"T o d d P a t t i s t" wrote in message
...
| john smith wrote:
|
|
| Ahhh! But where does the 240 come from?
| Does it not come from two of the three legs of a Y or Delta?
|
| It doesn't matter where the 240 comes from, it matters what
| the phase of each wire is relative to some reference. The
| US (and Europe, but at twice the voltage) use a 3-wire,
| single-phase, mid-point neutral distribution system for most
| residential loads. If you use the neutral as the reference,
| then there are two opposite phase wires or split phases. If
| you use the opposite wire as the ref, then there is a single
| phase 240 volt signal.
|
| Commercial sites receive 3-phase power, not single phase.
| The voltage difference between two of the three legs in that
| system is 208 volts, not 240 volts
|
| These are square root and cube root functions.
|
| No they are not - they are trig functions depending on phase
| angle.
|
| If they were 180 out of phase, it would cancel.
|
| Phase depends on the reference. You can ignore the neutral
| and just see it as a single phase 240 volt system using
| either hot lead as the reference. If you prefer, you can
| think of one hot lead as being the reference, the neutral as
| having a 120 volt signal on it and the other hot lead as
| having a 240 volt signal in phase with the 120 volt signal
| on the neutral.
|
|
|
|
|
| --
| T o d d P a t t i s t
| (Remove DONTSPAMME from address to email reply.)
|
| Make a commitment to learn something from every flight.
| Share what you learn.

Came across this:

If you have three phase (Y or Wye, which is fairly commonly provided to
businesses or industries but not common in homes) electricity, you can
get a ``sort of'' 240 volt circuit out of it by running between any two
of the three phases. The phase difference is only 120° instead of 180°
so one ends up with only 208 VAC or so between the wires. This is enough
to run most 240 VAC devices simply because the manufacturers aren't
fools and know that Y/Wye supplies are fairly common. This is also true
for a lot of computer equipment that requires 240 VAC (like some racks
or uninterruptible power supplies (UPS) or some big-iron computers).

Taken from this site:
http://www.phy.duke.edu/~rgb/Beowulf...ok/node60.html

--
Jarhead





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