Motor Controls Flashcards
7 cards from real ITMC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Motor Controls flashcards as text
In a jogging (inching) control circuit, why is a jogging relay sometimes used instead of simply using the start button?
Answer: To prevent the holding contact from sealing in the circuit during jog operation
A jogging relay breaks the seal-in (holding) contact circuit during jog mode so the motor runs only while the jog button is held, without latching into continuous run.
What does the term 'FVNR' stand for in motor starting methods?
Answer: Full Voltage Non-Reversing
FVNR stands for Full Voltage Non-Reversing, describing the most common across-the-line motor starter that applies full line voltage to start the motor in one direction only.
Which motor braking method injects DC current into the stator windings to stop the motor quickly?
Answer: DC injection braking
DC injection braking applies direct current to the stator windings after AC power is removed, creating a stationary magnetic field that produces a braking torque to stop the rotor.
A motor contactor's power contacts show pitting and carbon deposits. What is the recommended corrective action?
Answer: Replace the contact tips or the entire contactor per manufacturer recommendations
Pitted and carbonized contacts should be replaced per manufacturer guidelines because filing or sanding contacts removes the silver-alloy facing and shortens contact life.
What is the function of a reduced-voltage soft starter compared to a VFD?
Answer: It controls acceleration and deceleration during start/stop only, running the motor across-the-line at full speed
A soft starter controls voltage (and therefore current and torque) only during the starting and stopping ramp; once at full speed, it typically bypasses itself and the motor runs directly across the line.
In a motor control ladder diagram, which symbol represents a normally open (NO) pushbutton?
Answer: Two vertical lines with no connection (open gap)
A normally open pushbutton is represented by two vertical lines (contact symbol) with an open gap between them, indicating the circuit is open until the button is pressed.
An operator reports that a motor controlled by a three-wire circuit starts but immediately stops when the start button is released. Which component is MOST likely faulty?
Answer: Holding (auxiliary) contact on the contactor (open or missing)
If the motor starts but stops when the start button is released, the holding (auxiliary) contact is not sealing in the circuit, indicating it is open, worn, or wired incorrectly.