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Difference between single-phase and three-phase electricity explained

Difference between single-phase and three-phase electricity explained

If you’re looking for the answer to the difference between single-phase and three-phase electricity, you’ve come to the right place.

In this guide, we reveal what single-phase and three-phase electricity is, the difference between the two, and weigh up which option is better suited to your utility needs.

What is a single-phase electricity supply?

Single-phase and three-phase electricity are both electrical systems, each delivering a different amount of power.

Single-phase electricity is the power supply most commonly found in UK homes and is usually 230-volts. This type of electricity supply is generally fitted into houses equipped with gas central heating that have only one electricity meter. Single-phase distribution is mostly used for heating and lighting. It’s rare to find this type of system powering big electric motors.

Single-phase socket with a plug in the switchboard.

Single-phase systems use alternating current (AC) electric power, meaning your wall sockets deliver 230 volts. The voltage and current flow of single-phase systems switch direction and magnitude. These switches occur in cycles, usually at a rate of around 50 – 60 times per second.

Single-phase electricity supply delivers power in waves through two wires. One of the wires supplies the current, while the other completes the circuit, thereby providing the return path. These power waves reach their peaks at 90⁰ and 270⁰. When the power supply is not at its peak, the amount of power delivered is reduced.

Analogy: Single-phase electricity

To provide a simple analogy for an easier understanding, think of a cyclist pedalling along a road. The cyclist will apply force to one pedal to propel the bicycle forward. There is then a brief break before force is applied to the second pedal. Despite the constant pedalling of the cyclist, there are slight breaks in-between the moments of applied force.

The application of force to the pedals also varies in intensity along the way. The applied force begins at zero, increases to a peak, then decreases back to zero again. It then reverses itself before reaching its peak in the opposite direction, before returning to zero once more. A full cycle is 360⁰. This is representative of a single-phase system.

At times, there will be no output of power, and two peak power outputs, during the cycle.

What is a three-phase electricity supply?

Selective focus image with noise effect three phase single core cables connection in low voltage switchboard.

Single-phase systems are generally used in UK homes, whereas three-phase systems are most often used in commercial or industrial buildings. This is due to the difference in power needed. In some cases, if you have a higher-than-average use of electricity for your home then you would be advised to get a three-phase electricity supply. At Crown Energy, our friendly utility advisors will be able to recommend the right electricity connection for you based on your estimated usage.

Unlike single-phase systems with their two wires, a three-phase electricity supply shares the load across three live wires. These three livewires are deliberately fixed to deliver peak power at different times. As a result, all three phases of power enter the cycle by 120⁰. Meaning all three phases of peak power are supplied at different times during the full cycle. This three-wire approach to power delivery ensures there are no major peaks or dips in the supply.

Analogy: Three-phase electricity

To provide an analogy for a simpler understanding, picture a three-person tandem bicycle with the three cyclists pedalling in rotation. Unlike the scenario involving the single cyclist, a three-person tandem bicycle, cycled in rotation, means there is always one cyclist applying maximum force to the pedals, propelling the bicycle forward. This also means there is never zero output.

This shows how a three-phase electricity supply is far better equipped to handle industrial equipment. That includes large electrical motors, and appliances or machinery that require a constant or higher usage of power to run.

Single-phase vs three-phase electricity: How do I know which one is right for my property?

If you live in a UK home, and you consume an average amount of electricity, then the chances are your home has been equipped with a single-phase electricity supply system as standard. These systems are usually fitted in homes equipped with gas central heating that have only one electricity meter.

If you inhabit a larger home or own/run a commercial or industrial building that requires a greater amount of electricity, or more than one electricity meter, then you’ll need a three-phase electricity supply connection. Usually, a three-phase electricity supply connection is required for any premises with energy-guzzling machines such as stair lifts, or electrical motors, for example.

If you want to be completely sure of the type of electricity system required or installed in your premises ahead of getting your new electricity connection, please call Crown Energy on 0333 2000 204, and one of our friendly utility advisors can help.

You will need to tell us all the appliances and equipment that need power. We will then establish the amount of power required to run them all.               

Perhaps the easiest and most effective way to assume if your property is currently fitted with a single or three-phase electricity supply is by looking at the electrical fuse. This is also known as the service head or cut out. A three-phase system will usually have three 100amp fuses, while a single-phase will typically have only one fuse.

Single-phase and three-phase electricity compared

Circuit breaker type electric 3 phase installed on the wall. Electric protection. Blurred. Single exposure and chromatic distortion effect.

If you’re still a little unsure about the main differences between single-phase and three-phase electrical systems, here is a summary:

The primary difference between these two power delivery systems is the load capacity, and consistency of the power delivered.

When looking at a single-phase system, the delivery of power constantly peaks and drops off. Three-phase systems on the other hand prevent this from happening by delivering power through three different currents, in rotation. This ensures the delivery of power never dips below the system’s maximum capacity.

It’s very important for both security and safety that the power delivered in these systems is consistent. This is because both of these electricity systems have a maximum capacity (number of amps) at which they can operate.

UK homes are typically low electricity consumption buildings, that require single-phase systems. These homes generally require less than 20kVA to function effectively. Single-phase systems can also be simpler to construct and install. Whilst three-phase systems could be more complicated in design and will typically cost more to install.

However, a three-phase electricity supply can often be more efficient. Three-phase systems are designed to handle a greater load without any safety risks. These systems are usually used to power buildings that require a larger amount of electricity. These types of buildings need a system that continuously delivers a larger amount of power at a consistent and stable rate.

Recap: Single-phase electricity system

A single-phase electricity system is a type of electrical power distribution system that uses a single alternating current (AC) waveform. It consists of a single live conductor (phase), a neutral conductor, and, in some cases, a protective earth conductor. This system is commonly used for residential and small-scale applications.

Pros of a single-phase electricity system

Simplicity: Single-phase systems are straightforward and easier to install, operate, and maintain compared to three-phase systems.

Cost-Effective: Since single-phase systems are suitable for lower power applications, they often require less expensive equipment and wiring.

Widely Available: Single-phase supply is readily available in residential areas, making it convenient for powering households and small businesses.

Adequate for Light Loads: Single-phase systems are sufficient for powering lights, small appliances, and other low-power devices typically found in homes.

Cons of a single-phase electricity system

Limited Power Capacity: Single-phase systems have lower power capacity. In comparison to three-phase systems, they are less suitable for heavy-duty industrial applications.

Imbalanced Loads: Single-phase systems can experience imbalances when multiple appliances are connected, leading to voltage fluctuations and potential overload issues.

Reduced Efficiency: Due to higher currents flowing through the single conductor, resistive losses are more significant, resulting in lower overall system efficiency.

Limited Motor Performance: Single-phase motors have lower efficiency and starting torque compared to three-phase motors, making them less suitable for high-power applications.

Close up of a MCB (Micro Circuit Breaker) on a UK domestic electrical consumer unit or fuse box.

Recap: Three-phase electricity system

A three-phase electricity system is a type of electrical power distribution system that utilises three alternating current (AC) waveforms. It consists of three live conductors (phases) that are 120 degrees out of phase with each other, along with a neutral conductor and a protective earth conductor. This system is commonly used for industrial, commercial, and high-power applications.

Pros of a three-phase electricity system

Higher Power Capacity: Three-phase systems can deliver significantly higher power capacity compared to single-phase systems. Making them suitable for heavy-duty industrial applications and large motors.

Balanced Loads: The three-phase system distributes power across the three phases, reducing the chances of load imbalance and voltage fluctuations.

Improved Efficiency: Due to lower current requirements per conductor, three-phase systems experience reduced resistive losses, resulting in higher overall system efficiency.

Better Motor Performance: Three-phase motors are more efficient. They provide higher starting torque, and run more smoothly compared to single-phase motors. Thus, they are better-suited for industrial applications.

Cons of a three-phase electricity system

Complex Installation: Setting up a three-phase system requires additional equipment and wiring compared to a single-phase system, leading to higher installation costs.

Less Common in Residential Areas: Three-phase supply is less commonly available in residential areas. This limits its use primarily to commercial and industrial settings.

Higher Equipment Cost: Equipment designed for three-phase systems, such as motors and transformers, can be more expensive than their single-phase counterparts.

Increased Complexity of Control: Managing and controlling a three-phase system can be more intricate. It requires specialised knowledge and equipment for monitoring and protection.

It’s important to note that the choice between single-phase and three-phase supply depends on specific requirements. Firstly, the electricity usage in the premises. While three-phase is generally more efficient, single-phase supply is sufficient for many residential and small buildings where power demands are lower.

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