Tutorial Video
Maximum Demand Calculator
This automatic maximum demand calculator streamlines the process of maximum demand calculations. It can apply rules for installation types and loads and balance them across phases, ensuring an efficient, cost-effective, and realistic design that complies with standards and local regulations.
ℹ️ELEK Cable Pro Software is the only maximum demand calculator that does automatic phase load balancing.
This maximum demand calculator uses the Maximum Demand Tables C1 and C2 for domestic and non-domestic installations from Appendix C of AS/NZS 3000.
Maximum Demand Explained
Maximum demand refers to the highest level of electrical load that an installation experiences or is expected to experience under normal conditions. It represents the peak electrical power usage at any given time and is a critical factor in electrical design and infrastructure planning.
The maximum demand for an electrical installation is calculated to ensure that the electrical infrastructure, including cables, transformers, and other equipment, can handle peak loads safely and efficiently. This involves considering various factors such as the installation’s capacity, the physical distribution of electrical loads, the intended use of the equipment, and potential variations in current requirements.
There are two methods for calculating maximum demand:
- A summation of individual connected loads with the application of (custom) diversity factors.
- Using standard tables of ‘typical’ maximum demand ratings for different installation and load types.
In practice, a combination of these two methods is often utilised.
ℹ️The standard AS/NZS 3000 provides tables of typical maximum demand ratings for different installation and load types.
Diversity Explained
Diversity should be taken into account when assessing an installation’s maximum demand. Diversity is the engineering principle that not all electrical loads will operate simultaneously at their peak capacity in an electrical installation. This accounts for the varying usage patterns of different electrical equipment and allows for more realistic and often lower maximum demand estimates.
Incorporating diversity factors into maximum demand calculations avoids overestimating electrical loads, which can lead to unnecessary oversizing of electrical infrastructure. This results in a more efficient, cost-effective, and realistic design.
Diversity is applied using factors as multipliers that adjust the total connected load to reflect the likelihood of simultaneous operation to obtain the after diversity maximum demand (ADMD), where:
After Diversity Maximum Demand (A) = connected load (A) x diversity factor
Diversity factors are derived from empirical data, experience, and specific application scenarios. Diversity factors are incorporated with the standard maximum demand rules in AS/NZS 3000.
Diversity can be applied in several ways as follows:
- For items on a final subcircuit.
- Between similar final subcircuits (i.e. assume one circuit is 100 %, the second is 50 %, etc.).
- Between sub-distribution boards or submain cables, and
- At each distribution board.
ℹ️There is no replacement for practical knowledge and hands-on experience in evaluating diversity. The level of expertise required should correspond to the type of installation being designed.
Standards for Maximum Demand
| Designation | Title | Application |
|---|---|---|
| AS/NZS 3000:2018 | Electrical Installations “Wiring Rules” | Appendix C - Circuit Arrangements Appendix C2 - Maximum Demand |
AS/NZS 3000:2018, also known as the Wiring Rules, is a joint Australian/New Zealand standard that outlines the requirements for electrical installations. This standard is crucial for maximum demand calculations as it provides the guidelines for determining the peak load of electrical installations.
AS/NZS 3000:2018 Clause 1.6.3 states:
"The maximum demand of an electrical installation shall be determined, taking account of capacity, physical distribution, and intended use of electrical equipment in the electrical installation and the manner in which the present requirements might vary."
Clause 2.2.2 of the same standard outlines the acceptable methods for determining maximum demand:
| Method | Description |
|---|---|
| Calculation | The maximum demand can be calculated by considering the relevant information available for a particular installation. Guidance on determining maximum demand is provided for basic electrical installations via tables in the Standards. |
| Assessment | The maximum demand may require a special assessment where the electrical installation is large and complex or special types of occupancy exist. |
| Measurement | The actual measured maximum demand is the most accurate, and the rules require it to be used as the maximum demand for an installation. It is measured by recording the highest rate of electricity consumption for an installation over a sustained period (30 minutes as per the Australian Wiring Rules AS/NZS 3000:2018) when demand is at its highest. |
| Limitation | The maximum demand for an installation may be determined as the sum of the current ratings or thermal settings of the circuit breakers protecting the installation. |
This section focuses on the calculation method, which is fundamental for determining the maximum demand current in consumers' mains and sub-mains, per Clause C2.2.
The calculation aims to select an appropriate cable for consumers' mains or sub-mains.
⚠️Note that the maximum demand calculation method does not apply to final circuits.
Appendix C for Maximum Demand Calculations
The guidance provided in Appendix C of AS/NZS 3000:2018 must be followed to calculate the maximum demand. There are numerous useful tables:
- Table C1 - Maximum demand (rules) for single and multiple domestic electrical installations.
- Table C2 - Maximum demand (rules) for non-domestic electrical installations.
- Table C3 - Maximum demand (rules) using the energy demand method for non-domestic installations.
- Table C4 - Upstream circuit loading after diversity (alternative method for switchboards).
- Table C5 - Maximum demand for domestic cooking appliances.
- Table C9 - Guidance on the loading of points per final subcircuit.
Steps for Maximum Demand Calculations
The following steps outline the process for calculating maximum demand:
Calculating Demand for Final Circuits
Table C9 of AS/NZS 3000:2018 guides the calculation of the maximum demand of final circuits and helps determine the demand contribution of individual load groups.
Practical Tips for Calculations
Multi-phase Installations
Multi-phase installations are required based on the equipment's characteristics (i.e., three-phase motors, instantaneous water heaters, three-phase welders, or significant heating and air-conditioning loads) and maximum demand.
ℹ️Two-phase or three-phase supplies are typically required where maximum demand exceeds 100 A.
When designing multi-phase systems, the maximum demand is taken as the current predicted to be on the highest loaded phase. This involves calculating the total load for each phase, identifying the phase with the highest current, and using this value for cable sizing and safety assessments.
Grid Connections
For installations with a maximum demand that exceeds a certain threshold (typically 100 A for single-phase and 63 A for three-phase installations), an application for connection (AFC) to the electricity distributor will be required. A maximum demand determination per AS/NZS 3000 must be provided as part of the application process.
⚠️Balancing of the loading across the phases for the maximum demand will be mandatory.
Once the electricity distributor approves, the maximum demand shown on the application form defaults to the approved ‘supply capacity’ for the installation.
Precision and Accuracy
When performing maximum demand calculations, it is typically acceptable to calculate to one decimal place. This level of precision is sufficient for determining the demand contributions of individual load groups.
It is also reasonable to round up the total maximum demand figure to the following whole number, as cable current-carrying capacities are generally specified as whole numbers.
Future Expansion and Safety Margins
When calculating the maximum demand of electrical installations, it is essential to account for potential future expansion to ensure that the infrastructure can accommodate additional loads without requiring significant upgrades. Additionally, incorporating a safety margin in these calculations provides an extra layer of security, ensuring that even unexpected increases in load can be managed effectively.