Typical US residential distribution (many details omitted for simplification).
| |---------------- L1 (Line 1)
L1 ----| Pole | 120VAC
14KVAC | Pig |--------| 240VAC
L2 ----| | 120V |
N ----| |---------------- L2 (Line 2)
| |------- N (Ground_ED_ conductor)
Anywhere from 11,000 to 30,000 VAC, single-phase + transmission neutral,
enters the transformer which
has a primary winding and a secondary winding used to drop the
distribution voltage to the service voltage. The secondary winding
is 'center-tapped' and connected to GND. L1 and L2 are connected to the main breaker
in your service entrance panel. The N conductor from the pole pig is
connected to the grounded (neutral) bus-bar in the service entrance. The
grounding bus-bar in your service entrance is connected to a service ground
associated with the premises and that bus-bar is bonded to the grounded
bus-bar in your service entrance (and _only_ in your service entrance,
not downstream subpanels).
Note that the primary side of the pole pig is single phase for most
residential applications. The secondary side splits that single phase.
On Monday, November 18, 2013 1:14:09 PM UTC-5, TimR wrote:
And note what else it says. It has one hot leg labled "Phase A", the other
"Phase B". That means there are two phases present. Next, look at the
note: "The phase of hot leg 2 (Phase B) is in the opposite direction,
ie 180 degrees apart from the phase of hot leg 1 (Phase A)."
Perhaps you can explain it now to krw that this document clearly
shows two phases present and that they are 180 deg out of phase
with each other. It's precisely in agreement with what I've been
saying for two days now.
On Sun, 17 Nov 2013 19:14:56 -0700, Tony Hwang wrote:
For some reason, I didn't see this thread, and assumed it hadn't
posted. So I apologize for not having answered any issues.
I've learned a lot.
For example, the ground and the neutral, in my house, are connected
together in the main panel, but not in the sub panels.
I've learned the neutrals are different than grounds in other ways.
For example, they never branch (they always stay with their associated
hot wires). They only meet at the main breaker panel.
The grounds, on the other hand, go all over the place.
Plus, most of the time, they're not insulated (although they may
also be green).
This web site won't let me post anything longer than about a dozen
lines or so, so I'm going to break this post up into multiple posts...
"Danny D'Amico[_2_ Wrote:
Correct. That's a requirement of the electrical code, but why that is,
I can't say that I fully understand. All of the neutral wires connect
to the neutral buss in the main panel, and that neutral buss gets
connected to ground, whether it be a plumbing pipe or a ground rod
pounded into the ground outside your house.
So it's 2-phase?
From Professor Cardell's web page at
"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."
What needs to happen in here is for people to realize that talk about
three phase delta and wye circuits may be interesting, but it's noise in
here. We DIY'ers recognize that there is three phase power available
for equipment that uses it, but it's not something that we need to know
about, interesting though it may be. And, while I appreciate the input
from the professional electricians in here, we all know that our brains
are excellent housekeepers and that what we don't use will soon be
thrown out to make room for stuff we will use. Three phase power, and
how to wire it is something my brain is just itching to throw out. It
needs the space for stuff it will use, like how to fix a fridge or
spread drywall joint compound smoother.
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 :/
On Saturday, November 23, 2013 5:37:59 PM UTC-5, John G wrote:
I guess the IEEE and it's power engineer members must
be among those knowing very little or just enough to confuse,
because they clearly speak in terms of two phases being present.
From a paper presented at a recent IEEE power engineering conference:
"Distribution engineers have treated the standard "singlephase" distributio
n transformer connection as single phase because from the primary side of t
he transformer these connections are single phase and in the case of standa
rd rural distribution single phase line to ground. However, with the advent
of detailed circuit modeling we are beginning to see distribution modeling
and analysis being accomplished past the transformer to the secondary. Whi
ch now brings into focus the reality that standard 120/240 secondary system
s 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 secon
dary phases are separated by 180 degrees instead of three phases separated
by 120 degrees. "
It could not be any more direct and to the point.
email@example.com wrote on 24/11/2013 :
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.
What all of this means is that analysis software and methods must now
deal with an electrical system requiring a different set of algorithms
than those used to model and analyze the primary system. This paper
will describe the modeling and analysis of the SINGLE-PHASE center tap
transformer serving 120 Volt and 240 Volt SINGLE PHASE loads from a
It is interesting that you snipped the last Paragraph which says SINGLE
How clear is that? :-?
On Saturday, November 23, 2013 7:34:33 PM UTC-5, John G wrote:
It's not a paragraph, it's part of the same paragraph.
And the part you referring to says:
"This paper will describe the modeling and analysis of the single-phase cen
ter tap transformer serving 120 Volt and 240 Volt single-phase loads from a
The transformer is single phase on the primary side. The loads it drives a
single phase 120v and 240v loads. No one is saying anything different. Ho
w can you ignore the elephant in the room where the author immediately befo
explicitly addresses the exact core of the issue:
"Which now brings into focus the reality that standard 120/240 secondary sy
stems are not single phase line to ground systems, instead they are three w
ire 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 s
econdary phases are separated by 180 degrees instead of three phases separa
ted by 120 degrees. "
He explicitly says that TWO PHASES ARE PRESENT and they differ by 180 deg.
That from an IEEE engineer presenting a peer reviewed paper at a power
Or an app note from an electrical eqpt manufacturer:
"The two legs, represented by Phase A and Phase B, are
180 deg apart.
Or this white paper from another electrical eqpt manufacturer:
Note the reference to Phase A and Phase B in the foot note to
the diagram and that they are 180 deg apart. And that the diagram
is clearly labeled Phase A and Phase B.
Are all of them among the confused, who know very little?
I have a degree in Electrical Engineering. Other than this
disagreement, is anything I've posted in these two threads
incorrect? Good grief.
What exactly is your definition of phase? Because it's derived
from one primary phase, you can never have more than one phase?
In electrical engineering, science, math, the most basic meaning of
the word phase is to express the relationship
between two periodic waveforms. In this case, in a split-phase 240/120V
service you have two different waveforms, they are 180 deg out of phase wit
each other and you can see it on an oscilloscope. It's every bit as real a
seeing 3 phase waveforms on a scope. The 3 phases are seperated by
120 deg, the split phases service is seperated by 180 deg. That is EXACTLY
what the IEEE engineer is saying.
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