A 60-amp load requires a nine-gauge wire or less for chassis wiring and a four-gauge wire or less for power transmission. Safety margins generally dictate using a lesser gauge wire to avoid overloading. These two gauges, measured by the American Wire Gauge standard, differ in diameter by 0.0899 inches.
The four-gauge wire is relatively thick, at 0.2043 inches in diameter, while the nine-gauge wire is only 0.1144 inches thick. The greater thickness of the former gives it properties such as less resistance at 0.2485 ohms per 1,000 feet, a larger maximum current capacity for either mode and a large breaking force for soft-annealed copper wire, which is set at 1,210 pounds at 37,000 pounds per square inch. The nine-gauge wire has more resistance than the thicker wire, lower overall maximum current capacity and a weaker breaking force rating.