ECN Forum Forums General Topics of the Trade General Discussion Area Residential 3 Phase, Why / Why Not?

Germany is such a country: Standard service per apartment / small house is 3 x 63A @ 400/230, i.e. 43,5 kW.

In the residential area there are just two devices always (mandatorily) running on 3phase: Ranges/cookers (usually 3 x 16 A or about 11kW, wire gauge 2,5mm2) and instant water heaters (correct word?) between 18 kw and 27kW, wire gauge usually 4 to 6 mm2. Use of both is rather common, just I haven't got none of them, because I'm cooking , drying and heating (also water) on gas(NG) actually.

AC is not very necessary (climate), therefore we're depending on models from other markets usually often running on 1 phase with expensive wiring due to uncommon loads.

I think you are pretty right that on small induction motors efficiency is not a real issue, but in the simplest industrial context , 3p becomes indispensable because of better efficiency and much better torque of motors.

The cost thing is not obvious at all. Here we use probably less copper to transport the energy. Prices for breakers and other equipment here are extremely depending on production numbers. A standard B16 A breaker is about 1 to 2 $. A K20 (same brand, same housing, only different electric values) needed maybe for an AC device can be at 20 $. I buy a standard 40A/30mA RCD (sort of GFI) for about 25$, a 63A/30mA RCD is already almost the double price. It means, 3p can become cheaper than 1p in case it is regarded as standard.

The result are rather slim panels. And the price is my work, not the material.

To a first order approximation, you can get multi-phase power from a single phase source with motor run capacitors. The cap shifts the phase 90 degrees. Such lash-ups are designed and built by the manufacturer of the equipment (fridges, air conditioners and such), and are not usually "visible" to the user in terms of the electrical hookup.

Technically, couldn't one have a circuit with a shared neutral and three conductors at 120V line to neutral?

Charles, you didn't specify the phase relationship you have in mind between the "three conductors" to neutral. If they are at 120 degrees, what you describe is exactly 208Y/120. If you're thinking of taking the three conductors from a single-phase source, then, no, it won't work.



[This message has been edited by SolarPowered (edited 01-22-2006).]

If you have a true 120/208V 4w wye service (equal to Continental European 230/400V) you can have a multiwire circuit with three phases instead of the US two. You'd need a 3-pole breaker, just like a US 1ph multi wire reuqires a double-pole. in Germany and Austria that practice is frowned upon though, out of fear of lost neutrals with the small wires (roughly 15 AWG) usually involved in house wiring.

There's one nice thing to 3ph though: imagine hooking up a range with 12-4 cable on a 20amp 3-pole breaker... in my opinion smaller wires are a lot nicer to work with, so I prefer the European 3ph arrangements, especially with the higher voltage levels involved current gets fairly low.

Of course French 15A services are ridiculously small. But I think 35A per phase @230V is quite enough for most uses. After all that more or less equals a US 100 amp service, along with the ability to run power-hungry appliances on 400V.

Recently I read about an average US single family home (an old farm somewhere in Maine) having to upgrade to a 600amp service for installing a heat pump and two or three tankless water heaters... from an Austrian point of view that's flat out ridiculous! Most electricians who do residential work aren't even trained to work on cables as big as that! I don't even want to think in metric what wire size would be required for 600amps!

SolarPowered;

Yes, sorry about that... I did mean 208Y/120. It sounds like a fairly neat idea, but has anyone seen it in practice? That is, 3 lines, sharing a neutral, 120 degrees out of phase with only 120V loads.

I mainly read these forums out of interest and curiousity, btw...

In the office environment it is common to find 3p wye serving 120v loads. That is why they invented "super neutral" cable.

Rewire.... would that be Silvestri's house on Rymal Road?

Yes it is!
Er Sandro, where are you????

Quote:
"Recently I read about an average US single family home (an old farm somewhere in Maine) having to upgrade to a 600amp service for installing a heat pump and two or three tankless water heaters... from an Austrian point of view that's flat out ridiculous! Most electricians who do residential work aren't even trained to work on cables as big as that! I don't even want to think in metric what wire size would be required for 600amps!"

We've got at least two homes on our system that have 150 Kva padmounts on them (single phase). One of them is on a "cash only" basis for payment.
I'm told that the Dell household in Austin (the Dell who owns Dell computers) has it's own substation.
The bigger the house, the more they complain about their bill.