Motors and Controls Flashcards
6 cards from real Electrician practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Motors and Controls flashcards as text
What is the purpose of a Variable Frequency Drive (VFD)?
Answer: To control motor speed by varying the frequency of the supply voltage
A VFD controls AC motor speed by varying the frequency and voltage supplied to the motor.
In a motor control circuit, what is a 'holding contact' used for?
Answer: To maintain the starter coil energized after the start button is released
A holding (or seal-in) contact is an auxiliary contact that keeps the motor starter coil energized after the momentary start button is released.
How do you reverse the direction of a three-phase induction motor?
Answer: Interchange any two of the three phase conductors
Reversing any two of the three-phase conductors reverses the rotating magnetic field direction, which reverses motor rotation.
What does NEMA stand for in the context of motor control enclosures?
Answer: National Electrical Manufacturers Association
NEMA stands for National Electrical Manufacturers Association, which sets standards for motor control enclosure ratings.
A NEMA 4X enclosure provides protection against which of the following?
Answer: Water splash and corrosion
A NEMA 4X enclosure is designed to protect against water splash, dust, and corrosion, making it suitable for outdoor and food processing environments.
What is the purpose of a control transformer in a motor control circuit?
Answer: To provide a lower, safer voltage (typically 120V) for the control circuit
A control transformer steps down the line voltage to a safer, lower voltage (usually 120V) for the control circuit components.