Maximum demand decides the size of the consumer mains, the main switch and often the connection itself. Table C1 of AS/NZS 3000:2018 is the assessment route for domestic work. It takes the load of a house, group by group, and turns it into one current.
Why the table is not a sum
A house never runs every load at once. The oven, the shower heater, the dryer and every socket do not draw together, and a design that adds their full ratings would put in mains two sizes too big. Table C1 handles that with a rule for each group. Some groups take a fixed current. Some take a share of the connected load. Some step down as the count rises.
Cl 2.2 is the clause that requires the assessment. The table is the method.
A worked house
One dwelling, 230 V single phase. The load schedule is ordinary:
- A(i) Lighting — 24 points
- B(i) Socket-outlets and connected equipment up to 10 A — 28 points
- C Ranges, cooking appliances and laundry equipment — 9 kW connected
- F Storage water heaters — 3 kW connected
Put those into the tool with Table C1 and the single domestic mode. It works each group and then adds them.
| Group | Demand |
|---|---|
| A(i) Lighting | 5 A |
| B(i) Socket-outlets | 15 A |
| C Cooking and laundry | 19.57 A |
| F Storage water heater | 13.04 A |
| Maximum demand | 52.61 A |
Reading each line
Lighting uses a stepped rule. The first block of points takes one current, and each further block adds less. Twenty-four points lands on 5 A. Doubling the number of lights does not double the demand, which is the whole point of the table.
Socket-outlets work the same way and land on 15 A for 28 points. Note that this group covers permanently connected equipment up to 10 A as well as the outlets themselves, so a heat pump head or a bathroom fan belongs here rather than in a group of its own.
Cooking and laundry takes a share of the connected load. 9 kW at 230 V is 39.13 A connected, and the group takes half of it: 19.57 A.
Storage water heating takes the whole connected load. 3 kW is 13.04 A and all of it counts. A storage cylinder heats on a long, predictable cycle, so there is nothing to diversify.
The total is 52.61 A. That sits comfortably on a 63 A consumer mains and leaves headroom for later additions.
What changes the answer
Add an electric vehicle charger and the picture moves. So does a second oven, a spa pool or a resistive heating circuit. Each of those sits in its own group with its own rule, and some of them count at full value. It is worth running the assessment again whenever a large fixed load is added, not only at the design stage.
Multiphase supplies change the shape rather than the total. The tool divides the demand across the phases and reports the per-phase figure, because the per-phase current is what sizes the mains.
For a block of units, switch the mode. Table C1 has bands for blocks of living units, and the demand per unit falls as the count rises. Assessing ten units as ten separate houses gives a badly oversized main.
For anything that is not domestic, use Table C2 instead. The groups and the rules are different.
One caution
A high domestic demand can push an installation past the threshold where a prescriptive design is no longer enough. The tool raises a note when that happens. Treat the note as a prompt to check the regulation, not as the answer.
The result is a design aid. Verify it against the current standard.