CEA Motor Controls and Control Circuits Questions and Answers Flashcards

What is the primary purpose of a magnetic motor starter?

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.

In a three-phase motor control circuit, what is the function of the overload relay heater element?

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.

Which type of motor starter reduces inrush current during startup by applying reduced voltage?

Answer: Reduced-voltage starter

Reduced-voltage starters (such as autotransformer, wye-delta, or soft-start types) limit inrush current during motor startup.

In a control circuit, what does a normally open (NO) contact do when the coil is energized?

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.

What is a 'seal-in' or 'holding' contact in a motor control circuit?

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.

According to NEMA standards, what does a NEMA 12 enclosure protect against?

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.