EIAT and NEIEP Test Motor Controls 1 — Questions and Answers
Question 1: What is the primary purpose of a magnetic motor starter?
- To manually disconnect power from the motor
- To automatically start and stop a motor while providing overload protection (Correct answer)
- To regulate the speed of a motor during operation
- To convert AC power to DC power for motor use
Correct answer: To automatically start and stop a motor while providing overload protection
A magnetic motor starter combines a contactor for switching with an overload relay for protection, allowing automatic control of a motor.
Question 2: What does NEMA stand for in the context of motor controls?
- National Electrical Manufacturers Association (Correct answer)
- National Equipment Monitoring Agency
- North American Electrical Motor Authority
- National Engineering and Manufacturing Alliance
Correct answer: National Electrical Manufacturers Association
NEMA stands for National Electrical Manufacturers Association, the body that sets standards for motor starters, enclosures, and other electrical equipment.
Question 3: In a motor control circuit, a normally open (NO) contact is one that:
- Is always in the closed position during normal operation
- Allows current to flow only when the device is energized or actuated (Correct answer)
- Is permanently connected to prevent circuit interruption
- Opens when the coil is energized
Correct answer: Allows current to flow only when the device is energized or actuated
A normally open contact has an open circuit in its de-energized (normal) state and only closes to allow current when the coil is energized or the device is actuated.
Question 4: What is the function of a thermal overload relay in a motor starter?
- To increase motor speed during heavy load conditions
- To disconnect the motor if it draws excessive current for an extended period (Correct answer)
- To regulate the voltage supplied to the motor windings
- To reverse the direction of motor rotation automatically
Correct answer: To disconnect the motor if it draws excessive current for an extended period
A thermal overload relay protects the motor from damage by opening the control circuit if the motor draws more current than its rated ampacity for too long.
Question 5: In a 3-wire control circuit, the purpose of the holding (seal-in) contact is to:
- Prevent the motor from starting without a valid start signal
- Maintain the motor starter coil energized after the start button is released (Correct answer)
- Provide a second path for the overload relay current
- Limit the inrush current during motor starting
Correct answer: Maintain the motor starter coil energized after the start button is released
The holding contact (a NO auxiliary contact wired in parallel with the start button) seals in the circuit so the motor continues to run after the momentary start button is released.
Question 6: What is the typical control circuit voltage used in many industrial motor control panels?
- 480V AC
- 120V AC (Correct answer)
- 240V AC
- 24V DC
Correct answer: 120V AC
120V AC is the most common control circuit voltage in industrial motor control panels, supplied through a control transformer from the 480V power circuit.
Question 7: In motor control terminology, what does 'JOG' mode refer to?
- Running the motor at reduced voltage for extended periods
- Briefly energizing the motor to inch it to a specific position (Correct answer)
- A method of reversing motor direction at full speed
- Gradually ramping up motor speed over several minutes
Correct answer: Briefly energizing the motor to inch it to a specific position
Jogging (or inching) briefly energizes the motor for precise positioning by bypassing the holding contact so the motor only runs while the jog button is held.
EIAT and NEIEP Test Motor Controls 1
What is the primary purpose of a magnetic motor starter?