Wire Current and Resistance

Like garden hoses, electrical wires are only designed to carry a limited amount of current to prevent short circuits. Unlike water and garden hoses, however, the current capacity of a wire is not directly proportional to the gauge.

A six-gauge wire (American Wire Gauge standards), for instance, has a 4.11mm diameter and a current capacity of 37 amps for power transmission, while a twelve-gauge wire only has a 2.05mm diameter and 9.3 amps—more than half the capacity. This isn't just because the wire is smaller; the electrical resistance grows as it shrinks.

At 1.588 ohms per 1,000 ft., the twelve-gauge wire has more resistance than the six-gauge at 1.296 ohms per 1,000 ft. The resistivity of the wire becomes more concentrated in a smaller cross-section, and will increase with the length of the wire. By widening the wire's cross-section and shortening the wire, resistivity can be dispersed and weakened.

Current sensors from power monitoring device suppliers keep track of the current flowing through an electrical load to protect it from short circuits. An overcurrent or overvoltage can cause serious damage to the local grid, resulting in costly repairs, if not fires. The data can be used to improve electrical systems, like installing the correct resistors to control electrical energy.