NCCER Rigger flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Sling angle factor
- Multiplier applied to load to find sling tension: 1 divided by the sine of the angle from horizontal. At 30 degrees the factor is 2.0.
- Two-leg bridle tension
- Tension per leg equals load weight divided by twice the sine of the sling angle from horizontal. Lower angles sharply increase tension.
- Choker hitch capacity
- A choker hitch develops approximately 75 to 80 percent of the sling's single-leg vertical rated capacity because of bending and compression at the choke.
- Basket hitch capacity
- A basket hitch with vertical legs can develop up to twice the single-leg vertical capacity because the load is supported by two parts of the sling.
- Vertical hitch capacity
- A single-leg vertical hitch develops the full rated capacity marked on the sling, assuming the load is directly below the hook.
- Center of gravity rule
- The load's center of gravity must hang directly below the hook. An offset center of gravity causes tilt and unequal loading among sling legs.
- Load weight formula
- Weight equals volume multiplied by material density. Steel is about 490 pounds per cubic foot; concrete about 150; water about 62.4.
- Critical lift definition
- A lift commonly classified as critical when the load exceeds 75 percent of rated capacity, involves multiple cranes, or passes over occupied areas.
- Crane capacity and radius
- Rated capacity decreases as the horizontal distance from the crane's rotation center to the load increases. Always verify capacity at the actual working radius.
- Outrigger setup requirement
- Outriggers must be fully extended with floats or pads on stable, competent ground. On-rubber capacity charts are substantially lower than on-outrigger charts.
- Crane leveling tolerance
- A crane must be level within the manufacturer's tolerance, commonly one percent, before lifting. An unlevel crane causes side loading and capacity loss.
- Tag line purpose
- A tag line controls load rotation and sway. It is not rated rigging and must never be used to restrain the load's weight.
- Designated signalperson rule
- Only one designated signalperson directs the crane operator. However, anyone may give an emergency stop signal at any time.
- Sling assembly capacity
- The rated capacity of a sling assembly is limited by its weakest component, including shackles, hooks, master links, and the sling itself.
- Wire rope D/d ratio
- The ratio of sheave or pin diameter to rope diameter. Smaller D/d ratios reduce sling efficiency, roughly halving strength at very low ratios.
- Chain sling grades
- Grade 80 and Grade 100 are standard alloy chain sling grades. Chain slings must never be repaired or heated, and damaged links are removed from service.
- Shackle pin seating
- Shackle pins must be fully seated with minimal thread exposure, and screw-pin shackles should not be side-loaded during lifting.
- Web sling color code
- Industry color convention for single-leg vertical capacity: purple 1 ton, green 2, yellow 3, red 5, blue 8, orange 10 tons.
- Hook latch requirement
- Hooks must have a functioning latch or mousing. The load should bear on the saddle, never on the tip or the latch.
- Eyebolt loading rule
- Shoulder-type eyebolts are rated for angular loading. Plain, non-shoulder eyebolts are intended for vertical lifts only.
- Web sling removal criteria
- Remove synthetic web slings from service for cuts, burns, ultraviolet degradation, or missing or illegible identification tags.
- Bowline knot
- A fixed loop that will not slip under load. It reduces rope strength by roughly 25 to 40 percent, so it is not a rated connection.
- Clove hitch use
- A temporary attachment knot used to secure a line to a post or rail. It can slip if the load direction changes, so it needs backup.
- Trial lift procedure
- Raise the load a few inches, then verify balance, rigging security, and brake holding before continuing the full lift.
- Spreader beam function
- A spreader beam keeps slings near vertical at the load, reducing sling tension and horizontal compression on the load compared with a direct bridle.
- Rigging weight inclusion
- Total load must include slings, shackles, and spreader beams. Rigging weight can be a significant fraction of a light load.
- Four-leg load sharing
- With more than two legs, only two are assumed to share the load unless the load is rigid and the geometry proves equal loading.
- Off-center load share
- When the center of gravity is off-center, load share among attachment points is inversely proportional to horizontal distance from the center of gravity.
- Power line approach distance
- Minimum approach distance to energized lines is typically 10 feet for lines up to 50 kV. A spotter is used when working near lines.
- Lift plan contents
- A lift plan identifies load weight, center of gravity, rigging arrangement, crane capacity at radius, ground conditions, travel path, and signalperson.
- Pre-use sling inspection
- Slings and hardware are inspected each shift before use. Damaged gear is removed from service and tagged so it cannot be reused.
- Ground bearing pressure
- The pressure exerted through outrigger floats onto the ground. Soft or sloped ground requires mats or cribbing to spread the load.