What power is available to EU homes.

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What power is available to EU homes.

Postby gooberpat » Mon May 07, 2018 4:49 pm

I have a question about power to the average EU home.
(I know it differs a bit from country to country)

I know that EU power is nominally 220 - 240vac at 50hz. But what I am not sure about is what kind of power is available at the power panel of each individual home and how it is derived.
I believe 3 phase 220vac is delivered to the neighborhood.
Is that 3 phase from a delta or a Y? Is there a neutral?
Is the 220vac from neutral to each phase, or is it 220vac between any two phases.

Is there ever a case where all 3 phases are wired to an individual home?
If so is there a neutral involved?

Thanks in advance!
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Re: What power is available to EU homes.

Postby crlMidi » Sat May 12, 2018 7:46 pm

The nominal safe limit for AC live-to-earth (any phase) with normal cabling and switchgear is 250V. The generally-accepted tolerance for the voltage arriving at your house is +-10V. Until about 1980, national standards ranged from 220-240V. The universal European compromise is now 230V. This used to be critical because the light output and lifetime of a filament bulb are both very sensitive to the voltage. Nowadays, with efficient power regulators, a lot of devices are rated for 110-250V.

The frequency is 50Hz in Europe and 60Hz in the States.

The available choice between single and three phase seems to depend on your country, and it has varied over the years. As far as I'm aware, 3-phase has always been common in Germany and single-phase in the UK. Three-phase can be a nuisance, because the supply cuts out if one of the phases goes slightly over the limit you have paid for (for example washing machine + smoothing iron on the same phase). In France, the annual standing charge rises sharply as a function of the total instantaneous power you can draw; you get used to resetting the cutout though it isn't good for your electronic equipment. France is a big country so landline losses are important when the sun isn't shining on your solar panels.

Writing from memory, individual houses on single phase are limited to 12kW. If you have an electric cooker, and/or electric heating you need 3 phases. This may apply to air/water heat pumps because they usually have a direct heating element that can go up to 10kW in cold weather. The induction cooker units I looked at a few years ago used two phases.

In France, the domestic supply arrives with either 1 or 3 phases + neutral (star configuration) - never 2 phases. You supply your own earth, and obtaining the required low resistance can be difficult in dry and stony areas. One is heavily dependent on the differential earth leakage circuit breaker. Typically the main (supplier's) cutout is set to a leakage of 300mA; your switchboard must be equipped with 30mA cutouts.

Finally, I mention that in commercial and similar premises, the site engineer may introduce some impedance between earth and neutral, in order to limit the cumulative effect of multiple earth leakages. This causes the neutral tension to deviate significantly from 0V, and in particular to fluctuate wildly (for example when an elevator starts or stops). I remember an article in Elektor that mentioned trouble in the lab (in Holland) because of that. Equipment of UK and American origin may not be designed to survive deviations of more than 0.5V between earth and neutral; during my career I saw a lot of damage to expensive scientific instruments because of that.
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