HOLT Electricians Practice Exam

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What is the recommended branch circuit protection for a 20 horsepower 230-volt motor?

  1. 75 amperes

  2. 100 amperes

  3. 150 amperes

  4. 200 amperes

The correct answer is: 100 amperes

For a 20 horsepower, 230-volt motor, the National Electrical Code (NEC) provides guidelines for determining the appropriate branch circuit protection. To establish the correct size for branch circuit protection, one must typically consider the Full Load Amperes (FLA) of the motor, which is calculated using the following formula: 1. The Full Load Amperes for a 230-volt motor can generally be approximated using the formula: FLA = (Horsepower x 746) / (Voltage x Efficiency x Power Factor). Commonly, for a 20 HP motor operating at standard efficiency and power factor values, the FLA will hover around 60 to 80 amps. 2. According to NEC guidance, specifically Table 430.250, a 20 HP motor at 230 volts typically has a FLA of approximately 68 amps. 3. The branch circuit protection should be sized at no less than 125% of the FLA. Calculating this: 68 amps x 1.25 = 85 amps. This suggests that the breaker should not be lower than this value to adequately protect the motor without nuisance tripping during regular operation. 4. While options for circuit breakers include 75,

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