All electrical wiring and devices have an amperage, or amp, rating. This is the maximum amount of electrical current they can safely carry. Most standard household circuits are rated for 15 amps or 20 amps, while large-appliance circuits (such as for electric dryers and ranges) may be rated for 30, 40, 50 amps, or even more.
When installing or replacing wiring or devices, all of the parts you use must have the appropriate amperage rating for the circuit. For example, a 20-amp circuit must have 12-gauge wiring, which is rated for 20 amps. If you install 14-gauge, 15-amp wiring on that circuit, you create a fire hazard because the 20-amp circuit breaker protecting that circuit might not shut off before the 15-amp wiring overheats.