Cable / Wire Rope
Cable / Wire Rope stretches as a load is applied. The amount of stretch will increase as the load is increased. There are two types of stretch occurring here. The first type of stretch is called CONSTRUCTIONAL STRETCH. The second type is referred to as ELASTIC STRETCH.

Constructional Stretch
Constructional Stretch occurs as the outer wires of a strand close around its core and as the outer strands of the cable close around its core under tension. This closing action is the filling up of the spaces between the individual wires and the spaces between the strands. Unfortunately, this type of stretch is not consistent (because of all of the variables involved in the manufacture of the cable) and cannot be quantified into a formula. Constructional stretch can be removed by prestretching or prestressing (whichever term you prefer). We accomplish this in accordance with MIL-C-5688. We would be happy to fax you a copy on request.

Elastic Stretch
Elastic Stretch occurs as the individual wires elongate under load. This is a quantifiable factor until the yield point of the cable is exceeded. The factor varies according to load applied and the construction of the cable or strand. In short; the fewer wires and strands in a given diameter, the lower the stretch factor. If you require a calculation for elastic stretch for a particular cable, contact us at 1-800-851-2961 and one of our sales staff will acquire this information for you.

As previously discussed, we can reduce or eliminate constructional stretch by applying calculated loads to the cable or cable assemblies in accordance with MIL-C-5688. This specification also covers processes for proof testing. In most cases we can accomplish both processes in the same test sequence. If this would be advantageous to your assemblies, please inquire with one of our sales staff for pricing.

Measuring
Measuring strand, cable and wire rope properly is done in the following manner. Using a pair of calipers, move the anvils into contact with the peaks of two opposing strands (see illustration). DO NOT HAVE THE ANVILS MAKE CONTACT WITH FOUR STRANDS SIMULTANEOUSLY. This will give a false undersize reading. Most cable is manufactured to a plus tolerance. Please see the charts on page 4 which show bare cable and coated cable diameters.