Differences Between WLL and SWL

calendarSep 15, 2022 · 3 min read  ·
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WLL vs SWL

WLL and SWL are abbreviated terms commonly used in the field of engineering. “WLL” stands for “working load limit” while “SWL” stands for “safe working load.” The main differences between safe working load from working load limit is that “SWL” is the older term. Today, SWL is not used anymore because it has been completely replaced by the term WLL. Let us discover the reasons why engineers put an end to using the term “safe working load.”

“Safe working load” is also synonymous with “normal working load.” According to irata.org, “safe working load” is defined as “the breaking load of a component divided by an appropriate factor of safety giving a safe load that could be lifted or carried.” Safe working load is the amount of weight (load) that a lifting device can carry without fear of breaking.

Now, who sets the load capacity for certain lifting equipment? It is the lifting equipment’s manufacturer. The manufacturer recommends the maximum load capacity of his lifting equipment. The lifting equipment or device can be a rope, a line, a crane, hooks, shackles, slings, or any lifting device. To know the safe working load, the lifting equipment’s minimum breaking strength is divided with the safety factor that is constant or assigned to a particular type of equipment. Usually, the safety factor of a particular equipment ranges from 4 to 6. If the equipment poses a risk to a person’s life, the safety factor is raised to 10.

Since the definition of “safe working load” is not very specific and there are legal implications, the USA standards began to stop using this term. A few years after the USA standards began to stop using this term, the European and ISO standards began to follow suit. Later on, both the Americans and Europeans developed a more appropriate term and definition for the maximum load capacity of a particular lifting device. Both parties agreed to the use of the term “working load limit” or WLL.

Based again on the pdf file presented in itera.org, the specific definition for the working load limit is that it 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. This definition can also be added to refer to the following definitions: the maximum load that an item can lift; and the maximum load that an item can lift in a particular configuration or application.

The working load limit of a lifting equipment depends greatly on a competent and skilled manufacturer who can wisely designate its WLL value. It’s the responsibility of the manufacturer to determine the right or approximate WLL value for each lifting device. To come up with a WLL value, there are many factors to consider. This includes the speed of operation, the applied load, the length of each rope or line, size, number, and etc. Any factor that can affect the working load limit of a lifting device should be carefully observed.

Summary:

  • WLL stands for working load limit while SWL stands for safe working load.
  • WLL and SWL are terms often used in the field of engineering.
  • Safe working load is the older term of working load limit.
  • The definition for safe working load is the breaking load of a component divided by an appropriate factor of safety giving a safe load that could be lifted or be carried.
  • The working load limit is that it 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.

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