A house gains fixed heating. Ducted units, panel heaters and heat pump indoor heads all land in one place in a demand assessment. The owner wants to know whether the existing consumer mains still carry the house. This page adds 7.5 kW of fixed heating to a single phase house. It reports what the mains then see.
The inputs
- Table: C1, single domestic installation
- Supply: 230 V, single phase
- Group A(i): 22 lighting points
- Group B(i): 26 socket outlets and connected equipment up to 10 A
- Group C: 9 kW of range, cooking and laundry equipment
- Group D: 7.5 kW of fixed space heating and air conditioning
- Group F: 3 kW of storage water heating
Group D takes the connected rating of the fixed heating, in kilowatts. A plug-in heater is not fixed heating and belongs in group B(i) with the socket outlets that feed it.
The clause and the table
AS/NZS 3000:2018 Cl 2.2.2 sets the assessment of maximum demand. AS/NZS 3000:2018 Table C1 gives the rule for each load group in a single domestic installation. Each group carries its own rule, so the assessment is not a sum of connected loads.
The steps
The tool applies the Table C1 rule to each group and reports the group in amperes.
- A(i), lighting: 5 A
- B(i), socket outlets and equipment up to 10 A: 15 A
- C, ranges, cooking and laundry: 19.57 A
- D, fixed space heating, air conditioning and saunas: 24.46 A
- F, storage water heaters: 13.04 A
Group D entered as 7.5 kW and left as 24.46 A. The Table C1 rule for that group is the whole difference. The same 7.5 kW entered in a group with a different rule would produce a different figure.
The result
- Maximum demand: 77.07 A
- Demand per phase: 77.07 A
Group D alone is 24.46 A, close to a third of the whole assessment. Fixed heating is often the largest single group in a New Zealand house. The Table C1 rule discounts it less than it discounts the socket outlet group.
Remove group D from the same house and the assessment falls to 52.61 A. That gap of 24.46 A is what a heating retrofit costs the mains.
The reg 59 line
The tool holds a threshold of 80 A per phase for Electricity (Safety) Regulations 2010 reg 59(1). 77.07 A sits under it. No note appears on this result.
Push the fixed heating from 7.5 kW to 12 kW and the assessment becomes 91.74 A. The tool then raises a note. The note states that the demand is above the reg 59(1) threshold of 80 A per phase. It states that reg 59(2) then allows either a Part 2 route or a certified Part 1 design. It names the route. It does not say who may take it.
That threshold is the reason a heating upgrade turns into a mains conversation. A house assessed at 77.07 A sits just under it. One more heating circuit crosses it.
Before you commit
Check the consumer mains against 77.07 A in the cable size tool, with the real length and the real installation method. Check the main switch rating and the service fuse as well. A demand figure under 80 A does not mean the existing mains carry it. The cable can fail on voltage drop or on derating long before its rating runs out.
This page is a design aid. Verify every value against the current edition of the standard.
See also: AS/NZS 3000 Tables C1 and C2: demand groups, Office maximum demand per phase with Table C2 and Maximum demand and diversity.