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Uses a 2026 NEC reference screen; the edition adopted locally and the EVSE listing remain controlling.
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A
The branch-circuit screen applies 125% to this continuous charging current.
Residential Level 2 is commonly 240 V single phase; commercial equipment may use 208 V or 480 V three phase.
The result flags a breaker cap or supply mismatch; it does not approve the actual receptacle or hardwired assembly.
The minimum result is the next modeled standard breaker at or above the calculated circuit load.
A
Enter 0 to omit this comparison. Use only headroom stated on the same service and phase basis.
Voltage drop is a circular-mil planning approximation using the actual charging current.
The screen covers 14 AWG through 4/0 where a reference ampacity is available.
Default 75 °C is a planning choice, not a determination that the actual terminals permit it.
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The recommended row is the first modeled size passing both ampacity and this target.
The selected row is emphasized only; it does not override pass/fail logic.
This changes display and export rounding only; calculations retain full precision.
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Installation checks before purchase or permitting

Planning screen only: verify the adopted code, EVSE listing, load calculation, conductor conditions, protection, permits, and utility requirements with a qualified electrician and the authority having jurisdiction.

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SizeAmpacityMax EVSEVoltage dropResultCopy
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Home EV Charger Install Cost Calculator Estimate a home EV charger installation budget from circuit size and wire route with panel work, labor, permits and uncertainty included.
Electric Vehicle (EV) Charging Time Calculator Estimate EV charging time from battery and power limits with taper and losses, then check added range, session cost and departure fit.
Electrical Box Fill Calculator Calculate NEC-style box fill from conductors and fittings, then compare required volume with the marked box capacity and available margin.
Electrical Panel Load Calculator Estimate dwelling electrical service demand from general and major loads, then compare the result with the entered rating and headroom target.

An empty breaker space does not prove that a building can support an electric vehicle charger. The charging current must fit the branch-circuit rating, the connection, the conductor ampacity, the voltage-drop target, and the service or panel load calculation. Any one of those can become the binding limit.

CheckQuestion it answersWhat it does not prove
Breaker loadCan the selected breaker carry the configured continuous charging current?That the service or panel has spare capacity.
ConnectionDoes the receptacle or hardwired path support the chosen supply and breaker?That every product listing and local rule is satisfied.
Conductor ampacityDoes a table value meet the required circuit current?That terminal, insulation, ambient, bundling, or raceway adjustments are complete.
Voltage dropIs estimated loss along the one-way run within the planning target?That conductor ampacity passes.

Electric vehicle supply equipment (EVSE) controls the maximum current delivered to the vehicle. The car may draw less, but circuit planning begins with the EVSE's configured maximum because charging can continue for hours. Under the usual continuous-load treatment, 32 A points to at least 40 A of circuit capacity, 40 A points to 50 A, and 48 A points to 60 A.

Connection type matters before wire size is discussed. A 15 A or 20 A, 120 V receptacle has a narrow supply and breaker path. A modeled 50 A receptacle is limited to 208 V or 240 V single phase and a 50 A breaker. Hardwiring removes those receptacle caps from the screen, but it does not remove equipment-listing, disconnect, grounding, permitting, or inspection requirements.

Long runs introduce resistance. A conductor can have adequate ampacity yet exceed a voltage-drop target, so the first acceptable size may be larger than the ampacity-only choice. Copper and aluminum also use different resistance constants and table ampacities.

This kind of result is a planning screen, not an installation design. Final conductor selection depends on the adopted electrical code, EVSE instructions, terminal ratings, insulation system, ambient temperature, number of current-carrying conductors, wet-location rules, load management, and approval by the authority having jurisdiction.

How to Use This Tool:

Use the charger's configured output and the actual installation path, then treat every pass as a prompt for design review rather than approval.

  1. Choose a Charger preset or enter the EVSE maximum output current for a custom case.
  2. Select the Supply circuit, Connection type, and Breaker to review. A receptacle choice must match its supported voltage and breaker cap.
  3. Enter Load-calculation headroom from a separate service or panel calculation. A value of 0 leaves panel capacity unassessed.
  4. Enter the One-way conductor run, then choose conductor material, the applicable ampacity temperature column, and a voltage-drop target.
  5. Review Circuit plan, Breaker capacity, and Conductor screen. If no conductor through 4/0 AWG passes both modeled checks, reduce current or run length and obtain an engineered design.

Interpreting Results:

  • 125% circuit load is the configured EVSE current multiplied by 1.25. The recommended breaker is the smallest modeled standard size at or above that load.
  • Breaker capacity passes when the reviewed breaker is at least the 125% load. Equality passes.
  • Panel headroom passes at or above the 125% load, is tight from EVSE current up to that load, and is short below EVSE current. A zero entry means not checked.
  • First passing conductor is the smallest modeled row whose selected ampacity is at least the required load and whose estimated voltage drop is at or below the target.

A passing row does not certify the installation. Give the EVSE specification, conductor path, load calculation, and proposed equipment to a qualified electrical professional and the permitting authority.

Technical Details:

The calculation separates current sizing, supply power, connection compatibility, panel headroom, ampacity lookup, and resistive voltage drop. The recommendation is the first conductor row that passes both ampacity and drop; neither check substitutes for the other.

Formula Core:

For configured EVSE current I, the modeled continuous circuit load Ic is:

Ic=1.25×I

The standard-breaker result is the first modeled rating greater than or equal to Ic. Conversely, a breaker rating Ib supports at most Ib ÷ 1.25 amperes of modeled EVSE output.

Estimated charging power uses line voltage V. Single-phase power is VI; three-phase power includes the square-root-of-three factor.

P1φ=V×I1000 P3φ=3×V×I1000

Voltage drop uses one-way length L in feet, conductor circular-mil area CM, and resistance constant K of 12.9 for copper or 21.2 for aluminum. The path factor F is 2 for single phase and √3 for three phase.

Vd=F×K×I×LCM D%=VdV×100

Lookup Core:

The ampacity screen selects one 60 °C, 75 °C, or 90 °C column for the chosen material. These are the complete modeled lookup values.

Conductor Cu 60 °C Cu 75 °C Cu 90 °C Al 60 °C Al 75 °C Al 90 °C
14 AWG15 A20 A25 A———
12 AWG20 A25 A30 A15 A20 A25 A
10 AWG30 A35 A40 A25 A30 A35 A
8 AWG40 A50 A55 A30 A40 A45 A
6 AWG55 A65 A75 A40 A50 A55 A
4 AWG70 A85 A95 A55 A65 A75 A
3 AWG85 A100 A115 A65 A75 A85 A
2 AWG95 A115 A130 A75 A90 A100 A
1 AWG110 A130 A145 A85 A100 A115 A
1/0 AWG125 A150 A170 A100 A120 A135 A
2/0 AWG145 A175 A195 A115 A135 A150 A
3/0 AWG165 A200 A225 A130 A155 A175 A
4/0 AWG195 A230 A260 A150 A180 A205 A

Rule Core:

A conductor passes only when ampacity is greater than or equal to the 125% circuit load and voltage-drop percentage is less than or equal to the selected limit. The first passing size becomes the recommendation.

  • A 15 A, 120 V receptacle is limited to 120 V single phase and a 15 A breaker.
  • A 20 A, 120 V receptacle is limited to 120 V single phase and a 20 A breaker.
  • The modeled 50 A receptacle accepts 208 V or 240 V single phase and no breaker above 50 A.
  • Hardwired EVSE accepts every modeled single-phase and three-phase supply, subject to the other checks.

Safety and Accuracy Notes:

This screen uses unadjusted ampacity table values and a circular-mil voltage-drop approximation. It deliberately does not decide the final wiring method.

  • Use the temperature column permitted by the conductor, equipment terminals, and applicable code, not the highest available number by default.
  • Apply ambient-temperature, conductor-count, raceway, insulation, wet-location, and termination rules separately.
  • Panel headroom must come from a valid load calculation. Open physical space is not electrical capacity.
  • Follow the EVSE listing, connection rating, local code edition, permits, utility requirements, and authority having jurisdiction.

Worked Examples:

Hardwired 48 A charger on an 80-foot run

At 240 V single phase, 48 A becomes a 60 A continuous circuit load and 11.52 kW of estimated charging power. With copper, the 75 °C column, an 80 ft one-way run, and a 3% drop target, 6 AWG is the first modeled conductor that passes. Its table ampacity is 65 A and estimated drop is about 3.78 V, or 1.57%. Those results still require the installation adjustments and approvals listed above.

References: