Maximum Demand Calculator
Calculate maximum demand using Tables C1 (residential) and C2 (commercial) per AS/NZS 3000:2018.
Inputs
Lighting & Power
Heating & Cooling
Cooking Appliances
Water Heating
▶Other Loads
Results
Maximum Demand
Recommended Main Switch
80 A
Next standard size ≥ 63.48 A
Main Switch Rating
80 A (>= 63.47826086956522 A)
| Category | Raw (kW) | Diversity | After (kW) |
|---|---|---|---|
| Lighting | 3.00 | 0.83 | 2.50 |
| Power Point Circuits | 4.00 | 0.63 | 2.50 |
| Heating/Cooling | 0.00 | 1.00 | 0.00 |
| Cooking Appliances | 6.00 | 1.00 | 6.00 |
| Water Heater | 3.60 | 1.00 | 3.60 |
| Other Fixed Appliances | 0.00 | 1.00 | 0.00 |
| Motors | 0.00 | 1.00 | 0.00 |
| Total | 14.60 | ||
Maximum Demand for AS/NZS 3000:2018
Maximum demand is the greatest average power drawn over a defined period, used to size main switches and determine meter and supply capacity. In Australia, maximum demand is calculated using diversity factors from AS/NZS 3000:2018 Tables C1 (residential) and C2 (commercial). Diversity factors account for the fact that not all loads operate simultaneously at full capacity.
Residential maximum demand (Table C1)
- Lighting circuits: First circuit = 1 kW, additional = 0.75 kW each.
- Power point circuits: First = 1 kW, additional = 0.5 kW each.
- Heating & cooling: Larger load at 100%, the other at 50%.
- Cooking appliances: 1st = 100%, 2nd first 1 kW = 100% then 80%, 3rd+ = 60%.
- Water heating: Continuous load (100%).
- Fixed appliances: Each at 100%.
- Motors: Largest at 100%, others at 80%.
- EV charger: Continuous load (100%).
Commercial maximum demand (Table C2)
- Lighting: 75% diversity factor.
- Socket outlets: 0.5 kW per circuit at 50% diversity.
- Fixed appliances: 100%.
- Motors: 85% average diversity.
Main switch selection
Main switch rating must be ≥ the calculated maximum demand current. The calculator selects the next standard size (40A, 63A, 80A, 100A, 125A, 160A, 200A, 250A, 315A, 400A, 630A).
Common questions
How does AS/NZS 3000 require maximum demand to be calculated?+
AS/NZS 3000:2018 Appendix C provides standardised diversity tables for calculating maximum demand. Table C1 covers single-domestic and multi-domestic installations; Table C2 covers commercial and industrial. Each load type (lighting, power points, water heating, motors, EV chargers) is assigned a per-circuit kW value or a percentage diversity factor, and the sum gives the maximum demand in kVA or amps. The calculator implements both tables and selects the right one based on your installation type.
When do I use Table C1 versus Table C2?+
Table C1 applies to single-domestic dwellings (one home) and multi-domestic dwellings (apartments, units). Table C2 applies to all other installation types: commercial, retail, industrial, hospitality. If your installation mixes residential and commercial use, for example a shop with a flat above, calculate each part separately and add them. The calculator handles both tables and the dual-use combination.
How do diversity factors work for residential lighting and power circuits?+
Under Table C1 the first lighting circuit counts at 1000 W and each additional lighting circuit at 750 W. Power point circuits start at 1000 W for the first and 500 W per additional circuit. The diminishing values reflect that not every circuit is loaded simultaneously. Add larger appliances (cooking, water heating, heating, EV) per their own table entry rather than rolling them into the lighting or power totals.
How is maximum demand for an EV charger calculated?+
EV chargers are treated as a continuous load at 100 percent of their rated current with no diversity. A 32 A single-phase EV charger contributes about 7.4 kW; a 22 kW three-phase charger contributes 22 kW. Some supply authorities additionally require load management or controlled charging for installations with multiple chargers or limited supply capacity. The calculator includes EV charger as a dedicated load class.
How does maximum demand select the main switch rating?+
The main switch must be rated at least equal to the calculated maximum demand current. Convert kVA to amps using the supply voltage: divide kVA by 0.230 for single-phase, or by (1.732 times 0.400) for three-phase. Pick the next standard rating from 40, 63, 80, 100, 125, 160, 200, 250, 315, 400, or 630 A. The calculator does this automatically.
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