It is quite common in older French property to find that the electrical system is supplied in 3 phase, as opposed to single phase.  

When called to quote on electrical work on french properties by new proprietors, I am often asked what is the difference and what does it mean? And more often than not, there are numerous common problems such as when the kettle is switched on the power cuts off or when the hoover is used the power trips. This is because small electrical items can draw a large amount of current. E.g. A kettle can draw around 8amps for the period that it is boiling.

A 3 phase system can work well if you have and use a small amount of electrical appliances or a large incoming supply. With single phase these problems are less likely.  3 phase is a balance of loads. 

For example, using an incoming supply of 60amps [60A], the supply is split into 3 x 20A. Old houses in France usually have outbuildings so having 3 phase means that the supply might be split as follows: 20A for the house, 20A for the barn and 20A for the workshop. Bearing in mind that many years ago there would have been less use of electrical items such as kettles, hoovers, radios, tumble dryers, washing machines. Therefore, very little tripping of power in the kitchen. If you have purchased a property today with 3 phase and plug in all of your appliances – you are very quickly going to over draw on the 20A. E.g. a washing machine may draw 10amps, your freezer may draw 4-6 amps, then when you put the kettle on, another 8amps could be drawn and click you exceed the 20A and the power trips out. With single phase you have 60A feeding the house, you have one large supply coming directly to your dwelling. So your appliances can be switched on with no problem of overload.

I have recently worked on a property which had to be reverted back to 3 phase purely because there was not enough power to the house. I.e. it needed 90Amps minimum which could not be provided by single phase. Therefore I have had to very carefully balance all 3 phases at 30A.
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No phase can be exceeded, so a qualified electrician has to carefully balance the phases so that should all items be working at one time the current drawn will not overload any of the phases.