Motors and Motor Controls Flashcards
6 cards from real PC 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 Motor Controls flashcards as text
What is the primary function of a Variable Frequency Drive (VFD)?
Answer: Control motor speed by varying output frequency and voltage
A VFD controls motor speed by varying the frequency and voltage of the power supplied to the motor, allowing precise speed control.
What does a motor's service factor (SF) of 1.15 indicate?
Answer: The motor can operate continuously at 115% of its rated load
A service factor of 1.15 means the motor can operate continuously at 115% of its rated nameplate horsepower without harm under standard conditions.
Per NEC 430.14, motors must be located so as to prevent which condition?
Answer: Accumulation of dirt and moisture that interferes with ventilation
NEC 430.14 requires motor locations that prevent accumulation of dirt, moisture, and combustible materials from interfering with ventilation or endangering live parts.
What is 'locked rotor current' (LRC) in a motor circuit?
Answer: The high inrush current drawn when voltage is applied and the rotor has not yet begun turning
Locked rotor current is the maximum inrush current drawn from the supply when rated voltage is applied to a motor whose rotor is stationary.
Which NEC article governs air conditioning and refrigeration equipment containing hermetically sealed motor-compressors?
Answer: Article 440
NEC Article 440 covers air conditioning and refrigerating equipment with hermetic refrigerant motor-compressors and supplements Article 430 for this application.
On a three-phase motor, what is the effect of interchanging any two of the three supply phase conductors?
Answer: The direction of motor rotation will reverse
Swapping any two of the three phase conductors feeding a three-phase induction motor reverses the rotating magnetic field and therefore reverses the direction of shaft rotation.