Badger Électricité

Three phase supplies - Part One

Disgracefully, I haven't added any information here for over a month. So, I'd better make up for it by finding something dangerous & exciting....which brings me nicely to the subject of three-phase (triphasé) electricity.

The first thing to say is that 3-phase (as I will continue to refer to it as) electrical power is not some odd quirk that only the French have. It is the main form of power generation worldwide. What's different in France is that the use of 3-phase in domestic situations is fairly common (especially in rural areas) whereas it is almost unheard of inside houses in the UK. As far as I'm aware it is not something that the French would ever install into a new property, but in a renovation situation it can be worth having a think before getting EDF to change you over to single-phase (monophasé) - more on that later.

I'll explain the technical aspects of 3-phase in another article, but there are some commonly held beliefs that I'd like to correct, by way of a Q&A session:

Q: 3-phase is really dangerous, isn't it?
A: All mains electricity is dangerous. Even if your house has 3-phase power you are at no more risk of electrocution by it than single phase. A properly protected installation will keep you safe, but a ropey old installation could be lethal, regardless of type. However, if you are unlucky enough to receive a shock from a bad 3-phase installation the potential voltage between phases is in the region of 400 volts, as opposed to the theoretically standardised 230 volts of single-phase. 230 volts hurts & can kill you - 400 volts hurts more & is more likely to kill you, or at least do it quicker.

Q: Isn't 3-phase power more expensive?
A. No, it's the same as single phase. 3-phase electricity in France costs the same per kWh (kilowatt hour/unit) as single phase power. 3-phase standing charges are the same as single phase, for the same overall power. A single phase "abonnement" for 9kVA (45 amps) is the same as a 9kVA (3 x 15 amps =45 amps) 3-phase one.

Q: Don't I need different appliances if I have 3-phase in my house?
A: It's an option, but a 3-phase installation only provides 3-phase power where it's needed - the remainder of an installation will be good old single-phase so you can use any of your normal appliances in a standard socket. However, due to the nature of 3-phase distribution it can be advantageous to use 3-phase versions of some high current appliances such as cookers, hobs & water heaters. Some models can be wired for either 3 or single-phase. Why this is so is partly explained by the next answer.....

Q: My EDF bill says I've got 15 kVA (75 amps) of power. How come my electric cooker knocks out the EDF trip? It's only rated at 32 Amps.
A: 15 kVA 3-phase comes to you as 3 lots of 5 kVA. This translates to only 25 Amps per phase: you have a single-phase 32 Amp (over 7 kVA) appliance running at full capacity on one phase, which will therefore trip the supply. If the cooker could be wired to use all three phases, the problem will go away.

I could go on, but I can hear the sound of heads hitting keyboards...... If you have any specific questions about 3-phase electricity (or any other aspect of domestic wiring in France) please feel free to hit the "EMAIL your enquiry" button at the top of the main page.