On Thu, 06 Sep 2007 22:34:44 -0400, Stuart Wheaton
wrote:

Three phase is usually 208/120. 208 volts between phases and 120 volts
leg to ground. Many machines have a 200 volt tap for this situation.

Or 277V/480V. 277 between Phase to Neutral, and 480V Phase-Phase.
Found in larger high-rise buildings, large shopping malls, and light
industrial, because the higher voltage means much smaller wiring for
the same work produced.

When you get close to the end-use location for 120V/208V/240V power
you place a step-down transformer. That keeps the voltage drop to a
minimum.

Heavy industry (automobile plants, steel mills, forges, foundries,
mines, etc.) buys their power "in bulk" at the higher utility
distribution voltages in use in their area - 2,400V (almost extinct)
4,800V (LADWP Residential) 9,600V 14,500V 34,500V (LADWP Industrial)
etc...

The utility installs fuses or breakers and a KWH Meter recording the
power usage on the line going into the complex, and the end user takes
over.

The industrial user gets the power cheaper, but has to supply their
own underground or aerial cabling, step-down transformers and
switchgear, and knock the medium voltage down to the needed voltage at
the point of use. And they have to absorb the cost of all the
transformer and transmission losses that occur after they 'buy' the
power at the KWH Meter.

-- Bruce --