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# 3 phase ?

## 3 phase ?

#1
08-25-02, 06:24 PM
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3 phase ?

Just curious. What is the difference between 3 phase 220 and 1 phase 220? And when a building has 3 phase coming in how does 1 phase equipment run? Is htere a second set of wires bring the 1 phase in? Thanks Tim

#2
08-25-02, 08:19 PM
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Maybe someone can refer you to a site that has some drawings on it. I am trying to come up with a good explanation here and so far I have trouble wording it.

#3
08-26-02, 05:28 AM
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Join Date: Jul 2001
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Take a look at this and see if it helps. You are probably talking about 120/240 center tapped delta.

http://home.att.net/~benmiller/elecsys.htm

#4
08-26-02, 09:21 AM
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Overly simplified:
3 phase power has each hot conductor, 120 degrees offset from each other. Typical voltages are 208/120 or 480/277V.
Residential has two hots that might be originilly derived from portions of 3 phase, but goes through transformers to result in 2 hots, each 180 degrees offset from each other.

208V single phase motors work somewhat similar to 120V single phase motors. 208V three phase motors have different type of windings that permit them to take advantage of the 3 simultaneous hots and make them more efficient.

#5
08-26-02, 09:23 AM
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#6
08-26-02, 10:01 AM
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Ichbod lnked a drawing of wiring configs,,, anyone know where there is one of a wave or cycle?

#7
08-26-02, 02:13 PM
DaveB.inVa
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#8
08-26-02, 04:03 PM
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Here's my expanation of why Phase A = 120 volts + Phase B = 120 volts = 208.----Phase A is a Positive vector, 120 volts at 0 degrees. Phase B is a Positive vector, 120 volts at 120 degrees. We have two 120 volt coils in series, and if A is Positive then B is Negative for "additive" polarity. This means we add the "back-vector" of B to A .The "back vector" is 120 + 180 = 300 degrees, so B is 120 volts at 300 degrees,which is 60 degrees from A. The sum of A + B is a vector that bisects the 60 degree angle, a vector 30 degrees from A. 1/2 the lenth of this vector is 120 volts X cosine 30 degrees = 120 volts X .866. The full lenth is 120 volts X 2 X .866 = 120 volts X 1.73 = 208 volts.

#9
08-26-02, 07:20 PM
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