On Monday, November 25, 2013 3:10:28 PM UTC-5, wrote:
On Mon, 25 Nov 2013 08:21:10 +0000 (UTC), Danny D'Amico
wrote:
On Sat, 23 Nov 2013 16:09:26 -0500, someone wrote:
From Professor Cardell's web page at
http://www.science.smith.edu/~jcarde...ecPwr_HSW.html
"There are two wires running out of the transformer and three wires running to the house.
The two from the transformer are insulated, and the third one is bare. The bare wire is the ground wire.
The two insulated wires each carry 120 volts, but they are 180 degrees out of phase so the difference between them is 240 volts."
Why are all three of mine insulated?
http://farm3.staticflickr.com/2886/1...21cf1404_o.gif
First of all, in North America, the typical p[ower supply is NOT 2
phase. It is center tapped single phase. You have a line1, a line2 and
a neutral - the neutral being shared between the two lines. If the
load is ballanced between the 2 "sides" there is no current in the
neutral. The neutral is regerenced to ground for safety reasons.
In early reural electrification in the USA, single wire distribution
was used - using "earth return" It worked, but was fraught with
problems, and is virtually unheard of today..
Today's power distribution is 3 phase - with each phase feeding a
separate distribution transformer - which has a center tapped
secondary for residential power. 3 phase is supplied for industry and
some multi-unit residential buildings which run 120/208 instead of
120/240. This is because 3 phase power is 120 degrees phase to phase.
because the generating system IS 3 phase, there can not be 2 "phases"
180 degrees apart.
Tell that to my lying scope. You put the two hot legs of the
split-phase service on a scope and what do you see? Two
phases that differ by 180 degrees. If they didn't differ by
180 degrees, you would not have 240V. It's every bit as real as
seeing 3 phases on a scope that are 120 deg seperate.
White papers/app notes from two electrical eqpt manufacturers:
http://www.samlexamerica.com/support...Circuit s.pdf
http://www.behlman.com/applications/AC%20basics.pdf
IEEE peer reviewed paper delivered at a recent power engineering conference:
http://ieeexplore.ieee.org/xpl/artic...number=4520128
"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. "