On Mon, 25 Nov 2013 20:43:01 +0100, nestork
wrote:


bud--;3155057 Wrote:

The earth does not complete the circuit. Wires complete the circuit.


Bud, until recently I would have agreed with you. But, whomever wrote
this web page obviously knows something about electric power generation
and distribution and seems to disagree:

http://tinyurl.com/y4syno6

Look at the bottom paragraph in the section entitled "The Power Plant:
Three Phase Power" where it says:


And what about this "ground," as mentioned above? The power company
essentially uses the earth as one of the wires in the power system. The
earth is a pretty good conductor and it is huge, so it makes a good
return path for electrons. (Car manufacturers do something similar; they
use the metal body of the car as one of the wires in the car's
electrical system and attach the negative pole of the battery to the
car's body.) "Ground" in the power distribution grid is literally "the
ground" that's all around you when you are walking outside. It is the
dirt, rocks, groundwater, etc., of the earth.


I don't think he could have said it any clearer.
And he COULD have been more accurate. He is wrong, for instance, in
stating each tap takes off 2 phases. It GENERALLY takes off ONE phase
- which feeds a center tapped step-down distribution transformer. The
primary of that thansformer has only 2 conductors, and a single
winding. The secondary has 3 wires, and a center tapped winding,
providing SINGLE PHASE power to the local residential grid..
There are 2 basic 3 phase connection schemes, delta and wye. Wye has a
neutral (so requires 4 wires) while delta uses only 3 wires. Delta
connections take power from l1 to l2, l2 to l3, and l3 to l1. Wye
takes power from l1 to n, l2 to n and l3 to n.

BOTH are used. A 3 phase generator can be either delta or wye. In
North America MOST systems are wye, while in other parts of the world
delta is more common. (but in europe, 4 wire(wye) is used
(400/230volt)
Japan, on the other hand, uses a full 3 phase distribution system and
does not use center tapped transformers to provide high/low voltage to
homes - they actually feed 2 phases to each house like many MURBs in
North America - so they get nominal 120/208 instead of 120/240. Both
50 and 60 hz are used, and much of the country is 100 volt, instead of
120 - and some is 115. (must be fun if moving from place to place
within the country to get the right equipment ----)