EV Charger Wire Size by Power and Cable Run Length (Tables)

Short answer: pick the cable by current (it must not overheat) and then check voltage drop (the run must not be too long). For a 7.4 kW single-phase charger (32 A) a 6 mm² copper cable is the usual starting point; for an 11 kW three-phase charger (16 A per phase) 2.5–4 mm²; for 22 kW (32 A per phase) 6 mm². In North America the breaker is 125% of the charger current. The tables below are indicative — the electrician decides.

Step 1: Charger current

Charger	Supply	Current	Typical protective device
3.7 kW	230 V single phase	16 A	16 A
7.4 kW	230 V single phase	32 A	32 A
11 kW	400 V three phase	16 A per phase	16 A
22 kW	400 V three phase	32 A per phase	32 A
40 kW AC / small DC input	400 V three phase	about 63 A	80 A

Step 2: Cable size for the current (IEC, copper)

An EV charger is a continuous load, so base the size on the cable running at full current for several hours. Indicative values for copper conductors in common installation methods (conduit on a wall, or clipped direct), 30 °C ambient, a single circuit:

Current	Typical copper size
16 A	2.5 mm²
32 A	6 mm²
40 A	10 mm²
63 A	16 mm²
80 A	25 mm²

Grouping cables, burying them in insulation or hot ambient temperatures reduce capacity — the size goes up. The installation standard (IEC 60364) and local rules give the correction factors.

Step 3: Maximum run length for voltage drop

The longer the run, the higher the drop. Keeping drop to 3% is a common design target. The table shows the maximum one-way length for copper at an operating temperature of 70 °C.

Single-phase 230 V

Current	2.5 mm²	4 mm²	6 mm²	10 mm²	16 mm²
16 A	24 m	38 m	58 m	—	—
32 A	—	—	29 m	48 m	77 m
40 A	—	—	—	38 m	61 m

Three-phase 400 V

Current per phase	2.5 mm²	4 mm²	6 mm²	10 mm²	16 mm²	25 mm²	35 mm²
16 A	48 m	77 m	—	—	—	—	—
32 A	—	—	58 m	96 m	154 m	—	—
63 A	—	—	—	—	78 m	122 m	171 m

A dash means the size is too small for that current. The formula behind the table is simple:

• Single phase: drop (V) = 2 × length × current × resistance per metre
• Three phase: drop (V) = 1.73 × length × current × resistance per metre

Copper resistance is about 0.0225 Ω·mm²/m at 70 °C; divide by the conductor area. Example: 32 A, 6 mm², 25 m, single phase gives 2 × 25 × 32 × (0.0225 ÷ 6) = 6.0 V, which is 2.6% of 230 V.

North America: NEC and AWG

In the US and Canada, an EV charger is a continuous load: the branch circuit and breaker are sized at 125% of the charger’s rated current (NEC Article 625). Typical copper conductors at 75 °C terminals:

Charger current	Breaker	Copper conductor
16 A	20 A	12 AWG
32 A	40 A	8 AWG
40 A	50 A	8 AWG
48 A	60 A	6 AWG

For voltage drop, the NEC gives an informational target of 3% on a branch circuit and 5% overall. Aluminium conductors need a larger size and suitable terminals. Always follow the code edition and local amendments.

Practical advice

1. Upsize one step for runs near the length limit, for multi-charger sites or if you may upgrade the charger later.
2. Use the charger’s terminal range. Check the maximum cable size the charger’s terminals accept; a very large cable may need a junction box.
3. Do not forget earth and neutral. Use the same size for the neutral on single-phase circuits; the earth conductor follows the code.
4. Think about the protection. The breaker must protect the cable; see RCD requirements and surge protection.
5. Use a calculator for the final numbers — see the breaker and cable size calculator once it is published, and the installation requirements guide.

Supply, not only cable

The supply must carry the load. If the charger shares a supply with the building, dynamic load management can reduce the cable and the supply upgrade you need. And if your supply is single phase, a 22 kW charger will deliver only about 7.4 kW — see single-phase vs three-phase.