Journeyman Electrician Practice Exam

When sizing time-delay Class CC fuses for motor protection, they should be sized at the same value as which of the following?

1. Time-delay fuses

2. Non-time-delay fuses

3. High-speed fuses

4. Panel fuses

The correct answer is: Non-time-delay fuses

When sizing time-delay Class CC fuses for motor protection, it is important to size them at the same value as non-time-delay fuses. This is because non-time-delay fuses are typically designed to handle motor starting current without tripping immediately. They allow for temporary overloads that occur during motor startup and are generally sized to accommodate inrush currents, which can be several times the motor's full load current. Time-delay Class CC fuses have a built-in delay that allows them to withstand these inrush currents without blowing. Therefore, sizing them the same as non-time-delay fuses provides the necessary protection against short circuits while still allowing for the motor's normal starting behavior. Understanding the specific applications of these fuses is crucial, as the balance between protection and functionality must be maintained to avoid nuisance tripping while ensuring the motor is protected from faults. The other options, while related to fuses, do not specifically correspond to the unique characteristics required for effectively protecting motors.