A single phase motor has one set of windings and a three phase motor has three sets of windings.....therefore single phase powers a single phase motor and a three phase powers a three phase motor. It seems that the terms "single phase" and "three phase" comes from the application of the voltages? :roll:
why is it called 1 phase when its 110/220v. but 3 phase when its 3 "hots"
- Thread starter longbeach1125
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TOOL_5150
Senior Member
- Location
- bay area, ca
When dealing with US electricity, Single phase for residential and commercial should be considered "Split Phase", where 1 single phase winding in the transformer is tapped [or split] in the middle and grounded - so in reality you still have 1 winding - making it 1 single phase. 2 phase is totally different and should not be considered the same.
Heres a good diagram:
Looking closer at it, the polarity is incorrect, but the single winding and voltages are correct. For this topic, it should suffice.
~Matt
Heres a good diagram:
Looking closer at it, the polarity is incorrect, but the single winding and voltages are correct. For this topic, it should suffice.
~Matt
Exactly !!!When dealing with US electricity, Single phase for residential and commercial should be considered "Split Phase", where 1 single phase winding in the transformer is tapped [or split] in the middle and grounded - so in reality you still have 1 winding - making it 1 single phase. 2 phase is totally different and should not be considered the same.
Heres a good diagram:
Looking closer at it, the polarity is incorrect, but the single winding and voltages are correct. For this topic, it should suffice.
~Matt
iMuse97
Senior Member
- Location
- Chicagoland
Bob's right. There are a lot of things to say, and they've all been said in his link to that other thread.
Len
Senior Member
- Location
- Bucks County
phase
phase
Because 2 phase has 5 conductors
phase
Because 2 phase has 5 conductors
When dealing with US electricity, Single phase for residential and commercial should be considered "Split Phase", where 1 single phase winding in the transformer is tapped [or split] in the middle and grounded - so in reality you still have 1 winding - making it 1 single phase. 2 phase is totally different and should not be considered the same.
Heres a good diagram:
Looking closer at it, the polarity is incorrect, but the single winding and voltages are correct. For this topic, it should suffice.
~Matt
How about two hots on a wye system? Single Phase?
+9**- < my dog just typed this ... inter species communication ...bet there ain't any of that on the other thread.
brian john
Senior Member
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- Kilmarnock, Va
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- Retired after 52 years in the trade.
When I was an apprentice I asked this question and after several attemps of trying to explain this to me the JW said it's called that was because we call it that way, now ask me something else.
- Location
- Wisconsin
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- PE (Retired) - Power Systems
A lot of people confuse the number of phase conductors with the number of phase voltages, because they drop the identifying noun. Slang usually leads to mis-understandings.
In my simplified view, a phase voltage is measured between pairs of phase conductors not between a phase conductor and neutral. This is for consistency as not all electrical systems contain a neutral or grounded reference.
In my simplified view, a phase voltage is measured between pairs of phase conductors not between a phase conductor and neutral. This is for consistency as not all electrical systems contain a neutral or grounded reference.
TOOL_5150
Senior Member
- Location
- bay area, ca
How about two hots on a wye system? Single Phase?
+9**- < my dog just typed this ... inter species communication ...bet there ain't any of that on the other thread.
2 Hots from a wye would be a single phase. The 2 hots use 1 winding of the transformer, even if it is a 3 phase transformer, you are using 1 phase.
~Matt
- Location
- New Jersey
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- Journeyman Electrician
Wouldn't a WYE transformer use two windings for a single phase circuit utilizing "2 hots"?
TOOL_5150
Senior Member
- Location
- bay area, ca
Hmm, you sure are right - I was thinking of delta. OOps!
In that case, the 2 windings have a 'center tap' being the grounded center point, so its still somewhat similar to a single phase center tapped transformer. In any case, you arent using all 3 windings, so it isnt 3 phase, it sure isnt 2 phase, so by default it should be considered single phase.
Anyone believe that?
~Matt
Jim W in Tampa
Senior Member
- Location
- Tampa Florida
How about two hots on a wye system? Single Phase?
+9**- < my dog just typed this ... inter species communication ...bet there ain't any of that on the other thread.
That would be using a,b or b,c or c,b and is simply 1 phase of a 3 phase system and often is done.
Forget about voltage values, transformers, and number of wires...
A 60Hz generator with one pole outputs a voltage having a sinusoidal waveform when measuring the voltage across the two output terminals. In the early days, it was simply called an alternating current generator. Later, it was rationalized that energy could be generated, transmitted, and utilized more efficiently by using a generator with three poles, or more correctly three windings, each offset by 120? of a full rotation. The voltage output could be measured in several different ways depending on how the windings were interconnected and the terminals under measurement. Yet the most rudimentary method of measuring the voltages always yielded only three same-magnitude-voltage sinusoidal waveforms separated in timing by 120? or 1/3 cycle. Because of this empirical evidence, the output became known as three phase. To distinguish this type output from its forerunner, the single winding-generator's output was dubbed single phase because it had only a single waveform.
Now if you believe my story, your welcome.
Otherwise, keep on searching... 
tryinghard
Senior Member
- Location
- California
How many transformers/windings on 3ph open delta?
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Or, think of the number of line-to-line pathways there are.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
quogueelectric
Senior Member
- Location
- new york
why is it called 1 phase when its 110/220v. but 3 phase when its 3 "hots"
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.
I order to plot any wave or diagram one needs a REFERENCE on which to compare it to. 3 phase has 3 separate waveforms 120*out of phase with each other. When you take 2 out of 3 waveforms it creates a new single phase waveform which is the additive sum of the 2 -3 phase waveforms which is in a different time domain for peaks and zero crossings it is the definition of said reference time/voltage which to me seems to cause the confusion. It needs complex math skills to understand it totally so our trade tends to simplify diagrams for ease of explanation which can cause confusion. When you get to a calculus 3 level it all becomes very clear until then we will all struggle.
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