HOLT Electricians Practice Exam

What is the maximum percentage of motor nameplate current rating for an overload protection device with a nameplate temperature rise rating not over 40 degrees C?

1. 100%

2. 125%

3. 150%

4. 175%

The correct answer is: 125%

An overload protection device must be sized appropriately to ensure it can handle the motor’s starting and running loads without tripping unnecessarily. The National Electrical Code (NEC) generally provides guidelines for these ratings. For a motor with a nameplate temperature rise rating not exceeding 40 degrees Celsius, the NEC permits the overload protection device to be set at a maximum of 125% of the motor’s nameplate current rating. This allows for a reasonable margin to accommodate the inrush current that occurs when a motor starts, as well as any temporary overloads that might occur during its operation. Setting the protection device above 125% could lead to insufficient protection against overheating, exceeding the motor's design limits, and potentially causing damage to the motor. Thus, the 125% threshold balances the need for adequate protection while allowing for normal operating conditions.