How Much Spare Capacity Does Your Home Actually Have? Maximum Demand, Explained Simply

How much spare electrical capacity does your home actually have? The answer is a figure called maximum demand: an estimate of the largest load your home is ever likely to draw at one time, measured in amps. Compare that figure with the size of your supply and you know straight away whether there is room for the EV charger, ducted aircon or heat pump you are planning, or whether a switchboard or supply upgrade has to come first.

⚡ Quick Answers: maximum demand and spare capacity

• What is maximum demand? An assessed figure, in amps, for the biggest load your home is likely to draw at once. It is how electricians size supplies, mains and switchboards.
• How is it worked out? Using the method in the Wiring Rules (AS/NZS 3000), which weights each type of load rather than simply adding every appliance together.
• How big is a typical Sydney supply? Many single phase homes run on a supply of around 63 amps. Three phase homes have far more headroom.
• What eats capacity fastest? EV chargers, ducted air conditioning, induction cooking, electric hot water and pool equipment. These are the loads that push older supplies to the edge.
• How do I check mine? Use the free maximum demand calculator on this page for an estimate, or have the supply measured over a week with power logging.
• What if there is not enough? Options range from load management to a switchboard upgrade or a single to three phase supply upgrade. Adding big loads can also trigger paperwork with your network.

1. What maximum demand actually means

Your home almost never runs everything at once. Maximum demand is the realistic worst case: dinner cooking, aircon running, hot water heating and the car charging at the same time on a summer evening.

Electricians assess it using the method set out in the Wiring Rules. Each category of load contributes a weighted amount rather than its full nameplate rating, because standards assume normal households do not run every single circuit flat out simultaneously. The result is the figure your consumer mains, main switch and switchboard must be sized to carry.

If you want the full working, our companion guide on how to calculate maximum demand walks through the maths. This post stays on the practical question: how much room do you have left?

2. Calculated on paper vs measured in the real world

There are two ways to answer that question. The calculated method above is what compliance and design work is based on. The measured method uses a power logger on your switchboard for around a week to record what your home genuinely draws.

Real homes very often measure well below their calculated figure. That gap matters: it can be the difference between needing a supply upgrade and not needing one. For apartment buildings and homes close to the limit, power logging is the honest way to find out before anyone spends money.

3. The loads that eat capacity fastest

A few modern additions dominate every maximum demand conversation:

• EV charging. A dedicated 7kW charger is one of the largest single loads a home can add. Our guide to EV ready provisions covers how to plan for it cheaply.
• Ducted air conditioning. Large systems draw heavily on start up and run for hours on hot days.
• Induction cooking. A full induction cooktop needs its own properly sized circuit.
• Electric and heat pump hot water. Modest on its own, but it stacks with everything else unless it runs on controlled load or a timer.
• Pool pumps and heaters. Long run times make these bigger contributors than most owners expect.

Add two or three of these to a home built decades ago and the supply that once had plenty of headroom is suddenly full.

4. Check your spare capacity in two minutes

The embedded maximum demand calculator on this page gives you an estimate the same way an electrician would start: tick off your loads and it applies the Wiring Rules weightings for you. It is one of several free tools on our site, and it pairs well with a quick look at your main switch to see what your supply is rated at.

Treat the result as a conversation starter rather than a design. Site conditions, the state of your switchboard and the condition of your consumer mains all affect what your home can safely carry, and those need eyes on site.

5. What happens when the answer is "not enough"

Running out of headroom does not automatically mean a big project. In rough order of cost:

• Shift loads. Hot water on controlled load and appliances run overnight take pressure off the evening peak. Our off peak times guide explains the windows.
• Load management. Smart EV chargers can throttle themselves when the rest of the house is busy, keeping total draw under the limit.
• Switchboard upgrade. If the board is the bottleneck, a modern board restores room for new circuits. See our switchboard upgrade guide.
• Supply upgrade. The permanent fix for a genuinely full supply is upgrading from single phase to three phase, which changes what your home can run for good. Here is what changes in a three phase upgrade.

One more thing to know: adding a significant load can require a Notification of Service Work with your distributor, whether that is Ausgrid or Endeavour Energy. Our guide to when a load increase triggers a NOSW explains it, and you can check your network area in seconds with our postcode checker if you are not sure which network you are on.

Why the supply side is Level 2 ASP work

Everything from the street to your meter, including upsizing consumer mains and connecting a bigger supply, is network connected work. In NSW it can only be done by a Level 2 Accredited Service Provider, not a general electrician. That is the part of the job High Demand Electrical is accredited for on both Sydney networks.

How High Demand Electrical helps

We answer the capacity question properly: a site assessment of your supply, mains and switchboard, power logging where the paper figure is borderline, and a clear recommendation ranked from cheapest option to full supply upgrade. If an upgrade is the right call, we handle the network application, the Level 2 connection work and the switchboard in one job with one quote.

Maximum demand FAQs (Sydney)

Is maximum demand the same as the usage on my power bill?

No. Your bill measures energy used over time (kilowatt hours). Maximum demand is about the peak rate of draw at a single moment, which is what your cables and switchboard have to survive.

Does solar reduce my maximum demand?

Solar cuts your bills, but supplies are sized for what your home can draw from the grid when the sun is not helping. Do not count on panels to create headroom for new circuits.

What is a NOSW and will my new appliance trigger one?

A Notification of Service Work is paperwork your electrician lodges with the network when service work or a notifiable load change happens. Significant additions like EV chargers can trigger one. See our NOSW guide.

Can I just fit a bigger main switch?

No. The main switch is one link in a chain that includes the service line, consumer mains, metering and switchboard. The whole chain has to be rated for the demand, which is why capacity upgrades are assessed as a package.

Find out how much room your home really has

Run the calculator above for a first look, then get a power supply upgrade quote if the numbers look tight. Call 0402 559 777 and we will take it from there. Every job starts with a site assessment before scope and pricing are confirmed.