Maximum demand with Appendix C: Tables C1, C2 and C3
Maximum demand sets the current that consumer mains and submains must carry. Clause 2.2.2 allows it to be found by calculation, assessment, measurement or limitation. This guide covers calculation with Appendix C, which is what the free calculator does, including how to handle three-phase installations.
Three calculation methods
Column 2 for a single domestic installation or an individual living unit. Columns 3 to 5 cover blocks of living units.
Column 2 for residential institutions, hotels, boarding houses, hospitals and motels. Column 3 for factories, shops, stores, offices, business premises, schools and churches.
An alternative for commercial and light-industrial premises: VA per square metre of floor area for listed occupancies, plus special equipment.
Table C1 column 2: a single house or living unit
Work out each load group's allowance and add them. These are the load groups the calculator applies.
| Group | Loads | Allowance |
|---|---|---|
| (a)(i) | Lighting points; track counts as 2 points per metre | 3 A for up to 20 points, plus 2 A for each further 20 or part |
| (a)(ii) | Outdoor lighting over 1000 W in total | 75% of connected load |
| (b)(i) | Socket-outlets and permanently connected items up to 10 A | 10 A for up to 20 points, plus 5 A for each further 20 or part |
| (b)(ii) | 15 A socket-outlets | 10 A |
| (b)(iii) | 20 A socket-outlets | 15 A; with 15 A outlets as well, 15 A in total |
| (c) | Ranges, cooking appliances, laundry equipment | 50% of connected load |
| (d) | Fixed space heating, air-conditioning, saunas | 75% of connected load; count only the larger of heating or cooling |
| (e) | Instantaneous water heaters | 33.3% of connected load |
| (f) | Storage water heaters | Full-load current |
| (g) | Spa and swimming pool heaters | 75% of the largest spa, plus 75% of the largest pool, plus 25% of the rest |
| (j)(iv) | EV charging equipment | Full connected load |
| (k), (l) | Lifts and motors | By Paragraph C2.4.1 and Table C2 |
| (m) | Other appliances, e.g. kilns or welders | None up to 5 A; above 5 A by assessment |
Three-phase installations: assess each phase
Table C1 column 2 is applied per phase. Allocate each load to the phase it is connected to, work out the allowances for each phase on its own, and size the mains for the heaviest loaded phase. The Appendix C worked examples do it this way. Dividing a whole-house total by three is not the same method and can understate the heaviest phase considerably.
- L1: 30 lighting points (5 A) + 25 socket-outlet points (15 A) + 7.2 kW range at 50% (15.65 A) = 35.7 A
- L2: 20 socket-outlet points (10 A) + 7 kW ducted air-conditioning at 75% (22.83 A) = 32.8 A
- L3: one 15 A socket-outlet (10 A) + 3.6 kW storage water heater (15.65 A) + 7.4 kW EV charger (32.17 A) = 57.8 A
- Maximum demand: 57.8 A on L3. Treating the house as one load (121.3 A) and dividing by three gives only 40.4 A per phase.
Balanced three-phase equipment, such as a three-phase water heater, adds its share to every phase. The calculator lets you enter it once and shares its watts equally across the phases.
Table C3 energy demand for commercial premises
- Light and power, table average: 50 VA/m² × 800 m² = 40,000 VA
- Reverse-cycle air-conditioning, table average: 25 VA/m² × 800 m² = 20,000 VA
- Total 60,000 VA ÷ (√3 × 400 V) = 86.6 A per phase
Count one air-conditioning system type only: the office rows for cooling, reverse cycle, zonal reheat and variable volume are alternatives. Table C3 figures depend on climate, occupancy and how evenly equipment is spread through the area.
What Appendix C calculation does not cover here
- Blocks of living units (Table C1 columns 3 to 5).
- The switchboard diversity method of Table C4 and final subcircuit loading in Table C9.
- Maximum demand by assessment, measurement or limitation (Clause 2.2.2).
- Your network service provider's service and installation rules, which can set their own limits.
Work it out phase by phase
The free maximum demand calculator applies Tables C1, C2 and C3, assesses each phase, and shows every load group's contribution. Presets load the Appendix C examples so you can check it against the standard.