Wires are rated for the voltages as well as the wattage they can be used with. A wire with a larger diameter can carry more current than a smaller one. Using the wrong size wire can cause the wire to overheat and burn.
Fifty-amp Aluminum Wire
Aluminum wires are rated differently than copper wires. For a 50-amp aluminum wire, use No.4 AWG. The smaller the number on the wire, the larger the wire diameter. For example No. 4 is bigger in size than No. 6. Aluminum wires come in different types. Types THWN and RHW are the most commonly used ones. No. 6 is only good up to 40-amp.
Fifty-amp Copper Wire
For copper wire, No. 6 or No. 8 THWN can be used. No. 6 copper wire can support up to 55-amp at a temperature of 60 degree Celsius. No. 6 wire is strongly recommended. It's best if a bigger size wire is used.
When calculating a circuit, pay special attention to the voltage drop on the wire. Voltage drop is usually caused by the wire resistance. The smaller the wire size, the more the resistance. When selecting a wire size, if the run is more than 100 feet, go one size up.