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. In Australia, AS/NZS 3000:2018 covers EV charging in Appendix P, which is informative guidance rather than a normative requirement. Appendix P4.1 recommends each connecting point be protected by its own RCD of at least Type A rated at not more than 30 mA, and that where the charging station uses an IEC 62196 socket outlet or vehicle connector, protection against DC fault current is also provided, either a Type B RCD or a Type A RCD plus equipment that disconnects the supply on DC fault current above 6 mA, unless the charging station already provides it. In New Zealand, Clause 7.9 is normative, and Clause 7.9.4 requires a Type B RCD complying with IEC/TR 62432 for all EV supplies in non-residential installations. The clause states the RCD type, not a milliamp rating. amendment of the Standard 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.

Parameters

Every field this calculator accepts, what it means, the range it accepts, and how it feeds the result. Three fields sit under Advanced options; two of them change the answer and one only triggers a warning.

Charger type (level 2 single phase, level 2 three phase, direct current fast)

Selecting a type presets the rating in the form to 7.4, 22 or 50 kilowatts. In the calculation itself it has exactly one effect: a direct current fast charger forces the recommended residual current device to Type B. It does not change the current, the cable, or the breaker.

Charger rating (kilowatts, 0.1 to 350)

The design current is derived straight from this figure, so enter the alternating current input rating from the equipment nameplate, not the vehicle side output. For a direct current fast charger the advertised kilowatt figure is direct current output and the alternating current input is different again, so for those units take the input current from the manufacturer data instead of trusting this field.

Supply phase and supply voltage (single phase 230 volts or three phase 400 volts)

Single phase divides the rating by the voltage; three phase divides by the voltage times the square root of 3. Only 230 and 400 volts are accepted, and the form sets the voltage automatically when you change the phase. Three phase also forces the residual current device recommendation to Type B.

Cable length (metres, 1 to 1,000, one way)

Route length from the switchboard to the charger, measured one way. The return path is already in the voltage drop multiplier, so do not double it. Measure the real route including the drop down the wall and any detour around the building, since the voltage drop check is usually what decides the cable size on domestic jobs.

Conductor material (copper or aluminium)

Aluminium multiplies both the current rating and the conductor resistance by 0.78. Lowering the rating is correct in direction. Lowering the resistance is not: aluminium resists more than copper, not less. See the limits below before using an aluminium result.

Installation method (clipped direct, enclosed in conduit, buried direct)

Recorded with the calculation and shown in saved history, but it does not change any output in this engine. The current ratings used are clipped direct figures throughout. If the run is in conduit in a wall or buried, apply the relevant derating yourself or size the run in the cable sizing calculator, which does model installation method.

Ambient temperature (degrees Celsius, 0 to 70, default 40)

The only derating the engine applies. The factor is the square root of 75 minus ambient, over 75 minus 40, which is the polyvinyl chloride 75 degree form. At 40 degrees the factor is exactly 1.000, at 45 degrees it is 0.926, at 50 degrees 0.845. A run through a roof space in an Australian summer should be entered at 45 to 50 degrees, not 40.

Maximum voltage drop (percent, 0.1 to 10, default 5)

The limit the selected cable must satisfy. The AS/NZS 3000 Clause 3.6 figure of 5 percent applies to the whole installation from the point of supply to the equipment, so if the consumer mains and submain have already used part of that budget, enter only what is left for this final subcircuit, commonly 2 to 3 percent.

Existing load (amperes, 0 to 100)

Only used to raise a warning when the charger is 2.4 kilowatts or less and could share a circuit. It does not perform a maximum demand calculation and it does not check the mains or main switch capacity. For anything above 2.4 kilowatts it has no effect at all beyond one compliance line.

Assumptions and limits

This sizes a cable and picks a breaker for one dedicated charger circuit. Here is exactly what it assumes and where it stops.

What it assumes

• Design current is the plain rating divided by voltage. No continuous load uplift, no 125 percent factor, no diversity, no allowance for a charger that draws slightly above nameplate. A 7.4 kilowatt unit at 230 volts gives 32.2 amperes and nothing more is added.
• Cable selection walks the standard sizes and stops at the first that fits. It must satisfy the derated current capacity and the voltage drop limit. Base ratings are the engine placeholder copper clipped direct figures at 40 degrees Celsius, not transcribed from a licensed copy of AS/NZS 3008.1.1.
• Only ambient temperature derating is applied. No grouping factor for other circuits in the same enclosure, no thermal insulation factor, no burial depth or soil resistivity, no installation method column. The polyvinyl chloride 75 degree form is used regardless of whether the cable is actually cross linked polyethylene.
• Voltage drop uses resistance only. No reactance and no power factor, at an assumed conductor temperature of 75 degrees Celsius.
• The three phase voltage drop multiplier is 1, not the square root of 3. The percentage is also taken against the 400 volt line voltage. The conventional form is the square root of 3 times current times resistance times length, so three phase drop reported here is roughly 1.7 times optimistic. Re check any three phase run in the voltage drop or cable sizing calculator before you commit to a size.
• Aluminium resistance is scaled the wrong way. The same 0.78 factor is applied to both the rating and the resistance, so aluminium voltage drop comes out lower than copper when it should be roughly 1.6 times higher. Do not size an aluminium run from this tool without checking the resistance against manufacturer data.
• The residual current device rule is deliberately simple. Type B for a direct current fast charger or any three phase supply, Type A otherwise. That is a rule of thumb in code, not a reading of AS/NZS 3000 Appendix P, which is informative in Australia, or of the normative New Zealand Clause 7.9. Many chargers include their own direct current fault detection which changes the answer. Read the standard and the equipment datasheet.

What it does not do

• It does not check that the breaker is at or below the cable capacity, does not select a tripping curve, and does not do discrimination with upstream devices.
• It does not calculate earth fault loop impedance or maximum disconnection time, and it does not size the protective earthing conductor.
• It does not do a maximum demand calculation, so it will not tell you whether the mains, main switch or supply can carry the extra load. That is often the real constraint on an older home.
• It does not cover load management or dynamic current limiting, multiple chargers on a shared supply, isolation and switching arrangements, ingress protection, mechanical protection, or the socket outlet arrangements used for Mode 2 charging.
• It does not produce a certificate of compliance or anything a distributor will accept as an application.

Check every result against the current editions of AS/NZS 3000, AS/NZS 3001.1 and AS/NZS 3008.1.1, and have the design signed off by the person responsible for the installation. Nothing here is validated or certified, and the underlying figures have not been reviewed by a chartered professional engineer.

Worked examples

Three complete runs with every intermediate figure shown, so you can check the tool against your own arithmetic.