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Rewiring a Three-Phase Cable to take a Monophase Socket


Rich1972

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Hi

I had EDF around yesterday to look at the three-supply cable that takes power from the fuse box to an outbuilding. The three-supply only went into this outbuilding as the rest of the house runs on the standard domestic supply. While he was here the EDF engineer fitted a new fuse box and before he left he told me that if I wanted power to the outhouse I could just replace the three-supply socket with a domestic one, without having to replace the three-supply cable. So I turn off the power today and find that the cable has four wires (one black, one brown, one blue and one yellow/green earth). I tested all four wires and they're all live. I'm done no further work to it so I will get someone in to have a look, but should it possible to connect a normal, monophase socket to four live wires??

Rich

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A 3 phase supply is no more than 3x 220v lives referenced to a common neutral so in thoery you can connect to any phase and neutral for a single phase 220v supply. Beware though because between the phases the voltage will be 440 !

It does sound like a rather irregular arrangement and I'd be concerned as to how this is all configured and metered.

It sounds as if you have a 3 phase supply to your property but are only using one phase for the house and presumably have a single ph meter for that. If 3 phase is going to the outbuilding then it should be going through a separate 3ph meter.

Do you have 2 meters and are you sure the house is only on single ph ?

If you only have one then I wonder if what he's done is connect all 3 live's together then to a single phase in the house. I don't know the French regs but that doesn't sound too clever to me.

Definately a good idea to get someone in to check it out !

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Here's a photo of the new fuse box:

http://i50.photobucket.com/albums/f310/richinusseau/180cde57.jpg

The old three-phase cable goes into the new box via the small, old brown box at the top. There used to be two fuse boxes and now there is only one, with Monophase written on the side. The house can't have three-phase as all the electrical appliances work perfectly here, even those bought in the UK. But my electric mixer went haywire when I plugged it into the three-phase socket in the outbuilding. Unless the house is three-phase and is only operating on one. I really don't understand it enough. I'll get someone in anyway.

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The box doesn't really reveal anything to me I'm afraid but if it says Monophase then I would have to say that the probability is that it is that and that your house is indeed single ph.

"The house can't have three-phase as all the electrical appliances work perfectly here, even those bought in the UK".

Sorry but that is a meaningless statement and absolutely no basis on which to judge whether your house is single or 3 phase, the sockets will be 220v in either case.

If it is were 3 ph then the phases would be feeding different parts of the house to try and maintain a balance but would be totally transparent to the user.

I'm not surprised your mixer went bananas if you pugged it into 440v 3 phase [:-))]

I still don't like the idea that all 4 cables to the outbuilding are live but if EDF have done it one would like to think everything is correct but just for your own knowledge and peace of mind do get it checked.

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hi ok

 quote   The house can't have three-phase as all the electrical appliances work perfectly here, even those bought in the UK".

 This is a true story a friend of mine had some sockets and lights put in his boiler room by his wifes brother a uk sparky. He had taken the feed from a junction box wired the way the french farmers seem to do it here ,( explain this bit later ) he had taken blue for N brown for L and yellow/green for earth all worked well for 3 years , the fridge freezer ,  iron . kettle  etc  all worked ok then he wanted to move the washing machine into this room , so i put in the plumbing  we moved the machine turned it on it run for a few seconds then bang . I put a meter across L + N 220 volts ok   tried      N + earth 220 volts   ???    tried    L+   earth 440 volts   ??????

 ok the French farmers way is to use 4 core cable for 3 phase  blue = neutral  brown = phase black = phase and yellow/green = phase

most appliances  do not use earth , most have only a 2 pin plug on them  but when that motor on the washing machine started up  it did , they were very lucky for 3 years  ..... get it checked by a pro

 Dave

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[quote user="cheryla"]If you look at your electric bill it will say whether you're on monophase or triphase (or have you recently asked for the supply to be changed from triphase to monophase and that's what EDF's visit was for?).[/quote]

Ah ok, I'll dig out my last EDF bill and have a look. Thanks for the tip [:)]

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[quote user="Anton Redman"]What did you use to check that all the wires were live ? Did you check their voltage ?[/quote]

I just used my electric screwdriver with the built-in light (finger on the end and touch the live with the screwdriver tip).

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You need to follow the wiring properly as there is a posibility that you are being misled here - the statement monophase on the supply to the house could well mean that each indivdual circuit is on a single phase and not that the whole house is on the same phase e.g. the kitchen sockets are on 1 phase and the sitting room sockets on another but each socket is monophase. This would be unsurprising as your three phase supply would be pretty unbalanced if you are drawing solely from a single phase.
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[quote user="Rich1972"][quote user="Anton Redman"]What did you use to check that all the wires were live ? Did you check their voltage ?[/quote]

I just used my electric screwdriver with the built-in light (finger on the end and touch the live with the screwdriver tip).
[/quote]

 

Probably 220V - 400V will often fry the neon as well as the user! beware 400V does not take prisoners.

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