Extension Spring Safety Cable

An extension spring safety cable is a steel cable—typically 1/8 inch diameter—threaded through the hollow center of each extension spring on a garage door. The cable's ends are anchored to the spring bracket at the rear of the horizontal track and to the pulley bracket near the door. It runs the full length of the spring.

Extension springs store a significant amount of mechanical energy when stretched. When a spring breaks—and all springs eventually do—that energy releases instantly. Without a safety cable, the broken spring halves can be propelled at high speed into a vehicle, wall, or person in the garage. The safety cable intercepts the broken coils within inches of failure, containing them along the cable's path rather than allowing them to become projectiles.

Safety cables are required under UL 325 for residential openers that use extension springs, and virtually all current installation standards require them. Older doors installed before these standards became common may not have them—adding safety cables to an existing extension spring system is a straightforward retrofit that any technician should include during service visits.

A safety cable does not prevent the spring from breaking or prevent the door from dropping when a spring fails—it only prevents projectile injury. If a spring breaks, the door will become very heavy on one side and should not be operated until the spring is replaced.