The rope strength design factor is the ratio of the rated strength of the rope to its operating stress. If a particular rope has a rated strength of 100,000 lbs. and is working under an operating stress of 20,000 lbs., it has a rope strength design factor of 5. It is operating at one fifth or 20% of its rated strength.

Many codes refer to this factor as the "Safety Factor" which is a misleading term, since this ratio obviously does not include the many facets of an operation which must be considered in determining safety. Wire rope is an expendable item - a replacement part of a machine or installation. For economic and other reasons, some installations require rope to operate at high stress (low rope strength design factors). On some installations where high risk is involved, high rope strength design factors must be maintained. However, operating and safety codes exist for most applications and these codes give specific factors for usage. When a machine is working and large dynamic loadings (shock loadings) are imparted to the rope, the rope strength design factor will be reduced which could result in overstressing of the rope. Reduced rope strength design factors frequently result in reduced service life of wire rope.

O.S.H.A. (A.N.S.I.) Removal Criteria 5. A.N.S.I. Safety Codes, Standards and Requirements...
Rope must be removed from service when diameter loss or wire breakage occurs as follows:

*Also remove for 1 valley break. OSHA requires monthly record keeping of wire rope condition.

Note: Current industry recommendations and OSHA standards are based upon the use of steel sheaves. The manufacturer of plastic or synthetic sheaves or liners should be consulted for their recommendation on the safe application of their product and possible revision in rope inspection criteria when used with their product.