Three-phase power is one of those topics that mostly comes up when you are doing something specific - solar, EV charging, hot water heat pumps, electric kilns or workshop tools. Here is what it actually is and when you need it.
What single-phase and three-phase are
Standard Australian homes have single-phase power. One active wire plus a neutral. Total capacity is 60 to 100 amps for a typical home (around 14 to 24kW).
Three-phase power has three active wires plus a neutral. Total capacity is usually 60 amps per phase, so 180 amps total (around 40 to 45kW). Power is delivered more evenly and large loads can be spread across the phases.
When you need three-phase
Heavy single-phase loads that are at the limit of what a normal home can handle. Multiple EV chargers running at once. Welding gear in a serious workshop. Commercial kitchen equipment in a home setup. Large hot water heat pumps over 5kW. Industrial pottery kilns.
You also need three-phase to install some specific equipment - any 22kW EV charger, larger reverse-cycle air conditioning systems, certain swimming pool heaters.
When you do not need three-phase
Standard residential use. A typical 3-bedroom home with all modern appliances does not need three-phase. Including solar up to 13.2kW, one EV charger up to 7kW, electric hot water, electric stove, ducted air-con - all single-phase is fine.
How to tell what you have
Look at your switchboard. If you have one big main switch and one set of circuit breakers below, you are single-phase.
If you have three main switches (or one switch labeled with three poles) and circuit breakers grouped under each, you are three-phase.
Easier test: check your bill. The supply charge sometimes lists 'single-phase' or 'three-phase'.
What an upgrade involves
SA Power Networks has to bring three-phase service to your property if it is not already there. For homes already close to a three-phase street main, this is fairly straightforward. For homes in single-phase areas, SA Power Networks might need to do significant work.
Your switchboard then needs to be replaced with a three-phase board. New consumer mains. New main switch.
What it costs in Adelaide
If three-phase is already available at the property (just need to connect it): $2,500 to $5,000.
If SA Power Networks needs to bring three-phase to the property: $5,000 to $15,000 depending on what is needed.
Plus new switchboard: $2,000 to $4,000.
Worth doing speculatively?
If you are doing a major renovation and there is a chance you will want three-phase in future (workshop, electric vehicles, solar/battery), it can be worth pre-running the cable while walls are open. Adding three-phase later involves much more disruption.
For most homes, single-phase is fine and you do not need to think about it.