What size wire is required for a 120V circuit that is 215 feet long with a load of 39 amps?

To determine the appropriate wire size for a 120V circuit that is 215 feet long with a load of 39 amps, it is essential to consider both the current-carrying capacity of the wire and the voltage drop that occurs over long distances.

For a circuit carrying 39 amps, the first step is to consult the National Electrical Code (NEC) table for allowable ampacities of conductors based on their gauge. Generally, a #6 gauge wire can handle up to 55 amps in most installations, making it suitable for your load of 39 amps.

However, wire size must also take into account voltage drop, especially for longer runs. A typical rule of thumb is to keep voltage drop below 3% for branch circuits. Over a distance of 215 feet, a #10 wire would have too much voltage drop for a 120V circuit under a 39 amp load, and while a #8 gauge wire would be acceptable, it is often more conservative to opt for #6 to ensure ample capacity for safe operation and to minimize voltage drop.

Choosing #6 gauge wire not only fulfills the load requirement but accounts for potential future increases in demand and helps maintain adequate voltage at the load end of the circuit. Thus