What is the rated capacity of dual-element fuses for a motor based on its horsepower?

• A. 80A
• B. 90A
• C. 100A
• D. 110A

Answer: (C)

The rated capacity of dual-element fuses for a motor is typically calculated based on the horsepower of the motor. For electric motors, especially under typical conditions described in the National Electrical Code (NEC), dual-element fuses are designed to provide protection from overloads as well as short circuits.

When determining the appropriate size for dual-element fuses, a common rule of thumb is to size the fuse based on the horsepower rating of the motor. Specifically, for a motor with a horsepower rating of 20 HP at 240 volts, the corresponding fuse rating can often be found to be around 100A. This matches well with the rated capacity of 100A indicated in the correct answer.

This capacity accounts for both starting currents, which can be several times the full load current, and running conditions. Therefore, the choice of 100A appropriately reflects the necessary protection for a motor of this size, ensuring that it can handle operational demands without risk of blowing the fuses under normal conditions while still providing safety against overloads.