Three-Phase Power Explained: When Does Your Business Need It?

Three-Phase Power for Business Explained: What It Is and When You Need It

If you've heard the term three-phase power thrown around and aren't entirely sure what it means — or whether your business actually needs it — you're not alone. Getting three phase power for your business explained properly, without a lot of electrical jargon, makes a real difference when you're trying to make a sensible decision about your infrastructure.

The short version: three-phase power delivers more electricity, more consistently, and is essential for certain types of commercial and industrial operations. But it's not automatically the right choice for every business. This guide will walk you through the practical reality of what three-phase power is, which businesses genuinely benefit from it, and what the upgrade process involves.

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What Is Three-Phase Power?

Most domestic properties and small commercial premises are supplied on a single-phase supply — a two-wire system (live and neutral) delivering 230V. It's perfectly adequate for lighting, standard office equipment, and most domestic appliances.

Three-phase power uses three live conductors, each carrying an alternating current that is offset by 120 degrees from the others. This delivers a combined supply of 400V (line-to-line) and provides a smoother, more consistent flow of power. It also allows for much higher total loads without the need for oversized cabling or the risk of overloading a single circuit.

In practical terms, three-phase power can handle roughly three times the load of a comparable single-phase supply using the same cable size — which is why it becomes essential as power demands increase.

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Which Businesses Typically Need Three-Phase Power?

This is where three phase power for business is best explained through real-world examples rather than theory. You're likely to need a three-phase supply if your business involves any of the following:

Heavy Machinery and Manufacturing

Lathes, CNC machines, compressors, large pumps, and conveyor systems are typically designed to run on three-phase motors. These motors are more efficient on three-phase supplies and will either underperform or fail to start correctly on single-phase. If you're running a workshop or light industrial unit in Kent or across the South East, this is one of the most common reasons we see businesses requesting a supply upgrade.

Commercial Catering

Industrial ovens, combination steamers, commercial dishwashers, and large refrigeration systems can place considerable demand on an electrical supply. A busy kitchen supplying 200 covers a night will often need a three-phase supply to avoid constantly tripping circuits or running close to the supply limit.

EV Charging Infrastructure

With more businesses installing EV charging points for staff and customer vehicles, three-phase power is increasingly relevant. A single 7kW AC charger can run on single-phase, but if you're installing multiple chargers or faster 22kW units, a three-phase supply becomes essential. This is something we're seeing more of across commercial sites in Surrey, Greater London, and Kent as businesses prepare for the shift to electric fleets.

Data Centres and Server Rooms

Servers generate significant heat, and the cooling systems required to manage that heat are power-hungry. Data centres almost universally use three-phase supplies to distribute loads evenly and reduce the risk of imbalance or supply interruption.

Retail and Leisure Facilities

Large air conditioning systems, escalators, and extensive lighting rigs in retail environments or leisure centres often require three-phase power. If you're fitting out a new commercial premises in somewhere like Maidstone or Bromley, it's worth checking the supply specification before you finalise your equipment choices.

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When Single-Phase Is Sufficient

Not every business needs to upgrade. If your operation involves primarily computers, standard lighting, and plug-in equipment under a few kilowatts, a properly designed single-phase installation will do the job. A good electrician should be honest with you about this rather than pushing an upgrade that isn't warranted.

The key indicator is total connected load and diversity. If you're operating well within a 100A single-phase supply (roughly 23kW), a three-phase upgrade may not be necessary. If you're regularly tripping main breakers, noticing voltage drops when equipment starts up, or planning to add high-load equipment, that changes the picture.

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What Does Upgrading to Three-Phase Power Involve?

Checking the Available Supply

Three-phase power has to be available from the Distribution Network Operator (DNO) — in most of the South East, that's UK Power Networks. Not every street or business park has three-phase infrastructure nearby. The first step is confirming availability and making an application to the DNO for a new or upgraded service. This process can take anywhere from 6 to 16 weeks depending on the complexity of the work required at the network level.

Internal Wiring and Distribution

Once the supply is confirmed and installed, the internal electrical installation needs to be designed and installed to match. This includes a new metering arrangement, a three-phase distribution board, and correctly rated wiring throughout — all designed and installed to BS 7671:2018 (18th Edition), the current wiring regulations standard.

The installation must be certified by a competent person. For commercial premises, this means working with a contractor registered with a recognised body such as the NICEIC, which provides third-party oversight of electrical work and gives you confidence that the installation has been independently assessed against the relevant standards.

Costs

DNO connection costs vary significantly depending on distance from existing infrastructure, ground conditions, and whether reinforcement of the local network is required. As a rough guide:

• Simple three-phase upgrade at an existing served commercial premises: £1,500–£5,000 for DNO works
• New connection with civils work: costs can run to £10,000–£30,000+ depending on distance and scope
• Internal installation (distribution board, wiring, certification): typically £2,000–£8,000 depending on the size and complexity of the premises

These are indicative figures. Every site is different, and you should get a detailed survey and quotation before committing.

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When to Call a Qualified Electrician

You should speak to a qualified electrician before you apply to the DNO — not after. The reason is straightforward: the DNO will want to know your maximum demand figure, which needs to be calculated properly based on your connected loads and diversity factors. Getting this wrong can result in an undersized supply that causes problems down the line, or an oversized one that adds unnecessary cost.

A qualified electrician can also advise on whether load management or power factor correction might reduce your apparent demand and save money on the connection.

Any work on a commercial electrical installation — including a new three-phase supply — must comply with BS 7671 and be carried out by a competent person. For commercial premises, there is no substitute for using a contractor on an approved scheme such as the NICEIC. This isn't just good practice; it protects you legally and ensures your insurers can't raise questions about the standard of the installation.

If your business is based in Rochester, Sidcup, or anywhere across Kent, Surrey, Essex, or Greater London, the right time to have this conversation is before you plan your equipment layout — not after you've already placed orders.

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Thinking About Three-Phase Power for Your Business?

Cleary Electrical are a NICEIC-approved electrical contractor based in Rochester, Kent, working with commercial clients across the South East. We carry out three-phase installations, DNO liaison, distribution board design, and full commercial fit-outs — all certified to BS 7671.

If you'd like to discuss your requirements, we offer free, no-obligation quotes. Get in touch via our contact page and we'll arrange a site visit at a time that suits you.