CEA CEA Motor Controls and Control Circuits Questions and Answers 1 — Questions and Answers
Question 1: What is the primary purpose of a magnetic motor starter?
- To convert AC to DC power
- To provide remote switching and overload protection for a motor (Correct answer)
- To increase motor speed above nameplate rating
- To reduce the motor's power factor
Correct answer: To provide remote switching and overload protection for a motor
A magnetic motor starter combines a contactor for remote switching with an overload relay to protect the motor from excessive current.
Question 2: In a three-phase motor control circuit, what is the function of the overload relay heater element?
- It heats the motor windings to prevent condensation
- It senses excess current and trips the control circuit to stop the motor (Correct answer)
- It boosts voltage during startup
- It balances the three-phase load
Correct answer: It senses excess current and trips the control circuit to stop the motor
The overload relay heater element responds to sustained overcurrent by opening the control circuit, de-energizing the contactor and stopping the motor.
Question 3: Which type of motor starter reduces inrush current during startup by applying reduced voltage?
- Full-voltage (across-the-line) starter
- Reduced-voltage starter (Correct answer)
- Reversing starter
- Multi-speed starter
Correct answer: Reduced-voltage starter
Reduced-voltage starters (such as autotransformer, wye-delta, or soft-start types) limit inrush current during motor startup.
Question 4: In a control circuit, what does a normally open (NO) contact do when the coil is energized?
- It remains open
- It closes to complete the circuit (Correct answer)
- It opens the power circuit
- It reverses motor rotation
Correct answer: It closes to complete the circuit
A normally open contact closes when the associated coil is energized, allowing current to flow through that part of the control circuit.
Question 5: What is a 'seal-in' or 'holding' contact in a motor control circuit?
- A contact that locks out the panel door
- An auxiliary contact wired in parallel with the start button to maintain the circuit after the button is released (Correct answer)
- A contact that seals moisture out of the enclosure
- A contact used only in reversing starters
Correct answer: An auxiliary contact wired in parallel with the start button to maintain the circuit after the button is released
The seal-in contact is wired in parallel with the start pushbutton so the starter coil stays energized after the momentary start button is released.
Question 6: According to NEMA standards, what does a NEMA 12 enclosure protect against?
- Submersion in water
- Dust, dirt, and dripping non-corrosive liquids for indoor use (Correct answer)
- Explosive gases and dust
- Outdoor rain and sleet
Correct answer: Dust, dirt, and dripping non-corrosive liquids for indoor use
A NEMA 12 enclosure is designed for indoor use and provides protection against dust, dirt, and dripping or splashing non-corrosive liquids.
CEA CEA Motor Controls and Control Circuits Questions and Answers 1
What is the primary purpose of a magnetic motor starter?