Maximum Demand Stage Calculator

This tool helps calculate the maximum demand for electrical installations based on staged or progressive load additions. It is especially useful for multi-occupancy commercial buildings, residential complexes, or phased development projects. The logic used aligns with design principles found in AS/NZS 3000 Appendix C, and the stage-by-stage approach enables designers to predict electrical infrastructure capacity over time.

Theory and Background

The maximum demand of an electrical installation represents the highest level of current that may be drawn under normal operating conditions. This value determines the capacity of the supply network, switchgear, protection devices, and cabling. When planning projects with multiple stages or expansions, designers must ensure the initial infrastructure supports the final projected load while still being optimized for early-stage use.

Key Concepts in Staged Load Design

Progressive Demand: Each stage introduces new loads, such as tenancies or additional floor levels.
Demand Factors: Different load types (lighting, power outlets, HVAC) may apply demand factors that reduce the total assumed current draw.
Non-Simultaneity: Not all loads are active simultaneously. Diversity factors are used to reflect realistic usage patterns.

Calculation Methodology

The calculation of staged maximum demand typically involves:

Identifying all load groups (lighting, general power, mechanical, special equipment).
Applying appropriate demand factors to each load group (as per Table C2 of AS/NZS 3000).
Summing the adjusted currents for each stage.
Determining the cumulative maximum demand for each stage.

This staged approach allows consultants to balance capital investment with operational needs over time. For example, a distribution board may be sized for Stage 3, but initially only Stage 1 is connected. This minimizes oversizing while future-proofing the design.

Why Use Maximum Demand Staging?

Improved infrastructure planning and budgeting
More efficient transformer and switchboard sizing
Accurate estimation of demand-based tariffs
Enables compliance with local supply authority rules

Limitations

While the staged maximum demand method provides a structured approach, it's important to cross-reference calculations with actual measured data (if available) and consult supply authority guidelines. Furthermore, each project's usage pattern may vary, so the assumptions used in standard tables may require adjustment.

In summary, staged maximum demand calculations are a powerful way to anticipate load growth while ensuring safe, economical, and regulation-compliant electrical design.