5.2 Rigging Practices

Why Rigging Practices Matter on the Exam

Module 38102, Rigging Practices, is a 15-hour module inside the Equipment Installation domain and it covers the work that happens before a machine ever touches its baseplate: safely lifting, moving, and positioning heavy equipment. Rigging is also one of the highest-consequence topics on the exam — a misjudged sling angle, a worn wire rope, or a missed hand signal does not just cause rework, it can be fatal. NCCER's objectives for this module cover ASME crane hand signals, center-of-gravity and basic rigging/crane safety, crane pinch points, site and environmental hazards, attaching rigging hardware for routine and pipe lifts, and sling tension calculations — all of which show up as scored items.

Slings and Hitch Types

A sling is the flexible connector (wire rope, alloy chain, or synthetic web) between the load and the lifting hook. How a sling is wrapped around the load is its hitch:

• Vertical hitch — a single, straight vertical pull from hook to load; carries the sling's full vertical rated capacity
• Choker hitch — the sling passes through its own eye to cinch around the load; reduces capacity (typically to about 75-80% of vertical rating) because the choking action bends and stresses the rope
• Basket hitch — the sling passes completely under the load and both eyes go on the hook; roughly doubles vertical-rated capacity when rigged near 90 degrees, but that capacity drops sharply as the basket legs spread away from vertical
• Bridle hitch — two or more sling legs from separate points on the load converge at a single hook, commonly used to control an odd-shaped or long load and keep its center of gravity centered under the hook

Center of gravity governs where rigging points are attached: a load must be rigged so its center of gravity hangs directly beneath the hook, or it will tip, slide, or swing unpredictably in the air, even if the total weight is well within capacity.

Sling Angle and Tension: The Math the Exam Tests

As a sling leg is rigged farther from vertical (a shallower angle), the tension in that leg increases even though the load's weight has not changed. The relationship is:

Tension factor = 1 / sin(angle from horizontal)

At 30 degrees, each leg carries double its share of the load. This is exactly why OSHA prohibits rigging slings at angles less than 30 degrees from the horizontal — below that point, tension climbs so fast that a sling rated for the load's actual weight can be overloaded well past its working limit. On the exam, expect a question that gives you a load weight and an angle and asks you to apply this factor, or one that simply asks you to recall the four benchmark values above.

Rigging Hardware

• Shackles connect slings to hooks or lift points. Screw pin shackles use a threaded pin and are for temporary, hand-tightened setups; bolt-type (round pin with nut and cotter key) shackles resist backing out under vibration or rotation and are preferred for engineered or overhead lifts.
• Eyebolts come in shoulder (rated for angular pulls) and straight/non-shoulder (rated only for a straight, in-line pull) styles — using a straight eyebolt at an angle sharply reduces its safe capacity.
• Wire rope clips terminate a wire rope eye. The rule the exam expects you to know cold is "never saddle a dead horse": the U-bolt of the clip always goes on the short, dead end of the rope, with the saddle bearing on the long, live (load-carrying) end. Reversing it lets the U-bolt crush and weaken the live side, cutting capacity by 40% or more. A minimum of three clips is standard for a hand-formed eye.
• Turnbuckles adjust sling leg length for leveling a load during a multi-leg lift.

Wire rope slings must also be checked against their D/d ratio — the diameter of the pin or hook (D) divided by the rope diameter (d). A minimum 5:1 ratio preserves roughly 80-85% of rated capacity; a tight bend around too small a pin (a low D/d ratio) sharply reduces the sling's real capacity even though the rope itself is undamaged. Under OSHA 29 CFR 1926.251(c)(4)(iv), a wire rope sling must be removed from service once more than 10% of its total wires are broken within any length of eight rope diameters — along with kinking, birdcaging, heat damage, severe corrosion, or a missing/illegible capacity tag.

Crane Signals, Pinch Points, and Moving Heavy Loads

ASME B30.5 standardizes hand signals between rigger and crane operator: a single arm extended horizontally, palm down, moved side to side means "stop"; both arms extended horizontally, palms down, then crossed in front of the body means "emergency stop" — halting all crane motion immediately regardless of what signal was given before it. Riggers must also identify a crane's pinch points (where a boom, load block, or counterweight can trap a hand or body) and assess site and environmental hazards — overhead power lines, uneven ground, wind — before any lift begins.

When a machine must be moved short distances without a crane, millwrights use hydraulic bottle jacks, cribbing, and rollers: lift one end at a time, immediately crib the load with wood or steel blocking before working near it, never exceed a jack's rated capacity, and never rely on hydraulic pressure alone to hold a suspended load while personnel are underneath.

Key Takeaways

• Hitch type changes capacity: vertical = full rating, choker ≈ 75-80%, basket ≈ 2× near 90°, bridle keeps center of gravity centered on multi-point loads.
• Tension factor = 1/sin(angle from horizontal); at 30° from horizontal each leg carries double its share of the load, which is why OSHA sets 30° as the minimum sling angle.
• "Never saddle a dead horse" — the wire rope clip's U-bolt always goes on the dead end, saddle on the live end; use a minimum of 3 clips per hand-formed eye.
• A minimum 5:1 D/d ratio preserves about 80-85% of a wire rope sling's rated capacity.
• OSHA 29 CFR 1926.251(c)(4)(iv) requires removing a wire rope sling from service once more than 10% of its wires are broken within any 8-rope-diameter length.
• ASME B30.5's emergency stop signal (arms crossed) overrides any prior signal and halts all crane motion immediately.