Question 21 3AE02 - Third Assistant Engineer (Alt)

The Correct Answer is D **Explanation for Option D (controller circuit breaker):** When an electrical motor fails to start after pressing the "start" button on a power unit, the most common and first check in a troubleshooting sequence is always the electrical supply and protective devices. The circuit breaker is the primary protective device for the motor and its controller circuit. If the motor failed to start, the breaker is likely tripped (due to an overload or short circuit, or simply being left in the off position during maintenance), meaning no power is reaching the motor starter (contactor) or the motor itself. Checking and resetting the circuit breaker is the fastest and easiest initial step to restore power and determine if the issue is a simple trip or a more serious component failure. **Why the other options are incorrect:** * **A) controller contactor operating coil:** While a faulty operating coil would prevent the motor from starting, you would only check this after confirming that power is successfully reaching the controller. If the circuit breaker (upstream) is tripped, power isn't reaching the coil anyway, making the breaker the first check. * **B) pump discharge relief valve setting is too low:** The setting of the relief valve is a hydraulic parameter, not an electrical one. If the motor starts but stalls immediately, or if the system performance is poor, this might be a factor. However, it does not prevent the electrical motor from attempting to start when the start button is pressed. * **C) suction strainer condition:** A clogged suction strainer is a hydraulic issue that causes the pump to cavitate or starve for fluid. Like the relief valve, this condition would typically prevent the *pump* from operating correctly or cause the *motor* to overheat or stall after starting. It does not prevent the initial electrical start sequence from activating the motor.