Voltage Drop Calculator Australia — AS/NZS 3000AS/NZS 3000
Circuit details
Measure the one-way cable route. The calculator doubles this for single-phase (live + neutral return).
Voltage drop
Circuit details
Result
Minimum compliant cable size
✓ Compliant — AS/NZS 3000 Clause 3.6.2
⚠ Non-compliant — AS/NZS 3000 Clause 3.6.2
This voltage drop calculator uses the formula specified in AS/NZS 3000:2018 (Australian/New Zealand Wiring Rules). Voltage drop is calculated as Vd = ρ × L × I / A, where ρ is the conductor resistivity at 75°C operating temperature (0.0225 Ω·mm²/m for copper, 0.0357 Ω·mm²/m for aluminium), L is the total conductor length (doubled for single-phase to account for the return path, or multiplied by √3 for three-phase), I is the design current in amps, and A is the conductor cross-sectional area in mm². The result is compared against the AS/NZS 3000 Clause 3.6.2 limit of 5% of the nominal supply voltage — 11.5 V for 230 V single-phase circuits.
Frequently Asked Questions
What is the maximum voltage drop allowed in Australia under AS/NZS 3000?
AS/NZS 3000:2018 Clause 3.6.2 sets the maximum allowable voltage drop at 5% of the nominal supply voltage from the point of supply to any point of utilisation. For a standard 230 V single-phase supply this is 11.5 V. For 400 V three-phase (line-to-line), it is 20 V. Many designers use 2.5% for sub-mains and 2.5% for final circuits to stay within the 5% total.
Why does voltage drop matter?
Excessive voltage drop causes equipment to run at reduced voltage, which can lead to overheating in motors, poor lighting output, nuisance tripping of sensitive electronics, and reduced efficiency. For motors, even a 5% drop in voltage can cause a 10% reduction in torque output and significant heating. For long cable runs to outbuildings, pumps, or sub-boards, voltage drop is often the limiting factor in cable sizing, not current-carrying capacity.
How do I reduce voltage drop on a long cable run?
The most effective ways are: (1) increase the cable cross-sectional area — doubling the CSA halves the voltage drop; (2) reduce the current by splitting the circuit; (3) increase the supply voltage where permitted; or (4) use three-phase instead of single-phase for long runs, as three-phase has a lower voltage drop per amp for the same CSA. Moving the switchboard closer to the load is also effective.
What conductor resistivity does this calculator use?
The calculator uses ρ = 0.0225 Ω·mm²/m for copper and 0.0357 Ω·mm²/m for aluminium at an assumed conductor operating temperature of 75°C, consistent with the values in AS/NZS 3008.1.1 (Selection of Cables). These figures are slightly higher than the 20°C DC resistance values to account for the increased resistivity at operating temperature.
Does voltage drop affect my circuit breaker sizing?
Voltage drop and circuit breaker (overcurrent protection) sizing are separate calculations in AS/NZS 3000. The circuit breaker is sized for overcurrent protection, not voltage drop. However, a cable sized purely for current-carrying capacity may still fail the voltage drop check on a long run, requiring an upgrade to a larger cable — with the breaker adjusted accordingly if the cable rating changes significantly.