A common problem when installing a GFCI receptacle is knowing the maximum wattage that can run through that receptacle before the GFCI breaker trips due to excessive current. This problem arises due to GFCI breakers being rated only in amperage and not in watts. Determining the maximum wattage that can run through a GFCI receptacle only requires a knowledge of the wattages that will be drawn from the circuit, the voltage of the circuit and the amperage rating of the breaker connected to the circuit.
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Add together the wattage ratings for all appliances that will be connected to the GFCI receptacle. For example, if you intend to connect a two lamps that each draw 60 watts, your total wattage on the circuit will be 120 watts.
Multiply the amperage of the GFCI breaker attached to the electrical circuit by its voltage rating to find the maximum allowed wattage on the circuit. For example, if you are using a 15-amp breaker on a 120-volt circuit, your maximum allowable wattage will be 1,800 watts.
Multiply your maximum allowable wattage by 80 percent to determine the maximum continuous wattage allowed by the circuit. So in the example of 1,800 watts, the maximum continuous wattage would be 1,440 watts.
Compare your total wattage to the maximum continuous wattage that you calculated. If it is less than your current GFCI receptacle, it is within specification. However, if the total wattage is more, get a GFCI breaker with a higher amperage rating to place on the circuit containing the GFCI receptacle.