Guide to Power (Singe – Split and 3 Phase) 

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To the electrically un-attuned, three-phase and single phase power could be thought of along the same lines as mechanical power. Despite their differences, the two have one thing in common — they both transport power with pressure and flow. When discussing electrical power, pressure refers to force and flow means speed.

You calculate the power sent via single-phase and three-phase as follows — pressure times flow, or force times speed.

When it comes to mechanical power, people use several different terms in place of the words “force” and “speed.” For example, the terms “foot pounds” and “pounds per square inch” describe force. Meanwhile, the terms “rotating speed” and “gallons per minute” refer to speed.

With electrical power, the terminology becomes more restricted. For example, only one term, “voltage,” describes force. Meanwhile, only two terms — “current” and “amperes” — describe speed.

In past decades, the electrical power delivery standard was direct current (DC), in which the power flowed in a single direction. In today’s world, the standard for electrical power delivery is alternating current (AC), in which the flow of power works in an alternating direction.

Frequency of Alternating Current Differs by Nation

The power standard changed from direct current to alternating current because the latter supplies power with greater efficiency along wide lengths and distances. The frequency of alternating current differs by nation:


  • 60 Hertz (cycles per second) is the frequency of AC in the United States.
  • 50 Hertz (cycles per second) is the frequency of AC in many other countries.


In mechanical power, the power equation is a multiplication of foot pounds (pressure) and rotating speed (speed). In electrical power, the power equation is a multiplication of voltage (force) times current (flow).

In households, the most commonly used power circuit consists of single-phase, two-wire alternating current (AC) power, which powers everything from computers and appliances to televisions, hairdryers and fans. The majority of setups have two wires —neutral and power. Power runs between the two wires, starting at the power wire.


What Is Single-Split (Dual or 2 Phase) and 3 Phase?

The differences between single-phase, two-phase and three-phase systems are down to their configurations, which determine the level of voltage sent to the equipment at the receiving end. The heavier the load, the higher the requirements.


What Is Single Phase Power?

A single-phase three-wire system is an AC power distribution that saves conductor material across a single-phase system. On the distribution transformer, it only needs one phase at the supply side to qualify. A transformer that supplies a distribution system of three wires contains a single phase, primary input winding.

US uses 120V

The U.S. and other counties have different levels of standard voltage. In the U.S., the standard single-phase voltage is 120 V. In many other territories, the standard single-phase voltage is 230 V. Both consist of one voltage wire — 120 V or 230 V — and one neutral wire.


What Is Dual Phase Power?

Dual phase — alternately known as split phase — is basically the same thing as single phase. Dual phase consists of an Alternating Current (AC) with two wires. In the United States, the typical power setup in households consists of two 120 V power wires — a phase A and a phase B, which are out of phase by 180 degrees. Many prefer this approach for its flexibility.

In loads that use low power — such as the lights, television, stereo and computer peripherals — the power is supplied by either one of the two 120 V power circuits. In loads that employ high amounts of power — such as the washing machine, dishwasher, air conditioner and heaters —one 240 V power circuit acts as the supply.


What Is Three Phase Power?

Three phase power is a power circuit that consists of an Alternating Circuit (AC) with three wires. The majority of commercial buildings throughout the United States contain a three-phase power circuit. The power setup generally consists of four wires — 208 Y / 120 V — an arrangement seen as the densest and most flexible.

In comparison to a single phase, three-phase power arrangements supply puts greater sums of power — 1.732 times the single phase — on the same current:


  • In loads that use low amounts of power — such as the lights, television, radio, computer and scanner — the power can be supplied by any of the three 120 V single-phase power circuits.
  • For loads with medium quantities of power — such as in water heaters and air dehumidifiers — the power can be supplied by any of the three 208 V single-phase power circuits.
  • Loads that require high volumes of power — including heaters, air conditioners and heavy-duty garage equipment — are powered with a single 208 V three-phase power circuit.

Industry System In USA

Most industrial plants throughout the United States use three-phase, four-wire power setups, as this arrangement — 480 Y / 277 V — is the densest and most powerful. In comparison to the 208V three phase, the 480 V three phase offers a considerably greater power supply with either the same current or with 43% reduced current. The benefits of this setup are as follows:


  • Lower costs for construction, thanks to the smaller electrical devices and circuitry required.
  • Lower costs on energy, due to the conservation of electrical currents, which get transformed into heat instead of being lost.

When you consider the high-powered machinery involved, three-phase systems are responsible for the most incredible feats of architectural engineering that mankind has ever achieved.


Difference Between U.S. and Europe Power System

Power systems differ between North America, the United Kingdom, Continental Europe and Oceania.

European Power System

In Europe, the majority of power systems use three-phase 230 V/400 V applications. The main exception to this rule is on farms and in rural villages, where single-phase setups are relied on for power. The exception is due to the fact that rural areas typically have access to only one high-voltage conductor.

In the United Kingdom, federal law requires construction sites to power their tools and portable lights via 55 V center-tapped systems. Arrangements like these are employed with 110 V equipment, which does not require a neutral conductor. The purpose here is to reduce the possibility of electrocutions, which are often a serious threat in outdoor settings, particularly on damp and rainy days.

UK Transformers

One of the most common pieces of construction equipment in the U.K. is the portable transformer, especially the kind that transform energy between single-phase 240 V and 110 V. Power supplies at construction sites are provided directly via generator sets. One of the additional benefits of this arrangement is that 110 V incandescent lamps — typical of this setting — have filaments that are stronger and more equipped for the job at hand than the filaments of 240 V lamps.

Down in the antipodean commonwealth, which favors low-cost options, power grids provide single-wire earth return (SWER) transmission lines for remote loads.


North American Power System

3 Wire Sytem in USA

For residential homes and small commercial properties throughout the United States and Canada, three-wire single phase systems are the most common source of electrical power. The setup allows things to work in the following two ways:


·         120 V line to neutral

·         240 V line to line


The first of those sends power to standard outlets and grounded lights. Heavier pieces of equipment, such as refrigerators, ovens, dishwashers, heaters and other appliances, all of which need more powerful energy supplies, use the second.

The regulations of the wiring control split-phase circuits. The return conductor lacks the protection of a circuit breaker. As such, a neutral wire must exclusively be shared by opposite-line supply circuits. A neutral can be shared by two opposing-line circuits if a bar is present to connect the two breakers, as this allows both to trip at the same time, and it also stops 120 V from traveling through 240 V circuits. In an exclusive variation of terminology, 220 V is referred to as single phase in the United States but not abroad.


What Key Differences Exist Between Two and Three Phase Electric Power?

In buildings that rely on three-phase power supplies, engineers have developed electrical systems to ensure loads remain balanced. This avoids imbalances throughout each day as various parties use light, medium and heavy loads. Engineers have also applied this same principle for the power supplies they distribute to different buildings.

In the U.K., one phase is supplied with a neutral at currents as high as 100A for single properties. In Germany and other European countries, each property receives three phases and a neutral. However, the fuse rating in Germany is lower, and it is shuffled to prevent the impact that increased loads could have on the first phase.

The United States and Canada often resource a high-leg delta supply. In this setup, one winding is center-tapped, and this allows for three different levels of voltage. The main purpose for this delta-connected supply is to offer power to heavy-duty motors that need a rotating field.

Single-Phase Loads

With the exception of high-leg delta systems, a single-phase load can be run between any two phases. When single-phase loads are distributed across the phases of a system, it keeps the loads balanced and creates a more manageable situation for the conductors. In a balanced wye system of three phases and four wires, the three conductors and system neutral are uniform in voltage.

what is a neutral wire

When a supply transformer receives return currents from the homes and buildings of customers, the currents collectively share a neutral wire. If all the returning loads are distributed equally across each of the three phases, the neutral wire carries a returning current of zero. Use of the transformer capacity could be rendered inefficient, however, if the secondary side of the transformer has unbalanced phase loading.

If a gap occurs in the supply neutral, the voltage between phase and neutral will not continue. Lower voltage will occur on phases with higher loads, and higher voltage will occur on phases with lower loads.


Unbalanced Loads

On a three-phase system where the live-wire currents are unequal or fail to form a perfect 120-degree phase angle, the load is unbalanced because the power loss is higher than in a balanced system.

The electric motor is in a special class when it comes to three-phase loads. Deployed in various industries, the three-phase induction motor offers high speed and starting torque. The three-phase, which is known for its efficiency, outperforms single-phase motors of similar rating and voltage. Requiring less maintenance and with a relatively low cost, the three-phase motor lasts longer and vibrates less than the single-phase.

3 phase efficienty

Three-phase systems often also provide power to electric lighting, electric boilers and other resistance heating loads. Throughout Europe, three-phase feeds accommodate domestic electric stoves and heating units. You can also connect heaters between neutral and phase-in settings that lack three-phase access. In places where three-phase power is unavailable, a split-phase configuration makes it possible to access twice the normal amount of voltage for heavy loads.

A two-phase system utilizes two AC voltages divided by a 90-degree phase shift. Some of the first public air conditioners, as well as the earliest generators at Niagara Falls, ran on two-phase systems. A Scott-T transformer can be used to connect two-phase systems with three-phase systems. Two-phase systems have largely been phased out by three-phase systems, but certain remnants of the two-phase are still in existence.


What Are the Three-Phase Configurations? Wye (Y) and Delta (Δ) Circuits


Three-phase circuits come in two configurations — wye (Y) and delta (Δ). The wye configuration employs three and sometimes four wires, while the delta only uses three wires. In wye configurations, the optional fourth wire is usually grounded and offered as a neutral.

Neither the three-wire nor four-wire variations count the ground wire, which runs over transmission lines for the purpose of fault protection. In non-fault conditions, the ground wire doesn’t even hold a current.

 single-phase and three-phase loads at the same time

When you use single-phase and three-phase loads at the same time, the four-wire wye configuration goes into effect. An example of this would be when a power supply feeds lights as well as heaters. In places where a clutch of consumers share a neutral and have differing amounts of phase currents, the resulting currents are carried by a common neutral.

A delta connects a winding between different phases in a three-phase configuration. A wye connects each winding in a power supply between a phase and neutral point. A single three-phase or three single-phase transformers will work in these configurations.

In an open delta system — alternately known as the V system — the configuration consists of two transformers. If a transformer fails or becomes malignant in a closed delta that consists of three single-phase transformers, that delta can operate as an open delta. In addition to carrying current for their respective phases, the two transformers in an open delta also bring the third phase’s current.

In order for a delta system to detect stray currents, grounding is necessary. A zigzag transformer often protects delta configurations from surges. The zigzag transformer returns fault currents to the ground.


How to Check Three-Phase Voltage

In order to have three-phase electrical power, you must have a setup with three wires of connection for the purpose of transmission. North American electrical utilities produce currents of three phase that transmit power across electrical grids, and this supplies power to cities, towns and suburbs throughout the United States and Canada.

two wiring arrangements for transformers

In residential homes and small office buildings, single-phase power is the most common supply of energy. In stadiums and industrial plants, three-phase power is the standard type of power supply. The two wiring arrangements for transformers that run three-phase power are known as delta and star. There is a slight variation in voltage between the two, and it all depends on the wiring.

The steps required to check the voltage on a motor are easy to follow:


  • Turn off the disconnect switch on the motor. Take off the screws that bond that cover to the disconnect switch and set the cover aside.
  • Move the multimeter to the AC volts. Join the probe leads to the following lead connects — common and volts. If the multimeter has an auto-range feature, move to the next step. If not, choose a voltage range that exceeds your intended voltage.
  • Check the inside of the switch box to the motor. There should be two sets of wires. Once set should involve three incoming wires, and the other should consist of three outgoing wires.
  • The wires that are coming in should be attached to a terminal that features the following three characters — L1, L2 and L3. Alternately, the terminal might list them as Line 1, Line 2 and Line 3.
  • The wires that are going out should be attached to a terminal that features the following three characters — T1, T2 and T3. Alternately, the terminal might list them as Load 1, Load 2 and Load 3.
  • Of the three phases to the current, each phase is carried by a wire and represented in and out by a corresponding number. For example, L3 and T3 represent the third phase.
  • Test the L’s and T’s in pairs with multimeter probes. Place a probe on L1 and L2, then watch for the voltage display. Repeat this step with the combination of L1 and L3, and then L2 and L3. The voltage for each of these pairings should be identical.
  • When you run this test on pairings of the T’s — T1 and T2, T1 and T3, and T2 and T3 — the voltage for each pairing should be zero.
  • Turn on the disconnect switch. Test the T pairings once again. The voltage for each pairing should be the same as for the L pairings.


If you have an available neutral terminal, test the single-phase voltage between that and L1. Repeat the test between neutral and L2 and neutral and L3. The voltage tested here should be half of what came out for the line pairs.

In a rotary phase converter, one phase of a three-phase current could have a different voltage that the remaining two. In load conditions that involve running motors, the voltage will vary, but this is to be expected.

When you perform a voltage test, pay close attention to what you are doing and don’t allow yourself to be distracted. Doing these tests can be dangerous.

On some motors, the disconnect switch is the same as the on/off switch. Therefore, switching the disconnect to “on” will actually power on the motor.


Get More Information on Electrical Power

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In today’s high-powered, high-tech world, access to electrical power at all times and in all settings is not a luxury. It is a must. Global Electronic Services performs service work on a full range of industrial electronics, motors and other high-powered equipment. We recommend you stay current on electrical power developments for the good of your company.

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2 thoughts on “Guide to Power (Singe – Split and 3 Phase) ”

  1. This is just out of curiosity, figuratively speaking. If I had a 3 phase generator (10kva) and had the phases split all to 3 single phases for shed and home use, would the (10kva) be maintained in all of the 3 single phases?

    Much appreciation for receiving all thoughts and answers.

  2. No, a 10kva, 3-phase generator provides 5.77kva per phase. The 3-phase power is equal to the square root of the sum of the power in each individual phase squared. Assuming balanced loads (and you do want your phases to be balanced), this means 3-phase power is equal to the individual phase power times sqrt(3) (which equals 1.732). So the power in each phase is the 3-phase power divided by 1.732.

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