Cable Lifetime

The corkscrew effect, also known as birdcaging or helical twist deformation, represents one of the most catastrophic failure modes in medium-voltage reeling cables. It occurs when a cable develops a permanent spiral distortion that resembles the twisted form of a corkscrew or the expanded form of a wire cage — hence the colorful industrial terminology. Unlike simple insulation cracking or conductor breakage, which may occur at a localized point, corkscrew deformation is a systemic problem that compromises the cable’s structural integrity across its entire length or in extended sections. To understand what causes this failure, we must first recognize that a cable is not a monolithic object but rather a carefully engineered composite structure with multiple layers of conductors, insulation, and sheathing, all held in precise geometric alignment through precise manufacturing. When the cable is wound onto a reel and subjected to mechanical stress, that geometric alignment can be disrupted. The conductor strands, which are wound in a helical pattern, can slip out of position. The insulation layer, which must flex repeatedly without tearing, can separate from the conductors it insulates. The outer sheath, which protects everything inside, can develop stress cracks that accelerate moisture ingress and corrosion. The corkscrew effect amplifies all of these problems simultaneously.