Wire Rope Breaking Strengths

Understanding Wire Rope Breaking Strengths

Breaking strength — also referred to as minimum breaking load (MBL) — is the maximum force a wire rope cable is required to withstand before it fails. It’s one of the most critical specifications in selecting the right cable for your application.

Key Factors That Affect Breaking Strength:

• Material
  Stainless steel and galvanized wire ropes have slightly different tensile properties. Galvanized cable typically has a marginally higher breaking strength due to the properties of carbon steel, while stainless steel is chosen for corrosion resistance.
  
• Strand Configuration
  The construction pattern (e.g., 7×7 or 7×19) plays a major role. A 7×7 wire rope is more rigid and abrasion-resistant, while 7×19 offers greater flexibility but may exhibit slightly lower breaking strength per diameter.
  
• Cable Diameter
  Breaking strength increases with cable diameter. We provide detailed specifications for all cable sizes up to 3/8”, the maximum diameter we fabricate.
  
• Coatings
  While coatings like vinyl or nylon enhance abrasion resistance and longevity, they do not directly impact the steel cable’s internal strength. However, coating must be stripped before end fittings can be properly adhered
  

Terminations & Holding Strength

When swaging end fittings like wire rope stops, ball ends, or crimp sleeves, proper installation is critical to performance and safety. Not all end fittings are designed to maintain full cable strength. For example, aluminum stops and standard ball ends typically hold up to 60% of the wire rope’s rated breaking strength. For applications where full strength is required, carbon steel or stainless steel stops and ball shank fittings are recommended, as they’re designed to hold up to 100% of the cable’s breaking strength when installed correctly.

This secure connection — often referred to as a cold weld — is formed through high-pressure crimping. At Tyler Madison, we use up to a 120-ton hydraulic swage machine and perform pull testing on every assembly line to ensure your cable assemblies meet strength expectations.

Wire rope clips, by contrast, are not typically rated to full breaking strength unless installed in a specific double saddle configuration with accurate torque. They’re best suited for temporary solutions or situations requiring adjustability. Because proper installation in the field can be inconsistent, we generally recommend having your assemblies professionally made in-shop rather than relying on wire rope clips.

Safety Factors

The working load limit (WLL) is not the same as breaking strength. Industry standards recommend applying a safety factor — often between 5:1 and 10:1 — depending on the risk, application, and environment.

For example:

• Lifting applications may require a 5:1 safety factor
  
• Life-safety or fall-protection systems may require 10:1 or higher