CET CET Machine Room & Pit Equipment 3 — Questions and Answers
Question 1: What is the purpose of the motor brake on a geared traction elevator?
- Slows the car during normal operation
- Holds the car stationary when the motor is de-energized (Correct answer)
- Limits the top speed of the elevator
- Controls the door open/close speed
Correct answer: Holds the car stationary when the motor is de-energized
The motor brake is a spring-set, electrically released device that holds the sheave and car stationary whenever the drive motor is not powered.
Question 2: What is the maximum allowable wire rope (hoist rope) diameter used in most standard traction elevator installations?
- 1/4 inch
- 3/8 inch
- 5/8 inch (Correct answer)
- 1 inch
Correct answer: 5/8 inch
Most standard traction elevator installations use hoist ropes up to 5/8 inch (16 mm) in diameter, though actual size depends on the design load.
Question 3: In a machine room, what is the purpose of the 'selector' or 'dispatching system'?
- Selects the oil type for the hydraulic system
- Tracks car position and manages hall and car calls (Correct answer)
- Selects the appropriate brake type for the load
- Chooses which motor winding to energize
Correct answer: Tracks car position and manages hall and car calls
The selector is a position-tracking and dispatching system that monitors car location and manages the queue of hall and car calls for efficient service.
Question 4: What is the function of the deflector sheave in a machine room or overhead?
- Changes the direction of the hoist ropes between the drive sheave and the car or counterweight (Correct answer)
- Guides the governor rope
- Serves as a secondary traction point to increase rope grip
- Lubricates the hoist ropes automatically
Correct answer: Changes the direction of the hoist ropes between the drive sheave and the car or counterweight
A deflector sheave redirects the hoist ropes to properly align them between the drive sheave and the car or counterweight connection points.
Question 5: What safety device prevents an elevator from operating with the machine room access door open?
- Pit stop switch
- Machine room door interlock (Correct answer)
- Phase reversal relay
- Rope brake
Correct answer: Machine room door interlock
A machine room door interlock (access switch) de-energizes or restricts elevator operation whenever the machine room door is opened, protecting personnel.
Question 6: What is the purpose of the phase reversal relay in an elevator machine room?
- Reverses motor rotation for up and down travel
- Prevents operation if incoming power phases are reversed or missing (Correct answer)
- Switches between normal and emergency power
- Controls the direction of door travel
Correct answer: Prevents operation if incoming power phases are reversed or missing
A phase reversal relay monitors the three-phase power supply and prevents the elevator from operating if phases are reversed or a phase is lost, which would cause the motor to run backward.
CET CET Machine Room & Pit Equipment 3
What is the purpose of the motor brake on a geared traction elevator?