Updated December 2019. || Engineers can use a multitude of cables (including data, coaxial and instrumentation cables) in industrial settings for control networking, low and medium-voltage power transmission and distribution, and more.
Power cables for industrial use
Most cables that distribute power to motors are low-voltage designs rated for 2,000 V and below. That said, some facilities with partial responsibility over the utility power they consume use medium-voltage cables rated for 2,000 to 35,000 V.
Available as both single and multi-conductor designs, these power cables must be able to withstand high mechanical loads, speeds and accelerations. Common applications include machine tools, cranes, conveyors, portable designs and stationary heavy-duty equipment. Such cables can supply temporary ac or dc power to motors and generators, and can operate indoors and outdoors, depending on their temperature rating.
The proper cable for an application depends on its function and environment. For instance, only use an unshielded cable when it will operate in an enclosed space only accessible by trained professionals. Such enclosures prevent electromagnetic interference and keep plant personnel safely away from potentially live electrical charges.
Manufacturers usually construct low-voltage cables with aluminum or copper conductors, insulation and jacketing. Conductors can range anywhere from finely stranded bare copper wires to bunched strands of tinned annealed copper. They come in both shielded and unshielded versions and usually must be flame retardant and oil resistant.
Power cables feature conductors that are either stranded in layers inside or bundled or braided. The stranded design is easier to manufacture, so also costs less. It features long, layered cores and firm strands wrapped with an extruded jacket. In the bundled or braided design, the conductors are braided around a tension-proof center. By eliminating the layers, a uniform bend radius is ensured.
To accommodate the complex and sometimes cramped spaces where they operate, industrial power cables must also have tight bending radii, ranging anywhere from 5 to 15 times the overall cable diameter. Jacketing is also crucial to meet these bending radii requirements. Therefore, the use of flexible materials, such as PVC, TPE and CPE, not only helps these cables bend and flex, but also protects them from environmental damage.
Because the materials, shielding, and jacketing of industrial power cables all vary, so do their installation techniques. Installers can put cables:
• Into fixed duct, shafts and conduit
• Bury cables directly into the ground or even immerse the cables in water
• Lay cables along runs in open-air applications
Depending on where a cable is manufactured and used, it must meet a variety of approvals — including UL, CSA, TC, AWM, RoHS and CE. In the U.S., the National Electrical Code (NEC) sets the standards that designers must usually follow. These codes ensure that the cables have key performance features to satisfy machine requirements—for example, to stop the propagation of flames, satisfy the application’s maximum voltage draw, withstand extreme temperatures and maintain integrity even when exposed to oil.
Flexible cabling for communications (and power as well)
Flexible cables, or continuous-flex cables, are cables specially designed to cope with the tight bending radii and physical stress associated with motion control applications. These highly flexible cables were developed with unique characteristics to differentiate them from standard designs. These are sometimes called chain-suitable, high-flex, or continuous-flex cables.
A higher level of flexibility translates into an increase in service life for a cable inside a cable carrier. A regular cable typically manages 50,000 cycles, but a flexible cable can complete between one and three million cycles.
Flexible cables can be divided into two types; those with conductors stranded in layers inside the cable, and those that have bundled or braided conductors.
Stranding in layers is easier to produce, and therefore usually less expensive. The cable cores are stranded firmly and left relatively long in several layers around the center and are then enclosed in an extruded tube-shaped jacket. In the case of shielded cables, the cores are wrapped up with fleece or foils.
However, this type of construction means that during the bending process the inner radius compresses and the outer radius stretches as the cable core moves. This can work quite well because the elasticity of the material is still sufficient, but material fatigue can set in and cause permanent deformations. The cores move and begin to make their own compressing and stretching zones, which can lead to a “corkscrew” shape, and ultimately, core rupture.
The other construction technique involves braiding conductors around a tension-proof center instead of layering them. Eliminating multi-layers guarantees a uniform bend radius across each conductor. At any point where the cable flexes, the path of any core moves quickly from the inside to the outside of the cable. The result is that no single core compresses near the inside of the bend or stretches near the outside of the bend, which reduces overall stresses. An outer jacket is still required to prevent the cores untwisting. A pressure filled jacket fills all the gussets around the cores and ensures that the cores cannot untwist. The resulting flexible cable is often stiffer than a standard cable, but lasts longer in applications where it must constantly flex.
Selecting the right flexible cable for an application starts with a few fundamental parameters. First, determine the application type. Will the cable be stationary or will it be moving? If the latter, is the motion mainly flexing or is there torsional motion involved? Or does the application call for both flexing and torsion? Different applications have customized cables for that application.
Read the related article: How to Size and Select Cable for Motion Applications