Load schedule across boards
Maximum demand of a site’s boards by switchboard diversity.
Reads AS/NZS 3000:2018. Tables checked 26 Sept 2026.
Try a job 4
Each job fills in example values. Replace them with your values.
- Schedule a workshop site with four boardsThe demand of a main board, two boards and a mezzanine board by Table C4.
- Demand of a house with a garage boardThe single-phase demand of a house board feeding a garage board.
- Check a submain device against its boardWhether a 160 A submain device covers a busy board of 14 circuits.
- Site demand for a supply applicationThe site demand in kVA of a shop with a main board and two boards.
Inputs
Worked example with the default inputs. The live calculator replaces it when the page loads.
- Phases
- Three phase
- Voltage
- 400 V
- Boards, main board first
- 3 rows
- Boards conform to AS/NZS 61439 or AS/NZS 3439
- Yes
Demand per phase
325.5A
- Site maximum demand
- 225.5kVA
- Sum of ratings at the main board
- 465A
- Boards
- 3
This result is a design aid. Verify it against the current standard.
Calculation steps
- MSB: 8 devices, sum of ratings 465 A0.7x
AS/NZS 3000:2018 Table C4
- MSB: demand325.5A
AS/NZS 3000:2018 App C Para C2.4.4
- DB1: 12 devices, sum of ratings 260 A0.6x
AS/NZS 3000:2018 Table C4
- DB1: demand156A
AS/NZS 3000:2018 App C Para C2.4.4
- DB2: 8 devices, sum of ratings 150 A0.7x
AS/NZS 3000:2018 Table C4
- DB2: demand105A
AS/NZS 3000:2018 App C Para C2.4.4
- Demand per phaseResult325.5A
AS/NZS 3000:2018 App C Para C2.4.4
- Site maximum demand225.5kVA
About this calculator
How this is calculated
A load schedule lists the boards of a site and what each one draws. The tool works the maximum demand of each board by the switchboard diversity method of AS/NZS 3000 Appendix C, and carries it up the tree to the main board.
Para C2.4.4 sets the method for switchboards that conform to the AS/NZS 3439 or AS/NZS 61439 series. The maximum demand of a board is the sum of the overload ratings of its circuits, times a factor from Table C4. The factor falls as the number of circuit protective devices downstream rises.
On each board the tool counts its final subcircuit devices and one device for each submain it feeds. It adds the ratings of the final subcircuits and the rating of each submain device. The submain is a circuit of the board that feeds it, so a sub-board's demand is never added twice. Table C4 prints no factor below two devices, and the tool then takes the sum as the demand.
The ratings are per phase. On a three-phase board, enter the sum on the most loaded phase, and count a three-pole device once. The tool gives each board's demand in amps and in kVA, and the site's demand at the main board.
Each sub-board's demand is checked against the device that feeds it. A board whose demand is more than its submain device gets a warning.
The schedule prints as a sheet with one row a board.
| Step | Table or clause | What it decides |
|---|---|---|
| Devices on a board | Final subcircuits plus one a submain | The count Table C4 is read at |
| Sum of ratings | Para C2.4.4 | The circuits' ratings plus each submain device's rating |
| Diversity factor | Table C4 | The factor for the number of devices |
| Board demand | Para C2.4.4 | The sum times the factor |
| Submain check | The demand against the feeding device | Whether a submain device is smaller than its board's demand |
Worked examples
- A workshop site with four boards has a site maximum demand of 283.5 A a phase, 196.4 kVA. The main board's ratings add to 405 A.
- A house with a garage board has a maximum demand of 149.1 A, 34.3 kVA. The main board's ratings add to 213 A.
- A main board feeding one busy board has a site maximum demand of 200 A a phase, 138.6 kVA. The main board's ratings add to 250 A. The busy board's demand of 192 A is more than its 160 A submain device.
- A main board and two distribution boards has a site maximum demand of 325.5 A a phase, 225.5 kVA. The main board's ratings add to 465 A.
Limits
The method is only for boards that conform to the AS/NZS 3439 or AS/NZS 61439 series. For other boards, use another Appendix C method, such as the maximum demand tool. With the toggle off, the tool takes no Table C4 factor and gives the sum of the ratings.
It works from device ratings, not from the loads. A board full of large devices with small loads gives a high demand. A load-by-load assessment can give a lower figure.
See also: Maximum demand, Circuit loading and Max demand by phase.
Questions
Each answer describes what this tool calculates. The result is a design aid. Verify against the current standard.
How do you work out the maximum demand of a switchboard?
By AS/NZS 3000 Para C2.4.4, add the overload ratings of the board’s circuits and multiply by the Table C4 factor for the number of devices: 0.9 for 2 or 3, 0.8 for 4 or 5, 0.7 for 6 to 9 and 0.6 for 10 or more.
How are sub-boards counted?
A submain is a circuit of the board that feeds it. The tool counts it as one device on that board, at its device rating. So a sub-board’s demand is not added to its parent a second time.
Which switchboards does the method apply to?
Para C2.4.4 is for switchboards that conform to the AS/NZS 3439 or AS/NZS 61439 series. For other boards, use another Appendix C method, such as the load groups of Table C1 or C2.
What if a board’s demand is more than its submain device?
The tool warns. The device that feeds the board is then smaller than the demand the method gives. Check the device, the cable and the loads on the board.
How do I enter a three-phase board?
Enter the sum of the ratings on the most loaded phase, and count a three-pole device once. The tool gives the demand per phase and in kVA at the voltage you set.
Clauses and tables this tool reads
- AS/NZS 3000:2018 App C Para C2.4.4Maximum demand by switchboard diversity
- AS/NZS 3000:2018 Table C4Upstream circuit loading after diversity
Every clause and table, with how each was verified
Tables last checked on 26 Sept 2026.
Related tools
- Maximum demand calculatorEstimate maximum demand for domestic or non-domestic loads.AS/NZS 3000 Table C1/C2
- Maximum demand per phase calculatorSpread the load over three phases and see the imbalance.AS/NZS 3000
- Cable fault rating calculatorCheck that a conductor can withstand the fault current.AS/NZS 3008.1.2AS/NZS 3008.1.1AS/NZS 3000
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