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Two electrical supplies and two consumer units - Earth bond

Postby foxsterc » Mon Dec 05, 2011 3:55 pm


To give a bit of background. We brought two houses (that used to be one) and subsequently have two electrical supplies and two consumer units. We are in the process of converting the houses back into one but it will be some time before we can do the electrics.

The electrics in house one (where the only gas supply is) are modern and earthed correctly (checked by local electrician); this house contains the boiler which now serves both houses. This house has a lounge, 1 bedroom, kitchen and bathroom. Single Phase Supply.

House two has a new consumer unit and serves a new kitchen, lounge, and 3 bedrooms. 3 phase supply (no 3 phase appliances anywhere)

My question is earth bonding. Because house 1 is earthed and the cold and hot water pipes feed both houses does the supply in house two also need bonding to any pipes? Would the two consumer units conflict in any way?


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Postby ericmark » Tue Dec 06, 2011 1:23 pm

Because of what you have raised it is the electric supply company who must dictate what type of earthing you have. With TN-C-S there will likely be no problem. With TT then likely you will need to link them together.

What is more of a problem is the phases. One has to be very careful as you may have 400 volts where it is designed for 230.

I would say this is not a DIY thing and it really needs some one to visit and look at it not just asking on a forum.
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Postby sparx » Sat Dec 10, 2011 7:18 pm

I have had this issue with a property near me recently.
Best answer is to run a 'sub-main' from one consumer unit to supply the other one, then get electricity supplier to disconnect and remove other meter etc. that way only one bill and all main earth bonding from one source.
As Ericmark says normal practice is to put each supply down a road on phase rotation ie house one on 'RED', two on 'YELLOW', three on 'BLUE' four on 'RED' etc so it is possible for you to have 400v between circuits in the one house!
House 1 would be the best to supply house 2 via a circuit breaker (say 50A) and a suitable cable say 16mm2.
your electrician should be able to confirm this is viable,
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