HOLT Electricians Practice Exam

For motors that do not have a service factor rating of 1.15 and up, or a temperature rise rating of 40 C or less, the overload protection device must be sized at not more than what percentage of the motor nameplate ampere rating?

1. 100 percent

2. 110 percent

3. 120 percent

4. 125 percent

The correct answer is: 110 percent

In the context of overload protection for motors, understanding the appropriate sizing of protection devices is essential for ensuring both safety and reliability. When a motor does not possess a service factor rating of 1.15 or higher, or a temperature rise rating of 40 degrees Celsius or less, it is necessary to follow specific guidelines for sizing the overload protection device. The correct answer—sizing the overload protection device at not more than 110 percent of the motor's nameplate ampere rating—ensures that the motor is adequately protected from overheating and damage due to excessive current. This percentage is established based on the operational limits of the motor and is meant to prevent the overload device from tripping under normal operational conditions, while still safeguarding the motor from prolonged exposure to higher currents that could lead to failures. Choosing a percentage higher than 110 percent could risk allowing excessive current to flow to the motor during fault conditions, possibly leading to overheating or other damage. This threshold helps maintain a balance between operational effectiveness and the necessary safety measures to protect both the motor and the electrical system.