NCCCO - National Commission for the Certification of Crane Operators Sling Types and Load Distribution 1

Question 1

A two-leg bridle sling is used to lift a 10,000 lb load, with each sling leg inclined 45° from vertical. What is the approximate tension in each leg?

Accepted Answer

7,071 lb — the incline increases tension by a factor of 1/cos(45°)

Answer

At a 45° angle from vertical, the tension in each leg equals (load ÷ 2) ÷ cos(45°) = 5,000 ÷ 0.707 ≈ 7,071 lb. Departing from vertical always increases leg tension above the simple half-load value.

Question 2

Under ASME B30.9, what is the rated load capacity of a wire rope sling used in a choker hitch expressed as a percentage of its vertical hitch capacity?

Accepted Answer

75% — the standard choker derating factor for wire rope slings

Answer

ASME B30.9 rates wire rope slings in a choker hitch at 75% of vertical hitch capacity. The sharp bend at the choke point stresses the rope, reducing effective strength compared to a straight vertical pull.

Question 3

When inspecting a synthetic web sling, which of the following conditions requires immediate removal from service?

Accepted Answer

Surface abrasion that has worn through 10% of the outer yarn bundles

Answer

ASME B30.9 requires removal from service when abrasion, cuts, or wear penetrate or significantly reduce the load-bearing yarns. Wearing through any portion of the outer yarn bundles signals structural compromise. Faded tags and mild surface soiling do not meet the removal threshold on their own.

Question 4

What does the designation 'Grade 80' (G80) stamped on an alloy steel chain sling indicate?

Accepted Answer

The minimum tensile strength class of the alloy steel, which governs the chain's rated capacity

Answer

Grade 80 is a tensile strength classification defined in ASME B30.9 and NACM standards. It designates the minimum tensile strength of the alloy steel used, which directly determines the chain's working load limit. Higher grade numbers (e.g., G100, G120) indicate stronger alloys with higher rated capacities.

Question 5

A rigger uses a two-leg sling of equal leg lengths to lift a load whose center of gravity is offset significantly toward one end. What is the most likely result?

Accepted Answer

The leg over the heavier end carries a greater share of the load, potentially exceeding its rated capacity

Answer

Load distribution between sling legs depends on horizontal distance from each attachment point to the center of gravity, not on equal leg lengths. The leg positioned over or closer to the heavier side carries proportionally more load. Rigging without accounting for CG offset can overload one leg.

NCCCO (National Commission for the Certification of Crane Operators) Practice Test

NCCCO (National Commission for the Certification of Crane Operators) Practice Test

NCCCO - National Commission for the Certification of Crane Operators Sling Types and Load Distribution 1