Single-phase or three-phase power: how to decide for your home

Single-phase power arrives on one active conductor and a neutral. Three-phase arrives on three actives and a neutral, giving the house three supplies to share the load across. Most household appliances run on single phase either way; in a three-phase home each circuit connects to one of the three phases, and only equipment built for three-phase uses all three.

The benefit is capacity. A single-phase supply limits how much current the house can draw at once, set by the connection, the consumer mains and the main switch. Three phases spread big loads so they aren't all on one conductor, which is why three-phase suits homes where several heavy appliances run together.

Three-phase doesn't make an appliance use more or less energy. Your bill depends on what you use and your plan, though supply charges can differ for a three-phase connection, so check with your retailer.

Three-phase earns its place when large loads overlap. A big ducted reverse cycle system running on a cold July evening, alongside an induction cooktop, a heat pump water heater and an EV charger, is the classic example. So is a household with two EVs charging overnight, or one wanting a 22 kW charger, which needs three-phase.

Workshops are another. Some welders, compressors and machines are made for three-phase, and once the house has it, a three-phase submain can run to a shed sub-board. A major renovation or rebuild going all-electric is also a natural point to decide, because the board and mains may be changing anyway.

On newer estates in Tarneit, Truganina and Point Cook, plenty of homes now combine ducted air, induction and an EV. In older brick veneers around Altona and Laverton, the original supply may already be stretched by what the house runs today. Both are worth a load check before another big appliance goes in.

Three-phase isn't the only answer to a stretched supply. A heavier single-phase supply, with larger consumer mains and a bigger main switch on the existing connection, can carry a home adding a split system or two and an induction cooktop. It needs distributor approval, but it's a smaller job than changing phases.

Load management is the other tool. A sensor on the incoming supply measures what the house is drawing, and a compatible EV charger backs off when the oven, heating and hot water are all on, then picks up as the load drops. On a modest supply it's often what makes a wall charger workable without touching the connection.

It has limits. It can only control equipment built to respond, it slows charging on busy evenings, and it's worth asking what happens if the sensor or Wi-Fi drops out. If the planned loads can't be managed down far enough, three-phase gives the headroom instead.

The decision should come from numbers, not a hunch. An electrician looks at the existing supply, mains and switchboard, then lists the big appliances you have and plan to add, their size and which ones run together. Evening is usually the peak, with heating or cooling, cooking, hot water and car charging overlapping.

Bring the details. Air conditioner capacities, cooktop and oven models, the hot water system, the EV's onboard charger rating and any workshop equipment all change the answer. An EV only charges faster on three-phase if its onboard charger can accept the extra power, and plenty of cars can't take a three-phase charger's full output.

Look a few years ahead. If a ducted system and a second EV are likely soon, changing the supply once is less disruptive than doing it twice.

Your distributor decides whether three-phase is available at your property and on what terms, so availability is confirmed before you commit. On your side, four-core consumer mains replace the single-phase cable, the meter box is set up for a three-phase meter, and the switchboard gets a three-phase main switch, with existing circuits spread across the phases to balance the load.

Energy Safe Victoria counts consumer mains, the main switchboard, the meter box and the main earthing system as prescribed work. It's inspected by a Licensed Electrical Inspector and can't be switched on or left on until then, so changeover day means a planned outage.

In Powercor's area, a request to change from single to three-phase can only be submitted by a registered electrical contractor, and Powercor says all such works need a Certificate of Electrical Safety. The distributor fits the new meter on its own booking, so part of the timeline sits with them.

Most homes charge on single phase, and a 7 kW class wall charger on its own circuit suits a single-phase home where the supply and board have room. Three-phase opens up higher-capacity chargers, which only help if the car can accept the extra power.

For two EVs, the choice is usually three-phase with two chargers, or single phase with load management sharing capacity between the cars and the house. Overnight charging gives plenty of hours to work with, so a managed single-phase setup suits many two-EV households. Heavy daily driving plus a large ducted system pushes the decision towards three-phase.

The best time to change supply is when the switchboard or mains are changing anyway: replacing an old fuse board, a renovation or extension, or a ducted installation. That means one shutdown and one inspection, with the phases balanced for the new loads from the start.

Don't buy three-phase equipment before the supply is confirmed. Get the load assessment, confirm availability with the distributor, then order the ducted unit or charger to suit.