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Old 05-17-2010, 05:18 AM   #1
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Default Single Phase and Two Phase Difference?

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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Old 05-17-2010, 06:05 AM   #2
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Originally Posted by Golden Arc View Post
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.

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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Old 05-17-2010, 06:50 AM   #3
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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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Last edited by jrannis; 05-17-2010 at 06:54 AM.
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Old 05-17-2010, 07:34 AM   #4
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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.

Yeah there separated by 90 degrees. The original generators at Niagra falls were two phase generators here's an interesting read on two phase;
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Old 05-17-2010, 08:10 AM   #5
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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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Old 05-17-2010, 08:16 AM   #6
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The code book still covers two phase motors.

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Old 11-07-2013, 01:00 AM   #7
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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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