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A three-phase, three-wire, system is obtained from a delta-connected source. A three-phase, four-wire, system is obtained from a star-connected source.

A three-phase three-wire system comprises three conductors, called line conductors. The voltages measured between any pair of line conductors is called are called line voltages and, numerically, they are identical to phase voltages.

A three-phase four-wire system comprises three line conductors, and a neutral conductor. The voltages measured between any pair of line conductors are called line voltages and the voltages measured between any line conductor and the neutral conductor are called phase voltages. The value of a line voltage is 1.732 times the value of a phase voltage.

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12y ago
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11y ago

A four wire system is similar to the three wire system. A three wire system is from a delta service transformer coming in. For example if the service is 480, there will be 480 volts between each of the three legs. The delta is minus a ground. In a four wire system, the service coming in is off of a wye transformer. The forth wire is a ground. For example if the service is 480, there will be 480 volts between each of the three hot legs. If you measure between one of the hot legs to the forth wire (ground), it will measure 277 volts. Many times the wye (four wire) system is used in places where higher voltage is needed to run motors (480) and a service higher than 110 is needed to run lighting (277). No transformer is needed to get the 277. It just simplifies wiring.

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A three-phase, four-wire, system comprises three 'hot' conductors which are correctly called 'line conductors' and a 'neutral conductor' (not a 'ground' conductor, as indicated in the original answer). The actual voltages depend on the electricity standards in your country. In Europe, for example, the voltage between any pair of line conductors (called a 'line voltage') is 400 V, while a voltage between any line conductor and the neutral conductor (called a 'phase voltage') is 230 V. The potential of the neutral conductor is approximately that of earth, which by general agreement, is considered to be zero volts.

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10y ago

A three-phase, four-wire, system is an a.c. distribution system supplied from a three-phase distribution transformer or transformer bank having 'star' (or 'wye') connected secondary windings.

This arrangement provides three energised conductors, termed 'line conductors' and a single 'neutral' conductor which is at approximately the same potential as earth (ground).

In UK/Europe, this is the standard connection for low-voltage distribution, supplying 230-V single-phase supplies to residences which are connected between any one of the three line conductors and neutral, and 400/230-V three-phase supplies to offices and factories (400 V between any pair of line conductors, and 230 V between any single line conductor and neutral).

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10y ago

Two-phase is a system that was used before the advantages of three-phase were accepted. A two-phase system supplies two equal voltages 90 degrees apart in phase. This can be used to provide a rotating magentic field for motors, but it does not really provide the transmission efficiency of three-phase, which uses three voltages 120 degrees apart in phase, and has supplanted two-phase almost completely.

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13y ago

It all comes down to the economics.

Here's how it is:

In transmission, loads are always balanced, hence creating its own star point (not needing a neutral to take the out of balance current). This means that there is only need for 3 wires - one for each phase (ABC). Hence not needing to run another wire

In distribution however, the neutral is needed as this is able to take out the out of balance current as no loads are balanced (excluding 3phase motors etc).

By having the forth wire (neutral) allows the connection of single phase houses as electricity needs a circuit to flow.

The transmission side of a transformer (the primary side) is usually delta connected meaning that line and phase voltages are equal whilst line and phase currents vary by root 3.

The distribution side however (the secondary side) is star connected meaning that their phase and line currents are equal whilst their line and phase voltages vary by root 3.

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11y ago

The fourth wire of a wye three phase system is the grounded coil ends which form a neutral (N). The other ends of these coil wires are designated L1, L2 and L3. This allows line to line and line to neutral voltages to be obtained from the same system. Some low voltage wye connections are 120/208, 240/415, 277/480 and 347/600.

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13y ago

A four-wire system has an added conductor - neutral, necessary for supplying single-phase loads where one supply wire is hot and one is at ground potential.

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10y ago

3 wire is 2 hots which are 120 volts each and a ground.

4 wire is 2 hots which are 120 volts each and a ground and a neutral.

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13y ago

In three phase 3-wire system there is no Neutral present while in 3-phase 4-wire system there is presence of neutral.......

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Q: What is the difference between three phase three wire and three phase four wire system?
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Is there a difference between three phase and single phase electrical supplies?

Yes, there a difference between three phase and single phase electrical supply services.


What is the difference between a one phase and a three phase motor. And if a three phase motor is given a single phase supply will it run or not?

The difference between a single phase and a three phase motor is the amount of power conductors that feed the device. As to the other part of the question a three phase motor will not start or run on single phase. The phase angles on three phase are 120 degrees apart on a single phase system they are 180 degrees apart.


What is Electricity use difference between 3 phase and 1 phase?

A two-phase a.c. system is an archaic system, in which two phase voltages are generated 90 electrical degrees apart. It has nothing whatsoever to do with the US 'split phase' system that supplies North American homes. A two-phase system can be a four-wire system, or a three-wire system, and was useful because, unlike a single-phase system, it could create naturally rotating magnetic fields in induction motors. It has long been superseded by the three-phase system.


Difference between two phase and three phase welding machine?

Three phase uses a safety circuit away from the machine, two phases uses you as the safety circuit


In a modern industrial plant the most likely polyphase power system in use is a A. one-phase system. C. three-phase system. B. two-phase system. D. four-phase system.?

A "three-phase system" is a polyphase system having three phases. The term "polyphase system" just means a system having multiple phases. If it is used by itself, "a polyphase system" doesn't mean "a three-phase system".

Related questions

Is there a difference between three phase and single phase electrical supplies?

Yes, there a difference between three phase and single phase electrical supply services.


What is the difference between a one phase and a three phase motor. And if a three phase motor is given a single phase supply will it run or not?

The difference between a single phase and a three phase motor is the amount of power conductors that feed the device. As to the other part of the question a three phase motor will not start or run on single phase. The phase angles on three phase are 120 degrees apart on a single phase system they are 180 degrees apart.


Single phase and three phase circuit?

Yes, there is a difference between single phase and three phase circuits.


What is Electricity use difference between 3 phase and 1 phase?

A two-phase a.c. system is an archaic system, in which two phase voltages are generated 90 electrical degrees apart. It has nothing whatsoever to do with the US 'split phase' system that supplies North American homes. A two-phase system can be a four-wire system, or a three-wire system, and was useful because, unlike a single-phase system, it could create naturally rotating magnetic fields in induction motors. It has long been superseded by the three-phase system.


What is the difference between neutral point and earthing?

Earthing point is where conductor is directly connected to ground and its potential is always zero. Neutral is a return path in single phase system and in three phase system Neutral point will have zero potential if all the loads are balanced in the system. In un balanced three phase system even neutral point will have some potential


Why is there a difference between a domestic and industrial electricity supply?

actually there is no difference between them. However in some counteries, single phase is used for domestic and three phase is used for industrial.


Angle between three phases?

The generated angle between phases in a three phase system is 120 degrees.


Difference between two phase and three phase welding machine?

Three phase uses a safety circuit away from the machine, two phases uses you as the safety circuit


How many volt each phase in three phase?

600 volts between any two wires. The phase has nothing to do with voltages, only current relationship.


What is the difference between single and three phase on line UPS?

The difference between a single and a three phase online UPS is a 3 phase can supply a 100% unbalanced load on its output without affecting its performance. A single phase cannot supply a 100% unbalanced load on the output without affecting its performance.


In a modern industrial plant the most likely polyphase power system in use is a A. one-phase system. C. three-phase system. B. two-phase system. D. four-phase system.?

A "three-phase system" is a polyphase system having three phases. The term "polyphase system" just means a system having multiple phases. If it is used by itself, "a polyphase system" doesn't mean "a three-phase system".


What is an acceptable difference in resistance between phases on a 3 phase motor?

The currents between legs of a three phase circuit should be within about 10% of each other.