Voltage Drop Calculator Australia

AS/NZS 3000 Clause 3.6 allows a maximum total voltage drop of 5% from the point of supply to the furthest point of the installation. Some supply authorities require a tighter split — for example, Ausgrid in NSW requires no more than 5% total but recommends 2% on consumer mains and 3% on sub-circuits. Check your local distributor's service rules for any specific requirements.

Yes. In a single-phase circuit, current flows out through the active and returns through the neutral. Both conductors have resistance, so voltage is dropped across both. The single-phase mV/A·m values in AS/NZS 3008 already account for the loop resistance of both the active and neutral conductors, so you only need to multiply by the one-way route distance.

Current-carrying capacity and voltage drop are independent checks. A cable can be perfectly safe to carry the load current without overheating, but still drop too much voltage over a long distance. On runs beyond 30 metres, voltage drop regularly becomes the controlling factor and forces you to select a larger cable than current alone requires.

The formula is similar to single-phase, but you multiply by √3 (1.732) instead of 2, and reference 400V line-to-line instead of 230V. Three-phase circuits have inherently lower percentage drops because the denominator is larger (400V vs 230V) and the multiplier is smaller (1.732 vs 2). A circuit that fails at single-phase might pass comfortably on three-phase.

mV/A·m stands for millivolts per ampere per metre. It is a combined measure of how much voltage a cable drops per amp of current per metre of length. These values are published in AS/NZS 3008 Tables 35 to 42 and vary depending on cable size, conductor material (copper vs aluminium), insulation type, and whether you use resistance-only or impedance values. For cables up to 16 mm², resistance-only values are accurate enough. For larger cables, impedance values at the circuit's power factor give a better result.

Yes. The single-phase mV/A·m value in our calculator includes the loop impedance — active out and neutral return. You only enter the one-way route distance, and the calculation handles the loop internally.

The installation does not comply with AS/NZS 3000. If an inspector checks and finds the drop exceeds the limit, you may be required to re-cable the run with a larger conductor before the installation can be certified. The load will also underperform — motors run hotter, heaters deliver less output, and LED drivers may flicker or fail prematurely.

For cables 16 mm² and smaller, resistance alone gives an accurate enough result because the inductive reactance of small conductors is negligible. For cables 25 mm² and larger, the reactance component becomes significant — especially on long runs at low power factors. Use impedance values (which combine resistance and reactance at a given power factor) for large cables. This calculator uses the appropriate method based on the selected cable size.

Power factor affects the impedance-based component of voltage drop. At unity power factor (PF = 1.0), only resistance matters. As the power factor drops below 1.0 (common with motor and fluorescent lighting loads), the reactive component of impedance increases the total drop. A circuit running at PF 0.8 will have a noticeably higher voltage drop than the same circuit at PF 1.0 — especially on larger cable sizes where reactance is not negligible.

Yes, and many sparkies do this in practice. A common split is 2% on the consumer mains (from the meter to the main switchboard) and 3% on the final sub-circuits. The standard does not mandate this split — it only requires the total end-to-end drop to stay within 5%. But planning a split helps you size the mains and sub-circuit cables independently without accidentally using up the entire budget on one section.

Solar DC cables between the PV array and the inverter are governed by AS/NZS 5033, which sets a stricter limit of 3% voltage drop (some CEC guidelines recommend even lower). This is tighter than the general 5% limit in AS/NZS 3000 because DC voltage drop directly reduces the array's power output and efficiency. Use our Solar DC Cable Calculator for those specific calcs.

Yes, indirectly. Conductor resistance increases with temperature — copper at 75°C has roughly 18% higher resistance than at 20°C. The mV/A·m values in AS/NZS 3008 are published at the cable's maximum operating temperature (75°C for PVC, 90°C for XLPE), so they already represent the worst-case resistance. In practice, if the cable runs cooler than its rated temperature (because it is lightly loaded), the actual voltage drop will be slightly lower than calculated.