Question 181Electricity/Electronics - 1st Asst/Chief70% to pass
If the motor of the illustrated circuit fails to start and gives a loud hum when the start button is pushed, what is most likely the problem? Illustration EL-0007
AI Explanation
The correct answer is C) an open overload "OL" heater.
When the motor fails to start and gives a loud hum, it indicates that the motor is not receiving enough current to start. This is most likely due to an issue with the overload "OL" heater, which is responsible for protecting the motor from overcurrent conditions. If the overload heater is open, it will prevent the necessary current from reaching the motor, causing the observed symptoms.
The other answer choices are incorrect because an open main contactor "M" coil (A) would prevent the motor from starting entirely, an open overload "OL" relay contact (B) would also prevent the motor from starting, and an open disconnect switch "DS" (D) would disconnect power to the entire circuit, not just the motor.
Related Questions
#179 During its operation, loud buzzing and resultant welding of contacts of a magnetic relay may occur. Which of the following would be the likely cause? #180 If the contacts of a motor starter or controller fail to drop out when the 'stop' button is depressed, what could be the cause? #182 The motor starts when the start button in the illustration is pushed, but stops when the button is released. What is most likely the trouble? Illustration EL-0007 #183 As shown in figure "A" and "B" of the illustration, the potable water pump is short cycling by the action of the pressure switch as a result of an unusually high level in the potable water hydro pneumatic header tank. What is most likely the cause? Illustration EL-0043 #184 As shown in the illustration, what mechanism will disconnect the motor from the line in case of a sustained motor overload? Illustration EL-0080