What Size Wire for an EV Charger?

EV charging is a continuous load, so the circuit is sized at 125% of the charger current. A 32 A charger needs a 40 A breaker and 8 AWG copper. A 40 A charger needs a 50 A breaker with 8 AWG THHN in conduit or 6 AWG NM cable. A 48 A charger needs a 60 A breaker and 6 AWG.

The answer

40 A, 50 ft one way, 240 V, continuous load

8 AWG copper

THHN in conduit with 75 °C terminals

6 AWG copper

for NM (Romex) cable or 60 °C terminals

6 AWG aluminum (75 °C terminals)

Breaker and smallest wire for a 240 V EV charger (continuous load, 3% drop), by charger current and length
Case BreakerCopper · 75 °CCopper · NM / 60 °CAluminum · 75 °CDrop at copper size
16 A charger 50 ft run 20 A12 AWG 12 AWG 10 AWG1.3%
24 A charger 50 ft run 30 A10 AWG 10 AWG 8 AWG1.2%
32 A charger 50 ft run 40 A8 AWG 8 AWG 8 AWG1.0%
40 A charger 50 ft run 50 A8 AWG 6 AWG 6 AWG1.3%
48 A charger 50 ft run 60 A6 AWG 4 AWG 4 AWG1.0%
32 A charger 100 ft run 40 A8 AWG 8 AWG 6 AWG2.1%
40 A charger 100 ft run 50 A8 AWG 6 AWG 6 AWG2.6%
48 A charger 100 ft run 60 A6 AWG 4 AWG 4 AWG2.0%

Calculate for your exact distance

On this page

The 125% rule: charger amps versus breaker size

A charger that runs for three hours or more counts as a continuous load, so the circuit has to be sized at 125% of the charger current (NEC 210.19). That is why the breaker is a size above the charger rating: 16 A needs a 20 A breaker, 24 A needs 30 A, 32 A needs 40 A, 40 A needs 50 A and 48 A needs 60 A. Many plug-in chargers can be set to a lower current, which lets you use a smaller circuit.

NM cable or conduit?

NM (Romex) cable is sized from the 60 °C column of NEC Table 310.16 (NEC 334.80), which makes the wire one size larger than THHN in conduit on some circuits. At 40 A, that means 8 AWG in conduit with 75 °C terminals but 6 AWG in NM cable, and at 48 A it means 6 AWG in conduit but 4 AWG in NM cable. The table above shows both.

A 14-50 outlet or a hardwired charger

A 14-50 outlet sits on a 50 amp circuit, which supports a plug-in charger drawing up to 40 A (40 × 1.25 = 50). A hardwired charger can use the full circuit rating, so a 48 A unit on a 60 amp breaker is possible when the wire and panel allow it. Whichever you choose, the charger's installation manual and your local code decide the final circuit.

Long runs from the panel to the garage

Charging at full current for hours makes voltage drop worth checking. At 100 ft the copper sizes in the table stay the same as at 50 ft, because ampacity still decides them, but aluminum steps up one size for the 32 A charger. A permit and a licensed electrician are normal for EV circuits: confirm the load, the panel capacity and local rules before you buy wire.

How these sizes are worked out
  • Each size is the smallest copper or aluminum wire that meets two limits: the table ampacity for the breaker (NEC Table 310.16, with the NEC 240.4(D) small-conductor limits) and a 3% voltage drop. The larger of the two is shown.
  • Copper is shown for 75 °C terminals and for NM (Romex) cable or 60 °C terminals, and aluminum for 75 °C terminals. Continuous loads such as EV chargers are sized at 125% of the load (NEC 210.19).
  • Voltage drop uses conductor resistance only, with the wire at 75 °C. Reactance is ignored, which is accurate for short runs.
  • No ambient temperature or bundling derating is applied. Hot locations and conduits with many current-carrying conductors need larger wire.
  • This is general information, not a substitute for a licensed electrician or your local code. Read the disclaimer, or use the wire size calculator for your exact run.

This is general information based on NEC tables, not a permit or an installation plan. Local amendments, the equipment nameplate and an inspector decide what is acceptable. Read the disclaimer.

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