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For questions of this type, it seems the main issue may be one of definitions and industry terms. See if this makes sense:

Line voltage is a very ambiguous term. For instance, say you are wiring a doorbell transformer. You feed 120V into the primary, and 18V comes out the secondary. The electrician would say the output is "low voltage" and the input is "line voltage". He simply means the building wiring, or "lines". Now, if you go out to the breaker panel, you will measure 120V from each "leg" to neutral, but you can also measure 240V from leg to leg. It's all line voltage. Line voltage simply means the voltage present in that particular power distribution system.

Now the power in your house is "single phase" (well, in almost all homes, anyway). Single phase is fine for most anything, but motors are a special case. Motors need something to create a rotating magnetic field to get them turning. Single phase power doesn't have anything to do that, so they need some sort of a gimmick, like a capacitor, to create a "phase shift" to get the rotation.

Single phase AC (alternating current) simply means the voltage goes positive then back down to zero, then negative then back up to zero. That's one complete cycle. The cycle is divided into 360 degrees, like a circle. The positive voltage goes from 0 to 180 degrees, and the negative half 180 back to 0.

Now 3-phase power has, you guessed it, 3 hot wires. Each hot wire, when paired with a neutral, is a single-phase source. Heres the big difference: Phase A starts its positive cycle. When it is 120 degrees into the cycle, phase B starts going positive. When Phase B is 120 degrees finished with its cycle, phase C starts going positive. When phase C is 120 degrees into its cycle, that's a total of 360 degrees, and phase A is done with one cycle, and the whole process starts over. Picture 3 people doing "the wave" at a football game. Same principle.

This time difference, or "phase shift" is what makes 3-phase power unique. 3-phase motors use the phase shift directly to produce the rotating magnetic field they need to turn. Think of 3 people in a circle, tossing a ball around. see the "circular" motion? Now picture two people tossing the ball back and forth. No circular motion there. That's the difference between single-phase and 3 phase.

So, electricians use the term "phase" to refer to one of the three hot wires in a 3-phase (also correctly called multiphase or polyphase) power system. The term "phase" voltage is just as ambiguous as "line" voltage. To be accurate, you must specify whether you mean phase-to-phase voltage, or phase-to-neutral voltage.

Confused? if you go into a large commercial building with 3-phase power, many times the incoming panel will have voltmeters on the front. In one building, the first meter will be labeled "phase-to-phase voltage", and the second meter will be labeled "phase-to-neutral voltage". Go into the building NEXT DOOR, and the same meters will be labeled "line-to-line voltage" and "line-to-neutral voltage". See? the terms are used pretty interchangably.

In a 3-phase system, each phase, leg, or line has the same potential, or voltage (except for a very few wierd and pretty outdated systems). If you measure from phase A to Phase B you will get the same reading as B to C, also the same as C to A. So, measuring any two phases will tell you what the line voltage is, but that motor still needs all 3 phases to get the rotation.

To understand the different voltages you find in a 3-phase system, see the related questions for another answer that relates to that subject.

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Is transmission voltage a phase to phase voltage or a phase to ground voltage?

Transmission voltage is typically specified as a phase-to-phase voltage, which is the voltage measured between two of the three phases in a three-phase power system. This is the standard method of specifying transmission voltages in electrical systems.


How do you calculate phase voltage of a three phase four wire system?

To calculate the phase voltage of a three-phase four-wire system, divide the line-to-line voltage by √3. In a balanced system, where the line-to-line voltage is given, the phase voltage will be the same for each phase. The formula is V(phase) = V(line)/√3.


Why is phase voltage not twice line voltage?

Phase voltage is not twice line voltage in a three-phase system because the phase voltage is the voltage measured across an individual phase in a balanced system, while the line voltage is the voltage measured across any two phases. In a balanced three-phase system, the line voltage is √3 times the phase voltage, not twice.


How do you calculate the phase current when working with a 10kw 3 phase electrical motor?

To calculate the phase current of a 10kW 3-phase motor, you can divide the total power (10kW) by the square root of 3 (approx. 1.732) and then divide that result by the line-to-line voltage. The formula is: Phase Current (Amps) = Power (W) / (√3 x Line-to-Line Voltage (V)).


What is phase voltage and line voltage in star connection?

In a star connection, phase voltage is the voltage measured across each individual phase and neutral. Line voltage is the voltage measured across any two phases in the system. The line voltage is higher (√3 times) than the phase voltage in a star connection.

Related Questions

If you have a phase to phase voltage how do calculate the overall voltage?

First of all, there is no such thing as a 'phase-to-phase' voltage. The correct term is 'line-to-line' voltage. Secondly, without knowing what you mean by 'overall voltage', there is no way of answering your question.


If you are given that the line to line voltage is 380V how do you calculate the voltage of each of the 3-phase's?

380V ÷ √3 = 219.4


Why do you have voltage to ground but not voltage phase to phase?

There is phase to phase voltage in 3 phase system.AnswerYou don't get voltage 'phase-to-phase'; it's 'line-to-line'!


Is transmission voltage a phase to phase voltage or a phase to ground voltage?

Transmission voltage is typically specified as a phase-to-phase voltage, which is the voltage measured between two of the three phases in a three-phase power system. This is the standard method of specifying transmission voltages in electrical systems.


How do you calculate phase voltage of a three phase four wire system?

To calculate the phase voltage of a three-phase four-wire system, divide the line-to-line voltage by √3. In a balanced system, where the line-to-line voltage is given, the phase voltage will be the same for each phase. The formula is V(phase) = V(line)/√3.


If in the three phase connection phase to phase voltage is 400v what will be the phase neutral voltage?

The formula to use is, phase voltage /1.73 = phase to neutral (ground) voltage.CommentThere is no such thing as a 'phase to phase', or 'phase to neutral' voltage. The correct terms are 'line to line' and 'line to neutral'. So the above answer should read: line voltage/1.73= line to neutral voltage = phase voltage.


Is 220V line voltage or phase voltage?

Phase, if you are referring to line, as power line from pole.


How do you convert 3 phase RMS line-line voltage to RMS line-neutral voltage on an unbalance system Basically how do you calculate using trig for all 3 phase?

The term, 'unbalanced system' refers to an unbalanced load. Under normal circumstances, an unbalanced load leads to unbalanced line currents. The line voltages are determined by the supply and remain symmetrical, even when the load is unbalanced. As your question refers to a 'line to neutral' voltage (i.e. a phase voltage), you must be referring to a star (wye) connected load, in which case the phase voltage (line to neutral voltage) is 0.577 (the reciprocal of the square-root of 3) times the line voltage (line to line voltage).


What is line voltage in star connection?

Phase to phase voltage is 1.732 (the square root of 3) times the phase to star point (neutral) line voltage.e.g. if the line voltage is 220Vphase voltage = 1.732x220 = 380V (approx)Additional AnswerYou might also like to know that the line voltage leads the phase voltage by 30 electrical degrees. And, incidentally, the correct expressions are 'line-to-line' not 'phase-to-phase', and 'line-to-neutral' not 'phase-to-neutral' (think about it, a line voltage is measured from the junctions between adjacent phases, so they cannot be 'phase to phase'!)


How match 2 phase line voltage between them?

To match 2 phase line voltage it has to be the same voltage.


How do you convert line current to phase current?

The current is the same in the three live wires. The voltage can be described as the line voltage (phase to neutral) or the phase voltage (phase to phase) which is larger by a factor of sqrt(3). So a line voltage of 230 v corresponds to a phase voltage of 400 v.


How do you calculate 440v phase?

Let's get the terminology correct. A 'phase voltage' is measured across a phase, whereas a line voltage is measured between two lines. So there is no such thing as a 'phase to phase' voltage -it's a line to line voltage (hence the term 'line voltage').