What is Birdcaging in Cables

Birdcaging is the term given when stranded cable conductor or wire rope naturally unravels itself, due to the tension during the manufacturing stage being incorrect. It is also a term applied to armoured cables when the armour layer springs open to form structure that resembles a birdcage (and in doing so no longer offers the protection that the armour layer is designed to provide).

During the manufacturing process of cables, a phenomenon known as ‘birdcaging’ can occur, which can compromise the safety and quality of a cable. Birdcaging is a severe form of distortion often seen in stranded cable and wire ropes. This type of distortion causes the individual strands of the cable to unwind; the shape this expanding stranded takes resembles to a birdcage shape, hence its name.

This contortion is commonly caused by sheaves that convey to unintended rotation. When a resistant non-rotational cable experiences torsion caused by overly tight or incorrect positioned bundle of strands, this can result in the cable strands rising and warping out of their original position. This type of mechanical distortion poses a severe hazard - as soon as birdcaging occurs the cable is deemed damaged; it can result in further damage to the insulation of the cable and ultimately contribute to the breakage of the conductor(s).

Birdcaging can also occur during unreeling process from the drum if the incorrect method is applied, due to the twisting of the cable. Similarly, it can also occur when cable is reeled onto the drum if similar care if not taken. It can occur whether manual or automatic methods of reeling are applied. In the case of armoured cables, if the unreeling / redrumming process do not account for it then the torsion that is applied during the armouring process releases itself. Axial compressive loads are introduced into the armour causing radial expansion of the amour wires, resulting in a 'birdcage' where the armour layer opens up and in many cases splits the outer sheath of the cable.

If birdcaging is suspected, this should be reported and the cable made subject to investigation to determine whether it is suitable for installation or continued use. The safety, quality, and compliance of the cable may have been impacted.