HOLT Electricians Practice Exam

What is the maximum allowable ampere for short-circuit protection of a 5 horsepower, 230 Volt motor?

1. 40

2. 50

3. 60

4. 70

The correct answer is: 50

To determine the maximum allowable ampere for short-circuit protection of a 5 horsepower, 230 Volt motor, it is important to refer to the National Electrical Code (NEC) which outlines the sizing of short-circuit protective devices for motors. For a motor, you typically start by converting horsepower to kilowatts, then calculating the full-load ampere rating. The formula for a 230 Volt motor is: 1. **Full Load Current Calculation**: The full-load current for a 5 HP motor at 230 volts can be estimated using standard tables. The full-load current for a 5 HP motor is approximately 25 amps. 2. **Short-Circuit Protection Sizing**: According to NEC guidelines, for motors, the branch-circuit short-circuit protection must be rated at a maximum of 250% of the full-load current. So, for a 25 amp full-load current, the calculation would be: \[ 25 \text{ amps} \times 2.5 = 62.5 \text{ amps} \] 3. **Selecting the Correct Circuit Breaker**: Circuit breakers usually come in standard sizes. The nearest standard size that does not exceed this calculated value