DIY Doctor

How difficult / costly to install 15m cable for 12kw heater

Postby 3point14 » Sun Feb 27, 2011 5:56 pm

I want to install a (Google "") instantaneous water heater. I've used them loads of times overseas but here in the UK, I don't seem able to get an electrician to put one in or even to quote to do the work - are they all that busy ?

To me, it is an easy job. With the maths (for the 12kw model) you have 12000/230=52 amps so I'm guessing a 50 amp breaker ? or would diversity come into this ? I know we currently have at least one 63 amp breaker.

I'm not suggesting I do this job myself but I cannot see how it is not a nice little earner for a sparky because apart from running some 10mm2 (don't think I need 16mm2) cable and a couple of connections it just needs stapling to a couple of walls.

Any comments welcome as I need this done.
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Simply Build It

Postby ericmark » Mon Feb 28, 2011 2:58 am

As you say no different to fitting a shower as far as cable and load goes so no real problem fitting one as long as the incoming supply is big enough.

The incoming supply is nearly always through a 100A fuse holder but as the user you have no idea normally what size fuse is inside the fuse holder. Anywhere between 60A and 100A.

This may put some electricians off as all too easy you can end up with more than the supply fuse can handle and be blamed for the loss of power.

Other factors are the type and size of consumer unit. Today any cable buried has to be either one of the specials allowed or protected by a RCD. If the consumer unit will not take a RCD the cost to do the job could raise.

When installing units using high power the first step is to test the existing supply. The earth loop impedance, the existing demand, the size of supply will all be taken into consideration. It may be electricians in your area know the houses in that area don't have the supply you will need.

But it is not really any good asking on a forum. It is your local electricians you need to ask.

Part P has become a problem. Only electricians who pay a large annual fee can work on domestic premises and do all the work. Before 2004 electricians who were mainly commercial would do the odd domestic job but the government rules mean to do the odd job will cost over £100 to register that single job with the LABC. Unless the job is large for example complete re-wire then it is not worth doing the job if one is a commercial electrician. The only exception is where it is part of a bigger job for example an extension where the same building control fee can cover both building and electric work.

With those doing domestic electrics their scheme providers do place some heavy restrictions on them. Although the LABC can allow you to do work which does not comply with BS7671 if it is still safe. The domestic electrician has to follow it by the letter. Also he can only sign for work he has done and if some of the work has been done by some one else this can also cause problems.
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Postby 3point14 » Mon Mar 14, 2011 11:46 pm

Thanks very much for taking the time to give me such a detailed response. I've seen details of the electricians who put the rewire in not too long ago and will try to see if they can assist. Failing that, your help is ammunition to seek out someone qualified to do the work !
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