Field guide: wiring a 240V outlet, code citations (edition 2)

Plan the circuit before you pull a single wire

A 240V receptacle is not a 120V outlet with extra voltage. You are pulling two ungrounded conductors, sometimes a neutral, always an equipment grounding conductor. Decide the load first, then the conductor, then the breaker, then the box. Working backward from the receptacle face is how mistakes get made.

Verify the appliance nameplate. A welder, a dryer, a range, a mini-split, and an EV charger all share the 240V label and almost nothing else. NEC 210.23 governs permissible loads on branch circuits, and 210.21(B) covers receptacle ratings on individual versus multi-outlet circuits. Match the receptacle configuration (NEMA 6-15, 6-20, 6-30, 6-50, 14-30, 14-50) to the plug, not to what was on the shelf at the supply house.

• Confirm load in amps, not just watts. Continuous loads (EVSE, most welders in duty cycle) require 125% sizing per 210.19(A) and 210.20(A).
• Decide 3-wire (two hots + ground) versus 4-wire (two hots + neutral + ground). Ranges and dryers in new work are 4-wire per 250.140.
• Pick the breaker last. The conductor ampacity sets the ceiling, not the other way around.

Conductor sizing and the 60 C / 75 C trap

NEC 110.14(C) is where careful electricians get tripped up. Equipment terminations rated 75 C let you use the 75 C column of Table 310.16 for conductors larger than 1 AWG, but for 14 through 1 AWG the terminations are commonly 60/75 C and the device itself may be listed only at 60 C. Read the breaker and the receptacle markings before you size off the 75 C column.

For a 50A circuit feeding a 14-50, 6 AWG copper at 75 C is 65A, which works. 8 AWG copper at 60 C is 40A, which does not. NM cable (Romex) is sized at 60 C per 334.80 regardless of conductor temperature rating, so 6/3 NM on a 50A breaker is your typical residential range or EVSE pull. If you are in conduit with THHN/THWN-2, you get the 75 C column back.

If the install is for a 48A continuous EV charger, 6 AWG NM is at its limit at 55A (60 C ampacity for #6 NM) and the 125% rule pushes the minimum OCPD calc to 60A. Pull #4 or run THHN in conduit. Do not split the difference.

Grounding, bonding, and the neutral question

3-wire dryer and range cords were grandfathered for existing branch circuits under 250.140 exception, but any new circuit is 4-wire. The frame of the appliance must be bonded to the equipment grounding conductor, not to the neutral. If you are replacing a receptacle on an existing 3-wire circuit, you can keep 3-wire only if the branch circuit and the appliance bonding strap allow it. New circuit, new opening, new run: 4-wire, every time.

The EGC sizes off 250.122 based on the OCPD, not the ungrounded conductor. A 50A circuit needs a 10 AWG copper EGC minimum. If you upsized the ungrounded conductors for voltage drop, 250.122(B) requires you to upsize the EGC proportionally. This catches people on long EV charger runs.

• Bond the box if metallic. 250.148 requires the EGC to be spliced and bonded to any metallic box at every device.
• Torque the lugs. 110.14(D) made manufacturer torque specs enforceable. Carry a torque screwdriver, not a guess.
• Identify the neutral. White or gray, never reidentified from another color in sizes 6 AWG and smaller per 200.6.

GFCI and AFCI: read the room and read 210.8

210.8(A) GFCI requirements have expanded with each cycle. In the 2023 NEC, all 125V through 250V receptacles 50A or less in dwelling unit kitchens, garages, basements, laundry areas, outdoors, and within 6 feet of a sink fall under GFCI protection. That includes the 14-50 in the garage for the EV. Adoption varies by state and local amendment, so check what edition your AHJ enforces before you quote the job.

AFCI per 210.12 generally applies to 120V branch circuits in dwelling living areas, so a true 240V-only circuit (no neutral, no shared 120V loads) is typically outside AFCI scope. A 14-50 with a neutral feeding a range in a kitchen is a different conversation, and dual-function breakers solve both at once.

Box fill, cord whips, and the install itself

314.16 box fill is non-negotiable on 6 AWG conductors. A single 6 AWG counts as 5.0 cubic inches, the EGC counts once total, the device counts as two conductors of the largest size connected to it. A 14-50 in a 4-square box with a mud ring needs the math done on paper before the wire goes in.

For surface-mount installs, a 4-11/16 box with a single-gang raised cover is standard for a 14-50 or 6-50. Strain relief at the cable entry is required by 314.17(B). If you are landing on a hardwired EVSE instead of a receptacle, follow the EVSE manufacturer instructions per 110.3(B), they often specify torque and conductor type explicitly.

On a 14-50 for an EV, land the neutral even if the charger does not use it. Future-proofs the circuit and keeps you on the right side of 210.50 and the receptacle listing.

1. De-energize and verify with a known-good tester.
2. Pull conductors, leave 8 inches at the box per 300.14.
3. Land hots on brass, neutral on silver, EGC on green. Torque to spec.
4. Megger or insulation-test long runs before energizing.
5. Energize, verify L1-L2 at 240V nominal, L-N at 120V nominal, L-G at 120V nominal, N-G at near zero.