Wire size scenario
For a 50 amps copper circuit at 240 V single-phase, NEC 310.16 ampacity needs 8 AWG at 75 °C. Over 100 feet, voltage drop bumps the recommendation to 6 AWG (about 2.05% drop). Adjust the run below.
Recommended wire size
—Enter a load, length, and voltage to size the conductor.
| Ampacity needs | — |
|---|---|
| Voltage drop needs | — |
| Recommended (larger of the two) | — |
| Ampacity of recommended | — |
| Voltage drop of recommended | — |
At 240 V single-phase over 100 feet, a 50 amps copper load needs 6 AWG (about 2.05% drop). Ampacity alone would allow copper 8 AWG, but over 100 feet voltage drop pushes the recommendation up to 6 AWG to stay within the 3% target (about 2.05%).
This recommendation covers ampacity and voltage drop only, for copper at 75 °C. It does not apply ambient-temperature or conductor-count derating, the 125% factor for continuous loads, conduit fill, or terminal ratings — any of which can push the size up. Aluminum of the same load typically goes up one or two sizes. Always confirm with a licensed electrician and your local code (AHJ).
Ampacity per NEC 310.16; voltage drop per NEC Ch.9 Table 8 (75 °C copper).
Fifty-amp circuits are associated with ranges, welders, RV receptacles, spa equipment, and NEMA 14-50 outlets. The label is not a universal load calculation: duty cycle, continuous operation, receptacle configuration, and equipment instructions all matter.
A 14-50 receptacle can be installed for several purposes, but the connected load determines the design. Before using this recommendation, document whether 50 A is actual current, a receptacle rating, or a breaker rating. That distinction is crucial for continuous EV charging.
Code focus: The calculator compares ordinary ampacity with a 3% voltage-drop design target. It does not apply welder duty-cycle rules, range demand factors, spa requirements, or continuous-load sizing.
| One-way length | Ampacity minimum | Recommended size | Governing check |
|---|---|---|---|
| 25 ft | 8 AWG | 8 AWG | ampacity |
| 50 ft | 8 AWG | 8 AWG | ampacity |
| 100 ft | 8 AWG | 6 AWG | voltage drop |
| 150 ft | 8 AWG | 4 AWG | voltage drop |
For 50 amps of copper at 240 V, NEC 310.16 ampacity at 75 °C needs 8 AWG. Over a 100 feet run, voltage drop calls for 6 AWG, so the recommended size is 6 AWG — the larger of the two. Aluminum, derating, continuous load, and local code may change this; confirm with a licensed electrician.
On a short run where voltage drop isn't a factor, 50 amps of copper needs 8 AWG at 75 °C by ampacity alone (NEC 310.16). Longer runs need a larger size for voltage drop — this page assumes 100 feet.
Both. The conductor must carry the current (ampacity, NEC Table 310.16) and keep voltage drop within target (NEC Chapter 9 Table 8). The recommended size is the larger of the two. It still doesn't replace ambient or conductor-count derating, the 125% continuous-load factor, conduit fill, or terminal-rating checks — verify with your local code (AHJ).
Source links and page assumptions reviewed .
Estimate only, based on NEC 310.16 ampacity and NEC Chapter 9 Table 8 voltage drop. Not a substitute for a licensed electrician or your local code (AHJ). It does not fully model ambient or conductor-count derating, the 125% continuous-load factor, conduit fill, or terminal ratings. Verify against the current NEC and local code before wiring. Based on NEC 310.16 and NEC Ch.9 Table 8.