What Does WLL Mean and Why is it Important?
It can be confusing to decrypt all of these acronyms like SWL, NWL, WLL and MBS. But Henssgen Hardware is here for you, to educate you on terms like Working Load Limits and everything you need to know about our products.
Safe Working Load, SWL, (or Normal Working Load, NWL) is an outdated term that was used to indicate the amount of weight that a lifting device could safely carry without fear of breaking. It is a calculation of the Minimum Breaking Strength, or MBS.
The more up-to-date phrase for the term SWL is Working Load Limit, or WLL.
The specific definition for the Working Load Limit (WLL) is: The maximum mass or force which a product is authorized to support in general service when the pull is applied in-line, unless noted otherwise, with respect to the centerline of the product.
The manufacturer designates the right or approximate WLL value for each lifting device or use, and considers many factors including the applied load, the length of each rope or line, and many other factors.
It is critically important to heed this number, which is set forth by the manufacturer, when lifting with any device, including a line, rope or crane. The number is calculated by dividing the Minimum Breaking Strength (MBS) by a safety factor that is assigned to that type and use of equipment, generally ranging from four to six unless a failure of the equipment could pose a risk to life. In the event that the failure of the equipment could pose a risk to life, the safety factor is ten.
For example, if a hook has a Minimum Breaking Strength (MBS) of 1,000 pounds and a safety factor of five, then the Working Load Limit (WLL) would be 200 pounds.
The history to the change in terminology
There were legal implications to the term Safe Working Load, so USA standards phased this term out more than twenty years ago, followed by European and ISO standards just a few years afterward. This change took place because of the legal significance placed on the word ‘safe’.
The Americans and Europeans then developed a more appropriate term and definition for the maximum load capacity of a particular lifting device, agreeing to use the term Working Load Limit (WLL) for equipment such as hooks, slings and shackles.
In the cases of cranes, hoists and winches, the term Safe Working Load (SWL) was replaced by Manufacturer’s Rated Capacity (MRC), which is the maximum gross load which may be applied to the crane or hoist or lifting attachment while in a particular working configuration and under a particular condition of used.
SWL — Safe Working Load
NWL — Normal Working Load
WLL — Working Load Limit (Current term used)
MBS — Minimum Breaking Strength
MRC — Manufacturers Rated Capacity
Henssgen Hardware is committed to providing top quality products as well as all of the information you need in order to ensure the utmost in safety. Please contact us with any safety questions you may have and we’ll be happy to discuss your needs and which products are the best fit for you.