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

As I understand with a single-phase shared neutral situation, anything that may show up on the neutral is effectively canceled out as one line is at +120V as the other is at -120V.

How much would a neutral have to handle on the three-phase set up, ratio wise?

Charles, if you were driving 3 heating elements of equal size (one per phase) the neutral current would be as close to zero as your match of elements.
As soon as you start using reactive loads those ugly harmonics raise their ugly head and neutral currents start adding. You can get neutral current that exceeds the phase.

I did a service call on a monumentally HUGE mansion (5 floors) off Mulholland Hwy in Hollywood Hills, built around the 1950's with a 3 phase 480V 1200A service. 3 elevators, enough A/C to have you singing "Oh Canada" in any weather, indoor pool, a jacuzzi on the roof, a computer mainframe room kept at about the same temp as your refrigerators salad drawer, and of all things, a bowling alley

Other than that, the Governator has a ranch in Malibu Hills with 3phase 1600A at 208Y/120V.
Those are the only 3 phase houses I've actually "worked" on.. But I have come across a handfull with 400A 240V 1 phase..

Seems most of the new houses in "The OC" are 200A 240V single phase.

So Cal Edison has load requirements which must be met before they will even consider giving you 3 phase power whether you're commercial or resi. If you don't draw enough Kw/H to meet this after they give you the 3 phase service, they'll charge you for a "minimum demand" anyways, which last I heard landed you in the $800/month ballpark

Wolfgang,


Although I still think 3-ph is an unnecessarily complex for domestic work, that's at least a decent supply rating, unlike some of the French ones.

That sounds very cheap. The cheapest single-phase B-type in my trade catalog is a GE at a little over $4 (same price for all ratings 6A through 40A).


Interesting comparisons with here, where 63A RCDs are very common. From the same GE range, and converted at £1 = $1.78:

30mA / 40A $35
30mA / 63A $45
30mA / 80A $61
Ragnar,

In metric sizes, about 400 sq. mm.

That would just about pay my electric bill for an entire year!

Just for better understanding:
the US "200A single phase service" = 200A @240V = 400A @120V = 48 kW? = about standard German service size

or only half of it?

Wolfgang (Europe)

What size 'choc-bloc' would 400mm2 require?

Alan

ps. Just dug out my biggest choc-bloc, bought for my new meter tails. Hole diameter 7mm, marked for use on 25mm2 conductors, 'Legrand', NF approved. They probably go bigger.

[This message has been edited by Alan Belson (edited 01-24-2006).]

[This message has been edited by Alan Belson (edited 01-24-2006).]

You will not get a LV service of 1 MW (1200A @3 x 480)here. You'll usually get your own xformer @ 11 or 20 KV. This gives you acceptable cable sizes, just needing a bit more equipment.

Great! Then you can always look forward to something like this:
https://www.electrical-contractor.net/ubb/Forum5/HTML/001115.html

...happening in your very own back yard!!

Of course, in my case the biggest problem the POCO would have is keeping me out of the SCADA system!! I love to watch air break switches in action!

A 200-amp service means you can draw up to 200A on each "hot" leg of the 3-wire supply, so 200A x 240V = 48kW.

That's double the power of the typical modern British service of 100A / 24kW (although ours are only 2-wire with everything running on 240V, of course).