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Cable Size Calculator AS3008
This free electrical calculator determines the minimum cable size based on current-carrying capacity and voltage drop.
The calculations comply with Australian Standard AS/NZS 3008.1.1.
Your Calculated Cable Size Is:
The table number used from Standard AS/NZS 3008.1.1:2017 is provided with the result for your reference and checking of the results by you.
**Disclaimer**: Our electrical calculators are intended for use by qualified electrical professionals only. While we strive to provide accurate and up-to-date information, these tools are provided as a guide and should not replace professional judgment or compliance with relevant standards and regulations. Users must verify the results independently and assume full responsibility for their application.
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How to use
Calculator inputs explained
Voltage (V)
- The voltage is used to calculate the actual percentage voltage drop.
- By default, the supply voltage is 230 V for single phase and 400 V for 3-phase loads.
- In Australia and New Zealand, the nominal voltage for low-voltage systems and electrical installations is 230/400 V, as per the Wiring Rules AS/NZS 3000:2018.
Phase
- Select the phase arrangement to match the load. The options available are single-phase AC, three-phase AC, two-phase AC, or DC.
- This phase arrangement affects the voltage drop calculation because different voltage drop equations are used.
- Cable Pro Software performs more accurate voltage drop calculations than this calculator does, resulting in smaller cable sizes.
- Three-phase AC is used for larger loads and consumer mains. Balanced three-phase conditions are assumed, meaning the current in each of the three phases is the same.
- To calculate the voltage drop for an unbalanced three-phase load, a conservative approach is to assume a balanced three-phase load condition and perform calculations using the current flowing in the heaviest-loaded phase.
Load
- The load determines the current-carrying capacity of the cable. The load is specified in Amps, kilowatts, kVA, or horsepower.
- For a three-phase load, this should be the current of the highest-loaded phase or the total power on all the phases.
Maximum voltage drop (%)
- Section 3.6 in AS/NZS 3000:2018 covers the rules for Voltage Drop in low-voltage installations.
- The cable size will also be determined by the maximum allowable voltage drop limit.
- The voltage drop between the point of supply for the low voltage electrical installation and any point in that electrical installation must not exceed 5% of the nominal voltage of the point of supply.
- Where the point of supply is the low voltage terminals of a substation located on the premises containing the electrical installation and dedicated to the installation, the permissible voltage drop may be increased to 7%.
- Useful rules of thumb for voltage drop are to allow 0.5% for consumers mains, 1.5-2% for sub-mains, and 2.5 % for final subcircuits.
- Refer to our article Voltage drop limits for low voltage installations.
Power factor
- A poor power factor will result in a higher voltage drop, especially for large cable sizes (because their impedance is highly reactive).
- Enter the load power factor (assumed lagging). The power factor is used for accurate voltage drop calculations.
Cable length (m)
- The cable return path length is automatically included with the voltage drop calculations for single-phase loads.
- This is the distance between the supply point and the load location.
Conductor
- You can select the conductor material of the cable. The type of conductor, due to different impedance values, affects the current-carrying capacity and the voltage drop of the cable.
Insulation
- The cable's insulation material affects the maximum allowable operating temperature and, hence, the current rating.
- Cables with a higher allowable temperature (which depends on the insulation type) will have a higher current rating.
Installation
- Select the cable circuit's installation method that matches your installation.
- If the installation method changes along its route, choose the worst-case scenario (resulting in the lowest possible current rating) along its entire length. Typically, buried cable sections will have a lower current rating than those installed in the free air.
Frequently asked questions
What voltage drop (%) should be used?
- You should enter an allowable voltage drop limit considering your installation's maximum allowable voltage drop limit.
- The minimum cable size will be dictated by the voltage drop for circuits that are long or carry a small load current.
- The maximum allowable voltage drop limits for an electrical installation are covered by the standard AS/NZS 3000.
- Please take a look at the article Voltage drop limits for electrical installations.
How do I calculate multiple parallel circuits?
- The minimum cable size may consist of multiple parallel cables. You can increase the number of parallel conductors to reduce the active cable size.
- For example, a compliant cable size solution may be 1 x 630 mm2 or 2 x 185 mm2. Each solution can carry 1014 A and 918 A, respectively.
- This free calculator can only automatically size one cable per phase.
- You can use Cable Pro Web Software for multiple parallel cables per phase.
How can I determine a derating factor?
- The standards provide derating factor tables for the cable current ratings when your project's installation conditions differ from the standard conditions. You can determine derating factors from the standards tables.
- This article provides derating factor tables from standards.
- Cable Pro Web Software has a simple-to-use Wizard for derating factors.
How do I calculate voltage rise instead of voltage drop?
- Voltage rise is not different to voltage drop calculations.
- Voltage rise occurs in solar PV systems on the AC side between the power inverters and the network connection when power flows from the inverter back into the network.
- Australian standards and state regulations cover the requirements and limits for voltage rise. Refer to the article Voltage rise calculations.
- Cable Pro Software has a selection for voltage rise (%).
How do I enter a 3-phase current?
- The load current you enter for the cable sizing calculations is the maximum load current per phase.
- So for a 3 phase supply the load current would be the load on the phase which carries the highest load current (highest loaded phase).
Can I calculate the size for flexible aluminium cables?
- Cables with flexible aluminium conductors are popular nowadays. However, the standards do not provide current ratings or voltage drop values.
- Cable Pro Software supports flexible aluminium cables.
What should I enter for power factor?
- Poor power factor affects cable size significantly because it increases voltage drop, especially for large cables (they have high reactance).
- The Service and Installation Rules of New South Wales require that an electrical installation must have a power factor of 0.9 or greater lagging.
How do I calculate the cable size for an unbalanced 3-phase system?
- An approach to calculating the voltage drop for an unbalanced three-phase load is to assume a balanced three-phase load condition and perform calculations using the current flowing in the heaviest-loaded phase.
- In this case, voltage drop calculations can be performed by selecting phases as single-phase.