For a 50-amp, 240-volt circuit running 200 feet, use 4 AWG copper THHN/THWN-2 wire protected by a 50-amp double-pole breaker. This specific size satisfies both NEC ampacity minimums and keeps voltage drop under the recommended 3% threshold at this exact distance.
- Material: Copper conductors (stranded or solid).
- Temperature Column: 75°C termination rating (per NEC 110.14(C) for equipment rated 100A or less).
- Ambient Temperature: 30°C (86°F) baseline.
- System Voltage: Single-phase 240V (standard for 50A loads like EV chargers, welders, and subpanels).
- Installation Method: Individual conductors in standard conduit (maximum 3 current-carrying conductors).
The Math: Ampacity vs. Voltage Drop at 200 Feet
Many DIYers look at NEC Table 310.16, see that 6 AWG copper is rated for 65 amps in the 75°C column, and assume it is sufficient for a 50-amp breaker. At 50 feet, they would be right. At 200 feet, that assumption will cause equipment failure.
The National Electrical Code (NEC 210.19(A) Informational Note) recommends a maximum voltage drop of 3% for branch circuits to ensure reasonable efficiency. For a 240V system, 3% equals 7.2 volts.
We calculate single-phase voltage drop using the standard formula: VD = (2 × K × I × D) / CM
- K (Copper resistivity) = 12.9 ohms-cmil/ft
- I (Current) = 50 Amps
- D (One-way distance) = 200 Feet
- CM (Circular Mils of the wire)
| Wire Size (Cu) | Ampacity (75°C) | Circular Mils (CM) | Voltage Drop at 50A | Percentage Drop (240V) | Passes 3% Rule? |
|---|---|---|---|---|---|
| 8 AWG | 50A | 16,510 | 15.62V | 6.51% | No |
| 6 AWG | 65A | 26,240 | 9.83V | 4.10% | No |
| 4 AWG | 85A | 41,740 | 6.18V | 2.57% | Yes |
| 3 AWG | 100A | 52,620 | 4.90V | 2.04% | Yes (Overkill) |
As the table shows, 6 AWG results in a 4.1% drop. While the wire won't melt (it's rated for 65A), the equipment at the end of the run will only see ~230V under full load. Motors will run hot, EV chargers may throttle or throw fault codes, and sensitive electronics will brown out. Stepping up to 4 AWG brings the drop down to a safe 2.57%.
Decision Tree: Locking In Your Final Wire Size
The 4 AWG recommendation assumes a standard 240V, non-continuous (or 40A continuous) load. Use this decision matrix to confirm your exact pick based on your specific installation variables.
| Scenario | System Voltage | Load Type | Required Wire (Copper) | Breaker Size |
|---|---|---|---|---|
| Standard Subpanel, EVSE, or Welder | 240V | Non-Continuous (or max 40A Continuous) | 4 AWG | 50A (2-pole) |
| Heavy 120V Tool / Single-Phase Tap | 120V | Non-Continuous | 2 AWG | 50A (1-pole) |
| True 50A Continuous Load (e.g., commercial heater) | 240V | Continuous (50A actual draw for 3+ hrs) | 4 AWG | 60A (2-pole) |
| Aluminum Feed (Cost-saving alternative) | 240V | Non-Continuous | 1/0 AWG Al | 50A (2-pole) |
Why 6 AWG Fails and 4 AWG Wins
The most common mistake on 200-foot runs is sizing strictly for ampacity and ignoring voltage drop. Here is exactly why 6 AWG fails in the real world at this distance:
- Motor Overheating: If your 50A circuit feeds a well pump, air compressor, or shop dust collector, a 4.1% voltage drop means the motor receives less voltage. To maintain the same mechanical power output, the motor draws more current. This excess current generates heat, degrading the winding insulation and drastically shortening the motor's lifespan.
- EV Charger Throttling: Modern Level 2 EV chargers monitor input voltage. If the voltage sags below a programmed threshold (often around 215V-220V under load) due to wire resistance, the charger's internal contactor may open, halting the charge and throwing a 'Grid Fault' error on the unit's display.
- Why not 8 AWG? 8 AWG is rated for exactly 50A in the 75°C column. However, if the wire is pulled through a hot attic or bundled, it will derate below 50A, causing the breaker to nuisance-trip. Furthermore, 8 AWG at 200 feet yields a massive 6.5% voltage drop, which is entirely unacceptable for any modern electrical equipment.
By standardizing on 4 AWG copper, you eliminate thermal bottlenecks and ensure the equipment receives clean, stable voltage regardless of minor environmental variables.
Derating Factors That Force a Size Up
The 4 AWG pick assumes standard conditions. You must adjust your wire size if your installation hits any of the following physical constraints:
1. Conductor Bundling (NEC 310.15(C)(1))
If you are pulling multiple circuits through the same conduit, the heat generated by adjacent wires cannot dissipate.
If you pull 4 to 6 current-carrying conductors in a single raceway, you must apply an 80% derating factor to the 90°C column ampacity.
Math: 4 AWG THHN is 95A at 90°C. 95A × 0.80 = 76A. This is still well above the 50A requirement, so 4 AWG remains safe for up to 6 conductors. If you pull 7-9 conductors (60% derating), 95A × 0.60 = 57A. You are still safe, but approaching the limit. For 10+ conductors, bump to 3 AWG.
2. High Ambient Temperatures
If your conduit runs across an unventilated roof deck or through a boiler room where ambient temperatures regularly exceed 30°C (86°F), you must apply temperature correction factors. At 41-45°C (105-113°F), the correction factor for 90°C wire is 0.87. Again, 4 AWG provides enough overhead to absorb this penalty without dropping below 50A.
3. Switching to Aluminum (AA-8000 Series)
Copper is expensive. If you want to use aluminum SER cable or XHHW-2 aluminum conductors to save money on a 200-foot run, you cannot use 4 AWG.
First, 4 AWG aluminum is only rated for 65A at 75°C. Second, aluminum has a higher resistivity (K = 21.2 instead of 12.9). Running the voltage drop formula for aluminum at 200 feet shows that 4 AWG Al yields a 4.2% drop, and 2 AWG Al yields a 3.3% drop. To stay under the 3% threshold with aluminum, you must step all the way up to 1/0 AWG Aluminum (which yields a 2.6% drop).
When the AHJ or an Engineer Must Confirm
While the calculations above represent standard NEC-style guidance, your local Authority Having Jurisdiction (AHJ) or a licensed Professional Engineer (PE) must confirm the design under these specific conditions:
- Feeder vs. Branch Circuit: If this 200-foot run is a feeder to a subpanel rather than a dedicated branch circuit, NEC 215.2 recommends a 3% drop on the feeder AND a 3% drop on the branch circuit (5% total combined). If your upstream utility service is already experiencing a 2% sag, a PE may require you to bump to 3 AWG or 2 AWG copper to maintain overall system headroom.
- Local Municipal Amendments: Certain jurisdictions (notably in California and parts of the Pacific Northwest) have adopted strict energy codes that mandate a hard 2% maximum voltage drop for all new construction, overriding the NEC's 3% informational recommendation. A 2% drop at 200 feet requires 3 AWG copper.
- Utility Transformer Distance: If the utility transformer is located 300 feet away from your main panel, and you are running another 200 feet to a detached garage, the cumulative distance is 500 feet. The utility's impedance must be factored in. Use a professional voltage drop calculator modeling the entire chain, or consult the utility engineer.
The Final Verdict: For 95% of residential and light-commercial applications involving a 50-amp, 240V load at 200 feet, buy 4 AWG copper THHN/THWN-2 (or 4/3 NM-B if running through framing cavities without conduit, though conduit is highly recommended for this gauge). Pair it with a 50-amp double-pole breaker, torque the lugs to the manufacturer's specification (typically 45 in-lbs for standard 50A panels), and your installation will run cool, safe, and code-compliant.
