I need help understanding AC electricity and generators (1/3 phase)

[LouNY]

Correct,
and in one of the numerous posts on this thread there was mention that if it was out of phase at times the voltage would be zero.
That is absolutely correct that is why it is called alternating as it crosses thru zero every cycle.

 

[strantor]

Since every text book in the world has a split phase transformer defined wrong you need to publish your own.

I suspect that most textbooks probably have it worded properly, such as "L1 waveform is 180 degrees out-of-phase with L2 waveform as measured from ground/neutral." But that's not what what 99% of people say. They say "L1 is 180 degrees out of phase with L2" which implies a connection scheme rather than a relative voltage measurement, and is incorrect. It's laziness. Relative voltage measurements should always be given with a reference point.

 

[LouNY]

I suspect that most textbooks probably have it worded properly, such as "L1 waveform is 180 degrees out-of-phase with L2 waveform as measured from ground/neutral." But that's not what what 99% of people say. They say "L1 is 180 degrees out of phase with L2" which implies a connection scheme rather than a relative voltage measurement, and is incorrect. It's laziness. Relative voltage measurements should always be given with a reference point.

Relative measurements of any kind or type should always have the SAME reference point of they are not relative.

 

[strantor]

Relative measurements of any kind or type should always have the SAME reference point of they are not relative.

Well then I guess we can't measure 240V anymore.

 

[LouNY]

You got it, especially as related to 120, it can be derived from the same transformer.

PS. I do believe panels of 30 years ago were more complex that todays, the plc has changed much of panel building.
I had many a panel build that combined pneumatic, with mv and ma (DC) signals, relays and relay logic then throw in a mix of
480 3 phase maybe even your own transformer, for 120 (AC) and possibly even single legged 230 (AC) for European equipment.
Shielding including grounded panel dividers then toss in an isolation transformer or two.

 

[strantor]

You got it, especially as related to 120, it can be derived from the same transformer.

Ok, this is starting to get plain silly. I think this has gone as far as it is going to go toward any sort of agreement or resolution. I think all in attendance understand and agree (whether or not willing to admit):

1. Voltage is a relative measurement, from point A to point B, and any relative measurement is perfectly valid so long as you specify what those points are.
2. Most oscilloscopes are ground referenced and therefore point A is almost exclusively always ground; or in other words often enough that the vast majority of folks feel comfortable giving voltage measurements relative to ground without specifying that they're giving voltage measurements relative to ground.
3. In a split-phase center-tap-grounded residential supply the voltage waveform of L1 is out of phase with the waveform of L2, as displayed on a ground-referenced oscilloscope.
4. Because of the de-facto convention of assuming a ground reference for oscilloscope measurements and public comfort in foregoing the requirement to provide two points for a relative measurement in this case, an alarming number of folks have taken to saying "L1 IS 180 degrees out of phase with L2" with the assumption it will be understood that what they really mean is "the voltage waveform of L1 is 180 degrees out of phase with L2 as measured to ground," with the former devoid even of any indication that it refers to a voltage waveform (much less a ground referenced one), sounding deceptively like an implication that the secondary is actually connected 180 degree out of phase.
5. These are the words most of us are comfortable using, no matter how flawed they are, and any attempt to correct them will be met with strong opposition. Opposition not only to correction of the flawed phrase, but to anything the hopeful change-bringer might have to say thereafter.

 

[CobyRupert]

“This discussion is ridiculous...”
....but has anyone mentioned that getting shocked by 120V only stings a little, but touching one leg of a 240V circuit really hurts!

 

[strantor]

“This discussion is ridiculous...”
....but has anyone mentioned that getting shocked by 120V only stings a little, but touching one leg of a 240V circuit really hurts!

One time I slipped and braced myself with a sweaty arm against a slip ring that had rectified 480V on it (650VDC). It was invigorating.

 

[CobyRupert]

One time I slipped and braced myself with a sweaty arm against a slip ring that had rectified 480V on it (650VDC). It was invigorating.

So the circuit was grounded?
That is, there was another slip ring with 0Vdc (ref. to ground)?

I’m not that familiar with DC fault currents. (Other than touching a wrench from a battery post to car frame, when incorrectly having the neg terminal connected first)
What happens when you touch 650VDC not referenced to ground, but only referenced to the neg (-) leg? Do you still get a shock even though the shorting to ground (through a person) doesn’t complete any circuit loop back to rectifier?

With ungrounded AC circuits, you can still get a shock because of the capacitance coupling (to ground) that passes a (fault) current, but with DC there shouldn’t be any right?

 

[strantor]

So the circuit was grounded?
That is, there was another slip ring with 0Vdc (ref. to ground)?

I’m not that familiar with DC fault currents. (Other than touching a wrench from a battery post to car frame, when incorrectly having the neg terminal connected first)
What happens when you touch 650VDC not referenced to ground, but only referenced to the neg (-) leg? Do you still get a shock even though the shorting to ground (through a person) doesn’t complete any circuit loop back to rectifier?

With ungrounded AC circuits, you can still get a shock because of the capacitance coupling (to ground) that passes a (fault) current, but with DC there shouldn’t be any right?

The DC was coming from a mains-connected 3phase bridge rectifier, so it was still a ground-referenced circuit. I dont know what was the current path through my body; I suppose I must have been touching something else conductive & grounded, and probably was. It wasn't a planned experiment or I would have recorded such information, but as it were, just a clumsy bumble, I was probably a lumbering storm of flailing limbs. All I remember is an alarming alien mating call, a gurgling shriek like nothing ever heard and only realized in the aftermath that it had come from me, and I was slammed backwards against the frame of the machine I was working on and blood was coming from a gash on my head.