When it comes to the concern about rigging equipment- winch straps, ratchet straps, slings, chains and shackles- two terms appear on the product specification sheet: working load limit and breaking strength. These numbers are not confusing or interchangeable and can have a serious impact on job sites.
Every piece of rigging or load-bearing equipment carries its own breaking strength and working load limit ratings. These figures tell exactly how much weight that piece of rigging is designed to handle safely. Though usually they are clearly mentioned on documentation or product labels, there is confusion about what exactly both terms mean and how they relate to each other.
This blog will walk you through both ratings in simple language, explain the relationship between both and help you make informed and safe decisions regarding working load limit vs. breaking strength every time you rig a load.
Difference between working load limit and breaking strength
Below are the major working load limit and breaking strength difference:
Working Load Limit(WLL)
- Working load limit is the maximum load that rigged equipment can handle under normal working conditions. It is the number that you always refer to while selecting the equipment for the securement or lifting task.
- For example, a winch strap with a working load limit of 6,000 lbs should never be used to secure a load exceeding this weight. Doing so pushes the equipment beyond its actual capacity and into the situation where failure becomes a risk, even if the strap will not break immediately.
- The working load limit is not an arbitrary number; it is calculated as ⅓ of the breaking strength, which means the 3: 1 built-in safety factor is already included in it.
- A strap with a working load limit of 6,000 lbs has a breaking strength of 18,000 lbs. That safety margin exists to account for shock loads, dynamic loading, environmental conditions, wear and other variables that can reduce the strength of rigging during use.
Key points:
- Always a number when selecting for a rigging job
- Represents the maximum safe working load
- Equal to 1/3 of breaking load
- Applies under undamaged or normal conditions; damaged equipment can be removed from service on an immediate basis
- Just never be exceeded
Breaking Strength
- Breaking strength is the point where a piece of rigging will fail. It is loaded at the weakest component of the load- whether that is end fittings, webbing, tensioning device or hooks- that can no longer hold and give way.
- Breaking strength is determined by the weakest link in the system. If a ratchet strap uses end fittings, webbing, and a ratchet mechanism all rated to a breaking strength of 18,000 lbs. If any component has the lower rating, implying that hooks are rated to 15,000 lbs, the breaking strength of the entire assembly falls to a lower figure.
- That’s why it’s difficult to inspect every single component of the rigging assembly, not just the chain or strap itself. A strap with high strength paired with a worn shackle or undersized hook can reduce the safe capacity of the entire system.
Key points:
- Load at which riggings structurally fail
- Always higher than the WLL
- Determined by the weakest component in the assembly
- Never be used as a working reference
- Established through lab testing under controlled conditions
Key points for working load limit vs breaking strength comparison:
Working Load Limit:
- Maximum safe load for normal use
- Guide for safe load limits and daily operations
- Calculated using safety standards and margins
- Always obey the limit on the product label
Breaking Strength
- Force at which product fails or breaks
- Used for material rating and engineered calculations
- Determined via lab testing
- Exceeding this means failure
Choosing The Right Rigging For The Job
Selecting the appropriate rigging equipment starts with knowing the load, including dimensions, weight, centre of gravity and special handling requirements. From there, you can select the equipment with an accurate working load limit, factoring in rigging angle, number of legs and dynamic loading conditions. When in doubt, always increase the size. Using equipment with a higher working load limit than the minimum required adds additional margin and increases the service lifespan of your rigging. Our team at Brampton Straps, with the expertise of Mr. Jinder Atwal, is always available to help select appropriate equipment for specific applications.
FAQ’S
What is the key difference between working load limit and breaking strength?
The key difference between working load limit and breaking strength is that working load limit is the maximum force, and breaking strength is the load threshold.
What is the safety factor?
The safety factor is the ratio of breaking strength to working load limit.
Can I use breaking strength to calculate a lift?
No, because breaking strength is represented as a one-time lab failure under ideal conditions.
What factors reduce the actual capacity of rigging gear?
The factors that reduce the actual capacity of rigging gear include physical and environmental damage, along with other factors such as chemical exposure, UV degradation, high heat, cuts and so on.
What is shock load, and what is the impact on the weight load limit?
A shock load occurs when a load is impacted. A spike in force increases the static weight of an object and breaches the working load limit and breaking strength.