why is it called 1 phase when its 110/220v. but 3 phase when its 3 "hots"

[longbeach1125]

I always wondered this.

Thanks
Joe Sweeney

 

[chris kennedy]

I would say look at the number of primary conductors but that doesn't explain the open Delta.:roll:

 

[ultramegabob]

I am sure I am not using the correct language to describe it, but.... It takes two legs of power to make a phase A-B for single phase, for with three phase you have three combinations of legs of power, A-B, B-C, C-A. I hope this makes sense to ya...

 

[longbeach1125]

so if its 2 legs of power why is it called single phase?

 

[ultramegabob]

so if its 2 legs of power why is it called single phase?

it takes two legs to make a phase

 

[wireguru]

so if its 2 legs of power why is it called single phase?

look at the coil of the transformer between those 2 legs......theres your one phase...

 

[iwire]

why is it called 1 phase when its 110/220v. but 3 phase when its 3 "hots"

I always wondered this.

Thanks
Joe Sweeney

Joe your question sounds so simple but as has been shown on this forum many times there is (in my opinion) no easy correct answer. We have had threads about this question drag on for 100s of posts with no clear answer.

I gave up trying to figure it out, we call it single phase because that is what we have been told to call it. :grin:

Heres a link to a 650+ thread about the same question.

single vs. 3 phase


Good luck.

 

[skeshesh]

I would think it's because when you connect two "hot"s you have two vectors with one angle between them, hence one "phase" even though you have two "poles". When you have a three "pole" system though, you have to have angles between each three vectors, hence three "phase". Google symmetrical components and have a read through it might make more sense.

 

[infinity]

As Bob touched on there is no simple answer.

Joe,
In keeping with the voltages outlined in the 220.5(A) and elsewhere in the NEC, I would refrain from using the 110/220 volt description, 120/240 is more accurate.

 

[jaylectricity]

In keeping with the voltages outlined in the 220.5(A) and elsewhere in the NEC, I would refrain from using the 110/220 volt description, 120/240 is more accurate.

That's its own tough question. We should have a thread where everybody goes to their panel and measures the voltage on the main lugs and posts them here.

I'm sure that's already been done, so if you know which thread, please post it because I"d be interested in seeing it.

 

[infinity]

As Bob touched on there is no simple answer.

Joe,
In keeping with the voltages outlined in the 220.5(A) and elsewhere in the NEC, I would refrain from using the 110/220 volt description, 120/240 is more accurate.

That's its own tough question. We should have a thread where everybody goes to their panel and measures the voltage on the main lugs and posts them here.

I'm sure that's already been done, so if you know which thread, please post it because I"d be interested in seeing it.

I reading my post again I would reiterate that this is more of a personal opinion. Certainly if a post contains the 110/220 voltage we'll know what the person is talking about.

 

[mivey]

I reading my post again I would reiterate that this is more of a personal opinion. Certainly if a post contains the 110/220 voltage we'll know what the person is talking about.

Your personal opinion meets the current U.S. standard nominal system voltage of 120/240.

 

[infinity]

Your personal opinion meets the current U.S. standard nominal system voltage of 120/240.

That was my only real point. The question was posted in the NEC section of the forum and the NEC outlines in Article 220 and elsewhere the nominal voltages that we use every day. Maybe I'm just being a little too anal today. :roll:

 

[mivey]

That was my only real point. The question was posted in the NEC section of the forum and the NEC outlines in Article 220 and elsewhere the nominal voltages that we use every day. Maybe I'm just being a little too anal today. :roll:

Nah. What bugs me is the 110/240 type notation.

 

[lt2000]

I always wondered this.

Thanks
Joe Sweeney

The single 120/240 system is obtained from just one phase of a three phase system,it all done at the transformer at the pole.

gary

 

[mivey]

I had convinced myself I was not going to get sucked into this but I just can't help myself. Must be like a cat trying to resist an oscillating ball.

The single 120/240 system is obtained from just one phase of a three phase system,it all done at the transformer at the pole.

gary

No. It can also be obtained from using two phases. Some transformers are connected line-line on the primary side.

The least confusing way to go is to call it by the number of different line-line connections you have on the secondary and let it go at that (each line-line connection produces a single voltage waveform). From other threads, you can tell it is not quite that simple but this might be be simplest route to take.

add: This is the gist of ultra's post #3

 

[e57]

The single 120/240 system is obtained from just one phase of a three phase system,it all done at the transformer at the pole.

gary

Not all the time... My single phased power comes from a delta primary from two phases... (3-wires alternately taking two each block.)

Anyway IMO I thing single and 3 are used to differentiate from "Two Phase" distribution which would be delivered as such. 180 degrees apart.

As opposed to 3 phase distributed 120 degrees apart:

And derived as single phase in possibly this as such... Or earth return from one phase only, or from a Wye primary.

Again as 180 degrees apart, but still 120 from the other phases. And as someone pointed out to me on one of the long threads about this the single winding would be a single sine wave if you put it on a scope leg to leg 180 apart....

 

[Jim W in Tampa]

What you really have is 1 phase that has a center tap that is grounded. Hope that helps

 

[Twoskinsoneman]

What you really have is 1 phase that has a center tap that is grounded. Hope that helps

I've always thought of it along similar lines. 1 phase you basically have one transformer, one coil, you just are referencing ground in the middle of it.

3 phase you usually see 3 transformers, 3 coils, so 3 phases. I know that is a simplistic view but it always made sense to me.

 

[kwired]

How about if you can connect a 3 phase motor directly across the lines and it runs at proper speed and current then you must have 3 phase?