CET Electrical & Control Systems 2

Question 1

What is the primary function of a phase-loss relay in a three-phase elevator motor circuit?

Accepted Answer

Disconnect the motor if one phase is lost

Answer

A phase-loss relay monitors all three phases and disconnects the motor if any single phase is lost, preventing single-phasing damage.

Question 2

In an elevator control circuit, what does a 'slowdown' switch typically do?

Accepted Answer

Signals the controller to begin deceleration before reaching a landing

Answer

A slowdown switch triggers the controller to initiate deceleration so the car arrives at a landing at proper leveling speed.

Question 3

Which type of relay is commonly used in elevator circuits to provide a time delay before re-acceleration after a brief power interruption?

Accepted Answer

Time-delay relay (TDR)

Answer

A time-delay relay (TDR) holds the circuit open for a preset period, preventing immediate re-acceleration that could cause passenger discomfort or mechanical stress.

Question 4

What is the purpose of a 'door zone' signal in a microprocessor elevator controller?

Accepted Answer

Triggers the door open command only when the car is within ±3 inches of a landing

Answer

The door zone signal confirms the car is within approximately ±3 inches of a landing, enabling the door operator to open safely.

Question 5

In a variable-frequency drive (VFD) controlled elevator, what determines the motor's rotational speed?

Accepted Answer

The output frequency supplied by the VFD

Answer

Motor speed in a VFD system is directly proportional to the output frequency, allowing smooth acceleration and deceleration profiles.

(CET) Certified Elevator Technician Practice Test

(CET) Certified Elevator Technician Practice Test

CET Electrical & Control Systems 2