Is split-phase AC the same as "regular" AC?

[Fried Chicken]

I mean for all intents and purposes...

If you have 240v split-phase AC (as is common in the U.S.) is that mathematically, or technically any different than 240v to ground?

[bdunham7]

If you have 240v split-phase AC (as is common in the U.S.) is that mathematically, or technically any different than 240v to ground?

Yes, it is only 120VAC to ground on either line, that's one of the main points.  It's like a center-tapped transformer vs one without the CT.  How that affects a particular situation or device depends on a lot more specific information.  But if you have an isolated heating element or insulated motor then those devices won't know the difference provide the insulation is rated for a few kV as it should be.

[Analog Kid]

I mean for all intents and purposes...

If you have 240v split-phase AC (as is common in the U.S.) is that mathematically, or technically any different than 240v to ground?

Not sure just what you're asking here.
No, it's not the same as 240V to ground;
Each phase is 120 volts to ground.
Since the phases are 180° opposed to each other, there's 240 volts between the phases.
But you already knew that.

The only similarity between 240V split-phase and your notional "240V to ground" is ... 240 volts.
But in the case of the split-phase power ground is inbetween the phases.

So I'd say no, no mathematical or technical similarity.
Have to see what others say here.

[Randy222]

In US, the 240v is 1ph end-to-end transformer. You then center tap that and jam that tap into the earth. The center tap creates two inline coils where each coil creates 120vac(rms). Two in series creates (from the mag field) the 240vac(rms) end-to-end.

A "split" or tap could be done anywhere. If you wanted 60v and 180v then you tap it that way, it's still 240v end-to-end.

[brucehoult]

In US, the 240v is 1ph end-to-end transformer. You then center tap that and jam that tap into the earth. The center tap creates two inline coils where each coil creates 120vac(rms). Two in series creates (from the mag field) the 240vac(rms) end-to-end.

A "split" or tap could be done anywhere. If you wanted 60v and 180v then you tap it that way, it's still 240v end-to-end.

A couple of years ago a fault developed at the transformer at the road, and I had one phase 140V and the other phase 340V!

Surprisingly few things cared, either way. Mostly on the low voltage side the coffee machine pump wouldn't run, and the oven took an hour to come to pizza temperature instead of 15 minutes.

I had one cheap Chinese wallwart let out magic smoke, and there was a POP in my 3 weeks old dehumidifier and it stopped working. I took it back to the Noel Leeming store (not even the same one I'd bought it from actually) and said nothing and they had it fixed for free in 2 or 3 days.

Someone from the lines company came and pulled the fuses on the low voltage side and replaced them and then everything was back to normal. And they scheduled the same on the 11kV side as apparently they hadn't been changed in 40 or 50 years.

[AVGresponding]

In US, the 240v is 1ph end-to-end transformer. You then center tap that and jam that tap into the earth. The center tap creates two inline coils where each coil creates 120vac(rms). Two in series creates (from the mag field) the 240vac(rms) end-to-end.

A "split" or tap could be done anywhere. If you wanted 60v and 180v then you tap it that way, it's still 240v end-to-end.

A couple of years ago a fault developed at the transformer at the road, and I had one phase 140V and the other phase 340V!

Surprisingly few things cared, either way. Mostly on the low voltage side the coffee machine pump wouldn't run, and the oven took an hour to come to pizza temperature instead of 15 minutes.

I had one cheap Chinese wallwart let out magic smoke, and there was a POP in my 3 weeks old dehumidifier and it stopped working. I took it back to the Noel Leeming store (not even the same one I'd bought it from actually) and said nothing and they had it fixed for free in 2 or 3 days.

Someone from the lines company came and pulled the fuses on the low voltage side and replaced them and then everything was back to normal. And they scheduled the same on the 11kV side as apparently they hadn't been changed in 40 or 50 years.

Shouldn't that have had all your RCD/RCBO/GFCI's tripping?

[themadhippy]

Shouldn't that have had all your RCD/RCBO/GFCI's tripping?

why should it ,theres no imbalance  just over voltage

[IanB]

I mean for all intents and purposes...

If you have 240v split-phase AC (as is common in the U.S.) is that mathematically, or technically any different than 240v to ground?

If you ignore the grounding considerations, then 240 V AC is 240 V AC. There is no difference at all. However, 240 V AC at 60 Hz in the USA is not technically the same as 240 V AC at 50 Hz in other parts of the world. Resistive loads like heaters won't care, but motors and transformers will.

[paul cotter]

On a three phase supply with unbalanced loads a break in the neutral connection can cause chaos as one phase will increase in voltage(the less loaded phase) and the other will drop in voltage(the more heavily loaded phase) although the phase to phase voltage will remain as normal and three wire three phase machines will not see a problem. This is most likely the cause of the problem brucehoult experienced.

[themadhippy]

On a three phase supply with unbalanced loads a break in the neutral connection can cause chaos

Even more fun is when some numpty gets confused and swaps  phase 2 and neutral because they got confused with old and new wiring colours.

[paul cotter]

I have experienced this very problem with disastrous results. About 30years ago I was required to re-commission a back-up generator system for Symantec in Dublin, Ireland, where the entire distribution panel had been replaced and upgraded. The generator was a 300kVA, the phases were 3x240mmsq, the neutral was a single 240mmsq and the earth was a 90mmsq. An electrician had taken the generator leads from the old switchover panel and connected them into the new panel and I was called in to do an off-load run prior to full re-commissioning. The generator was somewhat remote from the panel but I could hear it well enough. So as requested I started up the generator from remote start contacts in the panel and ran it for about 10seconds. The generator speed was not as stable as it should have been and suspecting a problem I sent a stop signal. As the generator came to a stop, FLASH! BOOM! from the panel followed by repeated flashes and bangs that seemed to encompass the whole panel until a member of staff tripped the incomer ACB. The electrician had got his colours wrong and the 90mmsq earth had melted and fallen across the three bus bars causing extensive damage. The bars were copper clad aluminium and all had to be replaced.

[Fried Chicken]

I mean to say (sin(x+π/2) + c) - (sin(x-π/2) - c) = sin(x)

they are the same, right?

[Zero999]

It depends on what you mean?

If no current passes through the neutral point, then from an analytical point of view, the 0V point is arbitrary, so both split phase and ordinary phase can be considered to be the same. From a safety perspective, the highest voltage with respect to earth in a split phase system is 120V, but both conductors are above ground potential, compared to single phase which has 230V to earth.

If the neutral point is used, then in all cases, split phase is different to single phase.

[Siwastaja]

Yes, split phase is a single phase system, you can also think about it as two single-phase supplies in series. The advantage is getting two different voltage options, and possibly safety (with center tap being the earthed potential), but that's all.

[Randy222]

On a three phase supply with unbalanced loads a break in the neutral connection can cause chaos as one phase will increase in voltage(the less loaded phase) and the other will drop in voltage(the more heavily loaded phase) although the phase to phase voltage will remain as normal and three wire three phase machines will not see a problem. This is most likely the cause of the problem brucehoult experienced.

This will not change how the C.Tap works. Whatever voltage is on the primary the C.Tap on secondary cuts itself in 1/2.
There's nothing more than 1phase there on the secondary, tapped or not.

[Randy222]

Yes, split phase is a single phase system, you can also think about it as two single-phase supplies in series. The advantage is getting two different voltage options, and possibly safety (with center tap being the earthed potential), but that's all.

That seems to be a bit more confusing. "two single-phase"? Nope, there's only one phase no matter how many coils you put in series on the secondary, or place taps. The 3ph delta or Y could be called "three single-phase supplies", etc.

[brucehoult]

On a three phase supply with unbalanced loads a break in the neutral connection can cause chaos as one phase will increase in voltage(the less loaded phase) and the other will drop in voltage(the more heavily loaded phase) although the phase to phase voltage will remain as normal and three wire three phase machines will not see a problem. This is most likely the cause of the problem brucehoult experienced.

It's 2-phase split 480V.

Neutral was at 100V wrt ground due to the fault at the transformer. It didn't seem to vary with load, but I don't have any explanation for what nature of fault at the transformer would make it stable at 100V.

[langwadt]

On a three phase supply with unbalanced loads a break in the neutral connection can cause chaos as one phase will increase in voltage(the less loaded phase) and the other will drop in voltage(the more heavily loaded phase) although the phase to phase voltage will remain as normal and three wire three phase machines will not see a problem. This is most likely the cause of the problem brucehoult experienced.

It's 2-phase split 480V.

it is only 2 phase if the phases are not a multiple of 180 degrees apart

[brucehoult]

On a three phase supply with unbalanced loads a break in the neutral connection can cause chaos as one phase will increase in voltage(the less loaded phase) and the other will drop in voltage(the more heavily loaded phase) although the phase to phase voltage will remain as normal and three wire three phase machines will not see a problem. This is most likely the cause of the problem brucehoult experienced.

It's 2-phase split 480V.

it is only 2 phase if the phases are not a multiple of 180 degrees apart

First time I've ever heard that!

- 2 phase: 180º apart

- 3 phase: 120º apart

- 4 phase: 90º apart (logical but may not exist in practice)

Makes perfect sense.

Either way, you can take the hot wires of two adjacent phases and use them as a sqrt(4) or sqrt(3) or sqrt(2) greater sine wave voltage source.

[langwadt]

On a three phase supply with unbalanced loads a break in the neutral connection can cause chaos as one phase will increase in voltage(the less loaded phase) and the other will drop in voltage(the more heavily loaded phase) although the phase to phase voltage will remain as normal and three wire three phase machines will not see a problem. This is most likely the cause of the problem brucehoult experienced.

It's 2-phase split 480V.

it is only 2 phase if the phases are not a multiple of 180 degrees apart

First time I've ever heard that!

- 2 phase: 180º apart

- 3 phase: 120º apart

- 4 phase: 90º apart (logical but may not exist in practice)

Makes perfect sense.

Either way, you can take the hot wires of two adjacent phases and use them as a sqrt(4) or sqrt(3) or sqrt(2) greater sine wave voltage source.

180º is split phase, not 2 phase. 90º apart is 2 phase, like a stepper motor

when you have more than one phase you can generate any other phase angle with a linear combination of the phases

[IanB]

First time I've ever heard that!

- 2 phase: 180º apart

Mathematically, that would be true. But in conventional electrical engineering, "two phase" is reserved for other cases where the phase angle is not 180°. This is just a convenience of terminology. A centre-tapped transformer is conventionally referred to as "split phase".

[Analog Kid]

it is only 2 phase if the phases are not a multiple of 180 degrees apart

OK, time for me to set a cat amongst the pigeons here.

Yes, I've heard that stated over and over again.
That is one of the god-damndest stoopidest, most wrong-headed things I've ever heard of!
The supposition that two currents that are 180° apart do not constitute two separate phases, even though they clearly do.

Disclaimer: I never expect to ever win this argument, but I'll argue it anyhow.

This wrong-headed thinking apparently emanates from the electrical industry, who insist on calling 3-phase power "3-phase" and the 180°-apart power "split phase".

They won't admit that it does, in fact, constitute two separate and distinct phases. But somehow, because the phases are mirror images of each other, 180° apart, they won't call them separate phases.

I'm sure if physicists or electronic engineers had their say that split-phase power would be called 2-phase.

What is so fucking special about 180° that its phases don't get called phases?

Yes, I realize that this is yet another dust-up over terminology, but it strikes me as so blindingly, obviously wrong that I just can't hold my tougue.

Stupid sparkies.
How can you tell me that these waves don't constitute two different phases?




And yet if one of them is shifted by 1° then we can call them two phases?

[Monkeh]

I'm sure if physicists or electronic engineers had their say that split-phase power would be called 2-phase.

What is so fucking special about 180° that its phases don't get called phases?

2-phase already exists. It has rotation. Split-phase does not.

[Analog Kid]

2-phase already exists. It has rotation. Split-phase does not.

Please explain; what is meant by "rotation"?

[langwadt]

What is so fucking special about 180° that its phases don't get called phases?

with 180° you cannot make a linear combination of the two and get a get another phase, there's no rotation