How to Calculate Maximum Demand (AS/NZS 3000) — Free Calculator & Guide

Every switchboard upgrade, EV charger install and supply upgrade in NSW starts with the same question: what is the maximum demand of the installation? Get it wrong and you end up with nuisance tripping, an overloaded consumer main, or a knocked-back connection application. To make it easier, we've built a free maximum demand calculator that applies Table C1 of AS/NZS 3000:2018 and shows its working line by line. You'll find the calculator embedded at the bottom of this guide, ready to use — or open the full calculator page.

What maximum demand actually means

Your home might have 25kW of appliances connected, but you'll never run every hotplate, heater and light at once. AS/NZS 3000 recognises this with diversity: each load group in Table C1 is counted at a percentage that reflects real-world use. The total per phase — after diversity — is your maximum demand, and it's the figure your electrician, your distributor and your switchboard all care about.

How to use the calculator: step by step

Step 1 — Pick your installation type

Choose house or individual unit for a single domestic installation, or block of living units if you're assessing common mains for a strata or multi-unit site. The unit-block mode uses columns 3–5 of Table C1, where allowances per unit shrink as the number of units grows.

Step 2 — Choose single-phase or three-phase

On three-phase you'll enter quantities per phase (Red / White / Blue). Spread your single-phase loads as evenly as you can — the calculator warns you if the phases are out of balance, because your maximum demand is set by the busiest phase.

Step 3 — Add your loads

Work through the house one load group at a time: lighting points (a double batten counts per lamp holder, a double power point counts as two socket points), the cooking range in kilowatts, storage hot water, air conditioners (use the maximum input amps from the nameplate, not the cooling kilowatts), pool equipment and any EV charger. Appliances 10A and under on plugs simply count as socket points — the calculator handles the rest.

Step 4 — Read the result

You'll see demand per phase, the highest phase, and the next standard main switch size. Open "Show the full working" to see exactly how each line was calculated — handy for apprentices studying for their capstone, and for homeowners who want to sanity-check a quote. You can print the result as a PDF or copy a summary.

A quick worked example

A typical three-bedroom Sydney home — 28 lighting points, 14 double power points, a 9kW range, a 3.6kW storage hot water system and a reverse-cycle air conditioner drawing 11.5A — comes out around 63A single-phase. Add a 7kW EV charger and it jumps past 90A: suddenly you're talking about a supply upgrade or three-phase, which is exactly the conversation we have with Sydney homeowners every week.

When to call a Level 2 electrician

The calculator is an estimating and learning tool — it doesn't replace an assessment by a licensed electrician, and it doesn't know what your existing consumer mains, switchboard or street supply can actually handle. If your calculated demand is over 63A per phase, you're adding an EV charger, ducted air conditioning or a pool, or you're planning a granny flat or unit development, get it verified before you buy equipment.

High Demand Electrical are licensed Level 2 ASP electricians in Sydney. We confirm maximum demand on site, upgrade switchboards and consumer mains from 63A single-phase to 400A three-phase, and lodge the paperwork with Ausgrid, Endeavour or Essential Energy for you. Call 0402 559 777 for a straight answer on what your project needs.

This guide is general information for the Australian market and refers to AS/NZS 3000:2018 Appendix C. It is not a substitute for advice from a licensed electrician about your specific installation.

Try the maximum demand calculator

Use the calculator below — no sign-up, no watermark. Print your result and bring it to us to confirm.