Maximum Demand Calculator
Work out maximum demand for a house or small commercial job.
Table C1 (AS/NZS 3000:2018 Appendix C) - domestic installations only. Single dwelling is single phase only; a 3-phase single dwelling needs manual per-circuit phase assessment, not covered here.
Loads outside these groups (kilns, welders, X-ray equipment and the like) need individual assessment - not covered by this calculator (Table C1, load group (m)).
For guidance only. These calculators are planning aids for licensed electrical workers and inspectors. All results must be independently verified against the current editions of AS/NZS 3000:2018, AS/NZS 3008.1.2, and other applicable standards before being relied on for any installation. CertMate accepts no responsibility or liability for any work carried out, decisions made, or certification issued in reliance on these results. The certifying electrical worker remains solely responsible for compliance with the Electricity (Safety) Regulations 2010 and all applicable New Zealand law.
A load schedule, not a flat form
Maximum demand under AS/NZS 3000:2018 Appendix C isn't one formula - it's a schedule of every load group an installation actually has, each with its own diversity treatment, added together. This calculator mirrors that directly: choose a load type, enter its own fields, add it to the schedule, and move on to the next one. The running total updates as you build the list, the same way you'd work through it on paper.
Single dwellings and blocks of living units work differently under the standard, so the calculator splits them the same way. A single dwelling is entirely schedule-driven - lighting, socket outlets, ranges, heating, water heating and EV charging are all separate items you add as needed. A block of living units starts from a fixed core (living units, phases, per-unit heating) calculated directly from occupancy, then lets you add communal services, lifts and motors as their own schedule items on top.
Worked examples
Standard single dwelling
A typical single-phase house: lighting points, socket outlets, a range, and a storage water heater, each added as its own schedule item. This is the baseline case most residential jobs fall into, and a good one to sanity-check your usual method against.
House with EV charging and fixed heating
The same dwelling, with an EV charger and fixed space heating added as extra schedule items. EV charging in particular is easy to under-estimate since it's counted at full connected load rather than a diversified figure like most other groups.
Block of living units with lifts
A multi-unit block on a three-phase supply: living units and per-unit heating set the core load, then communal lighting, communal socket outlets, and two or more lifts are added as separate schedule items on top - each lift contributing at the standard's own group diversity treatment rather than full load.
Frequently asked questions
How does the load schedule work?
Pick a load type from the dropdown (lighting, socket outlets, ranges, fixed heating, water heaters, EV charging and more), fill in that item's own fields, then click Add. It joins a running schedule below with its own line and a live subtotal - repeat for every load group your installation actually has, then the total maximum demand updates as you go.
What's the difference between "Single dwelling" and "Blocks of living units"?
Single dwelling builds the whole result from schedule items you add one by one - every load group is independent. Blocks of living units instead starts from a fixed core (living unit count, supply phases, per-unit heating) that's calculated directly, since those groups are driven by one shared occupancy figure rather than being separately addable - communal services, lifts and motors are then added as additional schedule items on top of that core.
Can I include an EV charger?
Yes - EV charging is its own schedule item for a single dwelling, and a communal EV charging item for blocks of units. Table C1 treats EV charging at full connected load with no diversity applied, unlike most of the other load groups.
How are multiple lifts or motors in a block handled?
Add each lift or motor as its own schedule item with its full-load current - there's no fixed cap on how many you can add. The calculator applies the standard's own group diversity treatment across everything you've added of that type, rather than treating each one at full load independently.
Does this cover a three-phase single dwelling?
No - the single dwelling method in Table C1 is single phase only. A three-phase single dwelling needs a manual per-circuit phase assessment, which isn't something a single load-schedule total can represent.
Can I download or save my result?
Every calculation can be downloaded as a branded PDF showing the full schedule and total. If you're signed in to your CertMate account, you can also save a calculation and come back to search and reopen it later.
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