When makers and DIYers ask how to wire a 220 breaker box, they are almost always referring to installing a 240V subpanel to feed heavy loads like welders, EV chargers, or workshop machinery. Modern residential power is 120/240V split-phase, so '220V' is a legacy term for what we now wire as 240V circuits.

The direct answer: To wire a standard 60A 240V subpanel, you need a 4-wire feed (two hots, one neutral, one ground). Use 6 AWG copper THHN/THWN-2 wire. The black and red hots land on a 60A double-pole breaker in the main panel, the white neutral lands on the isolated neutral bar in the subpanel, and the bare/green ground lands on the bonded ground bar. This assumes a copper conductor rated at the 75°C ampacity column per NEC Table 310.16.

Decision Tree: Sizing Your 240V Feed and Breaker

Before pulling wire, you must match your breaker size and wire gauge to your actual continuous load. The National Electrical Code (NEC) requires branch circuits to be sized at 125% of the continuous load (loads expected to run for 3 hours or more). Use this decision matrix to select your exact materials.

Target Continuous Load Required Breaker Size (125% Rule) Copper Wire Gauge (75°C Column) Concrete Part Pick (Square D QO)
24A (Small welder / compressor) 30A or 40A 10 AWG (for 30A) / 8 AWG (for 40A) QO240 (40A)
32A (Level 2 EV Charger) 40A or 50A 8 AWG (for 40A) / 6 AWG (for 50A) QO250 (50A)
48A (General workshop subpanel) 60A 6 AWG QO260 (60A) — DEFAULT PICK
65A (Large detached garage) 90A 4 AWG QO290 (90A)

Default Recommendation: If you are wiring a subpanel for a general-purpose workshop or detached garage, terminate on the 60A / 6 AWG copper configuration. It provides 14,400 watts of total 240V capacity, which easily covers a 240V welder, a 120V lighting circuit, and a 120V receptacle simultaneously without voltage drop issues over runs up to 100 feet.

Tools, Materials, and Safety Prerequisites

Do not substitute components when working inside a live panel. Use the exact tools and ratings specified below to ensure secure terminations and prevent arc faults.

Materials List

  • Subpanel: Square D QO 12-Space 100A Main Lugs (Model: QO112M100C)
  • Feeder Breaker: Square D QO 60A Double-Pole (Model: QO260)
  • Wire: 6 AWG THHN/THWN-2 stranded copper (Black, Red, White, Green)
  • Conduit: 1-inch PVC Schedule 40 or 3/4-inch EMT with appropriate fittings
  • Lugs: ILSCO DBTP-4/0-6 (if your panel requires external lug adapters for 6 AWG stranded)

Tool List

  • Torque Screwdriver: Klein Tools 706-T (crucial for NEC 110.14(D) compliance)
  • Wire Strippers: Klein 11055 (handles 6 AWG cleanly without nicking strands)
  • Multimeter: Fluke 117 True-RMS (CAT III 600V rated minimum)
  • Non-Contact Voltage Tester: Fluke 1AC-II VoltAlert

⚠️ MAINS SAFETY CALLOUT: DE-ENERGIZE AND VERIFY

Working inside a main panel exposes you to lethal 240V potential and high fault current. Before opening the main panel cover:

  1. Turn OFF the main service disconnect breaker.
  2. Apply a Lockout/Tagout (LOTO) device to the main breaker handle.
  3. Use your non-contact tester on the branch breakers to confirm they are dead.
  4. Critical: The utility feed lugs at the very top of the main breaker remain LIVE even when the main breaker is off. Never touch the top lugs. If your panel layout forces you near them, contact your utility to pull the meter. Local code may require a licensed electrician for main panel tie-ins.

Step-by-Step: Wiring the 240V Subpanel

Follow this exact sequence to ensure proper wire routing, color coding, and torque specifications.

Step 1: Route the Conduit and Pull the Feed

Run your 1-inch PVC or 3/4-inch EMT from the main panel to the subpanel location. Use a fish tape to pull the four 6 AWG THHN wires (Black, Red, White, Green) simultaneously. Leave at least 8 inches of slack inside both enclosures. Apply a small amount of Polywater J pulling lubricant to the wires if the run exceeds 40 feet or includes more than two 90-degree sweeps.

Step 2: Terminate at the Main Panel (Source)

  1. Black Wire (Hot A): Strip 5/8 inch of insulation. Land on the left terminal of the 60A QO260 double-pole breaker.
  2. Red Wire (Hot B): Strip 5/8 inch. Land on the right terminal of the QO260 breaker.
  3. White Wire (Neutral): Strip 3/4 inch. Land on an available terminal on the main panel neutral bar.
  4. Green Wire (Ground): Strip 3/4 inch. Land on an available terminal on the main panel equipment grounding bar.
  5. Torque: Set your torque screwdriver to 35 in-lbs (verify against the QO260 datasheet label) and tighten all four terminations until the tool clicks.

Step 3: Terminate at the Subpanel (Load)

  1. Black Wire (Hot A): Land on the Top Main Lug (L1) of the subpanel.
  2. Red Wire (Hot B): Land on the Bottom Main Lug (L2) of the subpanel.
  3. White Wire (Neutral): Land on the isolated neutral bar. (Ensure the green bonding screw or bonding strap has been removed from this bar).
  4. Green Wire (Ground): Land on the equipment grounding bar, which must be bonded directly to the steel subpanel enclosure.
  5. Torque: Torque the main lugs to 45 in-lbs (standard for 100A panel lugs accepting 6 AWG wire) and the bar terminals to 35 in-lbs.
Pro Tip: Use a piece of black electrical tape to re-identify the white neutral wire at both ends if you are using it strictly as a hot wire in a pure 240V circuit. However, for a subpanel feed, the white wire must remain white and serve as the neutral to carry the unbalanced 120V return current.

The Most Common Botch: Bonding Neutral and Ground

The single most dangerous mistake when wiring a 240V subpanel is leaving the neutral bar bonded to the ground bar (and the metal enclosure) at the subpanel.

The Symptom: If you leave the green bonding screw installed in the subpanel, neutral current will split and flow back to the main panel on both the white neutral wire and the bare green ground wire. You may notice a mild tingle when touching the subpanel cover, or GFCI breakers downstream may nuisance-trip randomly.

The Hazard: If the white neutral wire ever breaks or comes loose upstream, the entire 120V return current will seek a path back through the green ground wire. This will energize the metal subpanel enclosure, the metal conduit, and the grounding pins of every tool plugged into the subpanel to 120V. This is a fatal shock hazard and a direct violation of NEC Article 250.32(B), which mandates that an equipment grounding conductor must not carry normal neutral current.

The Fix: Before terminating the white wire at the subpanel, locate the green bonding screw or copper bonding strap on the neutral bar. Remove it completely. The neutral bar must 'float' (be isolated from the steel box), while the ground bar must remain bolted directly to the steel box.

Verify and Test: Expected Meter Readings

Never assume the wiring is correct just because the breakers didn't trip immediately. Perform these exact tests with your Fluke 117 multimeter set to AC Volts (V~).

  1. Turn ON the main service disconnect.
  2. Turn ON the 60A QO260 feeder breaker in the main panel.
  3. Test 1 (Hot to Hot): Place one probe on the subpanel L1 lug (Black) and the other on L2 (Red).
    Expected Reading: 240V (Acceptable range: 228V - 252V).
  4. Test 2 (Hot A to Neutral): Probe L1 (Black) to the Neutral bar.
    Expected Reading: 120V.
  5. Test 3 (Hot B to Neutral): Probe L2 (Red) to the Neutral bar.
    Expected Reading: 120V.
  6. Test 4 (Neutral to Ground): Probe the Neutral bar to the Ground bar.
    Expected Reading: < 2.0V (Ideally less than 0.5V). If you read 120V here, your hot and neutral are crossed, or you have a lost neutral. Turn off the breaker immediately.

Final Code and Inspection Notes

When scheduling your rough-in and final inspections with your local Authority Having Jurisdiction (AHJ), ensure your installation meets these baseline requirements:

  • 4-Wire Feed: Since the 2008 NEC cycle, all subpanels (including detached garages and outbuildings) require a separate 4-wire feed. You cannot use the ground wire as a neutral return.
  • Disconnecting Means: If your subpanel is in a detached building, NEC 225.31 requires a local disconnecting means. A main breaker in the subpanel (e.g., QOM2100VH) satisfies this, or you can use the 60A breaker in the main panel if the subpanel is in the same building.
  • Grounding Electrodes: A detached structure subpanel requires its own grounding electrode system (typically two 8-foot copper ground rods driven 6 feet apart and bonded to the subpanel ground bar). This does not replace the green equipment grounding wire run from the main panel; it supplements it for lightning and surge protection.

By strictly following the 6 AWG / 60A parameters, isolating the neutral bar, and verifying your voltages with a true-RMS meter, your 240V subpanel will provide safe, code-compliant power for decades of heavy-duty workshop use.