Control cable: numbered conductors for panel and machine runs

Numbered conductors and what the numbers are for

Control cable is a 600-volt multiconductor assembly, usually from 18 down to 10 AWG, with two to thirty-seven conductors. Each conductor is numbered or colour-coded so a technician can identify it at both ends of a run without ringing it out. The numbers are printed on the insulation and repeated at intervals, and they are the reason this cable is worth more than its copper.

Constructions vary in the jacket. Many control cables carry a tray cable rating so they can be run in tray without conduit, and the print will say so. Some are sunlight resistant, some are not. A control cable without a tray rating is a cable for conduit and raceway, which limits where it can go. Where a cable is shielded and tray rated together, both markings sit in the same print string, and reading the whole string once saves a second look at the reel.

Shielded against unshielded

An unshielded control cable is just conductors in a jacket. A shielded one has aluminium foil wrapped around the bundle, or around each pair, with a tinned copper drain wire laid against the foil and brought out to a ground terminal. The shield intercepts electrical noise that would otherwise be induced into the control conductors.

For surplus, the shield is a sorting fact and a condition fact. It is a sorting fact because shielded and unshielded cable of the same gauge are different products. It is a condition fact because the drain wire is fragile: it breaks at a cut end, and a coil with the drain cut back beyond reach is harder to terminate cleanly.

Panel builds and machine runs

Cincinnati's machine tool and packaging machinery base builds panels and skids, and every one of them consumes control cable in cut lengths. A builder orders a reel, cuts runs to each device, and finishes the machine with several feet left on the reel. Multiply that across a year of builds and the shelf fills with part reels.

The second generator is the retrofit. A line is upgraded, a PLC rack is replaced, and the field wiring to the old rack is cut loose. Those cut lengths have ferrules or ring terminals on them, and the terminals are usually removed before the cable is coiled, which leaves the ends slightly shortened and the conductor ends tinned or twisted.

Reviewing a control cable lot

The conductor count and the shield are the two facts that decide where a coil can be used, so they come first. Length comes second, because control runs are usually short and a twenty-foot piece is a working length.

• Conductor count, gauge and whether the numbers are legible
• Shielded or unshielded, and the drain wire condition
• Jacket print, including any tray or sunlight rating
• Length per coil, measured from the jacket
• End condition: clean cut, ferrules removed or conductors twisted