good grief.
making measurements by moving around the reference point (what you are calling the "-") is not how you measure correlated AC signals.

moreover, a 'scope is a time-domain instrument, and not a simple DMM with two leads and an ADC.  

the reason the trace is stable on the 'scope display is because of a concept called a trigger -- and this is an important concept to understand.
the trigger point can be tied to one of the input channels, or an external sync signal.  the former is very common for most measurement applications.
the trigger "ties" the input signal against the selected timebase.  

and when you do trigger off one of the input channels, and simultaneously display a second input channel, you may discover something.
with this arrangement you can understand if there is a timing offset (=phase angle) between the two channels.
and in the case of L1 and L2 hanging off a CT transformer, you will find that L1 and L2 have a 180deg phase angle between them.

this is graphically shown in this helpful post:
https://www.ar15.com/forums/general/Electrical-engineers-get-in-here/5-2454480/&page=2#i92835020

no.  it's not a DC battery, it's an AC source.  
the error you are making is suggesting moving the reference point when taking multiple measurements.  
that sort of approach is not going to give you the right information.
change one thing at a time -- and importantly, keep the reference point the same.

this is not the primary reason for three wire split phase.
the reason for three wire split phase is that it doubles the amount of power that can be delivered while only increasing the amount of copper by 50%.
this efficiency comes about because of the 180deg phase difference between L1 and L2; the net result is that the N only has to carry the difference in abs(L1-L2) current.

as soon as someone says "L1 and L2 are in phase", the very next question should be "ok, then how is the POCO drop N conductor sized the same as the L1 and L2 conductors?"

go inspect the POCO service entrance wiring at your panel.  L1, L2, and N are all the same sized (wire gauge) conductors.

if L1 and L2 are "in phase", the N would have to be larger diameter (=greater ampacity) because it would have to carry the sum of the L1 and L2 currents.
but as you can see from your house and a bazillion others just like it, the N wire in the POCO drop is not in fact larger diameter than the L1 and L2 wires.  

and the reason that this is possible is because L1 and L2 are 180deg out of phase, and as a result the N carries the difference in L1 and L2 currents.

Not around here its not around here the Neutral from the power companies drop is half the size of L1 and L2. A drop with 2/0 Al will have a 1/0 neutral a 4/0 drop will have a 2/0 neutral

interesting.  in a split phase system, the worst case N current occurs when L1 current = max /and/ L2 current = 0 (or vice versa).
using the naming convention from the diagram below, if all of the "A" loads are on, and all of the "B" loads are off, the N is carrying the sum of the "A" loads.
and in theory, this could be up to main breaker rating (e.g. 150A, 200A, etc), so the N has to be sized against that.
in practice, however, the N current is the abs(L1-L2) current (due to the 180deg phase angle) -- and so if there is "reasonable" balance of "A" loads and "B" loads, the N is carrying a few to tens of amps.

Break that neutral and grab both sides you will find voltage.

At any give point in time, it's a DC measurement.
AC is an infinite amount of DC measurements (or should I say, as slow as your scope can sample).

Lot's of things not understood by many in this thread.

Moving the reference point is not changing the "right" information, it's only changing what you are seeing on whatever instrument you are using.

The heat signature of a deer walking in your yard can't be seen with naked eye, but use a IR instrument and now you can "see" the IR (instrument is a Rf mux), you can choose to have dark as hot, or white as hot, makes no diff at all, it's the same heat signature, same data.

The bad scope view is showing all the right info, just have the scope not setup the correct way for it to match the actual math and physics of what's really going on.

I gave one example as to why grounded CT was safer, I did not say it was the primary reason, and I did say there are more reasons why grounded CT was better.

Hah, there lays the confusion.

You are framing out of phase as if the the CT secondary provides + -- + to the 2pole+gnd panel. That's not really what's going on.

Look at the coil from a charge view. When the mag field pushes in one direction, one end of coil become + charge and the other end - charge, but the CT is not zero charge. I had already explained this.
At peak voltage one end is max + and the other end is max -. Now lets look at the CT at that time.

1) the CT is less + than the pos end
2) the CT is less - than the neg end
3) the CT is not zero
4) in fact, the CT is dead smack in the middle of the two ends at all times. If you wish to call it "ground" "earth" "zero", so be it, those are just labels.

Using the notation of + and - really only tells use in what direction the nice electrons will go, which is always - to +.

Hence why a CT is not a + -- +

In reality it's more like + +- -

No different than placing two 9v batts in series.

For two inductors in series that add their voltages, those two inductors (coils) have to be in-phase to add (windings in same direction).

Want proof, take two inductors and place them in series with windings in same direction. Put your AC volt meter on the ends, wipe the inductors with a magnet.
Ok, meter said something nice.
Now, disconnect inductors from each other, flip one over 180deg, connect them in series, connect the meter at the ends, what do you get?

So now do you still think the 1ph CT xfrmr (nameplate says "1ph") is delivering two phases, because saying "two 120's 180deg phase shifted" means two phases, which would be no diff at the ends.


The diversity issue you mention is a real thing, but it's not actually seen in a 1ph CT.

To illustrate the issue you can simplify down to DC.

Two 9v batts with + ends, and the two neg's connected. They are technically 180 from each other with a common neg. 3 wires come off the batt connection all the same size wire. A load end to end is ++, hence no diff, no amps. Place identical loads on each batt, you get 2x one load of amps on the common wire. This example is a product of out-of-phase power sources with a common middle point, the vector sum of amps appear as two vectors in-phase on the common line. That's a ampacity issue.

Hence, this is exactly what we don't see with the CT xfmr, the amps in the CT wire (you call it grounded N) carries the diff of L1 L2 and will never exceed just L1 or L2 amps. This is because the diff in amps on the CT is always two vectors that are in opposite directions (your "180"). When the L1-N and L2-N loads are identical, the vector sum on the CT = 0.

Vectors of amps does not define the phase of voltage supplies, but the mag field does. In this batt example, amps flow neg to pos, so two batts side by side with their neg connected together, with identical coils across each batt with winding in same direction (a CT coil), the left coil makes a mag field that is 180 from the mag field the right coil is making. The amps on left coil is flowing right to left, while the amps on right coil is flowing left to right.

I hope this helps.

Ah, or perhaps they have oversized L1 L2?

Relying on diversity is not a great practice, so I suspect they are oversizing?
What size KVA xfmr is it that's using 2/0 with 1/0 CT to service entrance?

You say of the battery example:

“They are technically 180 from each other with a common neg.”

But batteries produce voltage without regards to any magnetic fields. A battery does not care if it is 180 or 120 or whatever degrees from the other. As long as you don’t change change which terminals you are measuring with, the voltage stays the same. But just as you pointed out, if you flip an inductor over 180 degrees, as long as you don’t change which terminals you are measuring with, you will see an equal and opposite voltage from any change in the magnetic field.

So to make a fair comparison, if a battery is acting like an inverter 180 degrees from another inverter in a magnetic field, the battery would have it’s polarity reversed (equal and opposite voltage), so the circuit would be with the + of one battery connected to the - of the other to form the equivalent of the center tap. Which is as you said like two 9v batteries in series.

Relative to the center tap, each leg in a 1ph transformer acts as if they are 180 degrees from each other in regards to the magnetic field driven by the primary.

"Acts" is just how you view it.

The primary is single coil, the secondary is single coil with a CT. Each coil is wound in one direction for all turns of the winding.

The primary's magnetic field grows from zero, reaches a peak and then collapses back down to zero. can never be neg in magnitude, but it's poles will swap at 60Hz. One mag field, one coil, 1ph. Now, the secondary is inductively coupled and is acted upon by the mag field that is created by the primary. That pri mag field acts upon the whole sec winding at the same time, and it's a single mag field across the whole coil. To obtain electrically the dual sine wave on scope that appears to be 180 shift, the voltage seen across the CT sec winding would need to be + - - + (CT in the middle, etc), which is not possible when a single mag field cuts the full sec coil all at the same time. To literally get what you improperly see on the scope (two sines 180 apart) you would need to either physically fold 1/2 of the sec winding 180, or use two mag field where each mag field sweeps only 1/2 the sec coil (end to CT), and, the mag fields would need to always be 180 from each other (polar ends always opposite of each other) and flipping at 60Hz, or, 1/2 the sec coil would reverse it's winding direction and one mag field would create the + - - + on 1st mag polarization, and then - + + - when the mag field flips polarization. This last example it like connecting two 9v batts + -- + with the middle as common, and then flipping them at 60Hz, and at any given time the diff between the ends = 0, but end to middle common ("CT") will be +9v for 0.008333sec and then -9v for the next 0.008333sec, flipping back and forth.

The whole scope issue is visual BS only, and arises because 'you' are connecting both probe gnd's to the CT, 'you' literally have swapped the probes 180deg.

Take two 9v batts and connect them as + -+ - ("CT" in the middle). end to end you get 18v, end to CT you get 9v, but now grab your handy Rigol and connect your probes + -- +, hmmmmm, ch1 says +9v but ch2 says -9v. Hmmm, is that odd, "two phases" that are 180 from each other, or is it just the way you connected the probes? I venture a good hypothesis that it is because of the way the probes were connected.

Why would you connect the probes any way other than +--+? That's how the wiring works for the two 120V circuits! You wire the hot to the ends, and the neutral to the center terminal (one leg is the inverse of the other with respect to the primary of the transformer)! Of course if you connect the probes -+-+ (with differential probes of course not grounded probes) the waves measured by the two probes will be in phase. The waves measured by the probes will be in phase if you wire the probes +-+- too.

Measured 4 different ways.

-+-+ In Phase
+--+ 180 degrees out of phase
+-+- In Phase
-++- 180 degrees out of phase

Basically, the reason you see the 180 degree phase difference between the two 120V legs is because one of the legs is literally wired 180 degrees from the way the other one is.

PS: A note on oscilloscopes and probes. With standard oscilloscope probes, all measurements are references to a single ground reference. That is to say that all the ground clips and (if your oscilloscope is not battery powered) the ground plug of the power supply are wired together. Whatever you do, the "-", of grounded oscilloscope probes cannot be connected to different wires otherwise you you will short those two wires. The only wire that has 2 connections in this notation, is the center terminal. Thus with grounded probes the +--+ measurement is the only one you can even do. Even then I would not recommend it. If you tried any of the other measurement configurations with grounded probes, you would probably blow up your probes. So when you say "The whole scope issue is visual BS only, arises because 'you' are connecting both probe gnd's to the CT, 'you' literally have swapped the probes 180deg." You don't get a choice, connecting the ground connection of the probes to different locations and getting any measurement is impossible.

Each leg is a sine wave oscillating 120V from the middle zeroV, and 180 degrees out of phase and in reference to 0V which is either the neutral or ground. For electrical purposes there is no difference. The power plant is also grounded to the earth and the return current path is the earth, in the soil. Because the waves are 180 degrees out of phase, if you connect them, then the difference at peak is 240V, instead of 120V with reference to each other, and no earth return path is needed to complete the circuit with the source alternator as now the path is between two sets of windings on the same alternator instead of from one set of windings and back to that same winding via earth.

Jamming the CT to earth (which is also EGC and chassis gnd) is by choice. You won't blow up probes if the CT is isolated from earth/EGC.

Take a small AC xfmr, 120vac to say 9vac. Take a 100k potentiometer and connect it's ends to ends of xfrmr (9v). The wiper on pot becomes a tap, park the wiper at some arbitrary spot and then connect 2ch scope probes like "probe1(L1), probe1-gnd on wiper, probe2 on wiper, probe2-gnd(L2)".

I see two in-phase sines of different Vrms. Now move the wiper around.

Ok, change up probe2 so you are connected "probe1(L1), probe1-gnd on wiper, probe2-gnd on wiper, probe2(L2)".
Ah crud, magically creates a 2nd phase 180 from the other, but with different Vrms per channel. Put the wiper dead-nuts middle and Vrms of each channel is the same.

Once again, simple experiments and simple mathematical analysis shows us the 1ph xfrmr does not magically create a 2nd +180(or-180) phase. It just appears that way because someone decided to jam the CT into earth and call it "zero". Earth is also the EGC and chassis-gnd. But the trickery seen on the scope (two sines 180 apart) is just a product of how the probes are connected, it's literally one probe is physically flipped 180.

The resi xfrmr that has a nameplate that says the secondary is "240Vac(rms) 1ph 60Hz CT" cannot be changed, it's 1ph power and the tap cannot change that.

Have fun connecting those scope probes, but be careful when mucking around with 240vac(rms) and earth gnd'd CT.

You mean 1/2 of full sec winding is either folded over the 1st, or for 1/2 the full winding the direction of wire wraps is wound in opposite direction? In both cases, 1/2 full winding will have mag field polar ends flipped 180 from the other 1/2, and in this case the diff of voltage at the ends (L1 L2) will always be zero, and in fact this raises the issue mentioned many posts back, the CT wire would be carrying L1+L2 amps, and as such would need to be sized 2x bigger.

This is exactly the DC analysis of the AC, eg; two 9v batts connected +_______- -______+ (CT in middle). The CT carries vector sum of both ends (L1 and L2), and in this case the vectors are always in same direction, thus the resultant vector will have a greater magnitude. Want this to look like AC, ok, flip both batts 180deg at 60Hz at the same time.

The fact that in the std 240vac CT xfmr we agree the CT carries the diff of amps and never more than L1 or L2. This fact alone tells us the mag polar ends are N on one end and S on the other end, and then flips 180 at 60Hz. Single set of mag poles, one mag field, one single coil that has a CT, all 1ph.

Hey, it's miller time somewhere.

It is the new common core electronics maths diversities.

If you “fold over” winding of one direction, the winding direction does not change . You would have to generate a mirror image to get the winding to be in the opposite direction, there is not a physical transformation to do this with an inductor. So folding it over so to speak will reverse the apparent magnetic field on one side, but not reverse the winding. It's the same winding direction all across the secondary, so you get the opposite voltage depending on which way you look from the CT (L1 to L2 voltage 2x L1 to CT).



“Ok, change up probe2 so you are connected 'probe1(L1), probe1-gnd on wiper, probe2-gnd on wiper, probe2(L2)'
Ah crud, magically creates a 2nd phase 180 from the other, but with different Vrms per channel. Put the wiper dead-nuts middle and Vrms of each channel is the same.”

This here, yes! The CT is connected dead center. Relative to it, it effectively creates two phases 180 degrees from each other on the L1 to CT and L2 to CT! It's a product of how the probes are connected, and in standard 120V circuit wiring from a CT transformer, a product of how the circuits are wired.

Also: "then connect 2ch scope probes like 'probe1(L1), probe1-gnd on wiper, probe2 on wiper, probe2-gnd(L2)'."  How do you keep from shorting the wiper to L2 through the ground connection of Channel 1 and Channel 2? The grounds of the two probes are shorted together inside the oscilliscope.

I recently bought a house.  The previous owner was a machinist.  Very smart guy, fairly obsessive about labels, diagrams, and documentation (probably related to his success in a forty year career), but not an electrician.  He built a nice semi-finished shed in the back with a sub panel and all, had everything labeled.  "Well pump", "hot tub", "north outlets", "south outlets", "lights", "leg 1", "leg 2", "ground", "floating neutral"... begin brick-shitting.  I immediately cut the breaker in the main box to the sub panel and looked closer.  But it all ended well.  Turns out that to him "floating" and "unbonded" meant the same thing, and he had four properly-sized wires going back to the main panel.

You guys are talking the equivalent of difference between frequency modulation and phase modulation in RF transmission.

it's not obvious to some here that split-phase power is not a form of polyphase power.
just because the two CT legs are 180 degrees apart in phase does not mean it's a 2 phase (=polyphase) system, because by definition there is no net phase vector (= no phase rotation).
instead there are a lot of mental gymnastics involving moving the reference point on the 'scope leads as you go to explain things away.

https://en.wikipedia.org/wiki/Polyphase_system
A polyphase system must provide a defined direction of phase rotation, so that mirror image voltages do not count towards the phase order. A 3-wire system with two phase conductors 180 degrees apart is still only single phase. Such systems are sometimes described as split-phase.

The other point here is just because a system is a single phase, does not mean that one of the legs can't be 180 degrees out of phase compared to the other.

Thank you, AR-JEDI. Your explanations are quite good and logical. I appreciate them. The only time I get quizzical, is when this thread starts talking about batteries and changing scope points. Thanks again.

Don't worry. Batteries are about the most boring thing you could connect an oscilloscope to.

this and the fact that it's easy to make differential measurements with a 'scope by clipping the two probe ground leads together(*), selecting CH1-CH2 mode, and then only using the probe tips for measurement.   this approach allows one to measure any voltage the probes will safely stand off, without risk to the equipment nor the scope.  the equipment under test only ever sees the input impedance of the probes, and never the chassis ground.  and hence, given a four channel scope, you can concurrently measure the two legs of a split phase power system (using the N as the reference for the first and third scope inputs), triggering on CH1, and observe directly that there is a 180deg phase shift between the two legs.

ar-jedi

(*) someone will be along shortly to note that it is not strictly necessary to clip the probe ground leads together, since the channel grounds are tied together at the scope anyway.  pragmatically, connecting the two probe ground leads together makes it less likely that one will wander off and drop into your circuit...

Probes should be isolated from each other.

As far as the coil goes, try this

see this line ------------------------------------------- , take right hand and hitch-hike right-to-let (thumb pointing right).

Now if I fold the line over itself at a center point, it will kinda form a letter 'U' lying on it's side, open end facing left. Now, use the same right hand rule and follow the line of the U starting on bottom half, follow the U all the way around to the other end, you basically sweep out the 'U' in 3D space. Notice what happens, the coil wrap direction flips, your fingers flipped, and your thumb is now 180 from the 1st half of the sweep.

No. What I meant by this: “Basically, the reason you see the 180 degree phase difference between the two 120V legs is because one of the legs is literally wired 180 degrees from the way the other one is.”

You have your center tap:

CT

You have coil to the left towards L1:

L1 ////////// CT

Then 180 degrees from that you have the other side of the same coil wound in the same direction going to L2.

L1 ////////// CT ////////// L2

Note that this 180 degree physical = 180 degree phase difference is not generally applicable to any phase difference in a single phase system. If you somehow bent the inductor around the center tap so one leg was 120 degrees from the other, it won’t give you a 120 degree phase difference. Just a lower voltage 180 degree leg since the primary only has the one phase vector.

As to the sine wave from L1 to neutral, that was shown earlier.

Are we not looking at a “graph” of the voltage changing?

Are we looking at (N)0 to (L1)+120v swings? If so is it always that way or are we seeing (N)0v to (-120v to +120v).

Or maybe it’s something else all together?

You are seeing voltage over time. Each sine wave at 60 Hz occurs in about 16.7 milliseconds. For a trace of L1, or L2 for that matter, to the CT, you are seeing the voltage at zero, then rising to the full crest positive and then crossing zero again and going the whole trough negative and then back up to zeo again to start another cycle.

ETA, @ 120 volts AC RMS, you see it go from zero to +170 volts high, to zero then -170 volts low. The RMS value is also the DC equivilant of the AC signal.

While there is actual "electron flow" as described, that process is exponentially slower than the actual voltage traversing the wire.

Voltage is a vector? I know amps and 'B' field and 'e' field are vectors, but not so sure voltage is a vector. I mean you can apply vector math to voltage, but it's just to obtain the magnitude of the resultant.

For sake of this forum not supporting math or symbols in it's WYSIWYG editor.
Lets say ///////////////// is winding one way, and \\\\\\\\\\\\\\\\\\\\\\ are windings the other way.

If the xfrmr is L1////////////////CT///////////////////L2, then it's all wound the same way, and you get only single B field with one North and one South pole.

This editor wont let me illustrate, but if you flip the right half (CT to L2) up over the left half (L1 to CT) you get this (electrically, not visually, but I will show how you can see it on paper)
L1//////////////////CT/\\\\\\\\\\\\\\\\L2 , and this would create a set of NS poles, and the V diff between L1 L2 would always be zero.

On paper, take a pen and write this "////////////" on it, on top of each line place a small circle with x in it, on the bottom of each line add a small dot. This represents the amps flow through the wire, top side is into the page, bottom is back out at you. Now, simply turn your paper over 180, the amps are flowing 180 from before. This creates an opposing B field to the other coil. Remember that when you fold 1/2 of the CT coil over, you are not changing the CT connection (it's one big long wire, etc). Take a spring, stretch it a bit in the middle (the CT), then fold one side over the other. It's same as flipping a magnet over, the poles swap position.

Also remember the amps flow at any given time (except at a zero crossing). Amps will always be flowing across the full coil in direction of L1 to L2, or L2 to L1. This is how the CT will carry the diff between L1 and L2 amps, but never greater than L1 or L2, etc. If the amps so happen to terminate on the CT, that's fine, but the direction is what matters.

Look at a CT coil, amps will always be going left, or right, but never left and right at the same time.

The above is not necessarily correct.  While many scopes have all the channels share a common DC ground, there are some that do not.  For example, Tektronix makes two-channel and four-channel scopes where each scope channel ground has 600Vac of isolation relative to other channels and earth ground.  The series is TPS2000B; I have spent many hours using a TPS2014B (four-channel with 100MHz bandwidth) to measure inverter voltages, which I referenced to 170V below earth (voltage doubler using 120VAC input with neutral as the counterpoint of the two DC link capacitors to reduce motor currents with the positive portion of the AC waveform charging the upper cap and the negative portion charging the lower cap with balance resistors), and other channels were measured relative to earth ground or to an isolated voltage created with a flyback design.  I have also used the scope to watch how the isolated output changes as the AC input varies.  This scope is cool because the chassis is not earth unlike many common scopes and active differential probes are not needed.

Then don't flip the coil or fold the coil or whatever you are doing to get the coil to be wound the other way visually or electrically or whatever. “L1 ////////// CT ////////// L2” is the illustration I gave and “L1////////////////CT///////////////////L2" is the illustration you gave for how it's wound. We are apparently both arguing the same thing about how the transformer is wound.

Regarding this part:

"Also remember the amps flow at any given time (except at a zero crossing). Amps will always be flowing across the full coil in direction of L1 to L2, or L2 to L1. This is how the CT will carry the diff between L1 and L2 amps, but never greater than L1 or L2, etc. If the amps so happen to terminate on the CT, that's fine, but the direction is what matters.

Look at a CT coil, amps will always be going left, or right, but never left and right at the same time."

We are apparently also in agreement. The point I am making is that at any instantaneous point in time, one leg can have amps going away from the CT, while the other leg has amps going towards the CT. The thing is that while amps go the same direction on the coil for both legs at the same time, one of the legs is literally wired 180 degrees from the way the other one is.

keep going, i'm almost there.  

Yall have lost me on oscilloscopes and other crap.

But do you believe that a secondary coil is wired / wound like you say?

L1//////////////////CT/\\\\\\\\\\\\\\\\L2

If so, that's completely wrong.

If it were that way everytime a lineman cut a transformer 2 wire (for 120/208 wye)
It would burn up the transformer.

The ends of each 120 volt coil is wired in series and the ends of the coils are labeled A,B,C,D. The CT is B and C. A is L1 and D is L2

When a transformer is cut 2 wire you basically are paralleling  two 120 Volt coils on top of each other.  

Normal 120 240 configuration

L1(A)//////////(B)CENTERTAP(C)////////////(D)L2

When cut 2 wire

L1(A&C)///////////////(B&D)L2

Either L1 OR L2 is designated neutral, doesn't matter which.

I did not say it was wired that way, I said it's wired normally like L1//////////////////CT///////////////////L2

But when you flip the right half 180 on top of the L1-CT 1/2, you electrically get L1////////////////CT\\\\\\\\\\\\\\\\\\L2

If you physically wire the secondary like L1////////////////////CT\\\\\\\\\\\\\\\\\\\\L2, L1-to-L2 will always be zero. This is the equiv of two 9v batts wired + -- + or - ++ -.

And no, a two wire sec may or may not have one end jammed into earth. Your 240v CT would be HOT-HOT if you rip the CT out. Is this dangerous? Not really, you have HOT-HOT wiring in the home, but the 240v items are less commonly touched. HOT-HOT with EGC is still very safe, this is how a two-pole GFCI works (you dont need the CT for this GFCI breaker to work).

What does Europe use throughout their homes, 230v50Hz. Do they have one end of the 230v secondary jammed into the earth ("ground, zero volts") reference point? Something to go look at, quite interesting.

It's been a standard for a long time to use earth as the reference point, and as I mentioned many posts back, you too are touching earth quite often, so you gain a safety factor when earth is used as an electrical reference point vs having 100% isolated power lines. Pros & Cons even with power.

The CT amps are vector sum. The CT is a point on the L1 to L2 full coil. Do not look at it with a 3rd leg hanging down off the CT point. But now take two pigtailed light sockets and connect one L1-CT and the other L2-CT (CT as the N common). The bulbs are 100w each. Now look at the amps direction at the 1/4 and 3/4 points between the ends.

Now take your point in time (not a zero crossing), at that time the amps will be [L1 to CT , CT to L2] and on flip cycle (L2 to CT, CT to L1], hence the amps across the coil is always in one direction at any given time, L1 to L2 or L2 to L1. With identical loads, the full amps walk right through the two bulbs end to end (L1 to/from L2). When the loads are different some amps will terminate at the CT point (recall that all the amps that terminate at the CT is a vector sum which yields only a single resultant).

And this folks is why a secondary coil with CT is electrically + -+ - , or - +- + , or zero at any given time. This is exactly the two 9vdc batt example of placing them in series, and is exactly the potentiometer example I gave.

Lets give the transmission line example where the guy dangling from helicopter is connected to the high volts line.

Visualize a secondary coil with CT, stretch it out a bit so each coil has a little space between them, and the copper has no insulating enamel on it. The coil between L1 L2 is 240vac(rms). The physics of what's going on in the coil is when you take one end of the coil (L1 or L2) to be your reference point. Now, you are wearing thick rubber boots, your finger starts on L1 and follows the outside of the coil around and around and around until you make it to L2. For sake of ez analysis you do this while at a peak in sine wave at L1. As soon as you touch the coil at L1 you become charged at that voltage (if L1 is your ref point then you are zero diff), but as you "walk" the coil to the other end with your finger your electrical potential increases, and will never decline, keeps increasing until you reach L2, the full coil voltage. At no time ever do you walk down to the CT and then back up to the other end.

Moving the reference point to the CT only moves the reference within the math, but the physics of the coil has not changed a micro ounce. 1ph and 1ph only.

Yes, there is only one phase on the coil. This is only a 1 phase system. There is no argument there. But relative to that phase, one of the 120V legs is wired backwards making it 180 degrees out of phase relative to the other leg.

Can you please do me a favor? Since the start of the thread, you have been using the abbreviation, "CT", in your posts. You never defined what a 'CT' is. Which makes trying to understand what you are saying, hard. In addition, I have always used the abbreviation, "CT," as "CURRENT TRANSFORMER." All this time, I have been substituting the words, "Current Transformer," whenever you say, "CT." Most of the time, it makes no sense, at least to me.

Nothing is wired backwards. The coil is wound the same way end to end L1////////////////////CT//////////////////////L2

Where you stick those probes for making a measurement is what's tricking you. L1-CT vs L2-CT is still all single phase, when you make CT the common reference it's the exact same thing as two 9v batts wired + -+ - or - +- +

The two 1/2 coils (1 coil with a CT) are wired in series. Coils come with a dot on one end, two coils in same winding direction in series would be dot-nodot----CT----dot-nodot.

There's no 180 business going on, the math and physics tell us so.

Center Tap.

Thank you, sir. Key bit of information.

The center tap is the same for the two legs. It’s wired to the same side of any 120V outlets on either leg. For one of the legs the hot wire is the dot end of the transformer coil and for the other leg the hot wire is the nodot end. That’s backwards from one another.

CT Center Tap.

With all this 180 talk, maybe the CT can be called a 180tap, and a tap at the 1/4 position can be called the 90tap (or 270tap if you flip it 180).

Kept reading it that way too until ‘center tap’ popped into the melon...

How one decides to attach wires to a 3 leg'd CT coil is up to the person doing the wiring. The "dot" notation is standard nomenclature, has some definitions around it. A single coil with a CT has only one "dot" on it. If I start with two individual coils and I want to make the inductor bigger so I can get more volts at the ends, I wire the two coils in series like "dot//////////////nodot --- dot/////////////////nodot", the middle forms the CT. This is exactly the DC example of two 9vdc batts + -+ -

"+ ////////////////   -  +   ///////////////// -"
"dot//////////////nodot --- dot/////////////////nodot"

I promise you all, building an AR is more complicated than this power stuff.

The commie FTA has their public comment sh1t open now, I hope you all are ending your comment with "now GFY".

The "dot" notation of inductor is really a DC thing. AC is nothing more than infinite amount of DC analysis. With AC the dots "flip sides" at 60Hz(usa).
If I gave you two inductors, each in a hermetically sealed housing and I said "here, wire these in series to get 2x the voltage", you would not know what way the coil windings were going in each, but with a dot labeled on one terminal you immediately know which end is which, making it ez to wire w/o having to energize it to take a measurement. You wire them like you would two 9vdc batts to get 18vdc, etc.

That would be like the 240V circuit of the center tapped transformer yes. It does not have much to do with the relationship between the 2 120V legs created from the center tap.

I think most here are in agreement that there is only one phase, split in the middle. No matter how you slice it, it is still just a single phase. What get's under my skin is people who refer to both legs as "phases", as in plural. Out of phase with relation to the center tap, sure, but hardly two different phases.

Drives me nuts when people post about 110 and 220VAC. That changed around 1984.