A three-phase installation in Leicester has two separate costs. If you need a new or upgraded supply, the network operator (National Grid Electricity Distribution) quotes for that directly. That part mainly depends on how many machines you connect, how far they are from the board, how the cables are run and whether existing wiring can be reused.
Prices at a glance
| Job | Typical price | Time |
|---|---|---|
| New or upgraded three-phase supply from the network operator | Quoted by the DNO | Varies a lot: weeks to months |
| Three-phase distribution board, fitted and tested | Fixed price per job | Usually 1 day |
| Sub-main to a workshop, unit or second board | Fixed price per job | Usually 1–2 days, depending on route |
| Connection for one machine, with local isolator | Fixed price per job | Usually a few hours per machine |
| Three-phase industrial socket outlet | Fixed price per job | Usually a few hours |
| Trunking or cable tray, per run | Fixed price per job | Depends on length and height |
| Out-of-hours work to keep you trading | Priced before any work | Agreed at survey |
Why are there two separate costs for three-phase?
Because two different organisations do the work. The network operator owns everything up to and including the main fuse (the cut-out), and your electrician does everything after the meter.
In Leicestershire the network operator, known as the DNO, is National Grid Electricity Distribution. If your building doesn't have a three-phase supply, or the existing one isn't big enough, you apply to them and they quote for the connection. Your electrician can't do this part and shouldn't include it in their price.
The electrician's part is everything that turns the supply into usable power: the board, the cables to each machine, isolators, final connections, testing and the Electrical Installation Certificate. A fair quote keeps these two parts clearly separate, so you can see what each one costs and who is responsible for each date.
What does the DNO charge for a three-phase supply?
There's no standard price. The DNO quotes each connection on its own, and the figure can vary a great deal from one site to the next.
The main things that drive their quote are how far your building is from a suitable part of the network, how much capacity you're asking for, and whether the local network has spare capacity or needs reinforcing. If there's already three-phase cable in the street and the new service only needs a short run, the job is simpler. If the road or footpath has to be dug up, or a substation needs work, the cost and time go up.
Lead times vary too, from a few weeks for a simple job to several months for a complex one. Apply early, and ask the DNO to confirm the date in writing so your electrician can plan around it. Many industrial units, older workshops and some commercial premises in Leicester already have a three-phase supply that isn't being used fully, so it's worth checking before you apply.
What is included in the electrician's part of the job?
Everything after the meter, from the main switch to the last machine. A complete quote should cover each of these:
- Survey and load assessment
- Working out total demand and how it splits across the three phases.
- Distribution board
- A three-phase board sized for the load, with suitable protective devices.
- Sub-mains
- Heavier cables feeding the board, an outbuilding or a second board.
- Isolators
- A local switch at each machine so it can be safely made dead.
- Equipment connections
- Final circuits and connections to each machine or socket.
- Testing and commissioning
- Every circuit tested, phase rotation checked, machines run up.
- Paperwork
- Electrical Installation Certificate, labelling and, in homes, building control notification.
How do cable size and distance affect the price?
They're often the biggest variable. The further a machine is from the board, and the more current it draws, the thicker the cable has to be.
Cable size isn't only about current. On a long run, voltage drops along the cable, and the current Wiring Regulations (BS 7671, 18th Edition) set limits on how much is acceptable. Motors are sensitive to this, especially when they start. So a 40-metre run to the back of a unit may need a much larger cable than a 5-metre run for the same machine. Larger cables cost more per metre, need bigger glands and terminals, and take longer to install.
Armoured cable is usually used for sub-mains and runs outdoors or underground. A run to a detached workshop or across a yard may also need trenching and ducting, which is often quoted separately. Give your electrician a rough layout with the machine positions and the route you'd prefer, and ask them to state the cable type and size in the quote.
Does the way cables are run make a difference?
Yes. How the cables are supported and protected, known as containment, can add as much time as the electrical work itself.
In workshops and commercial units, cables are usually run in steel trunking, conduit or on cable tray, fixed to walls, steelwork or the ceiling. This protects them from damage and makes later additions easier. The cost depends on the length of the run, the height, what it fixes to and how many bends and drops there are.
Work at height may need a tower or a scissor lift, which affects the price and the time. Existing trunking or tray that has spare room can save money, so it's worth pointing out at the survey. In a home, cables are more often hidden in walls or floors, which brings its own making-good costs.
Can existing wiring be reused?
Sometimes, and it can bring the cost down. It depends on the condition, size and type of what's already there.
An existing three-phase board with spare ways, in good condition and with suitable protection, may only need new circuits added. Old boards, rewireable fuses or a board that's already fully loaded usually need replacing first. Existing cables can only be reused if they're the right size for the new load, in good condition and tested satisfactorily.
If you've taken over a unit with old wiring, an inspection and test of the existing installation (an EICR) is a sensible first step. It shows what can stay, what needs fixing and what has to go, so the quote is based on facts rather than guesswork.
What is phase balancing and does it affect the cost?
Phase balancing means spreading the load evenly across the three phases. It's part of good design, so it shouldn't be an extra, but it does affect how the board and circuits are laid out.
Three-phase machines draw from all three phases equally. Single-phase loads, such as lights, sockets, a kettle or a single-phase EV charger, each draw from one phase only. If too many of them sit on the same phase, that phase can be overloaded while the others have spare capacity, which can lead to tripping and wasted supply.
A good electrician works out where each single-phase circuit should go. On an existing installation, rebalancing may mean moving circuits between phases, which takes time. If the DNO has set a maximum capacity per phase, a well-balanced design helps you stay within it.
How much disruption will my business have?
Usually less than people expect, but the power has to be off at some point. When and for how long is part of the price.
Most cabling, containment and board fixing can be done while you carry on working. The disruption comes when connections are made to the live supply or the existing board, which needs the power off. That's often planned for early morning, the end of the day or a quieter day.
If you can't stop at all during normal hours, ask for out-of-hours work to be priced up front. Splitting the job into stages can also help, though it can add time overall. Tell your electrician about fridges, freezers, servers, alarms or machines that need a controlled shutdown, so it can be planned properly.
How do I get a fair quote for three-phase work?
Get a survey, give the same information to everyone, and compare what each quote actually includes. A quote without a site visit is rarely reliable for three-phase work.
Before the survey, gather the make, model and power rating from each machine's rating plate, a rough sketch of where everything goes, a recent electricity bill and any letters from the DNO. Mention future plans too, such as extra machines or EV chargers, because sizing the board for them now is usually cheaper than upgrading later.
Watch for quotes that leave out the isolators, containment or testing, quotes that include the DNO's work as a guess, or prices that only cover 'first fix'. Check the electrician on the Electrical Competent Person register, or the register of the scheme they say they belong to, such as NICEIC or NAPIT.
At NT Electric we survey first, then give one fixed price for our work, with the DNO's part shown separately.
Questions
Can I apply for the new supply myself?
Yes. You can apply to National Grid Electricity Distribution directly, and many businesses do. You'll need the load figures for your equipment. An electrician can help work these out, so the capacity you ask for matches what you'll actually run.
Can you start before the DNO has connected the supply?
Often, yes. The board, cables, containment and isolators can usually be installed in advance. The final connection, testing under load and commissioning have to wait until the supply is live. Planning the two together avoids a long gap.
Will I need a new energy meter?
If the supply changes from single-phase to three-phase, the meter usually has to change too. That's arranged through your energy supplier, not the electrician or the DNO. Ask your supplier early so it doesn't hold up the connection.
Do I need building control approval for three-phase work?
In homes, a new circuit or consumer unit is notifiable under Part P, which a registered electrician handles. In business premises Part P doesn't apply, but the Electricity at Work Regulations do, and you should still get an Electrical Installation Certificate.
Is it cheaper to use a phase converter instead?
For one or two small machines on a single-phase supply, a converter or inverter drive can be cheaper than a new supply. It won't suit every machine, and it won't help if your total load is too big. An electrician can check the motor plate.
Why do three-phase quotes vary so much?
Mostly because they're pricing different things. One may include containment, isolators and out-of-hours work while another leaves them out. Ask each to list the board, cable sizes, routes and connections, then compare line by line.