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Finding the Working Load Limit of A 2-Legged Sling

When you work in overhead lifting, slings are a common tool.  Like any good tool, they are safe and effective when used as intended.  When working with slings, it is important to understand the working load limit (WLL) and how it changes as the sling angle changes.  A common sling configuration is a two legged bridle, which has two slings connected with a link.  In many cases, this configuration could also be achieved by connecting two slings with a shackle for a more temporary sling configuration.  Whether using a bridle or two slings connected with a shackle, the change of sling angle affects the working load the same.  The effect is the same whether using wire rope, chain, or synthetics.

Understanding WLL

The WLL of any piece of equipment is the maximum force it can exert safely without imposing a risk of breaking the equipment and accidentally harming others.  This is not the same as the ultimate breaking strength.  Slings are designed with a WLL well under their breaking strength to account for the possibility of accidental shock load or other unexpected trauma to the sling.  Intentionally loading slings beyond the WLL is highly dangerous, illegal, and can irreparably damage the sling and equipment.  Never overload slings.

How to Calculate WLL

On every sling, the tag shows the WLL for different configurations: basket, choke, or vertical.  In a vertical lift, where the sling is connected at each end and hanging vertically, it can lift exactly the number specified on the tag.  But when a sling is lifting at an angle, as a two legged sling will, the load increases.  But how does it increase?

To find out the increase on the load, take the length of the sling and divide it by the height of the upper pick point when the sling is at tension.  For example, one leg of your sling is 10’ long and the top of the leg is connected 8’ above the bottom of the leg, 10/8 = 1.25.  If the tension on that slide was 1,000lbs, it would now be 1,000lbs x 1.25, or 1,250lbs of tension.

Staying Safe and Within Your WLL

One of the most common concerns among riggers is making sure they calculate load correctly for safe lifts.  There are too many variables to be covered in one blogpost, and this overview is not intended to cover all circumstances.  However, Certified Slings & Supply® offers several resources to help you rig safely.  Download our FREE load limit calculator app on the iTunes Store or Google Play.  We also offer rigging classes across the state or at your jobsite.  Finally, ask our team for help!  We want our customers to operate safely and efficiently so every lift is a great lift.  We’re available at 1-800-486-5542, or come into any of our Service Centers across the state.

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