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Single-phase vs three-phase power

There are two types of mains power supply for UK businesses: single-phase and three-phase.

Single-phase is the standard 230V supply provided by the wall plugs in homes, shops, and cafés. Three-phase is a more powerful 400V supply available for larger commercial and industrial sites with high energy demands.

This guide explores the differences between single-phase and three-phase power, helping you determine which one your business needs and how each affects operations and costs.

Contents

• What is single-phase power?
• What is three-phase power?
• Single-phase vs three-phase power
• Which type of power supply is best for businesses?
• Single-phase vs three-phase power costs
• How to check for a single-phase or three-phase power supply?

What is single-phase power?

Single-phase power is the simplest and most common type of AC (alternating current) electricity supply. It is available to devices and appliances in homes and small businesses through everyday, three-pin wall plugs.

It is affordable to install and operate, but unsuitable for applications requiring large amounts of power.

• Who is it for? Homes and small businesses like restaurants, cafés, and shops.
• What is it for? Everyday electrical needs, including lighting, small-scale heating, office equipment, kitchen appliances, and other 230 V devices.

How does single-phase power work?

Single-phase power is straightforward. It relies on a single “phase” (live) wire in a system of three wires to deliver electricity through three-pin wall plugs:

• Live “phase” wire: Carries the electrical current.
• Neutral wire: Completes the circuit.
• Earth wire: Provides grounding for safety.

A main fuse protects the circuit, while an electricity meter (usually a smart energy meter) records consumption.

Electricity is supplied at around 230V, oscillating in a single sine wave. This causes fluctuations in power, with brief moments (100 times per second at 50 Hz) where the voltage drops to zero, leading to minor interruptions. For example, lightbulbs appear to flicker when recorded in slow motion due to this oscillation.

Most low-power electrical appliances, such as lightbulbs, laptops, microwaves, and electric stoves, are designed to function with single-phase power. Each mains supply can support a combined power demand of up to 23 kW (230 Volts * 100 Amps).

However, high-powered equipment or machinery requiring a continuous, stable power supply will not function correctly (or at all) on single-phase power.

What is three-phase power?

Three-phase power is a more powerful and stable form of AC (alternating current) electricity, designed for businesses with high energy demands.

It provides the necessary power for heavy machinery and ensures a consistent energy supply, making it essential for businesses that exceed the limits of single-phase power.

Although costlier to install and operate, three-phase power improves efficiency and supports a wider range of electrical applications.

• Who is it for? Industries and large businesses, including factories, commercial buildings, and facilities with heavy machinery.
• What is it for? A variety of specialised equipment, such as elevators, air conditioning systems, large data centre servers, and manufacturing machinery.

How does three-phase power work?

Three-phase power delivers electricity more stably and efficiently using three live wires instead of one. Each phase carries its own alternating current, but they are offset from each other in a way that ensures a continuous and balanced power supply.

Unlike single-phase power, where voltage fluctuates to zero at certain points, three-phase power never drops to zero. Instead, the peaks of one phase compensate for the troughs of another, resulting in a smooth and consistent voltage output.

The combined voltage across all three phases is approximately 400V, making it ideal for running high-powered equipment efficiently.

However, individual phases can still be used separately to provide a 230V supply for standard appliances, making it a versatile system that supports both small and large electrical devices.

Businesses using three-phase power typically require half-hourly meters, as maximum demand exceeds 100 kVA, which mandates automated meter readings. However, businesses with lower power demands can opt for a specialised three-phase smart meter.

Single-phase vs three-phase power

The following table summarises the differences between these two types of power supply:

Which type of power supply is best for businesses?

The choice between single-phase or three-phase power isn’t entirely a business decision. It depends on an assessment by the Distributor Network Operator (DNO) based on your electricity demand and the local grid’s capacity.

Businesses can request a three-phase installation or upgrade, but availability depends on whether the DNO determines the grid can support it. If not, the business may need to fund infrastructure upgrades.

Let’s explore the key factors that influence this decision.

Factors affecting your business power supply

1. Peak power consumption
2. High-powered appliances
3. Local grid capacity and installation costs
4. Renewable energy integrations

1. Peak power consumption

When applying for a new power supply or upgrade, the DNO’s first assessment is your peak power demand (kW).

• Single-phase is usually recommended for peak demands below 18.4 kW (around 80% of the 23 kW maximum capacity).
• Some single-phase installations may still be approved for loads up to 20 kW, depending on local grid constraints.
• If demand is expected to grow, a three-phase upgrade may be necessary to prevent supply issues.

For example, a modest office expansion with extra computers, a business VoIP phone system, an always-on server, and minimal electrical heating can easily add 2 kW to peak demand.

Make sure to conduct a regular business energy audit to anticipate the DNO’s decision.

2. High-powered appliances

The type of electrical equipment your business uses also influences the DNO’s decision.

If your business relies on high-powered equipment, a three-phase power supply (or an equivalent solution) is essential to prevent:

• High running costs due to inefficiency.
• Performance issues like power fluctuations or voltage drops.
• Potential equipment failure from an inadequate power supply.

Here are examples of equipment that typically requires three-phase power:

3. Local grid capacity and installation costs

Whether three-phase power is available depends on the DNO’s existing infrastructure.

• In urban areas, three-phase is usually readily available.
• In rural or older industrial areas, cabling, transformers, or substations may be outdated or limited.

If the grid lacks capacity, the DNO may offer three-phase power under two conditions:

• If upgrades are already planned, you may get three-phase at no extra cost, but you’d need to wait for the work to be completed.
• If no upgrades are planned, your business would need to fund the necessary infrastructure, including transformers, new three-phase cabling and substations.

These upgrades can cost tens of thousands of pounds, depending on grid limitations. Engaging with your DNO early ensures you understand feasibility and costs.

4. Renewable energy integrations

If your business generates renewable power (e.g., solar panels, wind turbines, battery storage), the DNO will assess whether an upgrade is needed. In general:

• Systems of up to 11.04 kW can usually connect without prior approval under G98 regulations, regardless of power supply.
• Systems above 11.04 kW require a G99 application, and the DNO may recommend a three-phase upgrade based on grid capacity.
• If exporting large amounts of electricity, a three-phase supply improves efficiency and grid balancing.

Find out more about this process in our guide to selling solar power using a PPA.

Case studies of business power supply by sector

To help you quickly determine your power supply requirements, here are examples of how businesses of different sizes and sectors have their power supply configured.

Symptoms of an overloaded power supply

If your business power usage has increased over time but your power supply hasn’t been updated, your system may be overloaded. The two key warning signs are:

1. Lights flicker or dim when switching on large appliances

This is a classic symptom of a significant voltage drop. It occurs when a high-power appliance (e.g. motors, industrial ovens, air conditioning units) starts up, temporarily drawing power away from other devices.

The most noticeable effect is flickering or dimming lights, as lighting circuits experience a brief power drop. While this doesn’t immediately affect other electrical equipment, it’s a clear sign that your power supply is nearing its limits.

2. Your main fuse or circuit breakers trip frequently

If your fuses blow regularly or your circuit breakers keep tripping, it’s a strong indication that your power demand is exceeding what your single-phase supply can handle.

When demand starts approaching the limit of 23kW, your fuse or circuit breakers will automatically cut off the power to prevent overheating or electrical hazards.

There may be other causes, so conducting an energy audit to diagnose the exact issue.

Single-phase vs three-phase power costs

For small high-street businesses and offices, single-phase power is the more cost-efficient option. It requires no expensive upgrades, and its lower energy demand helps businesses avoid the high-power charges typically applied to systems that put strain on the national grid.

For large commercial businesses and industrial premises, three-phase power is often the better long-term investment. While installation costs are higher and additional charges apply for greater power usage, its more stable power supply extends the lifespan of high-power equipment and enhances operational efficiency, helping to offset long-term costs.

Now, let’s break down the CAPEX and OPEX costs of each:

Installation costs (CAPEX)

The cost of installing a new business electricity connection depends on several factors, including the type of power supply, whether it’s a new connection or an upgrade, and the internal wiring required to connect devices within your premises:

Single-phase

• New connection: £1,000–£3,000, including all wiring, the single-phase distribution board, and basic circuit breakers.
• Upgrade: £500–£1,500 for meter and fuse changes. DNO upgrades are often unnecessary, meaning no additional grid reinforcement costs.
• Internal circuits: Typically low cost, but long cable runs may require thicker, more expensive wiring to handle high currents efficiently.

Three-phase

• New connection: £3,000–£10,000 if sufficient local grid infrastructure is available. Requires more wires, fuses, a three-phase distribution board, and upgraded circuit breakers.
• Upgrade: If local grid reinforcement is required (e.g., new three-phase cables, transformer upgrades), costs can exceed £20,000, particularly in rural areas. However, if existing infrastructure supports it, upgrades may be under £10,000.
• Internal circuits: More efficient load distribution allows for smaller, less costly wiring. However, three-phase distribution boards and circuit breakers are more expensive than single-phase equivalents.

Operational costs (OPEX)

The ongoing costs of your power supply depend on network charges, energy efficiency, and maintenance requirements.

Network charges

All businesses must pay fixed and variable charges to maintain their electricity connection, covering both local distribution and national transmission networks. These charges differ based on the power supply:

• Single-phase: £200–£400 per year, including:
  • Business electricity standing charges
  • Meter operator charges (if applicable)
  • Distribution and transmission charges usually don’t apply due to capped power capacity.
• Three-phase: £2,000+ per year, including:
  • Standing charges
  • Higher meter operator charges (especially for half-hourly meters, common in this setup)
  • DUoS and TNUoS charges due to higher capacity connections.
  • Reactive power charges (variable) for businesses with high inductive loads (e.g., motors, refrigeration)
  • Potential peak demand charges (variable) during periods of high power consumption.

Electricity costs

The business electricity price per kWh is independent of the power supply type, meaning single-phase and three-phase power have comparable unit costs. Similarly, the terms of business energy contracts are generally the same for both setups.

💡 At Business Energy Deals, we specialise in helping companies minimise their electricity costs. Use our business energy comparison service today and switch business energy providers to access the cheapest tariffs.

Energy efficiency savings

Three-phase power supplies significantly improve business energy efficiency, reducing energy losses and voltage drops, especially in businesses using large machinery or long cable runs.

This efficiency helps lower operational costs for businesses that consume high amounts of electricity.

Maintenance costs

Maintenance costs depend on the entire electrical system, not just the power supply type.

• Three-phase supply: Reduces strain on electrical equipment, lowering the risk of overheating and extending the lifespan of motors and industrial machinery. However, more complex switchgear and protective devices (e.g., circuit breakers, contactors) can be costly to replace, and troubleshooting faults may take longer.
• Single-phase supply: Systems under heavy loads can cause higher wear and tear, leading to more frequent maintenance and potential equipment failures.

How to check for a single-phase or three-phase power supply?

There are a few ways for businesses to check whether their power supply is single or three-phase.

1. Ask your business electricity supplier or an electrician:
   • Your electricity provider can confirm your supply type.
   • An electrician can inspect your system and verify it for you.
2. Check your energy meter:
   • Single-phase meters display 230V.
   • Three-phase meters show 400V or have multiple voltage readings.
3. Look at your distribution board (fuse box)
   • Single-phase: One main fuse.
   • Three-phase: Three separate main fuses.
4. Check your power supply cables
   • Single-phase has two thick wires (1x live, 1x neutral, 1x earth).
   • Three-phase has four or five wires (3x live, 1x neutral, 1x earth).

FAQs – Single-phase vs three-phase power

Our business energy experts answer commonly asked questions regarding UK business power supplies:

Do businesses need planning permission to install a three-phase power supply?

No, planning permission is not required to upgrade to a three-phase power supply. Your local DNO will handle the installation at your property and any necessary local grid upgrades after approving your request.

However, any internal wiring needed to connect your appliances must comply with building and safety regulations, and if you don’t own the premises, you should check for lease or property restrictions.

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