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EV Charger Circuit Sizer

Size a Level 2 EV charger circuit: breaker from the 125% continuous-load rule, copper wire from the correct temperature column, and a voltage-drop check that can upsize the wire.

1. Enter your numbers  →  2. Check the answer  →  3. Read the steps before you trust it

A
ft

EV Charger Circuit Result

Breaker size
60A

125% rule: 48 A x 1.25 = 60 A minimum, rounded up to the next standard breaker.

Wire size (copper)
6 AWG

By ampacity: 6 AWG (65 A). No voltage-drop upsize needed.

Voltage drop
2.2758V

0.9482% of 240 V. Load voltage: 237.724 V.

Step-by-Step Engineering Calculation

  1. 1Charger current: I=48 AI = 48\text{ A} (continuous load)
  2. 2125% continuous-load rule: Imin=48×1.25=60.00 AI_{\text{min}} = 48 \times 1.25 = 60.00\text{ A}
  3. 3Standard breaker: 60 A (next standard size at or above 60.00 A)
  4. 4Wire by ampacity (THHN in conduit, 75 C column): 6 AWG (65 A)
  5. 5Voltage drop check, round-trip 120 ft: ΔV=48×0.3951×120/1000=2.28 V\Delta V = 48 \times 0.3951 \times 120 / 1000 = 2.28\text{ V} (0.95%)
  6. 6No voltage-drop upsize needed; 6 AWG is within the 3% guide.

Formula & Theory

Breaker >= 1.25 x I_charger | Delta V = I x R x (2 x L) / 1000

EV charging is a continuous load, so the circuit is sized at 125% of the charger current. Wire is then checked by ampacity in the correct temperature column and by voltage drop over the round-trip length.

Variable Definitions
I:
Charger current (Amperes (A)) – Maximum charging current from the charger nameplate or settings
V:
Supply voltage (Volts (V)) – Nominal supply voltage, typically 240 V for Level 2
L:
One-way distance (Feet (ft)) – Route length from panel to charger; voltage drop uses 2 x L

Worked Engineering Example

48 A charger, 240 V, 60 ft, THHN in conduit

A 48 A Level 2 charger 60 ft from the panel, copper THHN in conduit.

Inputs:
  • Charger current: 48 A
  • Voltage: 240 V
  • Distance: 60 ft
  • Wiring method: THHN in conduit
Result: Breaker = 60 A | Wire = 6 AWG Copper | Voltage drop = 2.28 V (0.95%)

Key Assumptions

  • •Copper conductors only; aluminium requires a separate table check.
  • •THHN uses the 75 C column and NM-B uses the 60 C column, assuming 75 C rated terminations for THHN.
  • •Voltage drop guide is 3% for the branch circuit; it is a guide, not a hard code limit in every case.

Limitations & Safety Scope

  • •Panel capacity, load management, derating for conduit fill and ambient temperature, and local code amendments are not covered by this calculator.
  • •Final installation must be verified by a licensed electrician and the authority having jurisdiction.

Frequently Asked Questions

What size breaker do I need for a 48 A EV charger?

48 A x 1.25 = 60 A, so a 60 A breaker as a planning value. The wire must then be checked in the correct temperature column and for voltage drop.

Why does NM-B give a different wire size than THHN?

NM-B cable is limited to the 60 C ampacity column, while THHN in conduit can use the 75 C column with 75 C rated terminations. The same copper size therefore has a lower ampacity as NM-B.

Related Calculators & Engineering Tools

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Wire Size Calculator
Voltage Drop Calculator
EV Charger Circuit Sizing
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Educational & Reference Notice: This calculator provides technical estimates based on standard physical formulas. Actual electrical installation, protective device sizing, and conductor selection must be verified against the applicable electrical code (NEC, IEC, CEC) by a licensed electrician or qualified professional engineer.