Cable size, voltage drop, max demand and kW ↔ amps — sorted in seconds.
Four calculators based on AS/NZS 3000 and AS/NZS 3008 methodology. Voltage drop limit is 5% of nominal supply voltage (11.5 V on 230 V single-phase). Copper conductors at 75°C operating temperature.
Single domestic installation — AS/NZS 3000 Appendix C, Table C1 methodology. Enter what's connected; factors apply automatically.
Enter any one of kW, kVA or amps — the other two update live. Real power (kW) uses power factor; apparent power (kVA) does not.
Power factor guide: resistive loads (heaters, ovens) ≈ 1.0; motors, aircon and mixed loads ≈ 0.8. DC has no power factor and no kVA.
Current-carrying capacity, copper V-90 (A)
| Size mm² | Clipped direct | In conduit | Partial thermal insulation | mV/A·m (1φ) | mV/A·m (3φ) |
|---|
Single circuit, 40°C ambient, guide values only. mV/A·m derived from conductor resistance at 75°C, unity power factor — matches AS/NZS 3008 tabulated values within ~2% up to 35 mm²; above 50 mm² cable reactance adds to the tabulated figure, so check the standard.
Voltage drop and cable sizing, plainly.
What's the maximum voltage drop allowed?
AS/NZS 3000 requires no more than 5% below nominal supply voltage at any point of the installation — 11.5 V on 230 V single-phase, 20 V on 400 V three-phase. A common design split is 2% for mains and submains, 3% for final subcircuits.
How is voltage drop calculated?
Vd = current × route length × the cable's mV/A·m value ÷ 1000. A 32 A load over 25 m of 6 mm² copper (~7.5 mV/A·m single-phase) drops about 6 V — 2.6% of 230 V, so it passes a 3% subcircuit limit with little margin.
What cable size for a 7 kW EV charger?
About 32 A continuous. 6 mm² copper suits short dedicated runs; voltage drop typically pushes 30–40 m runs to 10 mm². Planning one? We match EV charger installers in Adelaide.
Why does max demand matter?
Calculated maximum demand sizes your consumer mains, main switch and switchboard. Adding an EV charger or big aircon can tip an older 63 A supply over its limit — that's when a switchboard upgrade conversation starts.
How do I convert kW to amps?
Single-phase: amps = 1000 × kW ÷ (V × PF). Three-phase: amps = 1000 × kW ÷ (√3 × V × PF). DC: amps = 1000 × kW ÷ V. So 10 kW single-phase at 230 V, PF 0.8, draws about 54 A. The converter tab does it both ways.
What's the difference between kW and kVA?
kVA is apparent power (volts × amps); kW is real power (kVA × power factor). They're equal only when power factor is 1. Switchboards and supply are sized on kVA/amps, so amps ↔ kVA is the conversion that sizes the main switch.