To keep voltage drop under the NEC-recommended 3% limit for branch circuits, use 14 AWG copper up to 38 feet (15A/120V), 12 AWG up to 45 feet (20A/120V), and 10 AWG up to 96 feet (30A/240V). For runs exceeding these distances, you must step up one or two AWG sizes to prevent equipment damage and efficiency loss. The comprehensive chart below provides exact maximum one-way distances for copper and aluminum conductors based on a strict 3% voltage drop threshold at 75°C.
How to Read This Wire Size Chart for Distance
Before pulling wire through conduit, you need to understand what this data actually represents. This table is synthesized using the exact circular mil (CM) values from NEC Chapter 9, Table 8 (Conductor Properties) and applies the standard voltage drop formula: Distance = (Voltage Drop × CM) / (2 × K × Current). We use K=12.9 for copper and K=21.2 for aluminum, representing the resistance of the metals at a realistic 75°C operating temperature.
The distances listed are one-way lengths from the breaker panel to the farthest receptacle or load. If your physical tape measure reads 60 feet from the panel to the outlet, your one-way distance is 60 feet (the current travels 60 feet out on the hot wire and 60 feet back on the neutral, but the formula already accounts for the round-trip via the multiplier of 2). The ampacity limits shown are the standard maximum overcurrent protection ratings for these wire sizes under NEC Table 310.16.
| AWG Size | Material | Max Amps (Breaker) | 120V Max Distance (ft) | 240V Max Distance (ft) |
|---|---|---|---|---|
| 14 AWG | Copper | 15A | 38 | 76 |
| 12 AWG | Copper | 20A | 45 | 91 |
| 10 AWG | Copper | 30A | 48 | 96 |
| 8 AWG | Copper | 40A | 57 | 115 |
| 6 AWG | Copper | 50A | 73 | 146 |
| 4 AWG | Copper | 60A | 97 | 194 |
| 2 AWG | Copper | 90A | 102 | 205 |
| 1/0 AWG | Copper | 100A | 147 | 294 |
| 4/0 AWG | Copper | 200A | 147 | 295 |
| 8 AWG | Aluminum | 40A | 35 | 70 |
| 6 AWG | Aluminum | 50A | 44 | 89 |
| 4 AWG | Aluminum | 60A | 59 | 118 |
| 2 AWG | Aluminum | 90A | 62 | 125 |
| 1/0 AWG | Aluminum | 100A | 89 | 179 |
| 4/0 AWG | Aluminum | 200A | 89 | 179 |
Quick-Jump: Most Queried AWG Distances for 120V & 240V
Bookmark this section for the most common residential and workshop runs. These values assume a dedicated circuit with a single load at the end of the run.
- 15A / 120V Lighting or Receptacles (14 AWG Cu): Maximum 38 feet before stepping up to 12 AWG.
- 20A / 120V Kitchen/Bath Receptacles (12 AWG Cu): Maximum 45 feet before stepping up to 10 AWG.
- 30A / 240V Dryer or RV Outlet (10 AWG Cu): Maximum 96 feet before stepping up to 8 AWG.
- 50A / 240V Range or Hot Tub (6 AWG Cu): Maximum 146 feet before stepping up to 4 AWG.
- 100A / 240V Subpanel Feed (1/0 Cu or 2/0 Al): Copper maxes out at 294 feet; Aluminum maxes out at 179 feet (assuming 125A wire on a 100A breaker).
- 200A / 240V Main Service Subpanel (4/0 Al): Maximum 179 feet. If your run is 200 feet, you must bump to 250 kcmil Aluminum.
Which Column Applies to Your Installation?
A common point of confusion for DIYers is the temperature rating column on the wire spool versus the breaker. You will typically buy THHN/THWN-2 wire, which is rated for 90°C. However, NEC 110.14(C) dictates that your circuit's ampacity is limited by the lowest temperature rating of any connected component.
The 75°C Rule for Voltage Drop: While your ampacity (breaker sizing) is usually limited by the 60°C or 75°C column of NEC Table 310.16 due to termination ratings, your voltage drop calculation must use the 75°C resistance values. Why? Because a fully loaded wire heats up. Copper resistance increases by roughly 0.4% for every 1°C rise. If you calculate voltage drop using the 20°C (68°F) baseline resistance found in some basic physics textbooks, you will underestimate the voltage drop on a hot wire running through a sun-baked attic by nearly 20%. The chart above already bakes in the 75°C K-factor to protect you from this exact mistake.
How Derating and Bundling Modify Your Base Wire Size
Voltage drop and ampacity derating are two completely different physical problems, but they are frequently conflated. Derating (per NEC Table 310.15(C)(1)) is about heat dissipation. When you pull more than three current-carrying conductors through a single conduit, the wires heat each other up, and you must reduce their allowable ampacity.
Crucial distinction: Derating does not fix voltage drop. If you have four current-carrying wires in a pipe (e.g., two 120V multi-wire branch circuits sharing a neutral), you apply an 80% derating factor. If your load is 20A, 12 AWG THHN (rated 30A at 90°C × 0.80 = 24A) is perfectly legal for ampacity. But if that run is 80 feet long, 12 AWG will still suffer a 5.3% voltage drop. You must bump to 10 AWG to solve the voltage drop, regardless of the derating math. Always calculate ampacity first to ensure the wire won't melt, then calculate voltage drop to ensure the equipment will actually run.
Decision Path: Pick Your Exact AWG in 4 Steps
Stop guessing and follow this exact decision tree to arrive at your final wire purchase.
- Identify Load and Voltage: Check the equipment nameplate for Full Load Amps (FLA) and voltage. (e.g., 240V, 30A air compressor).
- Measure Exact One-Way Distance: Measure the physical path the wire will take from the breaker to the disconnect/outlet. Add 10% for slack and routing. (e.g., 110 feet physical = 121 feet one-way).
- Consult the Base Chart: Look at the 30A / 240V row. 10 AWG Copper maxes out at 96 feet. Your run is 121 feet. Decision: Bump up one size to 8 AWG Copper (max 115 ft). Still short. Bump to 6 AWG Copper (max 146 ft).
- Apply Conduit Derating (If applicable): Are there more than 3 current-carrying wires in the conduit? If no, your wire size is locked. If yes, verify the 90°C derated ampacity of 6 AWG (75A × 0.8 = 60A). 60A > 30A, so 6 AWG is safe.
The Concrete Pick: For a 240V, 30A compressor located 110 physical feet from the panel, your final pick is 6 AWG Copper THHN (or 4 AWG Aluminum if you want to save money and use anti-oxidant paste on the lugs). Buy a 250-foot spool to account for the hot, neutral, ground, and panel pigtails.
What This Chart Cannot Tell You
While this wire size chart for distance covers 95% of standard residential and light commercial runs, it has three blind spots you must account for on the jobsite:
- Motor Inrush Current (LRA): The chart uses Full Load Amps (FLA). Motors draw 500% to 700% of their FLA for a fraction of a second during startup (Locked Rotor Amps). If your air compressor or well pump is at the very end of a long run and struggles to start, or trips the breaker instantly upon startup, the momentary voltage drop is exceeding 15%. You must size the wire based on LRA, not FLA, which usually requires bumping up two additional AWG sizes.
- Termination Torque: Sizing the wire correctly means nothing if the connection is loose. NEC 110.14(D) requires terminations to be tightened to the manufacturer's specified torque. Use a calibrated inch-pound torque screwdriver for breakers and receptacles. A loose 6 AWG lug will arc and burn regardless of how perfectly you calculated the voltage drop.
- Local AHJ Overrides: The NEC 3% branch circuit and 5% feeder+branch combined voltage drop limits are technically 'Informational Notes' (recommendations) in many NEC cycles, though some local jurisdictions adopt them as strict law. Always verify with your local Authority Having Jurisdiction (AHJ) or inspector, as some utility companies require a maximum 2% drop for solar tie-ins or heavy machinery feeds.
For dynamic calculations on highly specific runs, cross-reference your final pick with the Southwire Voltage Drop Calculator to account for exact ambient temperatures and specific conduit types. For deep dives into termination rules, review the NFPA 70 National Electrical Code Article 110.14 directly.
