Question 132Electricity/Electronics - QMED70% to pass
In the illustrated motor controller, the motor fails to start. A voltmeter reading between 1 and 5 reads line voltage, while the voltmeter reading between 2 and 5 reads 0 VAC. What is most likely the problem? Illustration EL-0007
AI Explanation
The correct answer is B) an open stop switch contact (when not pushed in).
The reasoning is that with line voltage present between terminals 1 and 5, but 0 VAC between terminals 2 and 5, the issue is likely an open circuit in the stop switch contact. When the stop switch is not pushed in (open contact), it breaks the circuit and prevents the motor from starting, even though line voltage is present. The other options are incorrect because an open start switch (A) would prevent voltage from reaching the motor, an open main contactor coil (C) would also prevent the motor from starting, and an overload relay contact (D) would only open after the motor has already started.
Related Questions
#130 Why are motor controllers seldom troubled by grounds? #131 Which device will stop the motor shown in the illustration in case of a short-circuit (high current) motor fault? Illustration EL-0080 #133 If you hear a loud buzzing noise coming from a magnetic motor controller, what should you do? #134 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 #135 The motor fails to start on an attempted startup. With the start button depressed, a voltmeter reading between 1 and 5, as illustrated in figure "A", indicates line voltage available to the control circuit, what should be your next step in the troubleshooting process? Illustration EL-0007