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Z-Kinks

Anytime the tension on a cable is suddenly released, the possibility exists of forming kinks in the cable conductor. This class of kinks is of ten referred to as z-kinks. The soft copper strands, which make up all conductors, are elastic over a narrow range. If the cable is pulled so that it stretches over 0.1%, the copper can be stretched permanently so that it is longer than the original length.

The permanent elongation of the copper presents a problem when the tension on the cable is suddenly removed. Under, such a condition the elastic steel armor relaxes and may even overshoot going into compression. The weaker more pliable copper and plastic core is forced to follow the steel. If the tension on the cable is removed gradually, usually the cable has-time to rotate. If rotation is allowed, some of the elongation may be absorbed. However, if there is no rotation, the extra length of copper has no where to go. Under certain conditions, the copper can double back on itself. This "doubling back" often is in the shape of the letter "z" - thus the name "z-kink". Alternately the lengthened copper strands instead of folding back on the conductor may form a spike extending perpendicular to the conductor. These two types of kinks are illustrated in Figure 1.

A z-kink is detrimental only to the extent that the distance between the conductor and the armor can be significantly less than normal. This increases the likelihood of an electrical short developing at the z-kink. Such shorts are more apt to show up when the line is put under higher tensions, causing the-core to decrease in diameter slightly, or/and when the cables runs over a sheave.

figure 1.

Multi-Conductor Cable Z-Kink

Note that the entire insulated conductor has elongated and formed the "Z" shape. The dark material around the conductors is string filler.

Monocable Z-Kink

Note that the copper conductor only has become permanently elongated and formed a spike through the insulation layer.


Z-Kink in Single Conductor Copper Strand	Spiked Kink in Single Conductor Copper Strand


Z-Kink with Yielded Copper Strand	Z-Kink in Seven Conductor Copper Strand

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