Elevator Suspension Rope Factor of Safety

The factor of safety the code requires rises with speed, because a faster car imposes higher dynamic loads and because the consequences scale with it -- so a rope set entirely adequate for a slow freight elevator can be below the requirement for a high-speed passenger car, and the applicable minimum comes from the code's table against the actual contract speed. Five ropes on a 220 ft rise at 0.68 lb per foot each weigh 748 lb, and a 12,000 lb car with a 3,500 lb rated load and a 200 lb travelling cable is a 16,448 lb suspended load against 89,500 lb of combined breaking strength: a factor of 5.44. LEAVE THE ROPE WEIGHT OUT and it reads 5.70, better than the truth by 0.26. On this modest rise the difference is small; on a 700 ft rise the ropes weigh 2,380 lb and the factor falls to 4.95, which is a different conversation entirely. That is why compensation exists -- to offset the shifting rope weight as the car travels -- and why an installation without it sees a different load at the top and bottom of its run. The retirement criteria are what actually removes ropes from service. Broken wires per rope lay, reduction in diameter, corrosion, distortion, and unequal tension between ropes each condemn a rope regardless of what the arithmetic says; they are assessed by a qualified person on a mandated schedule, and a comfortable calculated factor does not extend a rope's life. A static calculation. It does not model dynamic loads from acceleration, emergency stops, safety application, or buffer engagement, all of which exceed the static load and which the code's factors are partly there to cover. It does not evaluate traction, sheave groove pressure, or the bending fatigue that actually determines rope life through the sheave-to-rope diameter ratio, it does not perform the statutory rope inspection, and it does not address governor ropes, compensation, or the suspension means on machine-room-less and belt-suspended installations, which follow different provisions. ASME A17.1 and A17.2, the equipment manufacturer, the elevator authority having jurisdiction, and a licensed elevator mechanic govern.

suspended load = car + rated load + travelling cable + rope weight below the sheave, where rope weight = count x rise x weight per foot; factor of safety = (count x breaking strength) / suspended load.

The suspended-load factor of safety, by name, with the ASME A17.1 speed-dependent minimums and the rope retirement criteria named. The minimum for the contract speed comes from the code table and is entered, not reproduced.

Division on the user's own rope and car data against a minimum they supply; no code table is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: car_weight_lb, rated_load_lb, travelling_cable_lb, rope_count, rope_weight_per_ft, rope_breaking_strength_lb, rise_ft, code_minimum_fs, rope_weight_lb, suspended_load_lb, breaking_total_lb, factor_of_safety, fs_without_rope_weight

• Rope weight belongs in the load and it is the term most often dropped; it grows with the riseASME A17.1
• The minimum rises with contract speed a set adequate for a slow freight car can fail for a fast passenger oneASME A17.1
• Retirement criteria are independent broken wires, diameter reduction and corrosion condemn a rope whatever the factor saysASME A17.2