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EV Charger Circuit Sizing

EV charger sizing is two problems: a continuous-load branch circuit, and a dwelling service that can absorb the add. Solving only the wall-connector breaker leaves half the job undone.
Code basis
625.41 / 625.42, 210.20(A)
Branch rule
125% continuous
Service check
220.82 / 220.83
Common landing
60 A for 48 A charge

The Procedure

5 steps, in the order the code applies them.

  1. Step 1

    Set the maximum charging current

    Use the EVSE configuration you will actually program, not the brochure maximum if the circuit will be limited lower.

  2. Step 2

    Apply 125 percent for the branch circuit

    EV charging is continuous. Multiply charge current by 1.25 to get the minimum branch-circuit and overcurrent size.

  3. Step 3

    Select conductor and breaker together

    Choose a standard breaker at or above the continuous-load value and a conductor that can be protected by it after termination and derating checks.

  4. Step 4

    Run the dwelling load calculation

    Confirm the service or feeder can accept the added EVSE demand under 220.82 or 220.83, including any listed EMS limit.

  5. Step 5

    Check voltage drop on the real route

    Long garage or detached-structure runs often upsize the feeder even when ampacity already passed.

Two different checks

The branch circuit must carry the charging load as a continuous load. Separately, the dwelling load calculation must show the service can carry the added load.

A charger can have a correctly sized branch circuit and still require service-side mitigation.

Long garage runs

EVSE loads run for long periods, so voltage drop matters even where the informational-note target is not mandatory.

Run wire size and voltage drop together before choosing copper or aluminum.

Decision Guide

The choices that change the answer, and how to make them.

  • 48 A charge needs a 60 A circuit

    48 × 1.25 = 60. Matching a 48 A setting to a 50 A breaker skips the continuous-load step.

  • Configure the EVSE to the installed breaker

    Dip switches or software must match the circuit. Leaving the unit at a higher setting than the breaker invites nuisance trips.

  • Branch success is not service success

    A correct 60 A EV circuit can still require a service upgrade or load management on a 100 A dwelling service.

FAQs

What size breaker for a 48 amp EV charger?
A 60 A breaker, because continuous-load sizing requires 125 percent of 48 A. The EVSE must also be configured to 48 A.
Do I need a load calculation to add an EV charger?
Yes if you need to know whether the existing service can accept the continuous add. Branch-circuit math alone does not prove service capacity.
Does voltage drop matter for EV chargers?
Yes on long runs. EVSE loads run for hours, so sag that looks minor on a short motor start becomes a sustained performance problem.

Calculated against the NEC 2023 edition using 625.41, 625.42, 220.57, 210.20(A). Confirm the edition adopted by your AHJ, which may differ and may carry local amendments.

Not covered by this tool

  • Motor, air-conditioning and welder circuits, which are sized under their own articles.
  • Conductors in free air and photovoltaic circuits.
  • Parallel conductor sets, taps and busbars.
  • Local amendments, which can be stricter than the published code.

Data last verified