Electrical Cable Size Calculator
Calculate minimum cable size, voltage drop, and current capacity for Australian electrical installations. Based on AS/NZS 3008 cable selection principles.
Disclaimer: This calculator provides estimates for guidance only. All electrical work in Australia must comply with AS/NZS 3000 and AS/NZS 3008 and be performed by a licensed electrician.
All Cable Sizes Comparison
| Size (mm²) | Voltage Drop (V) | Voltage Drop (%) | Current Capacity (A) | VD Status | Capacity Status |
|---|---|---|---|---|---|
| 1 | 67.58 | 29.38% | 14 | FAIL | FAIL |
| 1.5 | 44.54 | 19.37% | 17.5 | FAIL | FAIL |
| 2.5 | 27.65 | 12.02% | 24 | FAIL | FAIL |
| 4 | 16.90 | 7.35% | 32 | FAIL | PASS |
| 6Recommended | 11.21 | 4.88% | 41 | PASS | PASS |
| 10 | 6.76 | 2.94% | 56 | PASS | PASS |
| 16 | 4.30 | 1.87% | 73 | PASS | PASS |
| 25 | 2.69 | 1.17% | 97 | PASS | PASS |
| 35 | 1.92 | 0.83% | 119 | PASS | PASS |
| 50 | 1.35 | 0.59% | 144 | PASS | PASS |
| 70 | 0.97 | 0.42% | 184 | PASS | PASS |
| 95 | 0.71 | 0.31% | 222 | PASS | PASS |
| 120 | 0.57 | 0.25% | 259 | PASS | PASS |
| 150 | 0.46 | 0.20% | 294 | PASS | PASS |
| 185 | 0.38 | 0.16% | 336 | PASS | PASS |
| 240 | 0.29 | 0.13% | 392 | PASS | PASS |
| 300 | 0.24 | 0.10% | 446 | PASS | PASS |
How to Use This Cable Size Calculator
- Select the supply voltage and phase configuration (230V single phase or 400V three phase).
- Choose the cable material: copper (most common for residential) or aluminium (common for larger submains).
- Enter the circuit current in amps and the one-way cable length in metres.
- Select the installation method (conduit, clipped direct, cable tray, or underground).
- Adjust the power factor and maximum voltage drop percentage if needed (defaults are 0.8 and 5% per AS/NZS 3000).
- The calculator instantly displays the minimum cable size, voltage drop, current capacity, and a comparison table of all standard sizes.
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Frequently Asked Questions
What is the maximum voltage drop allowed in Australia?
Under AS/NZS 3000 (the Australian Wiring Rules), the maximum allowable voltage drop from the point of supply to the final subcircuit is 5%. This is typically split as 2% for the consumer mains (from point of supply to the main switchboard) and 3% for submains and final subcircuits combined. Keeping voltage drop within limits ensures equipment operates correctly and prevents excessive energy losses in the cabling.
What cable size do I need for a 32A circuit?
The required cable size for a 32A circuit depends on the cable run length, installation method, and allowable voltage drop. For short runs under 15 metres installed in conduit, 4mm² copper cable is often sufficient. However, for longer runs of 30 metres or more, you may need 6mm² or 10mm² to keep the voltage drop within the 5% limit. Always verify using AS/NZS 3008 tables and consult a licensed electrician for final cable selection.
What is AS/NZS 3008?
AS/NZS 3008 (Electrical installations — Selection of cables) is the Australian and New Zealand Standard that provides detailed guidance for cable selection. It contains tables for current-carrying capacity, voltage drop, short-circuit capacity, and earth fault loop impedance for various cable types, sizes, and installation methods. Licensed electricians and electrical engineers use this standard alongside AS/NZS 3000 (Wiring Rules) to ensure safe and compliant electrical installations.
Copper vs aluminium cable — which should I use?
Copper cable is the standard choice for residential and light commercial installations in Australia. It offers superior conductivity, requires smaller cable sizes for the same current rating, and is easier to terminate. Aluminium cable is more cost-effective for larger installations such as consumer mains and submains (typically 35mm² and above) and is widely used for overhead lines and underground distribution networks. Aluminium requires larger cross-sectional areas than copper for equivalent current capacity and has specific termination requirements to prevent issues with oxidation and thermal expansion.
Cable Sizing in Australian Electrical Installations
Cable sizing is a fundamental aspect of electrical design in Australia, governed primarily by two key standards: AS/NZS 3000 (Wiring Rules) and AS/NZS 3008 (Selection of Cables). Correct cable sizing ensures that circuits can safely carry the required load current without overheating, that voltage at the point of use remains within acceptable limits, and that protective devices can operate correctly under fault conditions. Undersized cables can lead to excessive heat generation, insulation degradation, fire risk, and poor equipment performance due to low voltage.
The two primary factors in cable selection are current-carrying capacity and voltage drop. Current-carrying capacity (or ampacity) is the maximum current a cable can continuously carry without exceeding its rated temperature. This depends on the cable construction, insulation type, installation method, ambient temperature, and grouping with other cables. AS/NZS 3008 provides detailed tables for each combination of these factors. For example, a cable enclosed in conduit has lower capacity than one clipped directly to a wall, because the conduit restricts heat dissipation.
Voltage drop is the reduction in voltage along the length of a cable due to its inherent resistance and reactance. Long cable runs with high currents experience greater voltage drop, which can cause motors to run slowly, lights to dim, and sensitive electronics to malfunction. AS/NZS 3000 limits the total voltage drop from the point of supply to any point of use to 5% of the nominal voltage. In practice, this means designers must balance cable size against run length — longer circuits require larger cables to maintain adequate voltage at the load.
Australian cable sizes follow a standardised series measured in square millimetres (mm²) of conductor cross-sectional area. The common sizes range from 1mm² for light-duty circuits up to 300mm² and beyond for heavy industrial feeders. Residential installations typically use 1.5mm² for lighting circuits, 2.5mm² for general power outlets, and 4mm² to 6mm² for dedicated appliance circuits such as ovens, cooktops, and air conditioners. Submains and consumer mains cables are commonly 16mm² to 70mm² depending on the total load of the installation.
Beyond current capacity and voltage drop, electricians must also consider short-circuit withstand capability, earth fault loop impedance (to ensure protective devices trip within required timeframes), and any applicable derating factors for ambient temperature, cable grouping, or thermal insulation. While this calculator provides a useful starting point for cable selection, a full design must account for all of these factors in accordance with AS/NZS 3008 and should always be verified by a licensed electrical professional.