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# Why is 230V Single-Phase?

12/10/2009 9:28 AM

hi all,

im having a confusion in 120v,230v,415v.if 230v is square root of phase voltage 415v then the wiring should be 3 wire and 1 neutral.and how 230v is called single phase

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Guru

Join Date: May 2007
Location: Harlow England
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#1

### Re: Why is 230V Single-Phase?

12/10/2009 9:49 AM

Your location would probably assist the discussion...

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Location: Alabama
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#2

### Re: Why is 230V Single-Phase?

12/10/2009 9:58 AM

Quote "im having a confusion in 120v,230v,415v.if 230v is square root of phase voltage 415v then the wiring should be 3 wire and 1 neutral.and how 230v is called single phase"

First 230 is not the sq root of 415 volts. 415 volts/ √3 = 240 volts which is the voltage from phase to neutral if this is a wye connection. Since you are only using 1 phase , it is termed single phase. It depends on you load. The output of some single transformers is 230 volts

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#3

### Re: Why is 230V Single-Phase?

12/10/2009 1:20 PM

It should be pointed out that the assumption that 230V is always single phase is itself incorrect. In North America, we have 230V 3 phase as well, and there is such thing as 230V 2 phase (true 2-phase, not just 2 legs of a 3 phase source).

3 phase power sources can be delivered as "Y" (aka "Star") or "Delta" connections. By far the most common worldwide is 4-wire Y connected systems, where there is a Neutral point in the transformer (hence the "Y" designation) so the Phase to Neutral voltage is less than the Phase to Phase voltage by the sq. rt. of 3. You can use the power from this system either as Delta, meaning Phase to Phase, or Y, meaning Phase to Neutral, but in the latter case, because it is NOT taking power from all 3 phases, it is called "single phase". When discussing Y systems then, we refer to the voltage with a "slash" in the rating, meaning it is configured with that neutral point brought out and thus can be used for single phase. So in IEC countries, that is 380/220, or 400/230, or 415/240. All of these are generally considered "nominal" voltages; each country and each utility may be slightly different, but equipment ratings are generally OK with any of them. In North America, the predominant low voltage Y distribution is 480/277V for industrial users or 208/120V for commercial users, and in fact there has been a movement to standardize on these over the years on new installations. But there are still a lot of legacy systems in place, some of which are 480V Delta, 440V delta, 230V Delta, and a relative odd ball (for the rest of the world) 230/120V delta, which does NOT use a Y configuration. In Canada, they also have 600V, both Delta and 600/347Y.

Residential users in IEC countries get the benefit of a simple system of just feeding a service with one phase and Neutral for that 230 (220-240) volt single phase. In the US and Canada, we have to use a separate 1 Phase transformer that provides 240/120V with a center tap. So for us, 240V 1 phase comes not from a phase to Neutral source but rather from opposite ends of a center tapped transformer, and Line to Neutral is 120V.

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#4

### Re: Why is 230V Single-Phase?

12/11/2009 3:05 AM

There is a good article in Wikipedia on this topic.

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