Notable Constructional Differences
There are several major differences between commercial and industrial cabling.
Inner Conductors. Industrial cabling tends to involve a lower-gauge, thicker cable for the inner conductors. This allows for less electrical resistance and enables a stronger overall connection despite vibrations, shock, or flexure.
Shielding. Twisted-pair cables for indoor industrial applications will nearly always leverage a braided shield, as that provides a higher resistance to electromagnetic interference (EMI) and RF interference (RFI). When braiding does not provide enough coverage, an additional foil layer of shielding can also be leveraged for more EMI/RFI mitigation with 100% coverage — this is particularly helpful for patch cables that are subject to more interference.
Noise sources such as motor brushes, high-powered switches, heaters, and even lightning can cause cabling to carry interference that can subsequently damage the connected sensitive electronic circuitry. This, in combination with mild to severe voltage transients that come with daily power surges, requires a degree of protection. While surge-protective equipment would handle the brunt of overvoltages, it is still important for cables to have an acceptable level of EMC. This way, unpredictable EMI does not slowly chip away at the functionality of equipment.
Jacketing. The jacketing material is a major consideration since typical thermoplastics will crack, melt, or bulge with exposure to harsh chemicals or oil. Thermoplastics such as Teflon or PVC are often leveraged for cable jacketing due to their recyclability — no chemical bonding occurs during the curing process so the material can be remelted and reformed. Additionally, thermoplastics tend to be much easier to strip, allowing for a higher degree of flexibility during the production process. These characteristics, however, make these cables particularly susceptible to heat and abrasions.
Thermosets (e.g. neoprene, EPR), on the other hand, cannot be recycled as easily due to the cross-linking that occurs between the polymer chains during the curing process. This allows the material to generally have far more inherent UV resistance and resistance to high/low temperatures. Cable jacketing subject to temperature extremes, transients, and mechanical stressors would likely not deform with a thermoset material.
Thermoplastic elastomers (TPE) evoke the benefits of both material types with the ability to be remolded while upholding the structural cross-linking in thermosets. In this way, they also maintain a higher tensile strength and durability than the average thermoplastic.
Materials such as polyurethane (PUR) or TPEs are often the ideal candidates for IE installations. PUR, for instance, is a synthetic rubber that can be formulated to resist oils, grease, and chemicals. This is especially important in robotic control applications where oil-based lubricants are often used. When compared to most rubbers, PUR has a higher abrasion/tear resistance and can also be relatively easily molded while also maintaining a high flexibility. It is often noted that thermosets such as neoprene are more flexible than PUR but PUR IE cables can easily have continuous flex ratings that go up to the tens of millions of cycles without performance loss — an important factor, considering cables in automated equipment can be flexed/bent thousands of times daily.
An Underwriter’s Laboratory (UL) rating from the UL-1581 standard listed in Table 1 ensures that the required tests for flammability have been performed for a general-purpose, plenum, or riser application. Figure 2 shows the various flammability ratings. Plenum cables are subject to the most severe qualifications since HVAC spaces can very rapidly spread flame throughout an entire facility with forced airflow. Along the same line, Low Smoke Zero Halogen (LSZH) cables mitigate the release of toxic/acidic smoke that can injure workers.
Connectors. Often, the most critical portion of a cable can be its connector heads. These are frequently the weak points in any installation due to the hazard of potential ingress and unmating due to vibrations/flexure. The traditional RJ45 connector used in Ethernet cables is often not suitable for industrial applications. This is where the circular M12, which was typically used for sensors, was adapted for industrial Ethernet. This is where the various codes for these connector heads become useful. For instance, the M12 X-coded connector contains 8 pins and leverages CAT 6A or CAT 7 copper cables for high-speed Ethernet with up to 10 Gbps of throughput. Table 3 shows some of these codes and their respective use cases.
The M12 connectors are typically at least IP67-rated, which is entirely dust-tight and can resist temporary water immersions. These connectors also feature locking mechanisms that are far more robust than the RJ45 connector with a threaded mate that is not easily unmated or deformed. The overmolding (Figure 3) allows for strain relief at the fulcrum point between the connector head and the cable where bending/flexing can cause the most damage while also providing ingress protection.
In many vision applications, screw-down RJ45 connecters are used in place of standard RJ45 connectors that can become dislodged due to jolting, vibration, gravity, and cable pulls often found in these types of applications. The secure, screw-down mating mechanism is also favored for use in industrial and military applications where exposure to excessive shock and vibration exists.
Each piece and part of an industrial Ethernet cable including the inner conductors, shielding, cable jacketing, and connector heads must be ideally suited to the harsh conditions in industrial environments. The survivability of these cables relies on a slew of parameters that can be summarized in some of the industrial Ethernet standards with the MICE methodology. These requirements lead to specific constructional difference in the cable’s assembly between the typical commercial cable and an industrial Ethernet cable.
This article was written by Dustin Guttadauro, Product Manager at L-com, Infinite Electronics, North Andover, MA. For more information, visit here.