Key Takeaways
- Three-phase power delivers three times the capacity of single-phase at the same current rating
- Common triggers for upgrade: EV charger deployment, commercial solar PV, large HVAC systems, industrial machinery
- DNO supply upgrades typically take 8–16 weeks and involve application, survey, and connection works
- Wire Now handles the complete three-phase upgrade process including DNO application across London, Hertfordshire, and Essex
What Is Three-Phase Power?
Three-phase power is an electrical supply system that uses three separate conductors carrying alternating current, each offset by 120 degrees. In practical terms, a three-phase supply delivers approximately three times the power of a single-phase supply at the same current rating. Most UK homes have single-phase power (230V, up to approximately 23kW). Commercial and industrial premises often have or need three-phase power (400V, typically 69kW and above).
When Does a Commercial Property Need Three-Phase?
A three-phase supply upgrade is typically triggered when the building's electrical demand exceeds what a single-phase supply can deliver. Common triggers include:
EV charger deployment: Installing multiple 7kW chargers or any 22kW+ chargers quickly exceeds single-phase capacity. A site with 6+ chargers will almost certainly need three-phase power.
Commercial solar PV: Solar systems above approximately 4kW require three-phase inverters for grid connection under G99 requirements. Most commercial systems are well above this threshold.
Large HVAC systems: Commercial air conditioning and heating systems with compressors above 5kW typically require three-phase motors.
Industrial equipment: Manufacturing machinery, large compressors, commercial kitchen equipment, and data centre power systems generally require three-phase supply.
General load growth: Buildings that have expanded their operations — adding floors, tenants, or equipment — may outgrow their original single-phase supply.
How Do You Upgrade from Single-Phase to Three-Phase?
The upgrade process involves coordination between your electrical contractor and the Distribution Network Operator (DNO):
- Load assessment — Your electrician calculates the total electrical demand to determine the required supply capacity
- DNO application — A formal application is submitted to the DNO requesting a three-phase supply upgrade
- DNO survey — The DNO surveys the site and the local network to determine if the upgrade can be accommodated
- Quotation — The DNO provides a quotation for the connection works
- Acceptance and scheduling — Once the quote is accepted, the DNO schedules the works
- Connection works — The DNO installs the new three-phase supply cable and meter
- Internal works — Your electrician installs a new three-phase distribution board and redistributes circuits
The total process typically takes 8–16 weeks from application to completion, though complex cases involving network reinforcement can take longer.
How Much Does a Three-Phase Upgrade Cost?
Costs vary significantly depending on the distance from the nearest three-phase supply point and the capacity required:
- DNO connection costs: £2,000–£10,000+ depending on distance and network capacity
- Internal electrical works: £3,000–£8,000 for new distribution board, cabling, and circuit redistribution
- Total typical cost: £5,000–£18,000 for a straightforward upgrade
Where the nearest three-phase supply is more than 50m from the property, costs can increase substantially due to cable trenching and civil works. Wire Now provides a detailed quote covering both DNO and internal costs before any work begins.
How Does This Affect EV Charging and Solar Installations?
If you're planning EV charging or solar PV, the three-phase supply upgrade should be considered as part of the overall project, not as a separate exercise. Coordinating both reduces cost, avoids rework, and shortens the overall timeline.
For example, a business installing 10 EV chargers and a 50kW solar system might need a three-phase supply upgrade. By planning all three elements together, Wire Now can optimise the distribution board design, minimise cable runs, and submit a single DNO application covering all requirements.
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