Maximum demand refers to the maximum electrical power or current drawn over a defined period within a system. It’s a critical design parameter:

• – Ensures circuits, consumer mains, distribution boards, and protective devices (e.g., switches, fuses) are adequately sized.
• – Prevents overloading of infrastructure and maintains safety and reliability.
• – Influences coordination with your Distribution Network Service Provider’s (DNSP) capacity rules.

In AS/NZS 3000:2018, Section 2.2.2 flags maximum demand as a fundamental design consideration, and Appendix C contains the reference tables designers rely on for calculations and diversity allowances .

Structure of Appendix C – What’s Inside

Appendix C organizes guidance by installation type and application:

• C1 – Domestic Installations: Covers single dwellings and multiple-dwelling scenarios. It groups loads like lighting, power outlets, cooking, heating, HVAC, etc.
• C2 – Non-domestic Installations: Targets commercial or industrial settings, with different grouping and diversity factors.
• C3 – Energy-demand Method: A more granular method for modeling diversified loads in larger or complex non-domestic situations.
• C4 – Upstream Circuit Loading: Helps determine loads on upstream cabling post-diversity application.
• C5 – Domestic Cooking Appliances: Includes special rules for ovens, ranges, cooktops—distinct from general load categories.
• C9 – Final Subcircuits: Provides guidance on the number of outlets or points per circuit, especially relevant for socket/outlet design.
• Additional tables (C6–C8, C10–C12) offer supportive guidance on miscellaneous load types or calculations .

Appendix C is classified as informative, providing guidance and standardized approaches that are commonly accepted in regulatory and engineering practice dynamics .

Recognized Methods to Determine Maximum Demand

AS/NZS 3000 supports four primary methods for determining maximum demand, which can often be combined depending on the project phase:

• 1. Calculation – Apply diversity factors from Appendix C to grouped load categories.
• 2. Assessment – Use professional judgment informed by known usage patterns, especially when loads are well understood.
• 3. Measurement – Use historical metered data over defined intervals (e.g., 15 minutes) to assess actual maximum demand.
• 4. Limitation – Where system constraints (like protective device thresholds) inherently cap demand.

For the calculation method, Appendix C serves as the authoritative source. The assessment approach lets designers adjust based on anticipated behaviour; measurement is especially valuable for upgrades or retrofits; limitation is applied where infrastructure imposes demand caps, such as in EV charging infrastructure .

Using the Tables: Domestic vs. Non-Domestic

Domestic (C1 + C5):

• – Group together loads: lighting, outlet circuits, heating, cooking, etc.
• – Apply the table’s diversity factors and special notes—especially for scenarios like multiple dwellings fed from one submain.
• – Use C5 for cooking appliances rather than counting nameplate ratings (€ e.g., ovens can have high diversity allowances) .

Non-Domestic (C2 + C3 or C4):

• – Group loads differently—e.g., lighting vs. general power vs. HVAC vs. process machinery.
• – Apply C2’s diversity allowances, or for complex systems, use the energy-demand method (C3) to model demand more precisely.
• – Use C4 to translate subcircuit loads into upstream submain/current loading after diversity .

Final Subcircuits (C9):

• – Appendix C focuses on consumer mains and submains, not final socket-outlet circuits.
• – For those, use the assessment or limitation methods, informed by C9’s guidance on number of outlets per circuit and load characterization .

Common Pitfalls to Watch For

• – Don’t overlook table footnotes. Many users mistakenly ignore exceptions for socket groups, multiple outlets, or nameplate limits that appear in notes .
• – Cooker loads require special treatment. Always refer to C5 rather than simply summing nameplates.
• – Final subcircuits versus submains. Avoid misapplying Appendix C to final outlet circuits.
• – Metered measurements matter. Where past usage data exists, measuring maximum demand over, say, a 15-minute interval can provide better insight — but verify the interval with equipment or DNSP requirements .
• – DNSP integration. Your DNSP’s Service & Installation Rules may further constrain demand assumptions, voltage drop, or circuit sizing .

Worked Example: Domestic Maximum Demand (Single Dwelling)

Here’s a simplified, yet practical, worked example using Appendix C1 and C5:

Scenario:

A single dwelling with the following loads:

• – Lighting circuits: grouped load of 10 A
• – General socket-outlets: grouped load of 15 A
• – Electric oven/cooktop: nameplate 18 A
• – Electric hot-water storage (off-peak): 20 A (diversified under hot-water clause)

Steps:

• – Lighting (10 A): From C1, assume a diversity factor—say 0.6. Demand = 10 A × 0.6 = 6 A.
• – Socket-outlets (15 A): Assume diversity of 0.8 → 15 A × 0.8 = 12 A.
• – Cooking (18 A): Use C5: say the table allows a 40% demand factor → 18 A × 0.4 = 7.2 A.
• – Hot-water (20 A): Assuming off-peak and per domestic rules, it may not count towards coincident maximum demand—effectively 0 A coincident demand.

Estimated total maximum demand = 6 + 12 + 7.2 = 25.2 A at the consumer main.

Note: The exact numbers (diversity factors) depend on the specific table entries and notes—so this sample is illustrative. Always use the actual values from C1 and C5 for rigorous design.