EV Charger Circuit Calculator
Enter your EV charger's rated output current and get the branch-circuit breaker and minimum conductor. NEC Article 625 treats EV charging as a continuous load, so the circuit is sized at 125% of the charger rating using the 240.6(A) standard breakers and Table 310.16 conductor ampacity.
How to use this calculator
- Pick a common Level 1 or Level 2 charger from the list, or enter your equipment's rated output current in amps (from the nameplate or the DIP-switch / app setting you selected).
- Set the nominal voltage if you want the kW readout; 120 V is Level 1, 240 V is Level 2. Voltage does not change the branch-circuit sizing, which is current-based.
- Adjust the conductor material, insulation and termination ratings, ambient temperature, and conductor count if your install differs from the standard basis.
- Read the breaker and conductor. The notes explain the 625.42 continuous-load rule, the 80% cord-and-plug limit, and any 240.4(D) small-conductor interaction.
- Size the equipment grounding conductor and check voltage drop separately using the linked tools below.
NEC reference
Sizing follows NEC 2020 Article 625. Section 625.42 defines electric vehicle charging as a continuous load; 625.41 requires the branch-circuit overcurrent device and conductors to be rated at not less than 125% of the maximum equipment load. The breaker is the next standard 240.6(A) rating at or above that figure, and the conductor is sized to the same requirement from Table 310.16 with 310.15 derating, the 110.14(C) termination cap, and the 240.4(B)/(D) conductor-protection limits. The Article 625 continuous rule is unchanged across the 2017, 2020, and 2023 editions.
Results are for reference only. Verify against the applicable adopted edition of the NEC and consult a licensed electrician for code compliance.
Common EV charger circuits: copper, standard conditions
| Charger output | Min circuit (125%) | Breaker | Copper conductor | Typical use |
|---|---|---|---|---|
| 12 A | 15 A | 15 A | 14 AWG | Level 1, 120 V plug-in |
| 16 A | 20 A | 20 A | 12 AWG | Level 1 max / small Level 2 |
| 24 A | 30 A | 30 A | 10 AWG | Level 2, 30 A circuit |
| 32 A | 40 A | 40 A | 8 AWG | Level 2, 40 A circuit |
| 40 A | 50 A | 50 A | 8 AWG | NEMA 14-50 plug-in max |
| 48 A | 60 A | 60 A | 6 AWG | Level 2 hardwired, common |
| 64 A | 80 A | 80 A | 4 AWG | High-power hardwired |
| 80 A | 100 A | 100 A | 3 AWG | Maximum Level 2 |
Standard conditions (86°F, 90°C insulation on 75°C terminations, 3 current-carrying conductors, copper). Aluminum, hot ambients, and long runs (voltage drop) change the conductor; use the calculator above with your actual conditions.
The 125% continuous-load rule for EV chargers
The single rule that governs an EV charger circuit is that the load is continuous. NEC 625.42 makes that determination for you: electric vehicle charging is a continuous load, full stop, because a charging session routinely runs longer than 3 hours. NEC 625.41 then applies the continuous-duty requirement, the same 125% factor found in 210.20(A) for any other continuous load.
So a 48 A charger is not on a 50 A circuit. It needs 48 x 1.25 = 60 A of protection and conductor ampacity, which is a 60 A breaker on 6 AWG copper. Sizing an EV charger circuit to the raw current instead of 125% is the most common mistake, and it produces a circuit that nuisance-trips or overheats the terminations under a full charging session.
Hardwired vs. cord-and-plug: the 80% rule
NEC 625.42 also caps a cord-and-plug (receptacle-fed) EVSE at 80% of the branch-circuit rating. That is the same 125% relationship inverted: 80% of a 50 A receptacle circuit is 40 A, so a plug-in charger on a NEMA 14-50 outlet is limited to 40 A output. To charge at 48 A or 60 A the equipment must be hardwired, where only the 625.41 rating applies. Manufacturers ship many chargers set to a conservative default; confirm the output setting matches the circuit you are sizing.
SAE J1772 charging levels
- Level 1: 120 V AC, typically 12 A to 16 A. Plugs into an ordinary receptacle; adds a few miles of range per hour. A 16 A unit needs a dedicated 20 A circuit.
- Level 2: 208 V or 240 V AC, 16 A to 80 A. The standard home and workplace charger. Most residential installs land at 32 A, 40 A, or 48 A.
- DC fast charging is a separate system supplied at higher DC voltages and is outside the scope of this AC branch-circuit tool.
Frequently asked questions
What breaker for a 48 amp charger?
48 x 1.25 = 60 A, so a 60 A breaker on 6 AWG copper. This is the canonical Level 2 answer and covers a Tesla Wall Connector, Grizzl-E, or similar unit set to 48 A output. Enter 48 A above to see the full arithmetic and the aluminum equivalent.
Can I put a 60 amp charger on a 60 amp breaker?
No. A 60 A continuous charger needs 60 x 1.25 = 75 A, which rounds up to an 80 A breaker on 4 AWG copper. The charger output current, not the breaker size, is what you multiply by 1.25. This is why 48 A is the largest charger that fits a 60 A circuit.
Does this size the ground wire?
No. The equipment grounding conductor is sized from the breaker rating under NEC Table 250.122, not the 125% circuit ampacity. Use the Equipment Grounding Conductor Size Calculator linked below with the breaker size this tool returns.
Does 6 AWG Romex work on a 60 amp circuit?
No. NM-B cable (Romex) is limited to its 60°C ampacity column by NEC 334.80, where 6 AWG copper is only 55 A, short of the 60 A a 48 A charger needs. On NM-B you must step up to 4 AWG. Running 6 AWG THHN/THWN-2 in conduit uses the 75°C column at 65 A and does qualify, which is why the default result above is 6 AWG. When your run is NM cable, set both the insulation and termination ratings to 60°C so the calculator uses the correct column.
What about voltage drop on a long run?
A detached garage or a long run across a property can push the conductor larger than the ampacity minimum to keep voltage drop within the recommended 3%. This calculator sizes for ampacity and overcurrent only; run the distance through the Voltage Drop Calculator before finalizing.
Related calculators
- Breaker Size Calculator: the general continuous/noncontinuous load sizing this tool is built on.
- Equipment Grounding Conductor Size Calculator: size the EGC from the breaker rating (Table 250.122).
- Voltage Drop Calculator: check the run length before finalizing the conductor.
- Wire Ampacity Calculator: derated ampacity of a specific conductor and insulation.
Studying for the licensing exam? Our own NEC Code Quickstart works all twelve exam calculations start to finish, each with the code reference. Also in paperback.
Running an electrical contracting business? Jobber handles scheduling, invoicing, and job management. Start a 14-day free trial.
For deeper NEC training on EV charger circuits and continuous-load sizing, Mike Holt's NEC courses are the industry standard.
Working from the printed code? NEC code books and tab sets are available from Mike Holt.
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