Single-phase vs three-phase power

From supporting our mundane electronic devices to powering large industrial businesses, electricity has played an essential role in the way we consume. In fact, there are several nonprofit institutions arguing that electricity should be considered a human right. The importance of electricity has become even more pronounced at a time when people across the world are forced to stay at home due to the pandemic. But understanding how electricity works can be a daunting task especially if you have zero knowledge in it. Still, having the basic know-hows has great benefits that you can use in the long term especially if you are maintaining a household or running a small business. In this article, we 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 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 phase 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 an example of a polyphase system that distributes three alternating currents using the same circuit. Power grids across the world often use this method to distribute power because of its high-efficiency and long-term cost benefits. In this supply system, three conductors provide alternating current each using the same voltage amplitude and frequency.

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The difference between the conductors equals to one third of a full cycle. This means that the voltage on the first conductor is at its peak at a third of a full cycle following the second conductor and another one third of a time in an entire cycle before the last conductor. Does that sound complicated to you?

Just keep in mind that the its output is always constant and never touches zero and that this delay allows constant power distribution to a linear load. It can also yield a magnetic field using an electric machine, as well as generate other types 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 not be present in some of these systems. The purpose of this wire is to enable the other three conductors to produce higher voltage while still having the capacity to support appliances that run on single-phase lower-voltage power. This configuration is called Delta. The second type of configuration is called 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 higher density than its counterpart, making it the best option for running industrial loads. This type also balances loads more easily, thereby reducing your need for huge neutral wires. It also boosts electronic capacity application, resulting in improved power efficiency.

Unlike a single-phase power unit, it does not need any additional motors for the initial start-up because 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, as opposed to the alternative, which provides power in pulsating mode. This means reduced vibrations coming out of the motor and generator.

You can also easily convert it into single-phase, whereas doing the opposite requires a more complicated process. Another advantage is longer-term cost efficiency. While a single-phase power supply has 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 and produces higher output in relation to the increase in the number of phases in the system.

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


While it may be the best idea for some use cases, there are disadvantages, too. Powering large industrial buildings through this connection may be complex as it necessitates symmetrical components that are 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, which in turn incurs less expenses. Having standby units may likewise be more expensive.

In addition, a faulty transformer needs to be shut down entirely, including all its load areas, which means restoring 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, which in turn leads to voltage fluctuations. Knowing these disadvantages is important in helping you make the most out of your three-phase power unit.

What is single-phase?

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


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. If 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 costs No uniform torque
Overheating Limitations on heavy loads

Despite its advantages, there are still several downsides to using this type of unit that you need to be aware of in order to prevent frequent disruptions and maximize its application. It incurs expensive insulation costs as it needs high system voltage. So, while a three-phase motor may need higher repair costs than its counterpart, you may shell out more money on insulation when using this type. It also does not have a uniform torque and this may affect the quality of its operation. 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. Lastly, if you require heavy loads, then this is not the type for you as it doesn’t work well with industrial motors.

Check out our guides on tomato plants, marine plywood and solar powered fountains as well.

How to identify them

Nearly all industrial buildings use a three-phase power supply given its efficiency and high performance. 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, simply locate the electric switchboard, which is a panel where 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, whereas the alternative can do an initial startup on their own without the need for any external device.


If you see two wires, then the power supply system is highly likely to be running on 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 its application. Because of its ability to carry heavy loads, as we covered in the previous part, only one type is used in industrial spaces such as large factories, mobile towers, data centers, shipboard and aircraft. In contrast, a single-phase power unit is applicable for smaller businesses and homes.

Electronic loads

In relation to the above, these simpler units can deliver up to 1,000 watts power at most, while 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 power supply is oftentimes plain and simple, while the other type of unit is far more complex.


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

For electricity, there are different types of converters 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, to allow a three-phase power system to run in a single-phase environment. It is made possible through the three most common types of converters, namely rotary, static and digital.

A rotary converter is the most popular options for the purpose. In simple terms, this type runs an 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, as well as enable balanced voltage levels. Meanwhile, the idle motor draws without turning the moving parts in the main machines, enabling it to mirror a three-phase supply. A rotary converter is suited to run all types of loads, including resistive, inductive and motor.

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 on 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, power rating and the method by which you plan to execute the conversion.

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 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 in the beginning, it will definitely be beneficial in the long run if you have the need for it.

How to test it

Testing a three-phase motor should be as easy as setting up an extension cord or waste oil heater if you know the right steps. While it is tempting to just simply replace the motor when it no longer starts, sputters or overheats, 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.

To properly diagnose the problem, it is important to have the right tools. These may include clamp-on ammeters, oscilloscopes, ubiquitous multimeters and temperature sensors. If you will 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 power source, along with other machines and equipment that are not part of the diagnostic. Next, shunt the conductors to ground and discharge the motor. Make sure to familiarize yourself with the motor specifications, which can help you in assessing the problem on 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, damage to the shaft or cooling fans and burnt marks. You should be able to rotate the shaft smoothly, otherwise repairs or replacements may be warranted especially on older motors. Newer ones, however, may be a tad difficult to rotate due to disuse but 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 earth using a multimeter and helps prevent electric shock due to insulation failure. A low-resistance reading, which is ideally below 0.5 ohms, means that both points are electrically connected to each other. If the reading points to higher resistance, which is equivalent to a value higher than 0.5 ohms, this means that the circuit is open and that there are problems with the motor’s insulation.

The succeeding 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, then 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, as well as 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 insulation resistance test, which compares the resistance level between every pair of phases, each phase of the motor and the motor frame. To do the test, set your insulation test to 500V, then put it on various combinations of L1, L2 and L3. Then, 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 megohm.

The final assessment is the running amp test. This helps identify how much power is being generated to run the motor. Motors that are more powerful should generate more current, which is 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 is an indication of a motor problem and 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, which has a chart as well.

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 in case you decide to tweak the load on your electrical system. To perform this, make sure that the main breaker is turned off and that no electricity would be flowing into the wires involved. Wearing safety gears such as high-voltage gloves is also recommended when conducting this task.

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. At this point, 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 from the converter to the motor’s ground screw. If you have 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, after having read this article, 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, as you will want to ensure the generator you choose to buy provides the level of voltage that these devices can in fact use. Remember how these generators were pumping out different amount of voltages? While 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.

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