Explainer

What Is Cheaper, 3 Phase or Single Phase?

Neither. A kilowatt hour costs exactly the same on both, and your network puts the two supplies in the same tariff class. The only real difference is what it costs to get three phase in, and that is a question nobody can answer from a website.

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Updated 6 August 2026 About a 10 minute read Written by licensed Sydney electricians

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The short answer

Neither one is cheaper. They are the same tariff

The question contains an assumption worth pulling apart before anything else, which is that electricity has a price that depends on how it arrives. It does not. You are billed on the total number of kilowatt hours you consume, and the meter does not care whether they came down one live conductor or three.

Ausgrid puts this beyond argument in its own price guide. A customer whose supply voltage at the metering point is either 230 V single phase or 400 V poly phase is assigned to the same Low Voltage tariff class. One class, one set of rates, whichever supply you have.

The daily supply charge does not differ either, which is the version of the claim that sounds most plausible. Ausgrid's residential network tariffs are a closed flat tariff, a time of use tariff and two demand tariffs, and not one of them is phase specific. The word "phase" does not appear anywhere in the network price list. Endeavour Energy, the other network covering parts of Sydney, is the same, and its daily access charge is identical across all four of its residential tariffs.

Then there is the demand charge, which is where a genuinely popular piece of advice falls over. It is often said that spreading your loads across three phases lowers your demand charge because no single phase peaks as hard. Ausgrid's guide says the opposite in plain terms: coincident demand is applied across the phases to determine the maximum demand. Your demand is the total across all three legs in the same half hour. A 12 kW load is 12 kW of demand whether it arrives on one phase or is split neatly over three.

One honest caveat, because this is a big market. We have not read every retail plan sold in New South Wales, and a retailer is free to structure a plan however it likes. We could not find a single one charging more for a three phase connection, and the network charges underneath them are demonstrably the same. If you want to be certain about your own plan, the document to look at is its Basic Plan Information Document.

Line by line

What actually differs, once you look at a bill

Three of the four things you pay for are the same on either supply. The fourth is the one everybody skips past, and it is the whole answer.

Scroll to see the full diagram →

What it means: everything that recurs is identical, and the one difference is a capital cost you pay once. That reframes the question completely. "Which is cheaper" has no answer, because they cost the same to run. The real question is whether the one off spend buys you something you actually need, and for most Sydney homes on a normal load the answer is no. For a workshop, a large solar and battery system, or a property that has run out of supply capacity, it can be the only sensible move.

It is worth being clear about what the amber box does not contain: a number. There is no price for a three phase upgrade published by Ausgrid, the Australian Energy Regulator, IPART or the NSW Government. Every dollar figure you will find for Sydney sits on an electrician's own marketing page, including some very confident ones. We are not going to add another, and the reason is in the next section.

Capacity

What you get for the same amps

This is the part that is genuinely different, and it is simple arithmetic rather than a sales argument.

Amps per phase	Single phase	Three phase	Extra capacity
32 A	7.4 kW	22.1 kW	+14.7 kW
40 A	9.2 kW	27.6 kW	+18.4 kW
63 A	14.5 kW	43.5 kW	+29.0 kW
80 A	18.4 kW	55.2 kW	+36.8 kW
100 A	23.0 kW	69.0 kW	+46.0 kW

Three phase at the same amps per phase gives you three times the power, not 1.73 times. That mistake turns up constantly, and it comes from misplacing the square root of three. The square root of three is the relationship between the two voltages, not a power multiplier. Because the phases are 120 degrees apart, the voltage between any two of them is 1.732 times the voltage from one to neutral: 1.732 times 230 volts is 398 volts, which is why we call it 400. The factor of three in the power comes from there simply being three phases. The figures above are worked at 230 volts per phase, and using the 400 volt line to line figure instead lands within a fraction of a per cent, the difference being that 400 is a rounded nominal.

The NSW Service and Installation Rules describe the supply as a 50 hertz waveform at a nominal 230 volts phase to neutral and 400 volts phase to phase, from a three phase four wire distribution system. Every single phase house in Sydney is connected to one leg of that same three phase system. Getting three phase is not a different kind of electricity. It is being given all three legs instead of one.

A word on the 63 amp figure, since it gets quoted as though it were a standard. It is not. New South Wales has no fixed service capacity: the Rules say a maximum demand determination made under AS/NZS 3000 is submitted with your connection application, and once the distributor approves it, that figure becomes the approved supply capacity for the installation. 63 amps is simply a common outcome on a modern Sydney home. Older services are often smaller. The number that governs you is on your own connection, not on a website.

The real case

Four places three phase genuinely saves money

None of them is your kilowatt hour rate. All of them are about what becomes possible.

Motors, and why they last longer

Three phase produces a rotating magnetic field on its own, so a three phase motor starts by itself. A single phase motor has no rotating field and has to fake one with an auxiliary winding and a start capacitor, sometimes with a centrifugal switch to drop them out once it is up to speed. Those extra parts are the ones that fail, and a workshop that has replaced a few start capacitors already knows it.

There is a regulatory tell here too. Australia's minimum energy performance standards for motors cover three phase cage induction motors from 0.73 kW up to 185 kW. Single phase motors are not in the scheme at all. That is a reasonable indication of where the efficient machines are expected to be. We are not going to quote you a percentage, because no authoritative Australian source publishes a like for like comparison, whatever the vendor pages say.

Cable, on long runs and big loads

For the same delivered power, three phase carries about a third of the current in each conductor. Ten kilowatts on single phase is 43.5 amps. The same ten kilowatts on three phase is 14.4 amps per phase. Since cable size is driven by current and by voltage drop over distance, that is a materially smaller cable for the same job.

There is a second effect people miss. In a properly balanced three phase load the three currents are equal and 120 degrees apart, so they cancel and the neutral carries nothing. More power over less copper is the reason three phase exists at all, and on a long run out to a shed or a pool plant room it is where the saving actually shows up.

EV charging, if you need speed

A single phase charger at 32 amps gives about 7.4 kW, which is roughly 40 km of range an hour and refills most cars comfortably overnight. Three phase takes you to about 11 kW at 16 amps or 22 kW at 32 amps, which is the difference between charging overnight and charging over dinner.

For a household car doing normal distances, overnight is fine and three phase is an expensive way to buy speed you will sleep through. Where it earns its keep is two or three EVs on one property, a vehicle doing high mileage, or a business with a car that has to turn around during the day.

Solar and batteries, where the limit is per phase

This is the strongest financial argument on the list, because Ausgrid writes its rule per phase rather than per property. Up to 10 kW of total inverter nameplate rating per phase can be approved through the streamlined process, and anything above that goes to technical review. On single phase that is your ceiling. On three phase the same rule gives you three times as much through the same fast path.

Ausgrid currently prescribes no export limit on installations up to 10 kW per phase, and assesses larger ones site by site. If you are planning a large array with storage and you are already near the single phase ceiling, this is a far better reason to price a three phase upgrade than anything on your bill.

The upgrade

Why nobody can quote this on a website

A single to three phase conversion is several jobs wearing one name. On the network side, the service conductors from the pole or the pit have to be replaced with three phase and reconnected, which is contestable work carried out by an Accredited Service Provider rather than by any electrician. Level 2 covers the service work: disconnection and reconnection, overhead and underground service conductors, and energising the network operator's equipment.

On your side, the consumer mains from the point of attachment to the switchboard have to be replaced, and the switchboard itself has to be able to accept three phase, with a main switch and busbar rated for it. Older boards frequently cannot, which quietly turns the job into a switchboard upgrade as well. The single phase meter is replaced with a polyphase meter, and since metering became contestable that meter belongs to whoever your retailer appoints as metering coordinator rather than to the network. There is no published price for that swap in New South Wales either.

Then there is the variable that decides everything, and it is entirely outside your property: whether three phase actually runs past you. If the low voltage mains in the street carry all three phases and one is spare, the work is contained. If they do not, extending or augmenting the street mains is Level 1 construction work, involving design, possibly poles or trenching, and it is a different order of cost and time.

So when a page tells you a three phase upgrade in Sydney costs a specific figure, it is describing a job it has not looked at. The most quasi-independent datapoint we could find was an industry publication noting quotes ranging from $60 to $600,000 depending on circumstances, which is really a way of saying the range is unbounded. What determines your number is the distance, whether the service is overhead or underground, the state of your board, and what is in the street. All four are visible in about twenty minutes on site, and none of them is visible from here.

The related question is whether you need the whole conversion at all. A great many jobs that get quoted as "we need three phase" are really about running out of capacity on the supply you have, and the answer is a bigger single phase service or a properly sized set of consumer mains. That is worth establishing before anybody prices the larger job.

Be sceptical

Four claims about three phase that do not survive checking

All four are on Australian electricians' websites right now. All four are checkable against public documents.

"Three phase is cheaper to run"

It is not, because there is no separate rate to be cheaper. Ausgrid assigns both 230 V single phase and 400 V poly phase customers to the Low Voltage tariff class.

Where this probably comes from is the genuine efficiency of three phase motors and cable, which is a plant and equipment saving, not a tariff.

"Three phase attracts a higher supply charge"

Also unsupported, and it is the same error pointing the other way. There is no phase based tariff code at Ausgrid or at Endeavour, and the daily access charge does not vary with phases.

If a plan you are offered does differ, it is a retail decision rather than a network one, and it will be in the Basic Plan Information Document.

"Spread the load and cut your demand charge"

Ausgrid measures coincident demand across the phases. The half hour total is the total, however evenly it is distributed.

Balancing your phases is still correct and is required, but for supply quality reasons rather than billing ones. Nobody should sell you three phase on a demand charge saving.

"Three phase gives you 1.73 times the power"

Three times, at the same amps per phase. The 1.732 is the ratio between 230 volts phase to neutral and 400 volts phase to phase, because the phases sit 120 degrees apart.

It is a small error with a large consequence, since it understates the capacity gain by nearly half and makes the upgrade look worse than it is.

The rules

When three phase stops being a choice

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The NSW Service and Installation Rules set the hard triggers, and they are worth knowing because they take the decision out of anyone's hands. Up to 100 amps per phase you may be supplied by one, two or three phases. Above 100 amps per phase you must have three phases and neutral. And any motor exceeding 2 kW requires three phases and neutral regardless of what the rest of your installation draws.

The Rules also list the load characteristics that push an installation to three phase on their own account, naming three phase motors, instantaneous water heaters, 400 volt welders and large heating or air conditioning loads. If any of those is on your list, the conversation moves from whether to when.

Balancing is a requirement rather than good practice. The Rules state that the customer's load shall be arranged to balance, as far as practicable, the loading on each phase of the distribution system. That is why a three phase installation is designed rather than simply connected, and it is also why a single phase inverter sitting on a three phase supply needs thinking about rather than assuming.

Work on the service conductors is contestable and has to be done by an Accredited Service Provider of the right level. Everything inside the property is licensed electrical work, and we lodge a Certificate of Compliance for Electrical Work within 7 days of testing, which since 1 July 2026 goes through the BCNSW eCert portal.

Good to know

Three phase questions

Is three phase cheaper to run than single phase?

No, and neither is single phase. You are billed on the total number of kilowatt hours you use, and it makes no difference how many conductors delivered them. Ausgrid assigns customers to a network tariff class on supply voltage, and its own price guide states that a customer measured at either 230 V single phase or 400 V poly phase is assigned to the Low Voltage tariff class. Same class, same rates. Ten kilowatt hours costs the same on either supply.

Does a three phase connection have a higher daily supply charge?

We could not find one anywhere in New South Wales. The word phase does not appear in Ausgrid's network price list at all, and there is no three phase residential tariff code: the residential codes are a flat tariff, a time of use tariff and two demand tariffs, none of them phase specific. Endeavour Energy is the same, with an identical daily access charge across all four of its residential tariffs. We have not audited every retail plan in the state, so the sensible check is your own plan's Basic Plan Information Document, but we found no retailer charging more for three phase.

Will splitting my loads across three phases reduce my demand charge?

No, and this is the most common thing said about three phase that is simply wrong. Ausgrid's price guide says coincident demand is applied across the phases to determine the maximum demand. In other words your demand is the total across all three phases in the same half hour, not the worst single phase. A 12 kW load is 12 kW of demand whether it arrives down one leg or is spread over three. Moving loads between phases is good engineering for other reasons. It is not a billing strategy.

How much does it cost to upgrade to three phase in Sydney?

Nobody can tell you from a website, and anyone giving you a figure without seeing the property is guessing. There is no price published by Ausgrid, the Australian Energy Regulator, IPART or the NSW Government for this work. The cost turns on whether three phase already runs past your property, how far the service has to come, whether it is overhead or underground, whether your switchboard can take it, and whether the street mains themselves need augmenting, which is a different order of work again. The only honest answer is a site specific quote.

Do I need three phase for an EV charger?

Usually not. A single phase charger at 32 A gives you about 7.4 kW, which adds roughly 40 km of range an hour and comfortably charges most cars overnight. Three phase takes you to about 11 kW at 16 A or 22 kW at 32 A. The question is whether you actually need to refill the battery in a few hours rather than overnight. What matters more than the phases is your approved supply capacity and what else is running, which your electrician checks before deciding whether an Ausgrid connection application is needed.

Do I need three phase for a bigger solar system?

This is where three phase makes a real and measurable difference, because Ausgrid's limit is written per phase. Up to 10 kW of total inverter nameplate rating per phase can be approved through the streamlined process, and above that goes to technical review. On a single phase supply that ceiling is 10 kW. On three phase the same rule gives you three times as much through the same streamlined path. If you are planning a large system with batteries, this is a better reason to consider three phase than anything on your bill.

How do I know if I actually need three phase?

From the maximum demand calculation for your installation rather than a rule of thumb. The NSW Service and Installation Rules set the hard triggers: above 100 A per phase you must have three phases and neutral, and any motor over 2 kW requires three phase regardless of your total load. The Rules also list the load characteristics that push you there anyway, including three phase motors, instantaneous water heaters, 400 V welders and large heating or air conditioning loads. Below those thresholds it is a judgement about how much you are stacking onto one supply.

Keep reading

If this turns out to be a capacity question rather than a phases question: the cable feeding your board is consumer mains, the board itself is a switchboard upgrade, and a supply large enough for an instantaneous unit is covered under hot water installation. See every post on the blog.

Wondering whether you actually need three phase?

Upfront pricing, with the price agreed before we start. We will tell you if a bigger single phase service does the job for less.

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