Working Load Limit

Working Load Limit in LED Rigging

Working Load Limit represents the maximum recommended working capacity of rigging hardware, incorporating appropriate safety margins to prevent failure under normal and abnormal conditions.

WLL Definition

WLL is the maximum mass or force a piece of rigging hardware should support in service. It incorporates:

Breaking Strength: The ultimate load causing failure

Safety Factor: Margin between WLL and breaking strength

Service Conditions: Assumes proper use and maintenance

Safety Factors

Common safety factors in entertainment rigging:

| Component | Typical Safety Factor | |-----------|----------------------| | Shackles | 5:1 | | Wire Rope | 5:1 to 7:1 | | Chain | 5:1 | | Spansets/Slings | 5:1 to 7:1 | | Hoists | 5:1 | | Truss | 5:1 |

Calculating WLL

WLL = Breaking Strength ÷ Safety Factor

Example:

• Shackle breaking strength: 25,000 lbs
• Safety factor: 5:1
• WLL = 25,000 ÷ 5 = 5,000 lbs

WLL Markings

Legitimate rigging hardware displays WLL:

Shackles: Stamped on body (e.g., "5T WLL")

Spansets: Sewn label with WLL and length

Chain: Tag or stamped link

Wire Rope: Documented in certificates

Hoists: Nameplate with rated capacity

Reduction Factors

WLL decreases under certain conditions:

Angle Loading: Sling angles reduce effective WLL

Dynamic Loading: Motion increases force above static WLL

Edge Loading: Sharp edges can cut slings (use edge protection)

Temperature: Extreme heat/cold affects some materials

Wear: Used hardware has reduced capacity

Inspection Requirements

Regular inspection maintains WLL integrity:

Visual Inspection: Before each use

• Check for visible damage, deformation
• Verify legible markings
• Look for wear patterns

Periodic Inspection: Regular intervals

• Detailed examination
• Measurement checks
• Documentation

Retirement Criteria: Replace when:

• Markings illegible
• Visible damage or wear
• Exceeded load (even once)
• Age limits reached

Documentation

Maintain records of:

• Hardware inventory with WLL ratings
• Inspection dates and results
• Manufacturer certificates
• Retirement and replacement log

Selection Guidelines

When selecting hardware:

1. Calculate required capacity 2. Add appropriate margin (never use 100% of WLL) 3. Select hardware exceeding requirement 4. Verify ratings from reputable manufacturer 5. Document selection in rigging plan