EV Charger Circuit & Load Calculator
Size EV charger branch circuits from kW rating — calculate amperage, continuous load, recommended breaker and wire gauge, and panel load impact with NEC 125% continuous load rules and PASS/FAIL checks.
Charger Details
kW
A
Live Results
Continuous Load Amps (125%)
37.50A
Charger Amps
30.00A
Panel Load After EV
187.50A
Recommended Breaker
40A
PASSRecommended Wire Gauge
8 AWG
PASSInput Summary
Charger kW7.20 kW
Voltage240 V
Existing Panel Amps150 A
Selected Breaker Size40 A
Selected Wire Gauge8 AWG
EV charger calculations follow NEC continuous load rules. Always verify final design with local electrical code.
How to Use This EV Charger Calculator
- Enter the charger power rating. Input the EV supply equipment (EVSE) power rating in kilowatts from the charger nameplate or manufacturer spec — common Level 2 values are 7.2 kW, 9.6 kW, 11.5 kW, and 19.2 kW. This kW rating drives the branch-circuit amperage calculation.
- Select circuit voltage. Choose 120 V for portable or limited Level 1/Level 2 circuits, or 240 V for dedicated Level 2 EV chargers — the standard for residential wall-mounted units. Voltage directly affects amperage: the same kW load draws twice the amps at 120 V compared to 240 V.
- Enter existing panel amperage. Input the main service or sub-panel bus rating in amperes — typically 100 A, 150 A, or 200 A for residential panels. The calculator adds the EV continuous load to this value to estimate total panel load impact and flag potential overload conditions.
- Optionally select planned breaker and wire gauge. Choose your planned circuit breaker size and wire gauge to run PASS/FAIL compliance checks against NEC continuous load requirements. PASS means the selected breaker meets or exceeds the recommended size and the wire ampacity supports the 125% continuous load current.
- Review recommendations, warnings, and local code. Compare recommended breaker and wire gauge against your selections, review high-load and panel overload warnings, and confirm the design with the current NEC edition and your local AHJ before installation — EV chargers are continuous loads requiring dedicated circuit planning.
Formulas & Example
EV charger circuit sizing converts kilowatt rating to amperage, applies the NEC 125% continuous load multiplier, and selects the minimum standard breaker and wire gauge that meet code requirements.
Charger Amps (A) = (Charger kW × 1000) ÷ Voltage
Continuous Load (A) = Charger Amps × 1.25
Recommended Breaker = smallest standard size ≥ Continuous Load
Recommended Wire = smallest gauge where ampacity ≥ Continuous Load
Panel Load After = Existing Panel Amps + Continuous Load
Standard breaker sizes (A):
15, 20, 30, 40, 50, 60, 70, 80, 100
Wire ampacity table (copper, AWG → A):
14→15, 12→20, 10→30, 8→40, 6→55, 4→70, 3→85, 2→95Worked Example
A 7.2 kW Level 2 charger on a 240 V circuit with a 150 A panel:
Charger kW = 7.2
Voltage = 240 V
Charger Amps = (7.2 × 1000) ÷ 240 = 30 A
Continuous Load = 30 × 1.25 = 37.5 A
Recommended Breaker = 40 A (smallest ≥ 37.5 A)
Recommended Wire = 8 AWG (40 A ampacity ≥ 37.5 A)
Panel Load After = 150 + 37.5 = 187.5 APair this tool with the Load Calculation Tool, Breaker Size Calculator, Wire Gauge Calculator, and Voltage Drop Calculator for complete EV circuit design verification.
Frequently Asked Questions
What size breaker do I need for an EV charger?▾
Size the breaker for the EV charger's continuous load current multiplied by 125% per NEC continuous load rules. First calculate charger amperage: (kW × 1000) ÷ voltage. Then multiply by 1.25 for continuous load and select the next standard breaker size at or above that value. For example, a 7.2 kW charger on 240 V draws 30 A; continuous load is 37.5 A, requiring a 40 A breaker. Never install a breaker larger than the ampacity of the conductors it protects.
What wire gauge is required?▾
The conductor must have ampacity equal to or greater than the continuous load current (125% of charger amperage). Using standard copper THHN ampacity values, a 7.2 kW / 240 V charger with 37.5 A continuous load requires at least 8 AWG copper (40 A ampacity). Larger chargers — 11.5 kW or 19.2 kW — require 6 AWG or 4 AWG respectively. Always verify conductor type, termination temperature, and conduit fill derating with NEC Table 310.16.
What is continuous load?▾
A continuous load is defined by the NEC as a load where the maximum current is expected to continue for 3 hours or more. EV chargers qualify as continuous loads because vehicles typically charge for several hours overnight. NEC 210.20(A) and 625 require branch-circuit and overcurrent device sizing at 125% of the continuous load current — meaning a 30 A charger circuit must be designed for 37.5 A, not 30 A.
How does an EV charger affect panel load?▾
An EV charger adds its continuous load amperage (125% of nameplate current) to your existing panel demand. A 7.2 kW charger on 240 V adds approximately 37.5 A continuous load to a 150 A panel, bringing estimated total load to 187.5 A before other demand factors. If total load approaches or exceeds the panel rating, you may need a service upgrade, load management device, or a dedicated sub-panel. Use the Load Calculation Tool for a full NEC demand load analysis.
Should I oversize the circuit?▾
Moderate future-proofing is reasonable — installing 6 AWG wire on a 40 A circuit allows upgrading to a higher-power charger later without rewiring. However, do not oversize the breaker beyond conductor ampacity; the breaker must protect the wire per NEC 240.4. Some installers size the circuit for a 48 A or 50 A charger even when installing a 32 A unit, which is acceptable if conductors and breaker are matched to the circuit rating and the EVSE is configured to its actual output limit.
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