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Wire size calculator / EV charger wire size

Wire size for a Level 2 EV charger

40 A, 48 A, and 50 A continuous examples at 240 V, including one row with 60°C terminals. The estimate is calculated, not a fixed gauge.

Level 2 charging is discussed here as a 240 V example because that is the voltage on the calculator’s 48 A continuous preset. The nameplate and the installation manual control the real voltage, the real continuous current, and the conductor metal. The Article 625 section numbers below follow the 2017/2023 NEC sources used here; check the locally adopted edition. This page does not design an EV installation, pick a breaker, or apply equipment-specific rules beyond the calculator’s general checks.

NEC 625.42 treats EV charging loads as continuous, regardless of charging duration. The general three-hour definition does not exempt a shorter charging session. This guide’s calculator keeps the continuous-load check enabled, including when a shared URL requests otherwise. There is no mixed-load line. The pre-adjustment conductor check uses 125 percent of the entered current against the terminal column; adjusted ampacity and voltage drop use actual current. NEC 625.41 separately requires overcurrent protection rated at least 125 percent of the equipment’s maximum load. The calculator does not choose that device.

The 40 A, 48 A and 50 A labels are charging currents, not breaker ratings. Their 125 percent values are 50 A, 60 A and 62.5 A respectively. A 50 A charging current must not be treated as a 50 A circuit. Confirm the equipment’s allowed circuit rating and installation instructions. A 75°C terminal row requires identified equipment; the general unmarked case for smaller equipment is 60°C. For NM-B cable the ampacity cap stays at 60°C even with 75°C equipment. The last row keeps the 48 A preset and changes only the terminal/cable cap.

Tesla’s Gen 3 Wall Connector manual, printed p. 7 illustrates the distinction: 48 A output uses a 60 A circuit, copper terminations only, and at least 6 AWG copper with 75°C equipment or 4 AWG with a 60°C breaker, using the specified 90°C THWN-2 conductors. These are that product’s instructions, not universal charger specifications. Southwire’s NM-B specifications confirm the 60°C ampacity limit.

40 A continuous is checked at 50 A before correction; 48 A continuous is checked at 60 A before correction; 50 A continuous is checked at 62.5 A before correction. Those products are the calculator’s continuous-load check, not a table of charger wire sizes.

Estimates under stated assumptions

Changing the length, the drop limit, or the terminal rating changes the result. Do not copy a gauge off this table without the assumptions beside it. Aluminum results are table comparisons, not permission to land aluminum conductors.

Hypothetical 240 V continuous loads. Not an EV charger installation. Table 8 resistance at 75°C, reactance omitted, small-conductor check on.
Example Assumptions Copper estimate Aluminum estimate
40 A continuous 240 V single-phase, 40 A continuous, 50 ft one way, 3% drop limit, 90°C insulation, 75°C terminals, 30°C ambient, 2 current-carrying conductors, small-conductor check on, Table 8 resistance only 8 AWG (Ampacity governs) 6 AWG (Ampacity governs)
48 A continuous 240 V single-phase, 48 A continuous, 75 ft one way, 3% drop limit, 90°C insulation, 75°C terminals, 30°C ambient, 2 current-carrying conductors, small-conductor check on, Table 8 resistance only 6 AWG (Ampacity governs) 4 AWG (Ampacity governs)
50 A continuous 240 V single-phase, 50 A continuous, 50 ft one way, 3% drop limit, 90°C insulation, 75°C terminals, 30°C ambient, 2 current-carrying conductors, small-conductor check on, Table 8 resistance only 6 AWG (Ampacity governs) 4 AWG (Ampacity governs)
48 A continuous, 60°C terminals 240 V single-phase, 48 A continuous, 75 ft one way, 3% drop limit, 90°C insulation, 60°C terminals, 30°C ambient, 2 current-carrying conductors, small-conductor check on, Table 8 resistance only 4 AWG (Ampacity governs) 3 AWG (Ampacity governs)

40 A continuous, copper. Voltage drop would allow 10 AWG. 10 AWG exceeds the NEC 240.4(D) small-conductor breaker limit for this load, so 8 AWG is required. Ampacity governs.

40 A continuous, aluminum. Voltage drop would allow 8 AWG. Ampacity requires 6 AWG, so ampacity governs.

48 A continuous, copper. Voltage drop would allow 8 AWG. Ampacity requires 6 AWG, so ampacity governs.

48 A continuous, aluminum. Voltage drop would allow 6 AWG. Ampacity requires 4 AWG, so ampacity governs.

50 A continuous, copper. Voltage drop would allow 10 AWG. Ampacity requires 6 AWG, so ampacity governs.

50 A continuous, aluminum. Voltage drop would allow 8 AWG. Ampacity requires 4 AWG, so ampacity governs.

48 A continuous, 60°C terminals, copper. Voltage drop would allow 8 AWG. Ampacity requires 4 AWG, so ampacity governs.

48 A continuous, 60°C terminals, aluminum. Voltage drop would allow 6 AWG. Ampacity requires 3 AWG, so ampacity governs.

Planning estimate only. Consult local code and a qualified electrician before buying wire or energizing a circuit. Presets are hypothetical loads; this tool does not design motor, PV, battery, appliance, or EV installations.

Sources for these cells: existing Table 310.16 numerical cells in NFPA’s public development record, pp. 142–143 (proposed changes are not treated as adopted code) and NFPA 70 (2017), Chapter 9 Table 8, printed p. 689, in a third-party-hosted copy. The same publication supplies 110.14 (terminals and aluminum), 210.19/215.2 (continuous loads), 240.4(D) (small conductors), 250.24/250.32 (grounding), and 625.41/625.42 (EV loads). Schneider Electric’s voltage-drop formulas support the arithmetic; Table 8 AC results here omit reactance and assume unity power factor. Resistance and geometry are construction- and temperature-specific. Adopted editions and local amendments can differ.

Related guides

Open the wire size calculator · Ampacity chart · Voltage drop calculator · Printable chart

Run the 48 A continuous example

The form starts from this page’s example. The address stays on this guide until you edit a field. After an edit, a shared link includes those settings in the URL, and opening that link sends the URL to the host.

Circuit

Headline metal

Both metals are compared. Verify equipment compatibility; some equipment permits copper only.

System

General NEC notes suggest 3% on a branch or feeder and 5% combined. Special equipment and local codes may require other limits; upstream drop is not included.

Estimated size

Enter the load current and the one-way distance. The size appears here, with the limit that set it.

Temperature and bundling

These conditions affect the table ampacity used for the comparison.

Conductor insulation

Use the rating marked for wet or dry conditions. THHN is 90°C dry; XHHW is 90°C dry or 75°C wet. For NM-B use 90°C insulation and a 60°C cap below.

Terminal / cable ampacity cap

Use the lowest applicable rating at either end, including cable limits. The general unmarked default is 60°C for equipment rated ≤100 A or marked for 14–1 AWG. Confirm equipment markings before selecting 75°C; NM-B remains capped at 60°C.

Equipment grounding conductors are excluded. Verify neutrals, harmonic loads, and all other current-carrying conductors in the raceway or cable; the automatic count does not check these.

AC impedance (Chapter 9 Table 9)

At power factor 1, the reactance term is zero, but Table 9 AC resistance still applies. Unlisted sizes have no Table 9 result.

Planning estimate only. Consult local code and a qualified electrician before buying wire or energizing a circuit. Presets are hypothetical loads; this tool does not design motor, PV, battery, appliance, or EV installations.

Questions

Does 48 A always mean 6 AWG?

No. A 48 A continuous example is an operating current plus a terminal rating, a length, and a voltage-drop limit. This calculator checks 125 percent of that current against the unadjusted terminal column, then checks 48 A against adjusted ampacity. Voltage drop uses 48 A, not the 125 percent figure. At 60°C terminals the estimate can be larger than at 75°C terminals. Equipment may permit copper only. This page does not design an EV installation.

Why does the calculator multiply a continuous charging current?

NEC 625.42 treats EV charging loads as continuous, regardless of charging duration. The general continuous-load definition is maximum current expected for three hours or more; it is not a way to opt out of Article 625. On this page, 40 A continuous is checked at 50 A before correction; 48 A continuous is checked at 60 A before correction; 50 A continuous is checked at 62.5 A before correction. Adjusted conductor ampacity and voltage drop still use the operating current. NEC 625.41 separately requires overcurrent protection rated at least 125 percent of the maximum equipment load. Mixed loads, energy management and listed 100-percent-rated assemblies are not modeled. Planning estimate only. Consult local code and a qualified electrician.

Can the charger use aluminum wire?

Only if the equipment lists aluminum and the terminals are used as instructed, including torque. The calculator still shows an aluminum column so the table values can be compared. That column does not establish compatibility. For example, Tesla’s Gen 3 Wall Connector manual requires copper terminations. Follow the actual equipment’s installation manual.