Working Load Limit vs. Breaking Strength: What Every Rigger Needs to Know

When it comes to rigging equipment — ratchet straps, winch straps, chains, slings, and shackles — two terms appear on virtually every product specification sheet: Working Load Limit (WLL) and Breaking Strength. These numbers are not interchangeable, and confusing them can have serious — even fatal — consequences on the job site.

Every piece of load-bearing wire or rigging equipment carries its own WLL and breaking strength rating. These figures tell the operator exactly how much weight that piece of rigging is engineered to handle safely. Though they are usually clearly stated on the product label or documentation, there is often significant confusion about what each term actually means and how they relate to one another.

This guide will walk you through both ratings in plain language, explain the relationship between them, and help you make safer, more informed decisions every time you rig a load.

Working Load Limit (WLL)

The Working Load Limit is the maximum load that a piece of rigging equipment is approved to handle under normal working conditions. It is the number you should always reference when selecting equipment for a lift or securement task.

For example, a winch strap with a WLL of 6,000 lbs must never be used to secure a load exceeding that weight. Doing so pushes the equipment beyond its rated capacity and into a zone where failure becomes a real risk — even if the strap does not break immediately.

WLL is not an arbitrary number. It is calculated as one-third (1/3) of the breaking strength, which means a built-in safety factor of 3:1 is already embedded in the rating. A strap with a WLL of 6,000 lbs, for instance, has a breaking strength of 18,000 lbs. That safety margin exists to account for dynamic loading, shock loads, wear, environmental conditions, and other real-world variables that can reduce the effective strength of rigging during use.

Key Points About WLL:

• Always the number to reference when selecting rigging for a job
• Represents the maximum safe working load — not the maximum possible load
• Equals 1/3 of the breaking strength (3:1 design factor)
• Applies under normal, undamaged conditions — worn or damaged equipment should be removed from service immediately
• Must never be exceeded, even briefly

Breaking Strength

Breaking Strength (also called Minimum Breaking Strength or MBS) refers to the point at which a piece of rigging will structurally fail. It is the load at which the weakest component of the assembly — whether that is the webbing, end fittings, hooks, or tensioning device — can no longer hold and gives way.

Breaking strength is determined by the weakest link in the system. If a ratchet strap assembly uses webbing, end fittings, and a ratchet mechanism all rated to 18,000 lbs breaking strength, the overall breaking strength of the unit is 18,000 lbs. However, if any single component has a lower rating — say the hooks are only rated to 15,000 lbs — the breaking strength of the entire assembly drops to that lower figure.

This is why it is critical to inspect every component of a rigging assembly — not just the strap or chain itself. A high-strength strap paired with an undersized hook or a worn shackle can dramatically reduce the safe capacity of the entire system.

Key Points About Breaking Strength:

• The load at which the rigging will physically fail
• Always higher than the WLL — typically 3x the WLL
• Determined by the weakest component in the assembly
• Should never be used as a working reference — it is a failure threshold, not a safe operating limit
• Established through laboratory testing under controlled conditions

The Relationship Between WLL and Breaking Strength

Understanding how WLL and breaking strength relate to each other is fundamental to safe rigging practice. The formula is straightforward:

Breaking Strength ÷ 3 = Working Load Limit

Or conversely:

WLL × 3 = Breaking Strength

The factor of 3 is the design factor (sometimes called the safety factor), and it is mandated by industry standards and regulations including those set by the Occupational Health and Safety (OHS) regulations across Canadian provinces and OSHA standards in the United States.

It is important to note that the design factor is not a buffer that allows you to exceed the WLL. It exists to protect against unforeseen variables — not to give operators extra headroom to overload equipment.

Common Mistakes to Avoid

• Using breaking strength as a working limit: This eliminates the safety factor entirely and puts operators at serious risk.
• Ignoring component ratings: Always check every component in the assembly — hooks, shackles, rings, and fittings — not just the strap or chain.
• Using damaged or worn equipment: Cuts, abrasions, corrosion, and UV degradation all reduce effective strength below rated values. Remove damaged equipment from service immediately.
• Failing to account for angle: In multi-leg sling configurations, the angle of the legs significantly affects the load on each leg. A wider angle increases the load per leg and can quickly exceed WLL.
• Assuming all products are equal: Always verify that equipment meets applicable standards (e.g., ASME, EN, CSA) and is sourced from a reputable supplier.

Why Proper Rigging Ratings Matter

Rigging failures are not just costly — they are dangerous. A dropped load, a snapped strap, or a failed shackle can cause serious injury or death to workers, damage to equipment and cargo, and significant legal and regulatory consequences for the employer.

Canadian workplace safety regulations require that all rigging equipment be rated, inspected, and used within its designated WLL. Employers are responsible for ensuring that workers are trained to understand these ratings and apply them correctly on every job.

At Hercules, we supply rigging equipment that meets or exceeds applicable Canadian and international standards. Every product in our inventory is selected for quality, traceability, and compliance — because when lives depend on the equipment, there is no room for compromise.

Inspecting Your Rigging Equipment

Even the highest-rated rigging equipment can become unsafe if it is not properly maintained and inspected. Before every use, operators should perform a visual inspection of all rigging components, checking for:

• Cuts, tears, or abrasions in webbing or rope
• Corrosion, cracks, or deformation in metal components
• Worn or damaged hooks, latches, and shackle pins
• Fading or illegible load rating labels
• Any signs of heat damage, chemical exposure, or UV degradation

In addition to pre-use inspections, a formal periodic inspection by a qualified person is required under most provincial OHS regulations. Hercules offers professional rigging inspections to help your team stay compliant and your equipment stay safe.

Choosing the Right Rigging for the Job

Selecting the correct rigging equipment starts with knowing your load — its weight, dimensions, centre of gravity, and any special handling requirements. From there, you can select equipment with an appropriate WLL, factoring in the number of legs, the rigging angle, and any dynamic loading conditions.

When in doubt, always size up. Using equipment with a higher WLL than the minimum required adds an additional margin of safety and extends the service life of your rigging. Our team at Hercules is available to help you select the right equipment for your specific application.