HOLT Electricians Practice Exam

Which type of overload protection device may be used separately from the motor starter?

1. Thermal relay

2. Hydraulic fuse

3. Dual element fuse

4. Magnetic contractor

The correct answer is: Dual element fuse

The correct answer is the dual element fuse. This type of overload protection device can function independently of a motor starter, providing a reliable means of protecting electrical circuits from overloads. The dual element fuse consists of two elements that respond differently to different time-current characteristics, allowing it to provide both short-circuit and overload protection. When an overload occurs, the slower acting element of the fuse allows for normal current surges that occur during motor startup but will melt and disconnect the circuit if the overload persists. This specific design is beneficial in applications where additional flexibility and enhanced protection are needed. The other options are typically associated with motor starters and may not operate as standalone devices. For example, a thermal relay is designed specifically to work in conjunction with motor starters, providing overload protection by responding to heat generated by the motor's current. A hydraulic fuse, while a form of overload protection, is more specialized and used in different contexts, primarily in hydraulic systems rather than electric motor circuits. A magnetic contactor, on the other hand, serves to control electrical power flow to devices and is not designed for overload protection on its own. Thus, in the context of standalone operation, the dual element fuse clearly emerges as the appropriate choice.