EV Charger Cable Sizing

EV Charger Installation Guide for AS/NZS 3000:2018

Electric vehicle charger installations are one of the fastest-growing areas of electrical work in Australia. Every EV charger requires a dedicated circuit designed to handle continuous loading (100 percent demand factor), which means cable sizing, protection, and maximum demand calculations are more critical than for most household appliances. This calculator sizes the cable and circuit breaker for an EV charger installation based on charger rating, supply phase, cable run length, installation method, and ambient temperature.

The tool applies the requirements of AS/NZS 3000:2018 for general wiring rules and AS/NZS 3001.1 for transportable structures and vehicle charging. It checks current-carrying capacity per AS/NZS 3008.1.1, voltage drop against the 5% limit in Clause 3.6, and recommends RCD type based on the charger configuration.

Key concepts

• Continuous load rating. EV chargers are classified as continuous loads because they can draw full rated current for hours at a time. This means the cable and protective device must be rated for 100 percent of the charger current with no diversity reduction. A 32 A charger requires a cable and breaker rated for at least 32 A continuously.
• RCD type selection. AS/NZS 3000 requires a minimum Type A RCD for EV charging circuits. If the charger does not include built-in DC fault detection (check the manufacturer datasheet), a Type B RCD must be installed externally. Most Mode 3 chargers rated above 16 A include internal DC leakage detection, but this must be confirmed before relying on a Type A RCD alone.
• Voltage drop. Long cable runs from the switchboard to the garage or carport are common in residential installations. The 5% voltage drop limit (11.5 V on a 230 V circuit) can force a cable size upgrade from 6 mm squared to 10 mm squared on runs longer than approximately 25 metres for a 32 A load.
• Maximum demand impact. Adding an EV charger increases the property maximum demand by the full charger rating (for example, 7.4 kW for a 32 A single-phase unit). Older homes with 63 A or 80 A mains may need a main switch or supply cable upgrade before the charger can be installed.

Common scenarios

1. Residential garage, 32 A single-phase. A homeowner wants a 7.4 kW wall-mounted Mode 3 charger installed in a detached garage, 30 metres from the switchboard. The cable run passes through the roof space (40 degrees Celsius ambient). At 32 A continuous, 6 mm squared copper is adequate for current but exceeds the 5% voltage drop limit at 30 m. The calculator recommends upgrading to 10 mm squared, with a 40 A Type A RCD and 32 A curve B MCB.
2. Commercial car park, three-phase 22 kW. A workplace installs a 32 A three-phase charger on a 35 metre run from the distribution board. Three-phase voltage drop is lower than single-phase for the same current, so 6 mm squared four-core cable is typically sufficient. The circuit requires a Type B RCD (or Type A if the charger has internal DC detection) and a 40 A four-pole MCB.
3. Older home, mains capacity check. A 1990s house with a 63 A single-phase main switch already has 45 A of existing maximum demand. Adding a 32 A EV charger takes the total to 77 A, exceeding the 63 A main switch. The calculator flags this, and the electrician must arrange a mains upgrade with the distribution network service provider before installing the charger.