Maximum demand per phase calculator
Spread the load over three phases and see the imbalance.
Reads AS/NZS 3000:2018. Tables checked 19 Sept 2026.
Try a job 4
Each job fills in example values. Replace them with your values.
- Balance a house demand across three phasesThe maximum demand on each phase of a three phase house, from Table C1.
- Balance an office fit-outThe demand on each phase of an office, from Table C2.
- Balance a block of unitsThe demand on each phase of nine units.
- Balance a workshop with a welderThe imbalance a single-phase 32 A welder outlet makes.
Inputs
Worked example with the default inputs. The live calculator replaces it when the page loads.
- Demand table
- Table C1 · domestic
- Phase voltage
- 230 V
- Loads by phase
- 4 rows
Heaviest phase, L1
18.04A
- L1
- 18.04A
- L2
- 15A
- L3
- 17.39A
- Sum of the three phase demands
- 50.43A
- Imbalance
- 16.85%
This result is a design aid. Verify it against the current standard.
Calculation steps
- Demand on L118.04A
AS/NZS 3000:2018 Table C1
- Demand on L215A
AS/NZS 3000:2018 Table C1
- Demand on L317.39A
AS/NZS 3000:2018 Table C1
- Heaviest loaded phaseL1
- Demand on the heaviest loaded phaseResult18.04A
AS/NZS 3000:2018 Table C1
- Sum of the three phase demands50.43A
- Imbalance16.85%
About this calculator
How this is calculated
The tool assigns each AS/NZS 3000 Appendix C load group to a phase. It then reads the demand on L1, L2 and L3, the heaviest phase and the imbalance. The max demand calculator assumes an even spread. This tool does not.
- Phase for each load. You tag every load group with L1, L2 or L3.
- Table. You pick Table C1 for a house or Table C2 for another occupancy. Each phase runs as a single installation.
- Demand on each phase. The tool applies the group rule to the loads on that phase alone. It gives the demand in amperes.
- Heaviest phase. It names the phase with the greatest demand. That figure is the primary result.
- Sum and imbalance. It adds the three phase demands. It then gives the imbalance between the heaviest and the lightest phase.
| Step | Table or clause | What it decides |
|---|---|---|
| Demand on each phase | AS/NZS 3000 Table C1 or C2 | The group rules applied per phase |
| Heaviest phase | Paragraphs C2.3.2.2 and C2.4.2 | The phase that sets the supply |
Worked example
A house with 30 lighting points on L1, 25 socket-outlets on L2, 8 kW of cooking on L3 and a 3 kW water heater on L1. The phase voltage is 230 V. L1 carries 18.04 A, L2 carries 15 A and L3 carries 17.39 A. L1 is the heaviest. The three demands sum to 50.43 A. The imbalance is 16.85 %.
Limits
- The tool applies the demand rule to each phase on its own. The sum of the phases can differ from the single-phase total.
- Enter the phase voltage, line to neutral. The tool refuses a line voltage on three phases.
- It does not move loads for you. Change the phase tags and run it again.
- It does not size the cable or the main switch.
See also: Maximum demand and diversity, Domestic maximum demand with Table C1 and Commercial maximum demand with Table C2.
Questions
Each answer describes what this tool calculates. The result is a design aid. Verify against the current standard.
What does the per-phase maximum demand tool do?
Assign each load group to L1, L2 or L3. AmpSize applies the AS/NZS 3000:2018 Appendix C demand rule to the loads on each phase on its own. It then reports the demand on every phase and the imbalance between the phases, and names the heaviest loaded phase.
Why is the rule applied per phase and not to the whole installation?
AmpSize spreads the loads across the phases first and applies the demand rule after. The result is therefore the heaviest loaded phase's demand, not an even share of a total. AS/NZS 3000:2018 Paragraphs C2.3.2.2 and C2.4.2 and Note 2 to Table C1 cover the per-phase treatment.
How is the imbalance worked out?
The imbalance is the gap between the heaviest and the lightest phase, as a percent of the heaviest phase. It is an AmpSize figure, not a value from the standard. A warning appears above 20 percent. Move loads between the phases and watch the number fall.
Which demand table should I pick?
Pick Table C1 for a domestic installation and Table C2 for a non-domestic one. Table C2 then asks whether the occupancy is residential or commercial, because it has a column for each. Both tables hold the AS/NZS 3000:2018 Appendix C data the maximum demand tool uses.
Does this replace the maximum demand tool?
No. The maximum demand tool covers a single installation and blocks of living units. This tool covers the case where you know which phase each load sits on. Both run the same Appendix C engine, so one phase of loads gives the same demand in either tool.
Clauses and tables this tool reads
- AS/NZS 3000:2018 Table C1Maximum demand, single and multiple domestic installations
- AS/NZS 3000:2018 Table C2Maximum demand, non-domestic installations
Every clause and table, with how each was verified
Tables last checked on 19 Sept 2026.
Related tools
- Lighting lumen method calculatorLuminaire count and grid for a room by the lumen method.AS/NZS 1680.1AS/NZS 1158.1.2
- EV charger circuit calculatorCheck EV chargers for spare capacity, cable size and RCD.AS/NZS 3000AS/NZS 3008.1.2AS/NZS 3008.1.1
- Switchboard form checkerCheck separation, access and clearances for a switchboard.AS/NZS 3000
Was this useful?
A question, or a value that looks wrong? Contact us.