EV charger breaker and cable size calculator
Enter the charger current, supply and run length. The tool suggests a breaker rating and a copper or aluminium cable size, and shows the voltage drop. It is a planning aid; the electrician sizes the final circuit.
Circuit details
Use 125 % of the charger current in North America automatically. Example values: 16 A (3.7 kW or 11 kW three phase), 32 A (7.4 kW single phase or 22 kW three phase), 48 A (11.5 kW at 240 V).
Result
Suggested breaker
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Suggested cable (per conductor)
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- Charger power
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- Voltage drop with this cable
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- Size for ampacity
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- Size for voltage drop
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How the calculation works
Current: the breaker is the next standard size at or above the charger’s rated current (or 125 % of it in North America). The cable must carry at least the breaker rating, using approximate ampacity tables: copper in conduit on a wall at 30 °C for IEC, and copper at 75 °C terminals for North American AWG sizes. Aluminium is derated to about 78 % of copper.
Voltage drop: drop = k × length × current × resistivity ÷ area, with k = 2 for single phase and 1.73 for three phase. Resistivity is taken at about 70 °C. The tool shows the drop for the suggested size.
What it does not include: grouping and insulation derating, buried cables, harmonic currents, short-circuit withstand, earth conductor sizing and local code rules. See the wire size article for worked tables, and the installation requirements guide for the other protection elements.
Related guides
Questions
What breaker size do I need for a 7.4 kW EV charger?
A 7.4 kW single-phase charger draws 32 A on a 230 V supply, so a 32 A breaker is normal in IEC countries. In North America a 32 A charger on a 240 V circuit uses a 40 A breaker because continuous loads are sized at 125 %.
Which cable size should I use for a 22 kW charger?
A 22 kW three-phase charger draws 32 A per phase. About 6 mm² copper suits runs up to roughly 50 m; 10 mm² suits longer runs. The calculator checks both current capacity and voltage drop.
Why does the result change with cable length?
A longer cable has more resistance, so the voltage at the charger drops. The tool picks the larger of the size needed for current and the size needed to keep the drop under your limit.
Is this calculator enough to wire a charger?
No. It is a planning aid. The installer must size the circuit to the local code, installation method, ambient temperature, cable grouping and the protective devices, and must test the installation.
Need help with the electrical design?
Send us the charger model, supply and cable run. Our engineers will check the circuit with you before you order.