30ma RCD and get the job certified by a REGISTERED sparks.....good luck

[gucciman]

thanks bright spark i think im gonna go for the cheapest option and replace the heating can, sourced one on the net for £42.

would love to install a thermostatic shower off the cylinder but would have to move the bath forwards as it is flush to the wall and again would have to remove a lot of wall tiles which would prob crack and we have no spare ones, the missus wont stand for surface mounted pipework, the bath is also boxed in with the same tiles. The guy who installed the bathroom didn't give much thought to future repairs or modifications as usual !
she does't want to stay in this house for much longer anyway so it's not worth the bother.

[gucciman]

oh and don't laugh but we always reccommend to our customers that they have an electric shower as they are great back up if their boiler fails !