Single-phase vs three-phase power

From supporting our electronic devices to powering large industrial businesses, electricity plays an essential role in the way we consume. Several nonprofit institutions argue that electricity should be considered a human right. The importance of electricity is more pronounced when people are forced to stay at home due to the pandemic.

Understanding how electricity works can be a daunting task. It’s especially if you have zero knowledge of it. Having basic know-how has benefits that you can use in the long term, especially if you run a small business.

This article will focus on the phase-in electricity and its everyday application. This article is dedicated to giving you a better understanding of single vs. three-phase power.

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What is a phase in electricity?

In general, the phase pertains to the distribution of load in electricity. The alternating current (AC) that powers your home can be classified into two types of connections: Single and three-phase. The former has less power and is often referred to as the “residential voltage.” On the other hand, the latter connection uses more power and is widely used in factories and large industrial units.

Understanding 3-phase power: What is it?

Three-phase power is a polyphase system that distributes three alternating currents using the same circuit. Power grids worldwide often use this method to distribute power because of its high efficiency and long-term cost benefits. Three conductors provide alternating current in this supply system, each using the same voltage amplitude and frequency.

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The difference between the conductors equals one-third of a full cycle. It means the voltage on the first conductor is at its peak at a third of a full cycle. The second conductor is at its peak two-thirds through a cycle. The third conductor is at its peak at the end of the cycle. Does that sound complicated to you?

Keep in mind that its output is always constant and never touches zero. This delay allows constant power distribution to a linear load. It can also yield a magnetic field using an electric machine and generate other types of arrangements through a transformer. Keep in mind that they all have the same neutral leg.

This generally has four wires, three conductor wires, and one neutral wire. The distance of these wires from each other is 120 degrees. It is worth noting that the neutral wire may not be present in some of these systems. This wire aims to enable the other conductors to produce a higher voltage. It’s while still supporting appliances that run on single-phase lower-voltage power.

This configuration is called Delta. The second type of configuration is Star, which needs a ground wire and a neutral wire.


Now that you have a basic understanding of this type, it is time to weigh its benefits. As previously mentioned, it offers a higher density than its counterpart. It makes it the best option for running industrial loads. This type also balances loads more easily, reducing your need for huge neutral wires. It boosts electronic capacity application, resulting in improved power efficiency.

Unlike a single-phase power unit, it does not need additional motors for the initial start-up. It has enough phase difference to provide for the initial torque. This self-starter system produces constant power for a smoother and vibration-free operation instead of the alternative. It provides power in pulsating mode. This means reduced vibrations are coming out of the motor and generator.

You can also easily convert it into a single phase, whereas doing the opposite requires a more complicated process. Another advantage is longer-term cost efficiency. A single-phase power supply has a lower repair cost. This is more economical in the long run because it does not require additional conducting materials and wiring.

It also allows you to save in the long run because power distribution using this system does not require heavy copper wires. Finally, this type of power connection requires less space. It produces higher output with the increase in the number of phases in the system.

While you’re at it, check out our guide on extension cords and cassette toilets.


While it may be the best idea for some use cases, there are disadvantages as well. Powering large industrial buildings through this connection may be complex. It necessitates symmetrical components used for operation and analysis. If something goes wrong, you may have to spend more on repairs and maintenance as you have to change every component.

You also need to replace the entire unit if something malfunctions since it shares a common core. As a result, this could be more costly on your end and cause extended disruptions. In comparison, you only need to change the specific faulty components with the alternative system. Therefore, it incurs fewer expenses. Having standby units may likewise be more expensive.

In addition, a faulty transformer needs to be shut down entirely. It includes all its load areas, which means restoring the connection would be difficult. This transformer is not compatible with an open-delta connection for temporary operation.

Lastly, this type of transformer is more vulnerable to unbalanced loading. It means voltage fluctuations. Knowing these disadvantages is important in helping you make the most out of your three-phase power unit.

What is a single-phase?

This is used for residential homes and smaller businesses as it carries lower loads. This type alters the AC’s voltage supply and adopts the neutral and phase wires. The former distributes the current load, while the latter returns the electricity or current.

This system usually starts at 230V and has a frequency of approximately 50Hz. Unlike the alternative, it needs additional circuits to function and has inconsistent voltage levels. It is better than the alternative if you need to run small machines like a MIG welder.


Most residential sites use this supply because of its relative convenience and simplicity. While a three-phase system has arguably more benefits, this type still has its merits that are worth considering. Suppose your objective is to power small appliances and machines like a gasless MIG welder or a heater. This type is the ideal option.

It is lightweight and has a plain and straightforward design. It is also easier to install and is cheaper in terms of distribution costs in rural areas. Finally, it ensures optimum operation and high transmission efficiency given its low current capacity.


Insulation costsNo uniform torque
OverheatingLimitations on heavy loads

Despite its advantages, there are still several downsides to using this type of unit you need to be aware of. It will help prevent frequent disruptions and maximize its application. It incurs expensive insulation costs as it needs high system voltage.

While a three-phase motor may need higher repair costs than its counterpart, you may shell out more money on insulation. It also does not have a uniform torque, affecting its operation quality. This unit is likewise more prone to overheating and slow performance.

Additionally, a motor starter or other extra circuitry is needed to do an initial start-up for this. If you require heavy loads, this is not the type for you as it doesn’t work well with industrial motors.

How to identify them

Given its efficiency and high performance, nearly all industrial buildings use a three-phase power supply. But not all of us can identify what kind of power one has right at the onset. If you want to know what type you have, locate the electric switchboard. In this panel, several circuits are connected and controlled to direct electricity.

In a residential unit, the switchboard is often placed near the front of the house or the kitchen cupboard. From there, you can identify the differences between the two by keeping an eye on the following factors:

External devices

Single-phase motors are not self-starting and often require a motor startup to run. In contrast, the alternative can do an initial startup independently without the need for any external device.


If you see two wires, the power supply system is highly likely to run in a single phase. These two wires are called Phase and Neutral. On the other hand, the alternative needs three conductor wires and has two configuration types called Star and Delta. A fourth neutral wire may also be present in this system.


Another way to identify the difference between the two is through their application. Because of its ability to carry heavy loads, only one type is used in industrial spaces. In contrast, a single-phase power unit is applicable for smaller businesses and homes.

Electronic loads

Concerning the above, these simpler single-phase units can deliver up to 1,000 watts of power at most. In comparison, the alternative carries electronic loads higher than 1,000 watts.

Output voltages

A single-phase power supply has a voltage level of 230V. On the other hand, its counterpart delivers up to 415V.

Circuit Complexity

One easy way to identify the difference is by looking at the complexity of the circuitry system. The construction of a single-phase supply is often plain and simple, while the other type of unit is far more complex.


The simpler one is beneficial if you run a household or a small business. But what if you decide to convert one type to the other? The process can be done with the help of a few tools, albeit complex. Speaking of tools, you may want to check out these equally important tools you should consider having at home. Consider engine-driven welders and plasma cutters.

There are different types of converters for electricity that allow you to switch from one to the other. But first, let’s talk about the actual process. This process forms a third voltage line, also called a sine wave. It allows a three-phase system to run in a single-phase environment. It is made possible through the three most common converters, namely rotary, static and digital.

A rotary converter is the most popular option for this purpose. In simple terms, this type runs equipment powered by a three-phase supply at full-rated power from a single-phase source. It requires a control panel and an idle motor or idle generator.

The control panel has a circuit that turns the idle motor on and off and enables balanced voltage levels. The idle motor draws without turning the moving parts in the main machines to mirror a three-phase supply. A rotary converter is suited to run all loads, including resistive and inductive.

Another type of converter is called static. This type runs three-phase motors from a single-phase supply at two-thirds of the horsepower. It uses capacitors to produce power across the motor’s third winding upon start-up. Once the main machine or motor is operating at an acceptable level, the capacitors are detached.

The third type is a digital converter, which adopts a digital signal processor to produce a third voltage. Combined with the initial single voltage, this creates a power supply running in three phases.

How much does it cost to convert from one to another?

The price of converting from one source to another depends on certain factors, including the type to be used and power rating. The method you plan to execute the conversion will affect the cost.

A 5 HP rotary converter costs about $350 to $450, while a 10 HP variant retails for about $650 to $750. A static converter is much cheaper, and you can find one for under $100. If you decide to hire a professional electrician to work for you, prepare to spend an average of $7 to $10 per linear foot. Make sure to hire a reliable contractor who offers a reasonable price without compromising the quality of work.

While converting from one to the other may be costly initially, it will be beneficial in the long run if you need it.

How to test it

Testing a three-phase motor should be as easy as setting up an extension cord if you know the right steps. While it is tempting to replace the motor when it no longer starts simply, this is not always a great idea in terms of cost.

Knowing the basic troubleshooting techniques would come in handy when something malfunctions and save you from added expenses.

It is important to have the right tools to diagnose the problem properly. These may include clamp-on ammeters or oscilloscopes. You’ll also need to know about ubiquitous multimeters and temperature sensors. Suppose you conduct the testing yourself instead of hiring a contractor. You should wear property safety gear such as gloves and grounding straps.

Before starting the tests, disconnect the motor from its source and other machines and equipment that are not part of the diagnostic. Next, shunt the conductors to the ground and discharge the motor. Make sure to familiarize yourself with the motor specifications. It can help you assess the problem with your motor.

There are different types of diagnostic tests. They often start with a general inspection, which is conducted by assessing the physical condition of the motor. This is a relatively easy process of identifying problems through indentations and damage to the shaft or cooling fans.

You should be able to rotate the shaft smoothly. If not, repairs or replacements may be warranted. Newer ones may be a tad difficult to rotate due to disuse. This should be addressed through some oiling.

After a visual inspection, it is time for a continuity test. This assessment checks the resistance between the motor’s body and the earth using a multimeter. It helps prevent electric shock due to insulation failure. A low-resistance reading means that both points are electrically connected, ideally below 0.5 ohms.

Suppose the reading points to higher resistance, equivalent to a value higher than 0.5 ohms. This means that the circuit is open, and there are problems with the motor’s insulation.

The next test is called a power supply test. This inspection makes sure that the supply is within expectations and is in line with the specifications of the motor. You can conduct this test by using a multimeter to check the motor’s voltage. Compare the reading with the applied voltage indicated in the motor’s specifications.

After this test, the next step is to assess the continuity of the motor winding from one phase to another. This assessment involves the six wires inside the motor and the terminals on each side of the box called L1, L2, L3, and T1, T2, and T3. The purpose of conducting this test is to assess the health profile of your machine’s supply. It also makes use of a multimeter.

Another assessment is called the insulation resistance test. It compares the resistance level between every pair of phases, each motor, and the motor frame phase. To do the test, set your insulation test to 500V. Put it on various combinations of L1, L2, and L3.

Using the same voltage setting, assess every lead from the motor phase to the motor frame. The insulation resistance should give a minimum reading of 1 megohm. The motor should be replaced if the value is below 0.2 megohms.

The final assessment is the running amp test. This helps identify how much power is being generated to run the motor. More powerful motors should generate more current, measured in ampere or amps.

With the motor turned on, assess the full load amps or FLA using a clamp-on meter. If the reading does not meet the specifications, it indicates a motor problem. Further diagnostic tests should be conducted.

If you’re doing a DIY project, you may also be interested in our SAE to metric conversion guide.

How to convert 3-phase to single 220v (& why you would do it)

Having a basic understanding of how to convert one to another will come in handy. It’s great if you decide to tweak the load on your electrical system. To perform this, ensure that the main breaker is turned off and that no electricity is flowing into the wires involved. When conducting this task, wearing safety gear such as high-voltage gloves is also recommended.

Next, connect two wires from the motor to a phase converter. Then, run the same wires from the converter to the power system. Using the wires’ ends, link the inputs to outputs. You should make sure to connect a ground wire from the power system to the converter’s ground screw. You should also run a separate wire to the motor’s ground screw from the converter. A voltmeter can be used at this point to measure voltages between the two points.

Buying a generator

If you’re in the process of buying a generator, there may be a few things you have started to think about. Would one type be better than the other? It’s important to know what it is you’re looking to provide electricity for. You want to ensure the generator you choose to buy provides the voltage level that these devices can use.

Remember how these generators were pumping out a different amounts of voltages? Roughly 90% of your devices will be in a position to handle the voltage generated by either machine. You don’t want to ruin the remaining 10% of your machines because you didn’t consider their electrical needs.

Here are the steps to convert your three phases to a single-phase system.

How to convert three phases to single?

  1. Run a safety check.

    You’ll want to wear rubber gloves and only use tools equipped with rubber or wooden handles. Turn off the main breaker switch before you start.

  2. Buy a phase converter.

    You can buy this online or at your nearest Home Depot. Make sure to buy the double HP rating of your current phase.

  3. Attach wires to the converter.

    The first wire will be from the motor to the converter. The second will be from your converter to your power supply.

  4. Attach the inputs to the outputs.

    Strip the ends of the wires and connect the inputs to the outputs, thereby converting the system to a single phase.


Is three-phase better than single-phase?

Yes, certainly. Three-phase systems produce more power. They are also less expensive. They are more efficient in supplying power than single-phase systems. Also, you only need one additional wire to set up a three-phase system and achieve this efficiency.

Is 240V single-phase or 3-phase?

In the US, residential power is 240V single-phase. However, 240V can also be three-phase if desired. You can do this by connecting two wires to your single phase. Otherwise, you can also take two wires and connect one to the neutral wire and the other to the single-phase system.

Is three-phase better than single-phase?

Certainly, three-phase will save you money. It will also give you more efficient power. A three-way conductor is better than a single conductor to power larger offices and factories with heavy industrial equipment. Single-phase systems are only ideal for homes and small spaces.

How do I know if I have three-phase power?

Head to your main control system. If you find that it looks like three switches into one, you probably have a three-phase system. If the switch is wider than 3 centimeters, you likely have a three-phase system. If you find one normal switch, you likely have only a single phase.