Tātaitai Maximum Demand

How this is calculated#

The tool works out the maximum demand of an installation from its loads. It follows the load group method of AS/NZS 3000 Appendix C.

1. Table. Table C1 covers domestic installations: one house or living unit, or a block of living units. Table C2 covers other installations. For Table C2 you pick the occupancy.
2. Load groups. You enter each load in its group, such as lighting points, socket‑outlet points or kW of cooking. The tool lists only the groups the table assesses for your choice.
3. Group demand. Each group has its own rule for its load. The tool applies that rule and gives the group demand in amperes. It converts each kW load at the phase voltage you enter.
4. Living units per phase. A block of living units can take more than one phase. The tool then divides the units by the number of phases and rounds up. It reads the column for that number of units per phase.
5. Total. The maximum demand is the sum of the group demands.
6. Per phase. On three phases, the tool divides the total by three. That assumes you spread the load evenly over the phases. Where you cannot, allocate the loads per phase and check the heaviest phase.

Phase voltage#

Enter the phase voltage, line to neutral, such as 230 V. The tool converts every kW load at that voltage. The 400 V between lines would read every kW group 42 % low. On a three‑phase supply the tool refuses a line voltage and asks for the phase voltage.

Common installations, worked with the tool#

Each line states its loads. Every line uses a phase voltage of 230 V.

• House on one phase. It uses Table C1 for one house. The loads are 30 lighting points, 25 socket‑outlet points, 8 kW of cooking and a 3 kW storage water heater. The maximum demand is 50.43 A.
• The same house on three phases. The maximum demand is 16.81 A per phase and 50.43 A over all phases.
• Block of 12 living units on three phases. Table C1 for blocks of living units, with the same load rows. The tool reads 4 units per phase. The maximum demand is 75 A per phase and 225 A over all phases.
• Office on three phases. It uses Table C2 for factories, shops and offices. The loads are 10 kW of lighting, 20 socket‑outlets and motors of 15 A, 10 A and 5 A. The maximum demand is 44.93 A per phase and 134.78 A over all phases.

New Zealand and Australia#

AS/NZS 3000 Appendix C applies in both countries, so the tool has no country select.

Keep the result#

Every input sits in the page address, so the link in your browser reproduces the calculation. The PDF button prints the result with its steps and table references. Saving a calculation to a project needs a free account.

See also: Commercial maximum demand with Table C2, Domestic maximum demand with Table C1 and Maximum demand and diversity.