Working Load Limit (WLL) = 20% of Tensile Strength, for the longevity of the cord and safe uses
Tensile Strength
Also known as the labeled strength, is the average testing strength at which the new and unused cord would break when tested in laboratory condition in accordance with Cordage Institute Standard Test Methods. The load, applied in parallel to the cord, slowly increases until the cord breaks.
Working Load Limit (WLL)
In practical uses, various factors would impact or reduce the strength of any rope/cord, including knots in the rope, abrasion, humidity, UV, former use and care, etc. To assure safe uses, its indispensable to adopt a safety margin in the cord/rope strength, which leads to Working Load Limit (WLL).
The Working Load Limit (WLL) is determined by dividing the tensile strength by a safety factor. To assure the longevity of the cord and maintain a comfortable margin for safe uses, a 5:1 safety factor (20% of the tensile strength) is adopted and recommended for emma kites UHMWPE cord for general applications.