HOLT Electricians Practice Exam

For continuous duty motors with a service factor of 1.15, overload devices must be rated to trip at what maximum percentage of the motor's nameplate full-load current?

1. 115 percent

2. 125 percent

3. 130 percent

4. 140 percent

The correct answer is: 125 percent

For continuous-duty motors with a service factor of 1.15, the motor is designed to handle a momentary overload above its nameplate full-load current, specifically 15% more than that rating due to the service factor. This means the motor could safely operate at 115% of its nameplate full-load current under normal conditions. However, the protection devices (overload relays) must allow for a safe operational period that accommodates this service factor. To ensure that the overload protection devices are appropriately rated without tripping unnecessarily during routine operations, they are typically set to trip at a maximum of 125% of the motor's nameplate full-load current. This provides a buffer for normal variations and brief overloads that the motor may experience while still ensuring protection against conditions that could potentially damage the motor. The 125% threshold accounts for scenarios where starting or temporary overloads occur, allowing the motor to operate effectively within its designed parameters without risking damage from these conditions.