EETC Motor Controls 2

Question 1

What is the purpose of an overload relay in a motor control circuit?

Accepted Answer

To protect the motor from sustained overcurrent due to mechanical overload

Answer

Overload relays monitor motor current and trip the circuit if sustained overcurrent occurs, protecting windings from thermal damage.

Question 2

In a three-phase motor starter, what does a 'contactor' do?

Accepted Answer

Connects and disconnects the motor from the power supply

Answer

A contactor is an electrically operated switch that connects or disconnects the motor from its power source via a control signal.

Question 3

Which type of motor starting method applies reduced voltage during starting to limit inrush current?

Accepted Answer

Autotransformer starting

Answer

Autotransformer starting uses a transformer to reduce the voltage applied to the motor during starting, reducing inrush current.

Question 4

What is the function of a holding contact (seal-in contact) in a motor starter circuit?

Accepted Answer

Maintains the contactor energized after the start button is released

Answer

The seal-in contact (auxiliary NO contact) in parallel with the start button keeps the coil energized once the start button is released.

Question 5

In a forward/reverse motor control circuit, what prevents both forward and reverse contactors from energizing simultaneously?

Accepted Answer

Electrical and mechanical interlocks

Answer

Electrical interlocks (NC auxiliary contacts) and mechanical interlocks prevent both contactors from closing simultaneously, avoiding a phase-to-phase short circuit.

(EETC) Electrical Technician Certification Practice Test

(EETC) Electrical Technician Certification Practice Test

EETC Motor Controls 2