CET Electrical & Control Systems 3

Question 1

What is the function of an 'up-direction' contactor in a traditional relay-logic elevator controller?

Accepted Answer

Reverses motor phase sequence to drive the car in the up direction

Answer

The up-direction contactor reverses the phase sequence of the motor supply, causing the motor to rotate in the direction that moves the car upward.

Question 2

In a microprocessor-based elevator control system, what is a 'serial link' typically used for?

Accepted Answer

Communicating data between the machine room controller and the car operating panel (COP)

Answer

A serial communication link (e.g., CAN bus or RS-485) transmits button calls, status data, and commands between the controller and the COP, reducing the number of traveling cables needed.

Question 3

What causes 'nuisance tripping' of the elevator main line circuit breaker?

Accepted Answer

Excessive motor starting current exceeding the breaker's instantaneous trip rating

Answer

High inrush current during motor starting can exceed the instantaneous trip threshold of an incorrectly sized breaker, causing nuisance trips.

Question 4

What is the purpose of a 'motor thermistor' or thermal overload device embedded in the elevator motor windings?

Accepted Answer

Detect excessive motor winding temperature and signal the controller to shut down

Answer

Embedded thermistors change resistance with temperature; when winding temperature exceeds safe limits, the controller detects the resistance change and shuts down the motor.

Question 5

In elevator electrical work, what does 'megger testing' verify?

Accepted Answer

Insulation resistance of wiring, motors, and cables

Answer

A megohmmeter (megger) applies high DC voltage to measure insulation resistance, verifying that insulation has not degraded due to moisture, heat, or age.

(CET) Certified Elevator Technician Practice Test

(CET) Certified Elevator Technician Practice Test

CET Electrical & Control Systems 3