CABLING

Cabling

Cabling (also known as twisting) is the process where cores are wrapped around one another, enabling the cable to be flexed. Without this rotation the core/s on the inside of the bend would be placed under compression and the core/s on the outside of the bend would be placed under tension, causing deformation of the cable, damage to the other cores in the centre of the cable and also breakages within the connectors.

Direction

Most cables will be manufactured with alternating left-hand (S) and right-hand (Z) layers. This is done to make the cable evenly balanced which can prevent it from twisting up in a single direction under dynamic use. Each core will also have back-twist applied to further prevent this twisting process and to ensure that the cable is as ‘dead’ as possible. It is most common to have the final layer as a left-hand layer, an example of which is a typical 19 core cable that would have:
- Centre - 1x core laid straight.
- First layer - 6x cores laid around the centre core with a right-hand lay.
- Second layer - 12x cores laid around the first layer with a left-hand lay.

Torsion

The exception to the rule of alternating layers is where the application will require torsion to be applied to the cable (such as coiled/spiral cables). In this instance it is advantageous to have all the elements cabled in a single direction as this will help the cable to return to its original form each time, even when extended and retracted frequently.

Lay-lengths

The lay-length is the distance in mm or inches over which a core travels from it’s starting position in a layer, for example: 12 o’clock on a clock face, around the cable and back to its original position at 12 o’clock. A cable with a short lay length will have a more ‘springy’ flexible feel to it, whilst a cable with a long lay length results in a stiffer cable. However cables with longer lay-lengths can be produced significantly quicker and use less material which provides benefits in both manufacturing time and cost, so there are good reasons for using a long lay-length where flexibility is not critical to the cable design. Habia Cable will nominally use a lay length of between 8x and 16x the cabled diameter, so for flexible cables, a lay-length close to 8x the cabled diameter will be used, whilst normal use cables will be closer to 16x the cabled diameter.

Twists per inch

Lay length is often specified as a given number of twists per inch. This relates to the number of times a core should travel from its starting position at 12 o’clock, around the cable and back again over a given distance. A cable requirement of 3 twists per inch would therefore require the same core to rotate around the cable and return to the 12 o’clock position 3 times over the distance of 1 inch (25.4mm) giving a lay length of approximately 8mm.

Flat cables

Habia Cable also has the capability to lay up to 8 components (depending on size) side by side for inclusion in a flat cable design. Flat cables provide a significant benefit with regard to bend radius if the cable is being flexed in a single direction, as the cable can be made with a noticeably smaller overall dimension and yet still contain several elements. However flat cables are not ideal for applications which require freedom of movement in more than one direction.