CET CET Roping & Counterweight Systems 1 — Questions and Answers
Question 1: What is the standard minimum number of hoist ropes required for a traction elevator under ASME A17.1?
- 1
- 2
- 3 (Correct answer)
- 4
Correct answer: 3
ASME A17.1 requires a minimum of three hoist ropes for traction elevators to provide redundancy and safety against rope failure.
Question 2: What is the purpose of the counterweight in a traction elevator system?
- Increases the traction between ropes and drive sheave
- Offsets the weight of the car and a portion of the rated load to reduce motor energy consumption (Correct answer)
- Provides emergency braking if the motor fails
- Stores energy for the door reopening system
Correct answer: Offsets the weight of the car and a portion of the rated load to reduce motor energy consumption
The counterweight balances the car weight plus approximately 40–50% of the rated load, significantly reducing the energy required to drive the elevator.
Question 3: What percentage of rated load is typically added to the car weight when calculating counterweight mass?
- 25%
- 40–50% (Correct answer)
- 75%
- 100%
Correct answer: 40–50%
Counterweights are typically set to equal the car weight plus 40–50% of the rated capacity to minimize motor loading in both directions.
Question 4: In a 1:1 roping arrangement, how does the rope travel distance compare to car travel distance?
- Rope travels half the distance of the car
- Rope and car travel the same distance (Correct answer)
- Rope travels twice the distance of the car
- Rope travels four times the distance of the car
Correct answer: Rope and car travel the same distance
In a 1:1 roping arrangement, the hoist rope and the car move the same distance for every rotation of the drive sheave.
Question 5: What is the advantage of a 2:1 roping arrangement compared to a 1:1 arrangement?
- Higher car speed for the same motor speed
- Greater mechanical advantage allowing a smaller motor to lift heavier loads (Correct answer)
- Simpler rope installation with fewer sheaves
- Higher traction between rope and sheave
Correct answer: Greater mechanical advantage allowing a smaller motor to lift heavier loads
A 2:1 roping arrangement provides mechanical advantage, effectively doubling the lifting force of the motor at the cost of half the car speed.
Question 6: What is the minimum design factor (safety factor) required for elevator hoist ropes under ASME A17.1?
- 4
- 7.6 (Correct answer)
- 10
- 12
Correct answer: 7.6
ASME A17.1 requires a minimum design factor of 7.6:1 (breaking strength to working load) for elevator wire rope hoist ropes in normal service.
CET CET Roping & Counterweight Systems 1
What is the standard minimum number of hoist ropes required for a traction elevator under ASME A17.1?