Residential Split Phase 180deg Phase Difference

[Fred B]

The simplest I've seen that shows the degree of phase difference is not from the view of the sine wave or scope (many residential electricians will never get their hands on a scope), but from the geometry of a triangle. Generally a 3 phase will be drawn as a delta or wye and a triangle with points A, B, C on the corners. As OP had stated the phase shift is 120 deg from reference between C,B,A on delta.

Now on single phase you are only dealing with any one line of the triangle, if you take points A,B and you add a point N in the middle, the degree of reference between the 3 points will be a flatened triangle or degree reference from the three points from N to A or B is 180 degree.

Cancelling out on a single phase doesn't occur in the way you are thinking because that A,B reference are on opposite ends of the triangle line, perfect world and all working correctly, when A is + B is an equally - voltage, the only time it cancels is at the N point, because of the nature of AC power, always fluctuating from a peak value + to a peak value -. Kind of like a teator totter, when one side is up the other side is down, only time it as canceled out is at the N point (or point of pivot) when the teator totter it is flat, but won't remain flat if someone on each end pushing to keep it going (generator). That is what is represented on the scope in the form of a wave pattern, point A and B of the teator totter reacting relative to the pivot point N.
Overly simplistic but should be close to accurate. (Perfect world)

 

[Hv&Lv]

I would instead draw it with one line +, one line -, and the center tap with one of each, like this diagram. Incidentally, in my opinion, the two sine waves should be drawn the same, not opposite like they are here:

View attachment 2558792

Yeah.. that’s one of those “damned if you do… “ things..

Its hard to get people to conceptualize the idea with a single picture. Two or three including a generator with magnets going through the coil, with arrows showing current direction would probably be better.
But then the neutral currents with 240 loads and 120 loads combined with the whole canceling out as in a MWBC comes into play. Then the drawing gets messy.

IMO, If the waves were drawn the same the result would be two coils showing 120 volts only. They have to be opposite to show the 240 on a drawing.

Its one of those where the math shows it nicer than a picture… In college this wasn’t difficult. When I try to explain it to the guys here at work with no formal education, it’s difficult and I have to come up with all kind of ways to explain how it works. Jigsaw movements, arms flailing, whatever it takes to get the point across…
Seems like the first one with all new guys is “If this wire is good for 100 amps, that’s a 200 amp service…” Nope…

Mind you, the guys aren’t stupid by no means.. They are good at what they do. They just haven’t had the training to understand electricity, relaying, etc..
It would be no different than me trying to go into a chefs kitchen and understanding everything he does without the education and training.

 

[winnie]

The voltage and phase are relative to what point you are using for a reference in the system. The 180deg out of phase is a bit of an oversimplification since it is relative to the neutral point L-N loads rather than L-L loads,

I agree, the key is the point of reference.

To take it one step further, consider a high leg delta, where one can simultaneously see (and use) the 120 degree 3 phase difference and the 180 degree split single phase difference.

Jon

 

[Hv&Lv]