How to Apply Diversity Factors in Maximum Demand Calculations (AS/NZS 3000)

Maximum demand is the highest electrical load that an installation is expected to draw at any one time. It is NOT the sum of all connected loads — it is the sum adjusted for the probability that all loads will not operate simultaneously at full load.

This adjustment is called the diversity factor (or demand factor, depending on the standard — more on that distinction shortly). Getting diversity right is the difference between specifying a 400 A main switchboard and a 1000 A one. Overestimate the maximum demand, and you waste tens of thousands of dollars on oversized equipment, cables, and transformer capacity. Underestimate it, and you get nuisance tripping on the main breaker, overloaded cables, and an expensive upgrade within months of commissioning.

AS/NZS 3000:2018 (the Wiring Rules) provides diversity factors in Appendix C. These are informative (not normative), but they are the accepted basis for maximum demand calculations in Australia and New Zealand. Every supply authority references them, and every electrical designer is expected to know them.

Demand Factor vs Diversity Factor: Clear the Confusion First

These two terms are used inconsistently across different standards and textbooks. Here is the precise distinction:

Demand factor = maximum demand of a load / connected load of that load

A single motor rated at 15 kW that draws 12 kW maximum in operation has a demand factor of 0.80. This factor applies to individual loads or load categories.

Diversity factor = sum of individual maximum demands / maximum demand of the combined system

If five motors have individual maximum demands summing to 60 kW, but the combined system maximum demand is 45 kW (because not all motors run at full load simultaneously), the diversity factor is 60/45 = 1.33.

AS/NZS 3000 Appendix C: The Structure

AS/NZS 3000:2018, Appendix C — Maximum demand

Appendix C provides maximum demand values and diversity allowances for different categories of load. The key tables are:

The fundamental approach is:

1. List all connected loads by category
2. Apply the demand factor for each category per the relevant table
3. Sum the diversified demands to get the total maximum demand
4. Apply any further diversity factor for the supply type (residential, commercial, industrial)

Worked Example: Industrial Workshop

Consider an industrial workshop with the following connected loads:

Connected Load Schedule

Total connected load: 170.5 kW/kVA

Without diversity, this workshop would need a 170 kW supply — approximately a 250 A main breaker at 415 V. Let us apply Appendix C diversity and see what the actual maximum demand is.

Step 1: Motor Loads

AS/NZS 3000:2018, Appendix C, Table C2 — Maximum demand for motor loads

AS/NZS 3000 Appendix C Table C2 provides the following method for a group of motors:

• Largest motor: 100% of full-load current
• Second largest motor: 100% of full-load current (if duty requires simultaneous operation)
• Remaining motors: apply a diversity factor based on the number of motors and the application

For an industrial workshop where motors are used intermittently (job shop, not continuous production line):

The largest motor is the hydraulic press at 22 kW. The CNC and crane are 15 kW each. The convention for intermittent-duty workshop motors:

• Largest motor: 100% = 22.0 kW
• Second largest: 80% = 15.0 x 0.80 = 12.0 kW
• Third largest: 60% = 15.0 x 0.60 = 9.0 kW
• Fourth largest: 60% = 11.0 x 0.60 = 6.6 kW
• Fifth largest: 60% = 11.0 x 0.60 = 6.6 kW
• Sixth: 50% = 7.5 x 0.50 = 3.75 kW
• Seventh: 50% = 7.5 x 0.50 = 3.75 kW
• Eighth: 50% = 7.5 x 0.50 = 3.75 kW

Diversified motor load = 67.5 kW (from 96.5 kW connected = 70% overall demand factor)

Step 2: Lighting Load

AS/NZS 3000:2018, Appendix C, Table C1 — Maximum demand for general loads

For an industrial workshop, lighting is typically all on during working hours. Apply 100% demand factor for the total lighting load:

Diversified lighting load = 8.0 kW

AS/NZS 3000 allows diversity on lighting only when there are multiple independently controlled circuits and a realistic probability that not all will be on simultaneously (e.g., a multi-storey office building with separate zone lighting). A single workshop — all lights on or all off — gets no diversity.

Step 3: Socket Outlets

AS/NZS 3000:2018, Appendix C, Table C1 — Maximum demand for socket outlets

Socket outlets in an industrial workshop are used for portable tools, test equipment, and general-purpose loads. Appendix C Table C1 provides:

• First 10 socket outlets: 10 A each = 23.0 kVA at 230 V
• But apply demand factor of 100% for first point, reducing for subsequent points

The practical approach per Appendix C for general-purpose socket outlets:

• First socket outlet: 10 A (2.3 kVA)
• Next 9: 5 A each (1.15 kVA each) = 10.35 kVA
• Remaining 10: 2.5 A each (0.575 kVA each) = 5.75 kVA

Diversified socket outlet load = 18.4 kVA (from 46.0 kVA connected = 40% overall)

Step 4: Air Conditioning

AS/NZS 3000:2018, Appendix C, Table C3 — Maximum demand for air conditioning

For two 10 kW air conditioning units in an industrial space, both are likely to operate simultaneously during hot weather:

• Both units at 100%: 20.0 kW
• No diversity between two units — they serve the same space and operate on the same thermostat cycle

Diversified air conditioning load = 20.0 kW

Step 5: Sum the Diversified Loads

Converting to current at 415 V, three-phase, assuming overall power factor of 0.85:

Result: 186 A maximum demand vs 280 A if no diversity were applied.

A 200 A main switchboard is adequate. Without diversity, we would have specified a 315 A board — 57% larger and significantly more expensive.

The Comparison Table: Industrial vs Commercial vs Residential

Diversity factors vary substantially between building types because usage patterns differ:

Common Mistakes

1. Applying Diversity to Already-Diversified Loads

If the motor load has already been diversified (as in Step 1 above), do NOT apply a further "overall" diversity factor to the motor subtotal. The diversity has already been applied. Applying it twice — first to the motor group, then again to the total — results in an underestimated maximum demand that leads to undersized equipment.

2. Confusing Demand Factor with Diversity Factor

As noted above, the two terms have opposite conventions (demand factor less than 1, diversity factor greater than 1). Misapplying a diversity factor of 1.33 as a multiplier (instead of dividing by 1.33) inflates the maximum demand by 77%. Or, conversely, using a demand factor of 0.75 as a divisor (instead of a multiplier) also inflates it. Be consistent with the convention of the standard you are working to.

3. Using Residential Factors for Commercial Premises

A shopping centre, office building, or hospital has fundamentally different load patterns from a house. Residential diversity factors assume staggered cooking times, off-peak water heating, and intermittent socket use. A commercial kitchen has all ovens on simultaneously during service hours. A hospital has lighting on 24/7 in many areas. Using residential diversity for commercial premises underestimates the maximum demand — sometimes severely.

4. Ignoring Future Load Growth

Appendix C calculates the maximum demand for the loads as they exist today. It does not account for future expansion. Good design practice adds a growth allowance of 15-25% for industrial premises and 10-20% for commercial premises. This is a design decision, not a standard requirement — but neglecting it leads to expensive upgrades within a few years of commissioning.

5. Not Checking Against Measured Data

For existing installations being upgraded or extended, the best diversity data is the actual measured maximum demand from interval metering. A 12-month interval meter record (from the supply authority or a power quality logger) shows the actual peak demand, time of peak, and seasonal variation. This measured data should be used to validate any Appendix C calculation. If the measured data significantly differs from the calculation, investigate why before proceeding.

Bottom Line

Diversity factors are engineering judgement codified into tables. They are not magic numbers — they represent statistical observations about how loads are actually used in practice. Apply them correctly, and you get a right-sized installation. Apply them incorrectly — either too aggressively or too conservatively — and you get either an overloaded installation or an unnecessarily expensive one. Both outcomes are avoidable with a systematic approach and a clear understanding of what the loads actually do.