Guide
Single phase or three phase: do you actually need the upgrade?
Updated
The cheapest three phase upgrade is the one you establish you do not need, so this guide is deliberately written to talk you out of it where that is the right answer.
The two genuine reasons
- Capacity
- The total load exceeds what a single phase supply can carry. Three phases share the load across three conductors, so the same incoming fuse rating carries substantially more power.
- Three phase equipment
- Motors, machine tools, lifts, large refrigeration and some catering and workshop equipment are built for a three phase supply. Converters exist, but for permanent installed plant a real supply is usually the right answer.
Cheaper answers to try first
- Check the main fuse rating. Some properties are on 60A or 80A where 100A is available on the same single phase service, which is a much smaller job than a phase change.
- Load management. EV chargers and heat pumps can be fitted with load curtailment that sheds or throttles them when the house draws heavily elsewhere, which is standard practice rather than a compromise.
- Do the diversity calculation properly. Adding every nameplate rating on the site produces a number nobody ever draws. A competent load assessment is the first thing a good contractor does and the last thing a bad one does.
- Reconsider the equipment. A single phase alternative for one machine can be cheaper than a network connection project, particularly where the network is far away.
Where three phase is the right call
Workshops with fixed machinery, farms with grain drying or milking plant, commercial kitchens, small industrial units, buildings with lifts, sites installing several EV chargepoints, and larger heat pump installations. In all of those the load is either genuinely large or inherently three phase, and load management is a delaying tactic rather than a solution.
What three phase does not do
It does not make an EV charge faster than the car's onboard AC charger allows, and it does not reduce your energy bill by itself. It gives you capacity and the ability to run three phase equipment. Those are worth paying for when you need them and worth nothing when you do not.
How to decide with evidence
Get a load assessment before you get a connection quote. The assessment tells you the capacity to request, the capacity you request drives whether network reinforcement is triggered, and reinforcement is the single largest step in most connection prices. Doing it in the other order is how people end up paying for capacity they never use.
Tell us the load and the distance through the quote form and contractors will tell you whether the upgrade is worth applying for at all.