Maximum Demand Calculation per AS/NZS 3000:2018 Clause 2.2 and Table 2.1

Maximum demand is the highest electrical load that an installation is expected to draw from the supply at any one time. It determines the sizing of consumer mains, main switchboard, distribution transformer, and upstream network infrastructure. Getting it right matters for two reasons:

• Undersizing causes overloaded cables, nuisance tripping, voltage drop issues, and in extreme cases, cable fires.
• Oversizing wastes money on unnecessarily large cables, switchgear, and transformer capacity — and can result in low fault levels that compromise protection discrimination.

AS/NZS 3000:2018 Clause 2.2 ("Assessment of maximum demand") provides the regulatory framework for maximum demand calculation in Australia and New Zealand. The primary tool is Table 2.1, which prescribes demand factors for various load categories. These demand factors account for the statistical improbability that all loads in an installation operate simultaneously at full rated capacity.

ECalPro implements the complete Table 2.1 methodology and additionally provides the engineering judgement tools (load profiling, time-of-use analysis) that Clause 2.2.2 permits as an alternative to the tabulated method.

ADMD (After Diversity Maximum Demand) is the maximum demand of a group of consumers after accounting for the diversity between them. It is a statistical measure used primarily by electricity distributors to size shared network assets (distribution transformers, LV feeders, HV cables).

Key characteristics of ADMD:

• ADMD applies to a group of consumers, not to an individual installation
• It assumes that peak loads of individual consumers do not coincide perfectly
• Typical residential ADMD values range from 3 kVA to 8 kVA per dwelling, depending on the climate zone, dwelling type, and presence of electric heating/cooling
• ADMD decreases (per dwelling) as the number of dwellings increases — the diversity effect strengthens with larger groups

What ADMD is NOT:

• ADMD is not the same as the individual maximum demand calculated per AS/NZS 3000 Table 2.1. Table 2.1 calculates the maximum demand of a single installation, which is higher than the ADMD contribution of that installation to the shared network.
• ADMD should not be used to size the individual consumer mains — use Table 2.1 for that purpose.
• ADMD does not replace engineering judgement for installations with unusual load profiles (e.g., all-electric dwellings, EV charging, crypto mining).

Electricity distributors publish ADMD tables specific to their service territory. For example:

ECalPro allows engineers to apply distributor-specific ADMD values when sizing shared infrastructure for multi-dwelling developments, while using the full Table 2.1 methodology for individual installation sizing.

AS/NZS 3000:2018 Table 2.1 organises loads into categories with specific demand calculation rules. ECalPro implements each category exactly as specified in the standard.

Table 2.1 structure and key load categories:

Domestic lighting and power (Category A):

Maximum demand = First 10 A at 100% + remainder at 50%

Example: 45 A total connected lighting and GPO load
  MD = 10 + (45 - 10) × 0.50
  MD = 10 + 17.5
  MD = 27.5 A     — (Eq. 1)

Cooking appliances (Category B — domestic):

For domestic cooking appliances, the demand factor depends on the number of appliances and their individual ratings. The sub-table within Category B provides:

1 appliance:    rated current × 0.80 (if ≤ 7.5 kW)
                rated current × 0.50 (if > 7.5 kW, min 30 A)
2 appliances:   sum of rated currents × 0.75
3+ appliances:  sum of rated currents × 0.50 + diversity per appliance

Motor loads (Category E):

The largest motor is taken at 100% of its full-load current. Subsequent motors are added at a demand factor:

Motor demand = FLC_largest × 1.00
             + FLC_second  × 0.75
             + FLC_third   × 0.60
             + remaining motors × 0.50     — (Eq. 2)

Starting current of the largest motor must also be checked against the supply capacity, per AS/NZS 3000 Clause 4.7.

Demand factors represent the ratio of the expected maximum demand to the total connected load. They vary significantly by building type because of the different usage patterns.

Domestic installations:

Domestic demand factors are generally well-defined by Table 2.1 because residential load patterns are statistically predictable. Key principles:

• Lighting and general power outlets: stepped demand (100% of first 10 A, 50% of remainder)
• Electric water heater: 100% if on continuous supply, or excluded if on off-peak controlled supply
• Air conditioning: largest unit at 100%, second at 75%, subsequent at 50%
• Pool pump and spa: 100% (non-discretionary load, assumed to coincide with peak)
• EV charger: 100% (conservative approach — AS/NZS 3000:2018 did not specifically address EV charging, but the 2025 amendment will include specific EV demand rules)

Commercial installations:

Commercial demand factors vary widely by building function. Table 2.1 provides general rules, but Clause 2.2.2 allows engineering assessment for specific building types:

Industrial installations:

Industrial demand factors depend heavily on the process. A factory with a single large process load (e.g., an electric arc furnace) may have a demand factor approaching 1.0, while a factory with many small machines operated in shifts may have a demand factor of 0.40–0.50. Engineering assessment per Clause 2.2.2 is almost always required for industrial installations.

AS/NZS 3000:2018 Clause 2.2.2 permits the maximum demand to be determined by engineering assessment as an alternative to the tabulated method of Table 2.1. This provision exists because Table 2.1 demand factors are based on typical installations — unusual or specialised installations may have significantly different load profiles.

When deviation is appropriate:

• Industrial installations with process-specific load profiles and known operating schedules
• Buildings with extensive sub-metering data from similar existing buildings
• Installations where the Table 2.1 result is clearly oversized (e.g., a warehouse with 200 GPOs but only 5 in use at any time)
• Installations with large seasonal variation (e.g., agricultural irrigation, ski resorts)
• Retrofits where historical consumption data is available from energy bills or BMS records

What the engineer must document (Clause 2.2.2 requirements):

1. Basis of assessment: The data, assumptions, and methodology used to determine the maximum demand
2. Load schedule: A tabulation of all loads with their rated power, expected operating hours, and coincidence factors
3. Diversity justification: Why the chosen diversity factors are appropriate for this specific installation
4. Comparison with Table 2.1: The Table 2.1 result should be shown alongside the engineering assessment result, with an explanation of the difference
5. Professional certification: The assessment must be performed by a suitably qualified person (typically a registered electrical engineer or licensed electrical contractor with design endorsement)

ECalPro supports the Clause 2.2.2 pathway by providing a structured engineering assessment template. The engineer enters individual loads with their rated power, duty cycle, and coincidence factor. ECalPro calculates the diversified maximum demand and generates a report that documents the assessment alongside the Table 2.1 comparison, satisfying the clause requirements for an auditable record.

Engineering assessment maximum demand:

MD = Σ (P_i × DF_i × CF_i)     — (Eq. 3)

Where:
  P_i  = rated power of load i (W or kVA)
  DF_i = duty factor (fraction of time operating, 0–1)
  CF_i = coincidence factor (probability of simultaneous
         operation with other loads, 0–1)

Important caution: Engineers who deviate from Table 2.1 assume liability for the adequacy of the maximum demand assessment. If the installation subsequently overloads the supply, the deviation from the standard method may be scrutinised. ECalPro includes a warning to this effect in the engineering assessment report.

Large installations typically have multiple distribution boards arranged in a hierarchy: main switchboard (MSB) feeding sub-distribution boards (SDBs), which feed final distribution boards (FDBs). The maximum demand at each level must be calculated by rolling up the demands from downstream boards with appropriate diversity between them.

The roll-up process follows these rules:

Level 1 — Final distribution boards:

Calculate the maximum demand of each FDB independently using Table 2.1. Each FDB is treated as a separate installation with its own load schedule.

Level 2 — Sub-distribution boards:

The demand on each SDB is the diversified sum of the FDBs it supplies, plus any loads connected directly to the SDB:

MD_SDB = Σ (MD_FDB_i × DF_board_i) + MD_direct     — (Eq. 4)

Where:
  MD_FDB_i   = maximum demand of each downstream FDB
  DF_board_i = board diversity factor (from Table 2.1 or engineering assessment)
  MD_direct  = maximum demand of loads connected directly to the SDB

Level 3 — Main switchboard:

The demand on the MSB is the diversified sum of all SDBs plus any loads connected directly to the MSB. An additional diversity factor may apply between the SDBs:

Note: These inter-board diversity factors are not directly specified in Table 2.1 — they are derived from engineering practice. AS/NZS 3000 permits their use under Clause 2.2.2.

ECalPro models the full board hierarchy. The engineer defines the board tree (MSB → SDBs → FDBs), enters loads at each board, and ECalPro cascades the maximum demand calculation upward through the tree. The result includes a one-line diagram showing the maximum demand at every node, enabling cable sizing for every feeder in the system.

Consumer mains sizing: The final maximum demand at the MSB level determines the consumer mains cable size. Per AS/NZS 3000 Clause 3.6.2(a), the consumer mains voltage drop must not exceed 1.5%. ECalPro links the maximum demand output directly to the cable sizing calculator, pre-populating the design current for the consumer mains.

Electric vehicle charging is a rapidly growing load category that AS/NZS 3000:2018 does not explicitly address (the standard predates mass EV adoption). However, Clause 2.2.2 provides the framework for including EV loads in the maximum demand assessment.

Typical EV charger ratings:

For multi-dwelling developments, the concurrent charging demand can be estimated using the diversity approach. Not all residents charge simultaneously, and smart charging systems can stagger the charging loads. ECalPro allows engineers to apply EV-specific diversity factors:

EV demand = N_chargers × P_charger × DF_ev     — (Eq. 5)

Where:
  N_chargers = number of EV chargers
  P_charger  = rated charger power (kW)
  DF_ev      = EV diversity factor

Typical DF_ev values:
  1–5 chargers:    1.00 (no diversity)
  6–20 chargers:   0.60–0.80
  21–50 chargers:  0.40–0.60
  50+ chargers:    0.30–0.50 (with smart load management)

ECalPro flags the EV charging contribution separately in the maximum demand report, enabling engineers and distributors to assess the network impact independently of the base building load.