On Monday, July 23, 2018 at 10:14:18 PM UTC-4, wrote:
On Mon, 23 Jul 2018 17:47:02 -0700 (PDT), trader_4
wrote:
On Monday, July 23, 2018 at 8:24:43 PM UTC-4, wrote:
I've never seen a two-phase residential panel at lowes or home depot..Â* Since they're so common, would you provide a link to one at homedepot.com or lowes.com?
OK, It has been 45 years since I have worked as an electrician. Perhaps the proper term should be dual phase or split phase. Does that work for you? I really didn't expect I'd be waking anyone up by responding to a 7 year old post.
We went through this round and round a few years ago. I was somewhere close
to your position. I said something along the lines that there are in fact
two phases present, 180 degrees apart. But that they are derived from one
of the three phases coming down the street and commonly referred to as
split-phase. But when you spit-something, what do you get? Two things.
I wouldn't call it a two phase panel though, that's not the common term
for it. But it is very common to refer to each of the hots as a phase.
I even found a presentation a power industry engineer made at
a conference where he made the case that to correctly analyze a split-phase
system you have to treat it like what it is, a system with two phases.
The other argument is that if I start with a 3 phase system going into
a building, everyone agrees that there are 3 phases there, right? You can see
them on an oscilloscope. Now let;s remove one. How many phases now?
Two. Now instead of the phases being 120 apart, let's move one so that
they are 180 apart. How many phases now? Two. And if you look at it on a
a scope, it looks exactly like a split-phase gsystem going into the
same building and it behaves exactly like it. Electrically you can't
distinguish one from the other, they are the same thing.
That's my case, others will probably draw different conclusions.
There is single phase, 2 phase (that I doubt anyone here has ever
seen) and 3 phase. If you only use 2 legs of a 3 phase circuit, it is
single phase.
You have to start with the electrical engineering
definition of phase. It's simply the relationship between two periodic
waveforms. That's how we got the term three phase power to begin with.
It's based on the fact that the power is being generated as three separate
waveforms which are separated by 120 degrees.
Here is a good discussion going back and forth:
https://forum.allaboutcircuits.com/t...-phase.105861/
I agree with Wbahn, the group moderator there, he's saying it's about semantics.
And note whenever anyone is challenged as to why it can't be called two phase,
it all falls back to arguments, like "but two phase was 90 deg phase difference
and it doesn't exist anymore". When challenged along the lines of how you
define phase, why if you change 90 to 180, which is just one of the many
possibilities, it suddenly can't be called two phases anymore, they have
no electrical engineering answer, no definition, it's just that they
say it isn't. Change the phase angle
from 90 to 95, would it still be two phases? Why when it reaches 180 is
it no longer two phases? When it's at 185, would it be two phases again?
The argument Wbahn makes about a single shaft generator, instead of
supplying 3 phase, make one that supplies 2 phases, at the 90
deg if you like. Two windings, differing by 90 deg, supplying two
hots with a common neutral. Would that be two phases? If not,
why not? And if yes, then why isn't it two phases if I change the
phase angle to 180? If you agree that there are two phases still
there, then that is indistinguishable from the split-phase service
that enters your house. It's all about semantics and you have to
start with the definition of phase. Phase is simply the relationship
between two periodic waveforms.
Here, from MIT, an introduction to power systems, where they start out
with the simple case of a power system with two phases.
Note it's only about two voltage sources connected to two
loads, with two voltage sources that can be at any phase angle.
Nothing about where the voltage source originated from or what the phase angle
is. Nothing about magic happening at 180 degrees, where it's no longer
a two phase system. It's the completely general electrical engineering
case of what defines a two phase power system and how you analyze it.
https://ocw.mit.edu/courses/electric...061S11_ch3.pdf
Make those two voltage sources be the two sides of the transformer on the
pole at your house and it;s the split-phase service that serves your house.
Where you ground that does not change the number of phases.
In fact 3 phase center tapped delta is just your regular single phase
center tapped transformer connected to a delta primary with another
transformer (or two) providing the 3d phase.
OTOH if you corner grounded that delta you would have 2 (hot)
ungrounded conductors and a neutral with 2 pole breakers but it is
clearly still 3 phase.
Two phase is a totally different breed of cat with 2 phases (4 wires)
90 degrees out of phase. This will usually be 2 transformers center
tapped with the center taps grounded (5 wire).
Split phase is a type of motor winding, perhaps the most common for AC
compressors and other applications that use a start capacitor and no
run capacitor. The "phase" is "split" by a start winding 90 degrees
out of phase with the run winding.
How you generate it doesn't matter. When this came up last time, I
even gave you a presentation made by a power engineer at a power industry
conference, about how split-phase service needs to be analyzed as a
two phase system, because that is actually what it is. I believe it
was also published, because I found it online. I don't think he got
laughed out of the room, but at the very least it was a power industry
source that said exactly what I'm saying. I just looked for it again,
couldn't find it. I'll look again later.