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3 Phase consumer unit wiring?

Postby Tony_G » Thu Nov 20, 2008 1:53 pm

French Electrics!

We have a house with three phase incoming power - there are 4 feeds from the EDF switch on the consumer side - 1 neutral and three live. there is 240v between neutral and each of the lives.

One live and the neutral are connected to a modern RCD 10way consumer unit and the house wiring uses three of the ways.

The main switch trips regularly and consultation with EDF elecited the advice that we should be using all three phases - fair enough, I understand the principle of three phase electric and balanced phases.

The bit I'm not sure I understand is 'Do I need a new consumer unit? The installed one has several wiring terminals for incoming lives to the bus bar but that would mean they were all electrically joined together. Do I need a new one to take 3 phase, do they have three bus bars to keep the three phases apart??

I want to understand what I need before thinking about getting quotes.

Thanks for any help


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Postby ericmark » Thu Nov 20, 2008 5:28 pm

The Isobar 4 range by merlin gerin part of the schneider-electric group do boards with a central neutral bar and are very suited to 3 phase to single phase use. But in UK we would be very careful on a three phase supply not to have more than one phase in any room although it does not say you must not it does have quite a few rules which with standard UK domestic we would not be bothered about. Although out BS 7671:2008 is designed to make our system similar to the rest of the EU it is not the same and although I have worked in other countries I was not involved with their rules and regulations so I would say you need to go to a French web site and get your advice from French electricians.

Postby sparx » Thu Nov 20, 2008 6:39 pm

don't know for sure if same as in Spain but there it is not unusual to find a 4 pole incoming RCD main switch with a Neutral and 3 live conductors BUT all 3 are connected to same phase!
So if tested to N each gives 230v but testing between cores shows zero not the 400v you would get from a 3 phase supply.
They run from each Live to a number of circuit breakers say 4 each giving a total of 12 circuits, sharing a common N.
They don't bother with busbars merely linking each set of MCB's with a loop of cable.
The reason given by 'Civiana' the Spanish electricity board is they put in 4 cores in case 3 phase is needed but for safety reasons only connect as single phase which is more than adequate for normal households, it's only 'Johnny foreigners' (Brits. & Germans) who use more!
Cable is only 6mm2 including N which would be fine for balanced 3 phase but when linked for single phase puts a heavy load on Neutral.
Don't know if same in France but it might be a good idea to check.

regards SPARX
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Postby david51 » Thu Nov 19, 2009 7:58 am

I am trying to find out about fitting a consumer box in spain. I have been told that the mcbs need to be double pole. My problem is I cannot get my head round how these are wired up. Is it because they have 3 phase. What i cannot understand is if you have a double pole ypu are spliting both live and neutral. But in UK all neutrals are joined together.
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Postby ericmark » Thu Nov 19, 2009 8:54 pm

No idea how things are wired in Spain I think you need to consult a local electrician.

However where a TT system is used the earth could be a very different voltage to neutral and where the ground may become dry there could be problems never seen in UK. So it is likely they use double pole MCB's or RBCO's on a TT supply.

With three phase one may need a 4 pole device.

I have seem so many different systems Algeria had 3 phase 110 volt and Turkey use three phase into flats but only one phase per floor.

So only way is to enquire local.
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Postby sparx » Fri Nov 20, 2009 8:40 pm

David51 Hola! TAKE CARE, Spain is quite hot on only allowing licenced electricians to do work there, Civiana will disconnect your supply if not happy, also more than one method of supply exists, various earthing arrangements also.
Try to find 'Manuel - electrasista' buy him a drink and ask questions, it worked for me some years ago!
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