Safety Factor (SF) for Manila and Wire: If a line has a breaking strain of 30,000 pounds and SF of 2.5, what is the SWL?

• A. 7,500 pounds
• B. 60,000 pounds
• C. 15,000 pounds
• D. 12,000 pounds

Answer: (D)

Safety factor indicates how much stronger the line is than the load it’s allowed to carry. The working load limit is found by dividing the breaking strength by the safety factor. With a breaking strength of 30,000 pounds and a safety factor of 2.5, the SWL is 30,000 ÷ 2.5 = 12,000 pounds. This means the line’s safe working load is 12,000 pounds, about 40% of its breaking strength, providing margin for dynamic effects, wear, and knots. If you had multiplied or divided by a different factor you’d get other values, but dividing by 2.5 gives the correct SWL in this case.