Circuit loading calculator
Count the points a final subcircuit can carry.
Reads AS/NZS 3000:2018. Tables checked 27 Sept 2026.
Try a job 6
Each job fills in example values. Replace them with your values.
- Load a control panelThe load on each circuit in the panel.
- Count sockets on a house circuitThe loading of twelve 10 A socket-outlets on a 20 A circuit.
- Count lights on a circuitThe loading of thirty lighting points on a 10 A circuit.
- Load a kitchen circuit with a hobThe demand of a 7.2 kW hob on its circuit.
- Load an office socket circuitThe loading of eight 10 A socket-outlets on a 20 A office circuit.
- Apply diversity upstreamThe loading of a submain that feeds six circuits.
Inputs
Worked example with the default inputs. The live calculator replaces it when the page loads.
- Circuit-breaker rating
- 20 A
- Cable size
- 2.5 mm²
- Installation
- Domestic
- Lighting points
- 0
- 10 A socket-outlets
- 8
- 15 A socket-outlets
- 0
- 20 A socket-outlets
- 0
- Fixed or stationary load
- 0 A
- Include a cooking appliance
- No
- Apply upstream diversity
- No
Sum of contributions
8A
- Circuit-breaker rating
- 20A
This result is a design aid. Verify it against the current standard.
Calculation steps
- Lighting points0A
AS/NZS 3000:2018 Table C9
- 10 A socket-outlets8A
AS/NZS 3000:2018 Table C9
- 15 A socket-outlets0A
AS/NZS 3000:2018 Table C9
- 20 A socket-outlets0A
AS/NZS 3000:2018 Table C9
- Fixed and stationary load0A
AS/NZS 3000:2018 Table C9
- Sum of contributionsResult8A
AS/NZS 3000:2018 Table C9
- Circuit-breaker rating20A
AS/NZS 3000:2018 Table C9
About this calculator
How this is calculated
The tool counts the points a final subcircuit can carry. It reads AS/NZS 3000:2018 Table C9. You enter the breaker rating, the cable size and the points on the circuit.
- Lighting points. Each point adds the current that Table C9 gives for a lighting point.
- Socket-outlets. The tool counts 10 A, 15 A and 20 A socket-outlets. Each group has its own contribution in Table C9.
- Fixed and stationary load. You enter the rated current of fixed loads. The tool adds it in full.
- Cooking and diversity. If you turn them on, the tool adds the cooking demand and applies the diversity for upstream devices.
- Sum of contributions. The tool adds all contributions.
- Check. It compares the sum with the breaker rating. The pair of cable size and device rating must also be one that Table C9 lists.
| Step | Table or clause | What it decides |
|---|---|---|
| Point contributions | AS/NZS 3000:2018 Table C9 | The current each point counts for |
| Sum | Table C9 | The total counted load |
| Pair | Table C9 | Whether the cable and device are listed together |
Worked example
- Eight 10 A socket-outlets on a 20 A circuit. The cable is 2.5 mm² in a domestic installation. The sum of contributions is 8 A. That is within the 20 A breaker rating, so the tool passes the circuit.
Limits
The tool fails a circuit when the sum is over the rating. It warns when Table C9 does not pair the cable with the device. It also fails a cooking range that the table does not permit.
It counts points. It does not check the voltage drop or the loop impedance. Use the cable size calculator for those.
See also: Maximum demand with Table C1 and C2, What size breaker for 4 mm² cable and the maximum demand tool.
Questions
Each answer describes what this tool calculates. The result is a design aid. Verify against the current standard.
What does the circuit loading tool do?
The tool adds the contribution of every point on a final subcircuit. Lighting points count 0.5 A each. A 10 A socket counts 2 A where a non-domestic installation has no air conditioning, or 1 A otherwise. The sum must not exceed the circuit-breaker rating.
Which tables does it use?
The contributions come from AS/NZS 3000:2018 Table C9. The cooking demand comes from Table C5. The upstream diversity factor comes from Table C4. The cable and device pairs come from the same Table C9 rows.
How many socket-outlets can I put on a 20 amp circuit?
In a domestic installation, each 10 A socket counts 1 A. Then 20 sockets reach the rating of a 20 A device. Where a non-domestic installation has no permanent air conditioning, each socket counts 2 A. Then 10 sockets reach the same rating.
Clauses and tables this tool reads
- AS/NZS 3000:2018 App C Para C2.5Demand on a final subcircuit
- AS/NZS 3000:2018 Table C4Upstream circuit loading after diversity
- AS/NZS 3000:2018 Table C5Maximum demand for domestic cooking appliances
- AS/NZS 3000:2018 Table C9Loading of points per final subcircuit
Every clause and table, with how each was verified
Tables last checked on 27 Sept 2026.
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