EV charger circuit sizing

NEC 220.57 continuous load, demand factors, breaker, and conductor sizing

Plan minimum circuit ampacity (125% rule), standard breaker size, copper or aluminum wire at 75°C with ambient correction, and a simple voltage-drop check. Use with our breaker sizing, wire ampacity, and voltage drop tools.

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NEC 220.57 — EV charger demand factor reference

Number of chargers	Demand factor	Notes
1	100%	Full rated current — continuous load rule applies
2	100%	Both at full — no demand factor reduction
3	100% of 2 largest + 75% of remainder	NEC 220.57(B)
4+	100% of 2 largest + 75% of remainder	Multi-unit / fleet savings

Level 2 EVSE — common sizes (reference)

EVSE output	Min ampacity (125%)	Breaker	Copper wire	Al wire
16A	20A	20A	12 AWG	10 AWG
24A	30A	30A	10 AWG	8 AWG
32A	40A	40A	8 AWG	6 AWG
40A	50A	50A	6 AWG	4 AWG
48A	60A	60A	4 AWG	3 AWG

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EVSE install and panel tools

Meters, conductors, and distribution gear electricians use on charger circuits.

Verify

Fluke 117 Electricians True RMS Multimeter

Dead-front checks before energizing EVSE
Non-contact voltage detection
CAT III 600 V for panel work

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Clamp

Klein Tools CL800 Digital AC/DC Clamp Meter

Confirm EVSE draw after install
True RMS for accurate loads
High-amp branch troubleshooting

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Copper

Southwire 10 AWG Stranded THHN (500 ft)

Typical 30 A branch / EV feeder building block
THHN/THWN-2 for conduit runs
Stranded for pulls

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Panel

Square D QO140L200PG 200A Load Center

Space for two-pole EVSE breakers
200A main — service upgrade planning
QO series common in retrofits

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Drivers

Klein 1000V Insulated Screwdriver Set

IEC 60900 rated insulation
Breaker and EVSE terminations
Multiple profiles in one kit

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NEC 220.57 and continuous loads

EVSE is treated as a continuous load: branch circuit ampacity is not less than 125% of the equipment rating. This calculator follows the live tool: demand-adjusted total amps × 1.25, then next standard breaker from the embedded ladder, then smallest conductor in the embedded 75°C table that meets ampacity after ambient derating.

Multiple chargers: For 3 or 4 identical units, the live script applies 100% of two largest plus 75% of the rest (simplified equal-nameplate model).

Voltage drop The drop estimate uses the script’s mΩ/ft tables and two-wire length × current. It is a planning aid — use the full voltage drop calculator for precise runs.

NEC 625.40 dedicated branch circuit

The advisory block flags when “shared circuit” is selected — NEC 625.40 expects a dedicated branch circuit for EVSE. Always confirm with the AHJ.

Frequently asked questions

What breaker for a 32 A Level 2 charger?

32 A × 125% = 40 A minimum circuit ampacity; the script picks the next standard breaker ≥ that value (40 A) and matches conductor to derated table ampacity.

Can I share the EV circuit with receptacles?

No — select “dedicated” for a compliant layout; the tool warns if you select shared.

Does installation type change the math?

The recovered script does not read the installation type field; it uses fixed 75°C copper/aluminum ampacity maps. NM-B or other methods may require additional limits (for example NEC 334.80) beyond this page.

EV charger circuit sizing