EV Charging Circuit Calculator (NEC 625)

🔋 EV Charging Circuit Calculator (NEC 625)

Continuous load, breaker and conductor for an EV charger.

Input mode

EVSE current (A)

Voltage (V)

Phase

EVSE Current

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Min Circuit (125%)

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Breaker

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Conductor (≈Cu)

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⚠️ NEC 625/210.20: EVSE is continuous → circuit & OCPD ≥ 125% of charger current. Conductor is indicative (75°C copper); confirm with derating and the full cable sizing calculator. Verify before professional use.

Standards & method

✓ Independently verified 12 July 2026

Governing standard

NEC (NFPA 70) Article 625

Clauses applied

625.41 — EVSE is a continuous load; the branch circuit and OCPD are rated at 125% of the maximum load · 625.42 rating · 210.19(A)(1) conductor sizing · 110.14(C) termination temperature limit

Core formula

I_circuit = 1.25 × I_EVSE · e.g. a 48 A charger requires a 60 A circuit

Why this matters

EV charging is a continuous load — it runs at full current for hours. The 125% rule is not optional, and it is the single most common error in EVSE installation: a 48 A charger on a 50 A breaker will trip and, worse, runs the conductor at its limit indefinitely.

Independently verified

12 July 2026 — Re-derived from the governing standard and checked numerically against worked reference cases from the standard itself — not merely tested for “returns a number”.

Results are for guidance. Verify against the current edition of the governing standard and have a qualified professional review before use in practice.

NEC 625 EV Circuit — Method

Electric-vehicle supply equipment runs for hours, so the code classes it as a continuous load. NEC 210.20(A) and Article 625 require the branch-circuit conductors and the overcurrent device to be rated at not less than 125% of the EVSE rated current. So minimum circuit ampacity = charger amps × 1.25; select the next standard breaker at or above that, and choose conductors with an ampacity at least equal to the breaker rating (after any temperature/grouping derating).

Frequently Asked Questions

What size breaker for an EV charger?⌄

EVSE is a continuous load, so the breaker must be at least 125% of the charger current. A 40 A charger needs 40 x 1.25 = 50 A, so a 50 A breaker; a 32 A charger needs 40 A.

Why multiply by 1.25?⌄

NEC 210.20(A)/Article 625 require continuous loads (3+ hours) to be sized at 125% so the conductors and breaker are not run at their full rating continuously, which would overheat them.

What wire size does an EV charger need?⌄

The conductor ampacity must be at least the breaker rating after derating. A 50 A circuit typically uses 6 AWG (about 6 mm2) copper at 75 C; confirm with ambient and grouping derating in the cable sizing calculator.

Can I plug a Level 2 charger into a normal outlet?⌄

Hard-wired or dedicated-outlet circuits are required for Level 2 EVSE; it cannot share a general-purpose circuit. The dedicated circuit is sized at 125% of the charger current.

How do I convert kW to charger amps?⌄

Single-phase: amps = kW x 1000 / voltage. Three-phase: amps = kW x 1000 / (root 3 x line voltage). A 7.4 kW single-phase charger at 240 V draws about 31 A.

EV Charging Circuit Sizing (NEC 625)

A home or workplace EV charger draws near its maximum current for hours at a time, which is the definition of a continuous load. The wiring rules therefore add a 25% margin so the circuit is never run at its limit continuously.

The 125% rule

Minimum branch-circuit ampacity and the overcurrent device = EVSE current × 1.25. Pick the next standard breaker, then conductors rated at least to that breaker after derating.

Putting it together

Convert the charger kW to amps if needed, apply 1.25, choose the breaker, and verify the conductor with the cable sizing calculator for the real installation method and temperature. For charge duration use the EV charging time calculator.

Related: EV Charging Time, Cable Sizing, Voltage Drop.

EV Charging Circuit Calculator

EV charging circuit (NEC 625) — Quick answer