Maximum Demand As3000 ((exclusive)) -

This shifts MD from a static calculation to a . Final Thought Maximum Demand is not about what could happen. It is about what reasonably will happen over 30 minutes, under normal use. Master the diversity tables, respect harmonics, and understand the economic consequences. That is the difference between a compliant design and an optimal one.

This post is intended for electrical engineers, trade professionals, and advanced students. Most electricians size a circuit breaker for the cable. Fewer truly master the art of Maximum Demand (MD) . In AS/NZS 3000, MD is not a worst-case guess; it is a calculated engineering decision that dictates the economics and safety of the entire installation. maximum demand as3000

Let's move beyond Table C1 and explore the why behind the clauses. Maximum Demand: The greatest expected load current (in amperes) or apparent power (in kVA) that will flow in a circuit, switchboard, or supply main under normal operating conditions for a defined period (typically 30 minutes). Key nuance: Normal operating conditions excludes fault currents or motor starting transients. The "30-minute" window aligns with thermal time constants of cables and transformers. 2. Why MD Matters More Than You Think A. Voltage Drop (Clause 3.6.2) Voltage drop is calculated using load current derived from Maximum Demand , not the sum of breaker ratings. Using breaker totals leads to oversized cables and non-compliance (VD will be too low to measure, but that’s not the point—economy is). B. Transformer and Service Sizing The supply authority (Distributor) uses your MD calculation to size their pole transformer and service mains. Overstate MD → you pay higher demand charges. Understate MD → nuisance tripping of main switch or service fuse. C. Main Switch and Busbar Rating Clause 2.3.2 requires the main switch to have a current rating not less than the calculated MD of the installation. 3. The Methodology: Clause C2 (Informative but De Facto Mandatory) Appendix C provides three methods. In practice, you use a hybrid approach. Method 1: Assessment of Load (Clause C2.2) For each final subcircuit, you apply a diversity factor . This is where 90% of errors occur. This shifts MD from a static calculation to a

Example: EV charger + AC + cooktop + dryer → a controller can stagger operation so the measured 30-minute MD never exceeds 63A, even though the sum of breakers is 150A. Most electricians size a circuit breaker for the cable

Main switch rating: Next standard size = (compliant).

| Load | AS3000 Rule | Calculation | Result (A) | |------|-------------|-------------|-------------| | Lighting | C5: First 10A @100%, rest @50% | 10 + (10×0.5) | 15 | | Sockets (2 circuits) | C6: 10A + 50% of remaining (16 outlets = 16A assumed total) | 10 + (6×0.5) | 13 | | Cooktop | C8: (0.4 × 27.8) + 10 | 11.1 + 10 | 21.1 | | Oven | C8: (0.4 × 20) + 10 | 8 + 10 | 18 | | Hot water | C7: No diversity (storage) | 15.6 | 15.6 | | AC | C9: Largest unit 100% | 16 | 16 |