That would depend where your located. This 120 degree system is quite common
in some areas.

The voltages aimed at are 125 / 216 vac so that the 120v loads get a little
high voltage and the 240 loads get a slightly low voltage, all within legal
acceptable standards.

The energy metering takes a full two element Whr meter instead of a 1.5
element meter used for regular 120/240 vac. Costs a bit more so it it
typically only used in high rises and other large residential blocks.


In apartment or condo blocks, usually each floor will be fed off two out of
three phases, in the construction I have been involved with. One neutral
conductor and three phase conductors can feed the whole building up the
electrical service shaft. This can save some copper and use one big 3ph 4W
transformer for the building. 6 phase star can be used in a similar method
but power theft is easier to accomplish by customers and it takes more
copper.

With a delta configuration only **one** centre tapped phase can be grounded.
This was called 3 ph 4 wire delta and the metering was too complicated for
many EE people and abandoned. This was common with a 120/240 vac residential
service where the customer wanted to run a small 3 phase meat slicer or saw.
A second transformer could be added at 60 degrees for open delta, quite
economically and get three phase and single phase.



"Martin H. Eastburn" wrote in message
...
The phase angle determines what you get.

Anyway - most 3-phase apartment house services are in fact 180 split
windings.
e.g. delta with centers of the delta sides are grounded. You don't get
multiple phases for normal home use.

Martin

Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
"Our Republic and the Press will Rise or Fall Together": Joseph Pulitzer
TSRA: Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
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On 6/9/2010 11:27 PM, Josepi wrote:
Or 120 degrees out of phase if fed off a network three phase system. Ths
can
be common in apartment buildings or large residental blocks. Now you get
the vector sum of two loads and have to consider the power factor also.

The end result is a low current, in the neutral, anyway, unless you have
pf
correction on one and not the other. Not likely in a residence.


"Martin H. wrote in message
...
Actually, the currents are added. The effect is subtraction.

One leg has a -1 vector tagged to it so when adding it becomes
subtraction.

Remember in the US and many other places the two voltages are 180 degrees
out of phase with the other.

Martin