The National Electric Code specifies the rules for safe installation and wiring of electrical devices, including switches, outlets and appliances. The code requirements governing lighting switches may seem counterintuitive to other electrical codes, but it provides guidelines for safe wiring.
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Switches must be marked for the voltage, current and type of current they can carry. The specification includes the maximum voltage, the maximum current and the type of current — either alternating current (AC) or direct current (DC). If a switch does not specify AC or DC, it may carry either type of current.
National Electric Code Requirements
National Electric Code 404.14 specifies that a switch may control a load that does not exceed the rating of the switch. If a lighting circuit has a 10 amp load operating at 125 volts AC, the switch that controls that circuit must be rated at a minimum of 125 volts, 10 amps AC, even on a circuit with a 20 amp circuit breaker. An exception is made for motors controlled by switches: The current must not exceed 80 percent of the switch's current rating.
Although NEC code allows a switch with an amperage rating lower than the circuit breaker rating, this may cause a problem if changes are made to the circuit. If the lighting load changes and exceeds the rating of the switch, the switch may overheat and cause a fire.