# Single Phase and Two Phase Difference?



## Golden Arc

I was reading the Audels Questions and Answers for Electrical Examinations book and it listed off some phases like single phase, two phase, and three phase as if there was a difference between single and two phase. I thought single phase and two phase were the same thing.


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## Bob Badger

Golden Arc said:


> I was reading the Audels Questions and Answers for Electrical Examinations book and it listed off some phases like single phase, two phase, and three phase as if there was a difference between single and two phase. I thought single phase and two phase were the same thing.


I have not seen the book so I cannot comment directly.

However in the past there was another system called two phase and it was not just two phases from a 3 phase.

http://www.3phasepower.org/2phasesystems.htm

http://en.wikipedia.org/wiki/Two-phase_electric_power

You could actually have 5, 6, 7 phase systems, as it worked out 3 phase worked out to be the most efficient of them.


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## Southeast Power

Just for the sake of those that cannot follow the link Bob posted, below are a couple of interesting sentences from Wikipedia. 

The generators at Niagara Falls installed in 1895 were the largest generators in the world at the time and were two-phase machines. The advantage of two-phase electrical power was that it allowed for simple, self-starting electric motors. In the early days of electrical engineering, it was easier to analyze and design two-phase systems where the phases were completely separated.[1] It was not until the invention of the method of symmetrical components in 1918 that polyphase power systems had a convenient mathematical tool for describing unbalanced load cases. The revolving magnetic field produced with a two-phase system allowed electric motors to provide torque from zero motor speed, which was not possible with a single-phase induction motor (without extra starting means). Induction motors designed for two-phase operation use the same winding configuration as capacitor start single-phase motors.
Three-phase electric power requires less conductor mass for the same voltage and overall amount of power, compared with a two-phase four-wire circuit of the same carrying capacity.[2] It has all but replaced two-phase power for commercial distribution of electrical energy, but two-phase circuits are still found in certain control systems.


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## slickvic277

Some one asked about 2phase on another thread. I've worked with it a little and this is how I explained it,





> It works like this,
> 
> Line A1 to Line B1 = 240v
> 
> Line A1 to neutral = 120v
> 
> line B1 to neutral = 120v
> 
> Line A2 to Line B2 = 240v
> 
> Line A2 to neutral = 120v
> 
> Line B2 to neutral = 120v
> 
> Now to confuse you even further,
> 
> Take either A1 or B1 and go to Either A2 or B2 and you get some where between 160 - 175 volts.
> I believe the phase were 90 degrees apart. Or almost.
> 
> It's an old system and it's only in use still in some very old area's.
> 
> There is also other voltages that were used in the old 2 phase system but the ones above are the only ones still in use, that I've seen.
> 
> There's also a 2 phase 4 wire system with no neutral but I've never seen one active.


and,




> Yeah there separated by 90 degrees. The original generators at Niagra falls were two phase generators here's an interesting read on two phase;
> http://www.3phasepower.org/2phasesystems.htm


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## Golden Arc

I looked it up on Wikipedia after i posted this and i saw what was posted above so i guess its an older phase system thats not used that much anymore. 


I think it did say 6 phase in that Audel book also.


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## drsparky

The code book still covers two phase motors.


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## metalmoto

I have a vintage two phase motor starting switch made by Allen Bradley. It uses 4 conductors. It was removed from a vintage 30 inch paper cutter from a printing company in Philadelphia PA. It appears to be made about the 1950's. An interesting piece of electrical history, and still functions perfectly.


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