3-Phase Installation Cost: UK Supply Upgrade Guide 2026

Common Reasons for 3-Phase Upgrade

• Large workshops and outbuildings — 3-phase motors, welders, compressors, and CNC machines require or benefit significantly from a 3-phase supply. Running large motors on single-phase is inefficient and limits the equipment you can use.
• EV fleet charging — a single 7 kW charger works on single-phase, but multiple chargers or a 22 kW 3-phase charger require a 3-phase supply. Commercial premises with fleet vehicles almost always need 3-phase.
• Multiple heat pumps — a large property with air-source or ground-source heat pumps may exceed single-phase capacity, particularly when combined with other high-power loads.
• Commercial kitchens — 3-phase ovens, induction hobs, and commercial refrigeration require 3-phase power. Any commercial food premises will typically need a 3-phase supply.
• Exceeding single-phase capacity — if the maximum demand assessment shows the installation will regularly exceed the available single-phase capacity, a 3-phase upgrade is the only solution. Overloading a single-phase supply causes voltage drop, nuisance tripping, and potential damage to equipment.

DNO Connection Costs

• Standard connection (network at boundary) — £1,000 to £1,500. Where the existing 3-phase network already runs past the property, the DNO needs to install a service cable, cutout, and meter. This is the best-case scenario.
• Short cable run required — £1,500 to £3,000. If the nearest 3-phase network is within a few hundred metres but not at the boundary, the DNO must run additional cable. Cost increases with distance.
• Network reinforcement needed — £3,000 to £10,000+. In rural areas or locations far from the existing 3-phase network, significant infrastructure work may be needed. The DNO may need to install a new transformer or run cables over long distances. These costs can be substantial.

3-Phase Board Costs (Trade Prices)

• Basic 3-phase distribution board (12-way) — £300 to £450 trade. Unpopulated metal enclosure with incoming 3-phase isolator. Suitable for small commercial or workshop installations.
• 3-phase board with RCBOs and SPD (18 to 24-way) — £600 to £1,200 trade. Populated with 3-phase RCBOs, single-phase RCBOs for individual circuits, and Type 2 SPD. Required for larger installations with mixed single and 3-phase loads.
• 3-phase protective devices — 3-pole MCBs £25 to £50 each, 3-phase RCBOs £80 to £150 each, 4-pole RCD £80 to £120, 3-phase SPD £120 to £250. These costs add up quickly on a large installation.
• Additional materials — 3-phase meter tails (25mm SWA typical) £80 to £150, earthing conductor, equipotential bonding, cable glands, trunking, and labels: £100 to £250.

• Small workshop upgrade (network at boundary) — £2,500 to £4,000 total. DNO connection: £1,000 to £1,500. Materials: £800 to £1,200. Labour: £500 to £900. Testing and certification: £200 to £400.
• Medium commercial premises — £4,000 to £6,500 total. DNO connection: £1,500 to £3,000. Materials: £1,000 to £1,500. Labour: £900 to £1,500. Testing and certification: £300 to £500.
• Large installation with network reinforcement — £6,500 to £12,000+ total. DNO connection: £3,000 to £10,000+. Materials: £1,200 to £2,000. Labour: £1,500 to £2,500. Testing and certification: £400 to £600.

• Application submission — completed online via the DNO's connections portal. Requires site address, maximum demand assessment, site plan, and proposed installation details. Allow 1 to 2 weeks for the application to be processed.
• DNO survey and quotation — the DNO surveys the site and provides a formal quotation. This typically takes 2 to 4 weeks from application.
• Acceptance and payment — once the customer accepts the quotation and pays, the DNO schedules the installation work. Payment is usually required in full before work is scheduled.
• DNO installation — the DNO installs the service cable, cutout, and meter. This is typically scheduled 4 to 8 weeks after payment, depending on the DNO's workload and the complexity of the work.
• Total timeline — 6 to 12 weeks from application to energisation is typical. Complex installations requiring network reinforcement can take 16 weeks or more. Plan the internal electrical installation to be ready before the DNO energisation date.

• Distance from 3-phase network — this is by far the biggest cost variable. If the 3-phase network runs past the property, the connection cost is minimal. If cables must be run hundreds of metres, the cost can exceed £10,000 for the DNO work alone.
• Required capacity — a 60A per phase supply is standard, but higher capacities (100A per phase or more) cost more from the DNO and require larger cables and distribution equipment.
• Number of circuits — more circuits mean a larger distribution board, more protective devices, and more testing time. A 12-way board for a workshop costs significantly less than a 36-way board for a commercial premises.
• Cable runs and containment — long cable runs between the meter and the distribution board, or between the main board and sub-distribution boards, add to material and labour costs.
• Earthing arrangements — a 3-phase installation requires adequate earthing. If the existing earthing is insufficient or needs upgrading, this adds cost. Under BS 7671 Regulation 411.3.3, RCD protection is required for socket-outlet circuits not exceeding 32A in all installations.
• Location — London and the South East are 15% to 25% more expensive than the national average for both DNO charges and electrician labour rates.