HOLT Electricians Practice Exam

In terms of electrical efficiency, what is indicated by using an inverse time breaker for motor protection?

1. Faster tripping under overload

2. Moderate tripping time under overloads

3. Slower tripping for startup currents

4. Consistent current flow

The correct answer is: Slower tripping for startup currents

Using an inverse time breaker for motor protection is designed to enhance the efficiency of circuit interruption during various electrical conditions. This type of breaker is engineered to allow a certain level of current to flow without interruption for a limited time. Specifically, it is more tolerant of starting currents that can be significantly higher than the normal running currents of a motor. When a motor starts, it typically draws a high inrush current, often several times its normal operational level, which can last for a brief moment. An inverse time breaker will not trip immediately under this surge, allowing the motor to start and reach its operating speed. The characteristic of inverse time means that as the overload condition persists, the breaker’s tripping time decreases, which ultimately protects the motor from damage caused by prolonged overloads. This capability is vital in applications where motors are subjected to high starting currents, thereby supporting smooth operations and preventing unnecessary interruptions in service. Thus, the choice indicating slower tripping for startup currents accurately describes the functionality of an inverse time breaker in optimizing electrical efficiency and protecting motors.