An office fitout tender needs two demand figures. One goes on the network connection application. The other sizes the submain and the board. Table C2 of AS/NZS 3000:2018 produces both from the load schedule. The network asks for the per phase figure.
The question
A tenancy fitout has 8 kW of lighting and 90 general socket‑outlets. It also has 20 socket‑outlets serving permanently installed heating or cooling. Two cooking or heating appliances draw 12 kW and 6 kW. The supply is 230/400 V three phase. The assessment gives the maximum demand per phase.
The inputs
- Table: C2
- Occupancy: commercial
- Phases: 3
- Phase voltage: 230 V, line to neutral (the tool converts each kW load at it, not at the 400 V between lines)
- Group A, lighting: 8 kW
- Group B(i), socket‑outlets up to 10 A: 90
- Group B(ii), socket‑outlets with permanent heating or cooling: 20
- Group C(i), cooking and heating appliances: 12 kW and 6 kW
The occupancy setting matters. Table C2 has separate columns. The commercial column applies a different rule to several groups than the residential column.
The clause and the table
Cl 2.2.2 of AS/NZS 3000:2018 requires the maximum demand assessment. Table C2 gives the rule for each load group. It covers installations other than a dwelling or a block of living units.
The steps
The tool applies one rule per group and reports each line separately.
- Group A, lighting converts 8 kW at 230 V and returns 34.78 A.
- Group B(i), 90 socket‑outlets returns 294.57 A. The rule takes a full allowance for the first outlets and a reducing share of the rest. 90 outlets therefore do not give 90 times one outlet.
- Group B(ii), 20 socket‑outlets returns 12.61 A.
- Group C(i), the 12 kW and 6 kW appliances returns 71.74 A.
Adding the four lines gives the demand across all phases: 413.7 A.
Dividing that by three gives the maximum demand per phase: 137.9 A.
The result
- Maximum demand per phase: 137.9 A
- Maximum demand, all phases: 413.7 A
The per phase figure carries one condition, and the tool states it with every three‑phase result. The division by three assumes the load is spread evenly over the three phases. Table C2 works from the heaviest loaded phase. Where the schedule is uneven, allocate each load to a phase first. Then run the heaviest phase on its own.
An office fitout is rarely even. Kitchen appliances land on one phase. A single 12 kW appliance loads that phase heavily before anything else connects. Check the allocation before the connection application goes in, because a rejected application costs more time than the check.
What the estimator does with it
137.9 A per phase sets the submain. Enter that figure as the design current in the cable size tool. Add the route length, the installation method and the grouping. The tool returns the conductor size. The next standard device rating above 137.9 A sets the protection. The cable must then pass the derated capacity check and the voltage drop check.
Record the load schedule with the price. A fitout scope grows between tender and construction. The demand figure shows why a larger submain became necessary.
This page is a design aid. Verify every value against the current edition of the standard.
See also: AS/NZS 3000 Tables C1 and C2: demand groups, Commercial maximum demand with Table C2 and Maximum demand and diversity.