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Electrical supply to house

Postby Brian Johnson » Wed Apr 21, 2010 4:57 pm

I am looking at the possibility of installing a Heat Pump to heat my house. I’ve talked to the supplier and they had advised that I need the following electricity supply available:
Max current: 35 + 23 = 55A (fused to 40A and 25A respectively)
Running current: 14.9 + 10.3 = 25.2A

I called by electric company to check what supply I have to my house and they say they can’t tell me. However they have sent me a form to complete to upgrade the supply to my house – and I don’t want to upgrade it if I already have the capacity.

I’ve checked where the supply comes in and it’s split to 2 breaker boxes. Each of these has a main 100A breaker (and lots of little ones…). There is 1 spare slot in one box and 2 spare in the other.

Is there any way that I can find out what amps I am supplied with?
Can I tell how much spare capacity I have?

Any help would be greatly appreciated…
Brian Johnson
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Simply Build It

Postby ericmark » Thu Apr 22, 2010 5:48 pm

No sorry you can't tell but it will be between 60 and 100 amp and 80 is common. The type of fuse used will normally take short overload and if I was doing the job I would fit it all and see what happens and only worry about changing supply size if main fuse was to blow.

I did had a very large house to wire. What I did was to fit a 160A three phase fused isolator then supplied three consumer units from that being careful not to use the supply from two consumer units in any one room so should the supply end up not being big enough it would be easy to split into 3 phase latter.

So all three fuses were at start fed from single phase.

At 25A run (you can forget start current as fuse will not likely have a problem with that) unless you also have electric showers then likely there will not be a problem. Much depends on what else you are using.

100A is the max rating for most consumer units and if you need more than 100A either three phase or single phase you will need to split supply and the large fused isolator is likely easiest way to take either 3 phase or over 100A single phase.

I have not seen a domestic supply over 100A not sure how it would be done but up to 100A no real problem.
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Postby sparx » Sun Apr 25, 2010 6:52 pm

25A running current is nothing,,,
if you fitted a sauna/shower/range cooker all of which use much more would you be asking this question?
As Eric says minimum supply fuse will be 60A, normally 80 or 100A.
I have lived in this large detached all-electric bungalow for 35 years with a 80A supply fuse, untill 3 years ago all heating, direct not nitestore, water heating was electric including 3X 8.5 kW showers in use when kids (all girls!) were at home! never blown fuse.
Now have solar for hot water & girls married off so less chance of it happening.....
Worry not and area board will not give more than 100A supply to domestic property now anyway.
regards Sparx
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Postby TheDoctor4 » Tue Jun 29, 2010 7:45 pm

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