How to Calculate the Total Resistance for a 120 Volt Circuit & a 15 Amp Breaker
- 1). Verify that you have a 15-amp circuit breaker. All circuit breakers have two of three possible factors printed on their side: volts, amps or watts. If it has "15 A" printed on the side, it's a 15-amp breaker.
- 2). Determine the amp rating by dividing the voltage by the watts. If the circuit breaker doesn't have "15 A" printed on its side, it will have its voltage and wattage ratings instead. To find the amps for a breaker with "120 V" (120 volts) and "1800 W" (1800 watts) printed on its side, divide 1,800 by 120; the answer comes out to 15, the number of amps for which the breaker is rated.
- 3). Divide the voltage of the circuit by the amp rating of the circuit breaker. For the 120-volt circuit with a 15-amp breaker, divide 120 by 15. The answer, 8, represents the total resistance for the circuit.