How to Size Wire for a 50-Amp EV Charger
A "50-amp charger" is usually a 40-amp load on a 50-amp circuit
Level 2 chargers (the NEC calls them electric vehicle supply equipment, or EVSE) are sold by the breaker they expect, not by the current they draw. A unit that plugs into a NEMA 14-50 receptacle delivers at most 40 A, because that is the largest continuous load a 50 A circuit is allowed to carry. A hardwired "50-amp" unit may be set to 40 A or to 48 A. The number that matters for wire sizing is the maximum output current on the nameplate, plus the current setting if the unit is adjustable. Read it before you buy wire.
The rules below follow the 2023 NEC. Most states have adopted the 2023 edition, some are still on 2020 or 2017, and the authority having jurisdiction (AHJ) and local amendments govern.
The 125% continuous-load rule
NEC 625.42 says EV charging loads are continuous loads, and 625.41 requires the overcurrent device to be rated at least 125% of the maximum load of the equipment. 210.19(A) applies the same 125% to the branch-circuit conductors. So:
- 32 A EVSE × 1.25 = 40 A breaker and 40 A of conductor ampacity.
- 40 A EVSE × 1.25 = 50 A breaker and 50 A of ampacity.
- 48 A EVSE × 1.25 = 60 A breaker and 60 A of ampacity.
Under 625.40 the EVSE gets its own individual branch circuit with no other outlets. The wire size calculator applies the 125% rule and the termination limits for you.
Which wire: 6 AWG, 8 AWG or aluminum
Ampacity comes from Table 310.16, but you are held to the temperature column your terminations are rated for (110.14(C)). Most breakers and most EVSE terminals are marked 75°C. NM cable (Romex) must be sized from the 60°C column no matter what its conductors are rated (334.80). Confirm each value in the table of your adopted edition.
| EVSE output | Breaker | Copper THHN/THWN-2 in conduit (75°C column) | Copper NM-B cable (60°C column) | Aluminum XHHW-2 in conduit (75°C column) |
|---|---|---|---|---|
| 32 A | 40 A | 8 AWG (50 A) | 8 AWG (40 A) | 8 AWG (40 A) |
| 40 A | 50 A | 8 AWG (50 A) | 6 AWG (55 A) | 6 AWG (50 A) |
| 48 A | 60 A | 6 AWG (65 A) | 4 AWG (70 A) | 4 AWG (65 A) |
Notice that 8 AWG copper carries exactly 50 A in the 75°C column: legal for a 40 A EVSE in conduit on 75°C terminals, with no margin and only if nothing derates it. 8 AWG NM-B is 40 A, which is not enough for that same charger. In cable, a 40 A unit needs 6 AWG and a 48 A unit needs 4 AWG. Many electricians run 6 AWG copper for any 40 A or 48 A unit because it covers both cases and leaves room for a hot attic or a bundled run. A run through a space above 30°C, or a raceway with more than three current-carrying conductors, also needs the correction and adjustment factors in 310.15.
Aluminum is a sound choice for a long run to a detached garage: 4 AWG aluminum is rated 65 A at 75°C and costs far less than 6 AWG copper. The terminals at both ends must be listed for aluminum (CU-AL or AL9CU marking). Some EVSE terminals are copper-only; then you splice to a copper pigtail in a box with a listed connector.
Voltage drop on long runs
The NEC does not set a voltage drop limit for a branch circuit, but the informational note to 210.19 recommends holding it to 3%. Low voltage only slows charging and warms the conductors, so this is a performance question, but inspectors ask about it on long runs. Using VD = 2 × 12.9 × I × L ÷ CM, a 48 A unit on 6 AWG copper (26,240 circular mils) stays under 3% of 240 V out to about 150 feet one way. A 40 A unit on 8 AWG makes it to about 115 feet. For a 48 A charger 200 feet from the panel, 6 AWG drops 9.4 V (3.9%) and 4 AWG drops 5.9 V (2.5%), so that run goes to 4 AWG. Run your own distance through the voltage drop calculator.
Receptacle or hardwired, and the GFCI question
A NEMA 14-50 receptacle lets the owner unplug the unit and take it along. Use a heavy-duty (industrial-grade) receptacle; a bargain range receptacle is not built for 40 A every night. Under the 2020 and 2023 NEC, 210.8(A) requires GFCI protection for 125- through 250-volt receptacles in a dwelling garage and outdoors on single-phase circuits of 150 V or less to ground, and 625.54 repeats it for any receptacle installed for EV charging rated 150 V to ground or less and 50 A or less. That means a 50 A GFCI breaker for a 14-50 in a garage. Jurisdictions still on the 2017 NEC did not require it, so verify the edition in force.
Hardwiring avoids the receptacle and, indoors, the GFCI breaker, since 210.8(A) covers receptacles only. The EVSE has its own ground-fault protection (a charge-circuit interrupting device), and a GFCI breaker stacked on top of it is a common source of nuisance trips, which is why many manufacturers recommend hardwiring. Outdoor hardwired units are a different case: 210.8(F) in the 2020 and 2023 editions covers outdoor outlets at dwellings on circuits of 50 A or less, so check it and the local amendments. A 48 A unit on a 60 A circuit does not need a separate disconnect under 625.43, which requires one only for equipment rated over 60 A or over 150 V to ground.
Will the service carry it, and what the inspector checks
A 48 A charger adds 11,520 VA to the house. 220.57 says to count an EVSE at 7,200 VA or its nameplate, whichever is larger, in the load calculation. If a 100 A or 125 A service cannot absorb it, you have three choices: upgrade the service, set the EVSE lower where it has a restricted-access adjustment (625.42 in the 2023 NEC), or install an energy management system that throttles the charger when the house is busy (625.42 and 750.30; the 2020 edition calls it automatic load management). Nearly every jurisdiction requires a permit and an inspection, and the inspector will check the breaker, the conductor size and type, the terminal ratings, the GFCI, the receptacle grade and the working space. These continuous-load and termination questions are staples of the electrician practice exam, and Voltbox puts the wire size and voltage drop calculators on your phone for the job site.
Step by step
- Read the nameplateFind the EVSE maximum output current, and its current setting if it is adjustable. A plug-in unit on a NEMA 14-50 is 40 A; hardwired units are often 48 A.
- Apply 125%Multiply by 1.25 for the breaker and the minimum conductor ampacity: 40 A becomes 50 A and 48 A becomes 60 A (NEC 625.41, 625.42, 210.19).
- Pick the conductorUse Table 310.16 in the column your terminations allow: 60°C for NM cable, 75°C for THHN/THWN-2 in conduit on 75°C terminals. 8 AWG copper (50 A at 75°C) covers a 40 A unit in conduit; 6 AWG copper (65 A) covers 48 A.
- Check voltage dropRun the one-way length through the voltage drop calculator and upsize if the drop is over 3% of 240 V. 6 AWG copper at 48 A passes to about 150 feet.
- Choose receptacle or hardwiredA 14-50 receptacle in a garage needs a GFCI breaker under the 2020 and 2023 NEC (210.8(A), 625.54). A hardwired indoor unit avoids the GFCI breaker and its nuisance trips.
- Confirm the service and pull the permitAdd the EVSE at 7,200 VA or nameplate (220.57) to the load calculation; use load management or a lower setting if the service is tight. Get the permit and the inspection.
Frequently asked questions
Can I use 8 AWG wire for a 50-amp EV charger circuit?
Only if the EVSE draws 40 A or less and the 8 AWG copper is THHN/THWN-2 in conduit on 75°C terminations, where it is rated 50 A. 8 AWG NM-B cable is limited to 40 A and does not qualify. Most installers use 6 AWG copper for any 40 A or 48 A unit.
Does a 48-amp charger need a 60-amp breaker?
Yes. 48 × 1.25 = 60 A, and the conductors need 60 A of ampacity: 6 AWG copper THHN/THWN-2 in conduit (65 A at 75°C), 4 AWG copper NM-B, or 4 AWG aluminum on terminals listed for aluminum.
Does a NEMA 14-50 for an EV need GFCI protection?
Under the 2020 and 2023 NEC, yes, in a garage or outdoors (210.8(A) and 625.54). Under the 2017 NEC it generally did not. A hardwired indoor EVSE does not need a GFCI breaker; check 210.8(F) for outdoor hardwired units.
How far can I run 6 AWG copper to an EV charger?
At 48 A and 240 V, 6 AWG copper stays under 3% voltage drop to roughly 150 feet one way; at 40 A, roughly 180 feet. Beyond that, go to 4 AWG. The 3% figure is a recommendation, not a requirement.
Written by TapForge Studios, a one-person Android studio run by a tradesman with a background in electrical, HVAC and life-safety work. Reviewed October 7, 2026. This guide is general information, not engineering, legal or tax advice; the adopted code edition, the manufacturer's instructions and the authority having jurisdiction govern.
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