Maximum Demand Calculator — AS/NZS 3000 🇦🇺

Assessment Methodology per Clause 2.2.2

AS/NZS 3000:2018, Clause 2.2.2 requires that the maximum demand of every installation be assessed before the design proceeds. The assessment must account for all loads that could operate simultaneously under the most onerous foreseeable conditions. The standard provides two approaches:

• Appendix C tables — mandatory demand factor formulas for each load category (the standard method)
• Measurement — actual metered data for existing installations being modified (Clause 2.2.2.2)

Step 1: Categorise All Loads

Every load in the installation is placed into one of the categories defined in Table C1. The main categories are:

• Lighting — total connected wattage of all luminaires
• Socket outlets — general-purpose outlets rated at 10A or 15A
• Cooking appliances — ovens, cooktops, wall ovens, considered per appliance
• Water heating — storage and instantaneous water heaters
• Space heating and air conditioning — the larger of heating or cooling load, not both
• Permanently connected appliances — each taken at its full rated current
• Motors — largest motor at 100%, additional motors per Table C1 rules

Step 2: Apply Demand Factors per Table C1

Each category has a specific demand reduction formula. For example, socket outlets in a domestic installation:

• First 10 A of connected load: 100%
• Next 10 A: 50%
• Remainder: 25%

For cooking appliances, Table C1 provides a stepped formula based on the number and rating of appliances. A single appliance up to 10 A is taken at its full rating; above 10 A, the first 10 A is at 100% and the remainder at a reduced percentage.

Step 3: Sum Category Demands

The individual category demands are summed to produce the total maximum demand for the installation in amperes. Per Clause C2.2, where both space heating and air conditioning are installed, only the larger of the two is included — they are not assumed to operate simultaneously.

Step 4: Multiple Dwellings (Table C2 / Table C3)

For multi-dwelling installations (apartment buildings, unit complexes), Table C2 provides diversity factors based on the number of dwellings. For example, 10 units with individual maximum demands of 15 kVA each do not require 150 kVA at the main switchboard — Table C2 reduces this to approximately 60–70% of the arithmetic sum.

Table C3 provides after-diversity maximum demand (ADMD) values in kVA per dwelling for use by electricity distributors when designing subdivision supply infrastructure. ADMD values typically range from 3.5 to 7.0 kVA per lot depending on the climate zone and whether gas is available.

Step 5: Select Equipment Ratings

The calculated maximum demand determines the minimum rating of the consumer mains cable (per AS/NZS 3008), the main switch, and the metering equipment. The result must also be communicated to the electricity distributor for their network capacity assessment.