On Saturday, November 23, 2013 7:56:02 PM UTC-5, Dean Hoffman wrote:
On 11/23/13 4:37 PM, John G wrote:



You are of course correct but lots of people who know very little or

just enough to confuse themselves keep dragging PHASE into discussions

about houshold electrics.

The normal houshold supply in the USA is ONE phase with a centre tap

grounded to produce 120 volts above ground and 120 volts below ground or

240 volts between the ENDS :/







Well, what we think of as single phase isn't. It's actually two

phase. Trader 4 posted a link to an IEEE paper in another thread.

He http://tinyurl.com/lpwq82z

Thank you. Good to see someone looked at the link and realizes what it
says.

That link is from the highest credibility source
you could possibly get, but aaddresses the very core of the issue:

"Which now brings into focus the reality that standard 120/240 secondary systems are not single phase line to ground systems, instead they are three wire systems with two phases and one ground wires. Further, the standard 120/240 secondary is different from the two phase primary system in that the secondary phases are separated by 180 degrees instead of three phases separated by 120 degrees."

I supplied other links to references from electrical eqpt manufacturers that clearly show and describe 2 phases, 180 deg out of phase with each other as well:

http://www.behlman.com/applications/AC%20basics.pdf

http://www.samlexamerica.com/support...Circuit s.pdf

So far, the other side has no references.




I work with irrigation which mostly relies on three phase power. We

sometimes tap power off grain bin sites which many times have "single"

phase 240. We'll use a transformer to produce 480 and add a phase

converter for the third phase. The converter adds one phase to the two

already there to run three phase motors.

It never occurred to me to think of "single" phase as actually two

phase until Trader posted the link. It has to be or phase converters

wouldn't make our irrigation systems run.

Granted, none of this probably matters to Joe Homeowner wiring a

garage light or a stove.


I'm still waiting for the definition of the meaning
of phase from those that deny that the two hot legs on a split
phase 240/120V service are 180 deg out of phase with each other.
That is what started all this. They appear to be hung up on the
fact that it's derived from a single primary phase. How it's
derived doesn't change what you get, what you can see on a scope,
how it drives a load, etc.
You brought up an example of generating an additional phase via
a transformer. Earlier I brought up another, very common example
too, open delta three phase.

For most 3 phase loads, 3 transformers are used to step down
from the primaries. They have 3 transformers, one connected to
each of the 3 utility primary phases. So far, I think everyone
agrees with that. Three phases in, three phases out.
Now, for light 3 phase loads, to save the cost
of an additional transformer, by using a center tap transformer,
the utility can supply 3 PHASE POWER, using only two transformers,
connected to only TWO of the utility primaries. The utility calls
that 3 phase power. The customer calls it 3 phase, the 3 phase
motors run on it, you can see 3 phases on a scope. Yet it's derived
from only TWO of the utility primary phases. Two phases in,
three phases out. Following the arguments of those on the other side,
then that should only be called two phase power. Yet there it is,
3 phase.