When you sign off on an electrical Certificate of Compliance—whether that's a CCEW in NSW, a Certificate of Electrical Safety in VIC, or a Form 4 in QLD—maximum demand is your legal guarantee that the switchboard won't cook the consumer mains or pop the street pole fuse at dinner time. Get this calculation wrong, and you're the one answering the 7:00 PM callout on a freezing Friday night to explain to an angry customer why their new induction cooktop knocked out power to the entire house.
Under AS/NZS 3000:2018 (Wiring Rules) Appendix C, maximum demand is the engineering check behind sizing consumer mains, sub-mains, and switchgear busbars. It is the practical line between an installation that runs safely for decades and tens of thousands of dollars wasted on an unnecessary street trenching upgrade.
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1. Quick AS/NZS 3000 Table C1 Diversity Matrix
Table C1 in Appendix C of the Wiring Rules sets the statutory diversity allowances for single domestic installations. Here is the site cheat-sheet every sparky and apprentice needs on their phone:
| Table C1 Load Group | Equipment & Circuit Types | Table C1 Diversity Allowance (Single Domestic) | Critical On-Site Rule & Inspection Trap |
|---|---|---|---|
| Load Group (a) | Lighting Points & Exhaust Fans (≤150W) | 3 A for first 20 points + 2 A per additional 20 points (or part thereof) | Track lighting = 2 points per metre. High GPOs (>2.3m) and exhaust fans ≤150W count as lighting points. |
| Load Group (b)(i) | 10A Socket-Outlets (GPOs) | 10 A for first 20 points + 5 A per additional 20 points (or part thereof) | Double GPO trap: A double power point counts as 2 separate points, not 1! |
| Load Group (b)(ii) | Socket-Outlets > 10A (15A/20A/32A) | Full rated current of highest outlet + 50% of remainder | Applies to caravan inlets, heavy workshop outlets, and dedicated high-draw plug points. |
| Load Group (c) | Cooking Appliances (Range, Oven, Cooktop) | 50% of connected full load current | Applies strictly to consumer mains and submains sizing. Final subcircuit cables must be sized to full load or Table C5. |
| Load Group (d) | Fixed Space Heating & Air Conditioning | 75% of the larger load only (Heating OR Cooling) | Heating and cooling are mutually exclusive in domestic use. The smaller system is completely suppressed (0 A). |
| Load Group (e) | Instantaneous Water Heater | 33.3% (one-third) of connected load | Massive peak draw (e.g. 18 kW / 78 A) but runs for very short bursts. Heavily pushes installations toward 3-phase. |
| Load Group (f)(i) | Storage Water Heater (Continuous Supply) | 100% full load current (typically 15 A / 3.6 kW) | Must be counted at full rating if connected to general tariff domestic supply without timer controls. |
| Load Group (f)(ii) | Storage Water Heater (Off-Peak / Controlled Load) | 0 A (Excluded from Maximum Demand) | Switched remotely by the DNSP (Tariff 31/33/J) during low-grid periods. Does not load the peak service line. |
| Load Group (g)/(h) | Motors, Spa Baths & Pool Equipment | 100% of largest motor + 50% of remaining motors | Motor nameplate running current (FLA) is used. Locked-rotor starting currents are handled by circuit breaker trip curves. |
| EVSE (Clause 7.9) | Electric Vehicle Chargers (EVSE) | 100% rated current (Continuous Load) | No diversity permitted under AS/NZS 3000 Amendment 2 unless a certified Dynamic Load Management System (DLMS) is fitted. |
| Solar PV & Battery | Rooftop Inverters & Energy Storage | 0 A Deduction (Cannot reduce maximum demand) | Mains must be sized for night-time or storm conditions when solar generation is zero. |
2. What is Maximum Demand vs Connected Load?
If you added up the full-load nameplate rating of every single circuit breaker on a modern 4-bedroom switchboard, the raw connected load would easily push 150 to 200 Amps (30 kW to 45 kW).
Sizing consumer mains for that number would mean trenching 70mm² heavy industrial cables down suburban driveways. We don't do that because homeowners never run the kettle, toaster, oven, induction hob, ducted air con, clothes dryer, and 40 downlights at the exact same second.
Under AS/NZS 3000, maximum demand is the design peak electrical current drawn by an installation during normal operation, calculated by applying statutory diversity factors to connected equipment to reflect non-coincident usage.
- Connected Load: The raw theoretical sum of all appliances running flat-out simultaneously. Good for calculating fault levels, completely unrealistic for cable sizing.
- Maximum Demand (After Diversity Maximum Demand — ADMD): The statistically realistic peak current your mains conductors must survive. For most single-phase Australian dwellings, this lands between 40 A and 70 A.
3. The 4 Methods to Determine Demand (Clause 2.2.2)
Clause 2.2.2 of the Wiring Rules gives licensed electricians four legal pathways to establish maximum demand:
Method 1: Calculation (Appendix C Tables)
The standard route for new residential and commercial installations. Uses empirical diversity formulas: Table C1 for single and multi-domestic dwellings, and Table C2 for commercial buildings, shops, and factories.
Method 2: Assessment
Used for specialized industrial plants, automated machinery, or unique duty cycles where standard tables produce absurd numbers. Requires written engineering justification or manufacturer duty-cycle data.
Method 3: Measurement (Clause 2.2.2(c))
Recorded using a calibrated energy logger over a representative 15-minute or 30-minute peak window. This is common when adding equipment (like a commercial coolroom or CNC mill) to an existing commercial switchboard with years of utility interval data.
Method 4: Limitation (Clause 2.2.2(d))
Maximum demand is fixed by an upstream protective device, like an appropriately rated main circuit breaker or RCBO, or an automated load-shedding control system. If the load exceeds the limit, the device trips or sheds non-essential circuits before mains conductors overheat.
4. AS/NZS 3000 Table C1 Rules & Load Groups Breakdown
Table C1 looks straightforward on paper, but the footnotes in Appendix C are where most apprentices lose marks on their Capstone and contractors get pulled up by network certifiers:
A. Lighting (Load Group (a))
The standard allows 3 A for 1 to 20 points, and 2 A for each subsequent 20 points (or part thereof).
- What counts as a point? Every downlight, pendant, batten holder, or exterior floodlight is 1 point.
- Track Lighting: Under Note 4, track lighting is calculated at 2 points per lineal metre of track.
- Exhaust Fans & Sensors: Permanently wired small fixtures rated ≤150 W (bathroom exhaust fans, ceiling fans, sensor lights) count as lighting points, NOT general power outlets.
- High-Mounted Outlets: GPOs mounted higher than 2.3 metres above the floor for wall TVs, clocks, or rangehoods count under Group (a) (lighting), not Group (b).
B. 10A Socket-Outlets / GPOs (Load Group (b)(i))
Standard domestic 10A outlets are assessed at 10 A for the first 20 points, plus 5 A for each additional 20 points (or part thereof).
A standard double GPO plate has two independent switched sockets. It counts as two (2) points. If a home has 25 double GPOs and 4 single GPOs, your point count is (25 × 2) + 4 = 54 points.
C. Cooking Appliances (Load Group (c))
Domestic ranges, wall ovens, cooktops, and induction hobs are assessed at 50% of connected full load current.
Remember: This 50% diversity applies strictly to the consumer mains and submains feeding the board. The dedicated subcircuit cable from the breaker to the cooktop isolator cannot use this diversity—it must be sized for full design current under AS/NZS 3008 Cable Sizing Rules. You can convert nameplate power ratings directly with our kW to Amps Calculator.
D. Fixed Space Heating & Cooling (Load Group (d))
Fixed air conditioning and electric space heating are calculated at 75% of full load.
If a house has a 6.0 kW ducted reverse cycle system (26 A cooling / 22 A heating) and 2.0 kW of electric underfloor heating in the ensuite (8.7 A), you compare total cooling (26 A) against total heating (22 A + 8.7 A = 30.7 A). Because heating is the larger load, cooling is suppressed (0 A) and the demand is 30.7 A × 0.75 = 23.0 A.
E. Water Heaters (Load Groups (e) & (f))
- Controlled Load (Off-Peak - Group (f)(ii)): 0 A. If the storage tank is on an off-peak relay (Tariff 31/33 or night ripple control), it is excluded from maximum demand because the network provider only switches it on during low-grid periods.
- Continuous Storage (Group (f)(i)): 100% full load. A standard 3.6 kW continuous hot water cylinder draws
3600 ÷ 230 = 15.65 A. - Instantaneous Water Heating (Group (e)): 33.3% full load. While 33.3% provides healthy diversity, an 18 kW three-phase instant heater still injects
(18,000 ÷ 230) × 0.333 = 26.1 Ainto single-phase demand.
5. Maximum Demand Calculation Domestic Single Phase Example (4-Bedroom Home)
Here is a live job scenario every domestic contractor faces today: an all-electric 4-bedroom build with an induction cooktop, ducted reverse-cycle air con, continuous electric hot water, and a pool pump. Let's run the numbers through Table C1 line by line to see why an all-electric single-phase build pushes a standard 80A service fuse right to the edge.
- Lighting: 34 LED downlights + 2 bathroom heat/light/exhaust units (2 × 150W fans) + 1 exterior sensor floodlight = 37 total lighting points.
- Power Outlets: 24 double GPOs throughout living/bedrooms + 4 single GPOs (fridge, dishwasher, rangehood, microwave) = 52 total GPO points.
- Cooking: 7.2 kW induction cooktop + 3.0 kW built-in pyro oven = 10.2 kW total (44.35 A at 230V, verified with our kW to Amps Calculator).
- Air Conditioning: 6.5 kW cooling / 7.0 kW heating ducted reverse-cycle system (Max rated input current: 14.5 A).
- Hot Water: 3.6 kW storage cylinder on continuous domestic tariff (15.65 A).
- Pool Pump: 1.1 kW (1.5 HP) variable speed pool pump (5.5 A).
Step 1: Calculate Load Group (a) (Lighting Demand)
Total points = 37. Points 1 to 20 = 3 A. Remaining 17 points (part of next 20) = 2 A.
Group (a) = 3 A + 2 A = 5.0 A
Step 2: Calculate Load Group (b)(i) (10A Socket-Outlets Demand)
Total points = 52. Points 1 to 20 = 10 A. Points 21 to 40 = 5 A. Remaining 12 points = 5 A.
Group (b)(i) = 10 A + 5 A + 5 A = 20.0 A
Step 3: Calculate Load Group (c) (Cooking Appliances Demand)
Total connected load: 10,200 W ÷ 230 V = 44.35 A. Apply 50% diversity allowance.
Group (c) = 44.35 A × 0.50 = 22.18 A
Step 4: Calculate Load Group (d) (Air Conditioning Demand)
Largest system load = 14.5 A. Apply 75% diversity allowance.
Group (d) = 14.5 A × 0.75 = 10.88 A
Step 5: Calculate Load Group (f)(i) (Water Heating Demand)
Continuous tariff 3.6 kW storage water heater at 100% full load rating.
Group (f)(i) = 3600 W ÷ 230 V = 15.65 A
Step 6: Calculate Load Group (h) (Motors / Pool Pump)
Single pool pump motor assessed at 100% running full load.
Group (h) = 5.50 A
Step 7: Total Calculated Maximum Demand & Mains Sizing
Total Demand = 5.0 + 20.0 + 22.18 + 10.88 + 15.65 + 5.50 = 79.21 A
Site Reality: At 79.21 A, this installation scrapes under an 80A single-phase pole fuse by less than 1 Amp. You would install a 100A main switch and run minimum 16mm² copper XLPE or 25mm² PVC consumer mains (check exact derating with our AS 3008 Cable Sizing Calculator). If the mains pass through ceiling insulation, you need 25mm² XLPE. Add a 32A EV wallbox down the track, and demand jumps to 111.2 A—an instant blackout.
6. Worked Example 2: Three-Phase Balancing with Ducted A/C
When a build blows past single-phase limits, upgrading to 400V Three-Phase (Phase L1: Brown / legacy Red; Phase L2: Black / legacy White; Phase L3: Grey / legacy Blue) solves the problem. But you cannot simply dump all your power points on Phase A and the cooktop on Phase B. AS/NZS 3000 requires calculating maximum demand per phase, and your consumer mains cable size is governed by whichever single phase is drawing the heaviest load.
AS/NZS 3000 Harmonised Wiring Colour Hazard
Here is how to balance the same home on 3-phase, incorporating an 11 kW (16 A per phase) 3-phase EV wallbox and a 12.5 kW ducted air conditioner (7.5 A balanced per phase):
| Table C1 Load Group | Phase A / L1 (Brown) | Phase B / L2 (Black) | Phase C / L3 (Grey) |
|---|---|---|---|
| Group (a) (Lighting - 37 pts) | 3.0 A (13 points) | 3.0 A (12 points) | 3.0 A (12 points) |
| Group (b)(i) (10A GPOs - 52 pts) | 10.0 A (18 points) | 10.0 A (18 points) | 10.0 A (16 points) |
| Group (c) (Cooking - 10.2 kW) | 15.65 A (7.2 kW Cooktop × 50%) | — | 6.52 A (3 kW Oven × 50%) |
| Group (d) (3-Phase Ducted A/C) | 5.63 A (7.5 A × 75%) | 5.63 A (7.5 A × 75%) | 5.63 A (7.5 A × 75%) |
| Group (f)(i) (Hot Water) | — | 15.65 A (3.6 kW Continuous) | — |
| Group (h) (Pool Pump) | — | — | 5.50 A (1.1 kW Motor) |
| EVSE Cl 7.9 (11 kW 3-Phase) | 16.0 A (Continuous 100%) | 16.0 A (Continuous 100%) | 16.0 A (Continuous 100%) |
| Phase Maximum Demand: | 50.28 A | 50.28 A (Governing Phase) | 46.65 A |
The Trade Result: By splitting the general power (18/18/16 points) and lighting (13/12/12 points) across all three phases, no phase exceeds the first 20-point block. The demand drops from a dangerous 111 A single-phase down to just 50.28 A per phase. This comfortably complies with standard 63A or 80A 3-phase service fuses, runs cooler, experiences minimal voltage drop, and avoids phase-imbalance penalties from the distributor.
7. Modern High-Draw Traps: EV Chargers, Induction & Solar PV
Home electrification is booming, but street cables haven't magically grown thicker. Three high-draw additions are catching sparkies out across Australia:
Trap 1: EV Charger Maximum Demand Under AS/NZS 3000 (100% Continuous Rule)
Do not make the mistake of treating an EV wallbox like a general power point under Group (b). Under AS/NZS 3000 Clause 7.9 and Table C1, Electric Vehicle Supply Equipment (EVSE) is a continuous, sustained load. A dedicated 32A single-phase charger adds 32.0 A at 100% directly to your calculation.
How contractors avoid the $6,000 trench: Install an EV wallbox with a current transformer (CT) clamp and an approved Dynamic Load Management System (DLMS). Under Clause 2.2.2(d) (Limitation), if household draw reaches 55A, the charger automatically throttles back, legally capping the installation's maximum demand within the existing service fuse limit.
Trap 2: Does Solar Reduce Maximum Demand Under AS/NZS 3000? (0A Offset Rule)
Under AS/NZS 4777.1 and AS/NZS 3000 Clause 2.2.2, rooftop solar PV and home batteries cannot be subtracted from calculated maximum demand for consumer mains or switchboard sizing. Mains must be engineered for the absolute worst-case scenario: an overcast winter evening at 6:30 PM when solar generation is 0.0 kW and batteries are depleted.
Trap 3: Full-House Gas-to-Electric Conversions
Swapping gas hot water and gas cooking for an induction cooktop and a continuous electric cylinder adds over 35 A of diversified load to an existing switchboard. On an older 40A or 50A service common in pre-1985 Australian suburbs, this will trip the service fuse almost immediately.
AS/NZS 3000 Compliance Warning
8. When Is a 3-Phase Upgrade Required? (Service Fuse Limits)
Each state network provider sets hard limits on what you can pull through a single-phase service before they force a three-phase connection:
| Network Provider (DNSP) | Applicable State Service Rules | Standard Single-Phase Service Fuse | 3-Phase Upgrade Trigger Threshold |
|---|---|---|---|
| Ausgrid / Endeavour Energy | NSW Service and Installation Rules (SIR) & Level 2 ASP Rules | 63 A to 80 A (100A in select new underground estates) | Demand > 63 A (older connections) or > 80 A |
| Essential Energy | NSW Regional Service Rules | 63 A or 80 A | Demand > 63 A |
| Energex / Ergon Energy | Queensland Electricity Connection Manual (QECM) | 63 A or 80 A | Single appliance > 5.0 kW (20A) or Maximum Demand > 63 A |
| CitiPower / Powercor / AusNet | Victorian Electricity Supply Industry (VESI) Rules | 63 A or 80 A | Demand > 63 A or single-phase load > 15 kVA |
| SA Power Networks (SAPN) | South Australian Service & Installation Rules | 63 A (100A strictly on written application) | Demand > 63 A |
| Western Power | WA Electrical Requirements (WAER / WASIR) | 32 A or 63 A | Demand > 63 A (strictly enforced) |
9. Top 5 Site Audit & TAFE Capstone Mistakes
1. Counting Double GPOs as 1 Point
Every double GPO has two separate outlets and must be counted as 2 points under Table C1 Note 2. Sizing a 30-double-GPO house as 30 points instead of 60 points undercalculates socket demand by 10 Amperes!
2. Applying 50% Cooking Diversity to Final Subcircuits
The 50% diversity factor in Table C1 Group (c) applies strictly to the consumer mains. If you run a 2.5mm² TPS cable on a 16A breaker to a 7.2 kW cooktop claiming "diversity covers it", that cable will melt and fail insulation resistance testing under AS/NZS 3017.
3. Forgetting the "Greater Load" Rule for Heating/Cooling
Never add both air conditioning and electric space heating together. Only calculate 75% of the larger system; the smaller system is mutually exclusive and counts as 0 A.
4. Subtracting Solar Inverter Capacity from Mains Demand
Mains cables must be capable of carrying peak domestic demand without any solar contribution. Certifiers will immediately reject any grid connection application that uses solar PV as an offset to avoid consumer mains upgrades.
5. Sizing 3-Phase Mains on Average Load Instead of Governing Phase
In a 3-phase calculation, you cannot simply add the total demand of all three phases and divide by three. If Phase A draws 52A while Phase B draws 25A, your consumer mains cable must be sized to safely carry 52A continuous current under AS/NZS 3008 derating rules.
Before you order cable or submit a connection application to Ausgrid, Energex, or Powercor, run your site numbers through our free AS/NZS 3000 Maximum Demand Calculator to check phase balance, calculate diversity, and verify switchboard sizing in minutes.