Maximum demand is the largest current an installation actually draws at any one moment. It is almost never the simple arithmetic sum of every connected load — diversity reduces the figure, because not every appliance runs at full rated current at the same time. WireWrite's NZ maximum-demand calculator applies the diversity assessment method in AS/NZS 3000 Appendix C and recommends a main switch and consumer-mains size from the result.
A typical NZ home might have a 9 kW oven, a 3 kW hot-water cylinder, 12 power outlets, lighting, and a 7 kW EV charger. The arithmetic sum of those rated loads is well over the supply capacity. In practice the oven cycles, the cylinder element is on a controlled load, lighting is at a fraction of rated, and the EV charges overnight. Diversity factors capture that reality.
AS/NZS 3000 Appendix C describes two methods electricians can use:
Adding up every connected load in a switchboard schedule (the protective-device "load" column) and treating that as maximum demand will always oversize the consumer mains. AS/NZS 3000 explicitly requires the diversity assessment for installations above single-circuit final sub-circuits. The calculator lets you enter each load group and applies the published allowances per appliance type.
You'll get the assessed maximum demand in amperes per phase, the recommended main-switch and consumer-mains size from standard NZ ranges, and a phase-balance suggestion if the installation is three-phase. The result is suitable as the calculation reference on your design records and certificates.
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NZ maximum demand calculator using AS/NZS 3000 Tables C1, C2, C7. Domestic and non-domestic. Free, auto main-switch recommendation.