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Granny Annexe

Postby jackhawk » Tue Mar 23, 2010 8:03 pm

Hi all,

Only basics now i'm afraid.

Main house max demand 210a with diversity.

Granny annexe 115a with diversity.

I recommended extra phase to supply annexe as it will be ran as a new house by mother-in-law.

Not happy with that, they had second opinion and now have split tails with sub CU supplying annexe 25m away on 16mm2 T&E.

So 100a supply cutout, 114a 25mm2 tails, splitter box 100a max, meter 100a and overhaed cables 100a (as per e on) supplying two houses. Combined max demand after diversity 325a. Don't like what has been done. LABC inspecting and testing as I have walked. My concern is a family being cooked due to overloaded supply cables, tails, meter, splitter box.

I know this is basic but I can't write it all again as my will to live has been tested already.

Any opinions are very welcome.

Kind regards

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Simply Build It

Postby ericmark » Wed Mar 24, 2010 10:19 pm

If one adds all the sockets on a ring main and work out the power that could be demanded it seems the MCB will never hold but it does. And if it does trip it does not cause danger.

The two houses are similar likely the fuse will not blow and all will work OK. But end of day max draw is 100A as that's the incoming fuse size.

25m away on 16mm2 T&E may cause volt drop problems and there may be an issue where a short circuit will not trip a protective device in the required time however this will show up when the ELI tests are completed and it will fail the tests for installation certificate.

I have had problems where I was told to install a 32A socket with 4mm cable and I questioned the cable size for the distance. Told to get on with it I did and then measured the ELI and fitted a B20 MCB. This tripped and I was asked why only 20A was fitted answer was easy that was largest permitted for that circuit. I reminded them I had questioned the cable size and was then told to renew.

Nothing I had done was wrong or dangerous and you are in same position. Granny annexe may have to be limited as to max MCB size I have not calculated but other than problems with being plunged into darkness if fuse blows there is no danger. So emergency lights and jobs OK as to danger aspect.

Once fuse has blown a few times it will all get changed anyway so not really anything to worry about.

That's my opinion anyway.

As to walking off a job that's different. To my mind if cards in there is nothing to stop anyone going on the sick and putting in notice so it would be hard for any one to do anything to you but if self employed then even if you died the people you were doing job for could claim against your estate and one has to be very careful.
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Postby jackhawk » Thu Mar 25, 2010 12:30 pm

Hi ericmark,

Thanks for your reply. It was a rushed post as the first two attempts vanished into space and I lost the will to live. I have re done a full indepth post now as per my original.

See wot you think.

Kind regards

Rank: Tradesman
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Posts: 37
Joined: Tue Sep 04, 2007 9:02 pm

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