There is one label on the back of every appliance in your house and one piece of arithmetic that turns it into a straight answer about your circuits. The rest is background.
Pricing agreed before we start. We usually reply the same day.
Volts, amps and watts describe three different things about the same electricity, and the reason they stay confusing is that they are almost always explained in the abstract. In an Australian house they are not abstract at all. One of them is fixed for you, one is printed on the label, and the third is the one that decides whether your breaker trips.
Volts are the pressure. The supply here is nominally 230 volts single phase, set by AS 60038, with a tolerance of plus 10 and minus 6 per cent, so anywhere between roughly 216 and 253 volts at the socket is normal and none of it is your decision. It used to be 240 volts under the older standard, which is why plenty of appliance labels still say 240, and why one source will tell you a power point is good for 2300 watts and another will say 2400.
Amps are the flow. This is the one people have backwards. A ten amp power point does not supply ten amps. It permits up to ten amps. What actually flows is decided at the other end by the appliance, and the socket, the cable and the breaker are simply built to carry it safely. Nothing is being pushed into your toaster that the toaster did not ask for.
Watts are the two multiplied together, and they tell you the rate at which the appliance turns electricity into something useful. Here is the part worth keeping: because the voltage is essentially fixed, watts and amps in an Australian house are the same fact expressed in two units. Divide the watts on the label by 230 and you have the amps. That single move turns every appliance in the house into an answer.
Every appliance sold here carries a rating plate. It is usually a small silver sticker on the underside or the back, and it holds the entire answer.
Scroll to see the full plate →
What it means: the plate is telling you what the appliance needs and what it will draw when it is running. The volts are a requirement it is expecting the house to meet, and the house always does. The amps and the watts are a statement about the appliance itself. If a plate shows only watts, divide by 230. If it shows only amps, multiply by 230. Either way you end up with the number you actually wanted, which is how much of a circuit this thing is going to occupy.
The wattages below are typical rather than exact, since every model differs. The conversion is not: it is the same division every time.
| Appliance | Typical watts | Amps at 230 V | What that means |
|---|---|---|---|
| LED downlight | 10 W | 0.04 A | You could run a hundred of them and no circuit would notice |
| Laptop charger | 65 W | 0.28 A | Effectively nothing, whatever you have heard about standby power |
| Fridge | 150 W | 0.7 A | Small draw, but it runs all day, which is where the cost comes from |
| Microwave | 1,000 W | 4.3 A | Comfortable on any power point |
| Kettle | 2,200 W | 9.6 A | Almost the entire capacity of a 10 A point, on its own |
| Portable heater | 2,400 W | 10.4 A | Over a 10 A point on paper, which is why many are sold at 2,000 W |
| Ducted air conditioner | 5,000 W | 21.7 A | Never on a power point. Its own circuit, sized for it |
Read down the amps column and the shape of a household becomes obvious. Everything that makes light or moves information is negligible. Everything that makes heat is enormous. A single kettle asks for more current than two hundred and forty LED downlights, and that is not an exaggeration, it is 9.6 divided by 0.04.
The other thing the column shows is why trouble arrives in pairs. A kettle at 9.6 amps is comfortably inside a 10 amp power point. A toaster at 850 watts is under 4 amps and is also comfortable. Plug them into two different sockets in the same kitchen, though, and they are very likely sharing one circuit and one breaker behind the wall, and 13 or 14 amps through a circuit protected at less than that is exactly the situation the breaker exists for.
So there are two limits, not one. The socket has a rating, and the circuit feeding a row of sockets has its own. The first is printed on the front of the power point. The second is only visible at the switchboard, and knowing which one you hit is the difference between moving an appliance and needing another circuit.
Almost every explanation of this reaches for water in a pipe. Voltage is the pressure, current is the flow rate, and power is how much work the water does when it arrives. As far as that goes it is a good analogy, and it is worth keeping for pressure and flow.
Where it misleads is what it implies about who is in charge. A pipe under pressure with the tap open delivers whatever the pipe allows, and that makes people picture the socket forcing current into the appliance. Electricity does not work that way in a house. The voltage is imposed on the appliance and the current is drawn by it. Two things plugged into identical sockets, sitting at the identical 230 volts, will draw wildly different currents, and the difference is entirely inside the appliance.
That difference has a name and a unit, which is the fourth term nobody asks about. Resistance, measured in ohms, is how hard the appliance makes it for current to flow, and it is what ties the other three together: at a fixed voltage, low resistance means high current, and high resistance means almost none. A heating element is deliberately built to have low resistance, which is exactly why it draws ten amps and glows. A phone charger is built the other way.
It also explains the most dramatic thing that can happen in a circuit. A short circuit is resistance collapsing to nearly zero, usually because two conductors have met that were never meant to. The voltage does not change, so the current rises until something interrupts it, and that something is the breaker doing precisely the job it was installed for. Our post on what causes a short circuit goes through the usual culprits.
None of these are trivia. Each one is a question we get asked on site, and each one is answered by the same division.
Why the kettle and the toaster trip the breaker together
Individually they are both fine. Together they are asking one circuit for more current than it is protected to deliver, and the breaker opens before the cable in the wall gets hot.
Nothing is faulty when this happens. It is the protection working exactly as designed, and the fix is either a different socket on a different circuit or another circuit put in.
Why portable heaters stop at 2,400 watts
Because 2,400 watts is 10.4 amps at 230 volts, and a standard power point is rated at 10. That is why so many heaters are sold at 2,000 watts instead, which lands at a comfortable 8.7 amps.
It is also why running one on an extension lead rated below the appliance is a genuinely bad idea rather than a technicality. The lead is now the narrowest part of the path.
Why your bill is in kilowatt hours, not watts
Watts are a rate, like speed. Kilowatt hours are a quantity, like distance. A 2,000 watt heater is drawing 2 kilowatts while it runs, and three hours of it is 6 kilowatt hours.
This is why a 150 watt fridge can cost more per year than a 2,400 watt heater. The fridge runs constantly and the heater runs in July.
Why a motor's amps do not multiply out
On anything with a motor, some of the current does useful work and some of it moves back and forth without doing any. Volts times amps gives volt-amps, the apparent power. Watts is the part that becomes motion.
The ratio is called power factor, and it is why an air conditioner or a pool pump can draw more current than its wattage suggests. On kettles, heaters and toasters the two are effectively identical.
Dividing by 230 answers the question for one appliance on one socket, and that covers most of what a homeowner needs. It stops being enough the moment you start adding things up, because a house is not the sum of its nameplates. Nothing runs everything at once, so the wiring rules set out a proper method for working out maximum demand, with a figure assigned to each category of load rather than a straight total. That is the calculation behind sizing a circuit or a supply, and it is covered on our consumer mains page.
Cable is the other place the simple version runs out. A cable's current rating depends on how and where it is installed, so the same conductor carries less when it is buried in insulation or bundled with others than it does in free air. The number on a catalogue page is a starting point, not an answer.
And adding capacity is a job rather than a sum. A new circuit, a 15 amp outlet or a larger main switch all have to be certified as electrical work, which is why the useful thing to do with this page is not to plan an installation from it but to walk into the conversation knowing what the numbers mean. If a breaker is tripping regularly, that is worth a call rather than an experiment.
Both answers turn up because both have been true. The standard supply voltage is 230 volts under AS 60038, with a tolerance of plus 10 and minus 6 per cent, so roughly 216 to 253 volts is normal at the socket. The older standard was 240 volts plus or minus 6 per cent, and equipment built for it works perfectly well on the newer figure because the ranges overlap almost completely. It is why some appliance labels still say 240 V, and why you will see a standard power point described as 2300 watts by one source and 2400 by another.
Divide by 230. That is it, for anything plugged into a normal single phase socket in this country. A 1000 watt microwave draws about 4.3 amps. A 2400 watt heater draws about 10.4 amps. The reason it is that simple is that watts are volts multiplied by amps, and the volts are fixed by the network rather than chosen by you, so the only variable left is the appliance. Going the other way, multiply the amps by 230 to get watts.
A standard Australian power point is rated at 10 amps, which is about 2300 watts at 230 volts, or 2400 at the old 240. That is the rating of the socket, not a promise about the circuit behind it: several power points usually share one circuit and one breaker, so two appliances on separate sockets in the same room can still add up to more than the circuit is protected for. A kettle and a toaster is the classic pairing that finds this out.
A kilowatt is a rate and a kilowatt hour is a quantity, which is the same difference as between speed and distance. A 2000 watt heater is drawing 2 kilowatts at any instant it is running. Leave it on for three hours and it has used 6 kilowatt hours. Your retailer bills the kilowatt hours, because that is the electricity you actually consumed, and the watts on the label only tell you how fast the meter turns while the thing is on.
Because on anything with a motor or certain power supplies in it, some of the current does useful work and some of it sloshes back and forth without doing any. Volts multiplied by amps gives you volt-amps, the apparent power. Watts is the real power, the part that actually becomes heat, light or motion. The ratio between them is the power factor, and it is why an air conditioner or a pump can draw noticeably more current than its wattage suggests. For heaters, kettles, toasters and filament lamps the two are effectively the same.
No, and the plug is deliberately designed to stop you. Australian plugs and sockets are covered by AS/NZS 3112, and a 15 amp plug has a wider earth pin that physically will not enter a 10 amp socket. It is one of the better pieces of safety design in the house: the incompatibility is mechanical rather than a warning label, so the mistake cannot be made by someone who is not paying attention. If an appliance came with a 15 amp plug, it needs a 15 amp outlet on a circuit built for it.
An ohm measures resistance, which is how hard the appliance makes it for current to flow. It is the fourth term in the set and it explains the other three: at a fixed 230 volts, a low resistance draws a lot of current and a high resistance draws very little. A heating element is deliberately low resistance, which is why it draws ten amps and gets hot. You never need to measure it as a homeowner, but it is worth knowing it exists, because a short circuit is resistance collapsing to almost nothing and current rising until something opens.
What changes when an appliance arrives with the wider earth pin, and why it is a circuit question rather than a socket question.
Resistance collapsing to almost nothing, current rising until something opens, and what actually causes it in a house.
Once you can turn a label into kilowatt hours, working out what is actually costing you money gets a lot easier.
If the answer turned out to be that you need more capacity rather than better arithmetic: a bigger main switch or more circuits is a switchboard upgrade, the cable feeding the board is consumer mains, and where the wiring behind it all is original, that is rewiring. See every post on the blog.
Upfront pricing, with the price agreed before we start. We work out what is actually on the circuit rather than guessing.
