NCCCO Load Moment Indicators and Safety Devices 3 — Questions and Answers
Question 1: When an LMI system displays a load percentage of 95%, what should the crane operator do?
- Proceed normally since the load is under 100%
- Slow all crane movements and prepare to stop operations (Correct answer)
- Immediately shut down the crane
- Increase boom angle to reduce the load percentage
Correct answer: Slow all crane movements and prepare to stop operations
At 95% of rated capacity, the operator should slow movements and exercise extreme caution because small changes in configuration can quickly push the load past the rated limit.
Question 2: Which factor does an LMI system use along with load radius and boom angle to calculate rated capacity?
- Wind speed at boom tip
- Boom length and configuration (Correct answer)
- Hook block weight only
- Counterweight temperature
Correct answer: Boom length and configuration
Boom length and configuration (including jib attachments) are essential inputs that the LMI uses together with radius and angle to determine rated capacity from the load chart.
Question 3: An anti-two-block (ATB) device activates and stops hoist-up movement. What should the operator do first?
- Bypass the ATB and continue hoisting slowly
- Lower the load or extend the boom to create clearance (Correct answer)
- Call for maintenance to reset the system
- Increase line speed to pull through the two-block condition
Correct answer: Lower the load or extend the boom to create clearance
The correct response is to lower the load or adjust the boom configuration to re-establish clearance between the hook block and the boom tip sheaves.
Question 4: Which of the following is NOT a standard input sensor for a crane LMI system?
- Boom angle sensor
- Load cell or pressure transducer
- Ambient air temperature sensor (Correct answer)
- Boom length sensor
Correct answer: Ambient air temperature sensor
Ambient air temperature is not a standard LMI input; standard sensors include boom angle, boom length, and load measurement via load cell or pressure transducers.
Question 5: A rated capacity limiter (RCL) differs from a basic LMI primarily because it:
- Only monitors hook block weight
- Automatically stops crane motion when rated capacity is reached (Correct answer)
- Requires manual input of all load data
- Only functions on lattice boom cranes
Correct answer: Automatically stops crane motion when rated capacity is reached
An RCL not only indicates load percentage but also automatically intervenes to stop crane motions that would exceed rated capacity, whereas a basic LMI only provides warning.
Question 6: What condition can cause an LMI to display an artificially low load reading, creating a false sense of safety?
- High ambient temperature
- Dynamic loading from sudden starts or stops (Correct answer)
- Low hydraulic fluid viscosity
- Operating on a slope within allowed limits
Correct answer: Dynamic loading from sudden starts or stops
Dynamic loading from abrupt crane movements creates transient forces not fully captured by the LMI's static sensors, potentially causing under-reading during the motion.
Question 7: The NCCCO standard requires that LMI devices be calibrated:
- Only when they display obvious errors
- In accordance with the manufacturer's recommendations and after major repairs (Correct answer)
- Every five years regardless of use
- Only by the crane operator using an internal calibration menu
Correct answer: In accordance with the manufacturer's recommendations and after major repairs
Calibration must follow the manufacturer's schedule and is also required after any major repair or component replacement that could affect sensor accuracy.
NCCCO Load Moment Indicators and Safety Devices 3
When an LMI system displays a load percentage of 95%, what should the crane operator do?