Choosing the right communication cable

Voice and data cabling from the communications room to the outlet can represent a sizeable investment to install or replace. It is worth taking the time to consider the choices of cabling, striking a balance between capital costs of installation and having an infrastructure that will not be obsolete in a few years.

Understanding the networking protocol and related bandwidth it will need to support are important factors in determining cable type. The most common protocol for data networking is Ethernet, and specific Ethernet protocols may be selected by bandwidth such as 10 Megabit, 100 Megabit, 1,000 Megabit (or 1 Gigabit), and 10 Gigabit. The protocol usually is chosen by the information technology group or person responsible for the network applications and network architecture.

The lower the bandwidth, the less data that travels through the cable, and the lower the performance—which requires a less expensive cable. Likewise, higher bandwidth means higher performance and higher cost. The overall trend in the industry is that data packets have become larger. Applications that once used only text now use graphics.

Another trend is to augment text with video, or to replace text entirely with video. This is common for training and presentation material. Access to the Internet also has driven the need for more network bandwidth. There once was a time when product catalogs were printed and shipped to the office. Now most catalogs are online downloads. All of this has driven the need for more network bandwidth.

The standards

When choosing a cable type for networking (both voice and data), the cabling standard for reference is “TIA/EIA 568.B: Commercial Building Telecommunication Standard.” Several parts of the standard address different components of the cabling infrastructure. This cabling standard works in conjunction to support the IEEE 802.3 Ethernet Standards. Table 1 lists the cable type and the Ethernet protocol supported. The Category 5e, 6, 6 shielded, and 6a cables are all four-pair copper 100 ohm twisted-pair cables designed for a maximum cable channel distance of 100 meters, or 90 meters from the communication room to the outlet.

The TIA 568.B Standard and its companion document, “TIA/EIA 569: The Commercial Building Standard for Telecommunication Pathways and Spaces,” are two resources for the design of communications infrastructure in a commercial building environment. The resources for communications cabling in the industrial building environment are not as well developed as they are for the commercial environment. There isn’t an industrial standard comparable to the commercial cabling standards. Good engineering judgment is required to adapt the commercial standards to industrial applications.

Unlike a commercial environment, industrial environments vary depending on the industry; each environment represents specific conditions that the engineer must consider. The considerations for a power generation plant are different than those for a micro-electronics manufacturing facility. In a power generation facility, the designer needs to consider the impacts of temperature variations, large magnetic fields, and areas of very high voltages. In a micro-electronics manufacturing facility, the designer may need to consider exposure to chemicals, high radio frequency exposure, and the impact of the cable itself to a clean room environment.

The commercial environment

In a typical office building or similar space, 100BaseT and 1GBaseT Ethernet are still the most popular protocols used on the network. These protocols support the bandwidth for most office-type applications because 1GBaseT is able to support network bandwidths to the desktop for the next 5 to 10 years. Cat 5e and Cat 6 will support these protocols; Cat 5e cable is the less expensive of the two.

Although both of these cable types will support the same types of Ethernet, the Cat 6 cable is rated to a higher frequency with higher performance characteristics. When the networked starts to get stressed due to high-bandwidth applications, the Cat 6 cable may have more tolerance for the installation and component abnormalities that tend to affect performance.

If you think you have issues with the quality of the installation or the electromagnetic interference (EMI) noise in the environment, a Cat 6 cable with its additional headroom in performance might be worth the added cost. When specifying a Cat 5e cable that you plan to work at 1GBaseT and last for the next 8 years, consider the purchase of top-tier components. Some cable manufacturers don’t make their own termination components, but these companies usually have warranty agreements with companies that do manufacturer the jacks and patch panels. With any of the cable types noted here, abide by manufacturers’ warranties and use certified installers.

What about Cat 6A, Cat 6 shielded, or fiber optic cable to the desktop? There are some desktops that could use 10GBaseT to the workstation, but these are rare circumstances. If you are planning for an installation to last 10 to 15 years, then one of the above choices may make sense in allowing a migration to 10GBaseT. With these types of cables, there is more to consider than just cable and termination cost.

For Cat 5e and 6 cable, the Cat 6 cable material will cost more, but the cost of labor and the impacts to cable tray and conduit fill are about the same.

When considering the Cat 6 shielded and Cat 6a cables, it also is important to note that the cable diameters are larger. The nominal diameter of Cat 6 cable is 0.2 in.; the diameter of a Cat 6a cable can be 0.31 in. (Some cables are larger or smaller, depending on the manufacturer.) This increased size of the Cat 6a cable will affect the sizing of cable trays and pathways in order to support the larger cable. For example, a 6×12 in. tray filled to 50% with Cat 6 cable of a nominal cable diameter of 0.2 in. would hold about 1,200 cables. The same number of cables for a Cat 6a cable with a nominal diameter of 0.31 in. would require a cable tray size of 6×30 in. That is a significant increase in cable tray size and cost.

Fiber optic cable has its own pros and cons. A four-strand fiber optic cable is no larger then a Cat 5e cable at 0.19 in. diameter. The cable itself is really no more delicate than the twisted-pair cables, although kinking a fiber optic cable may cause it to break, while kinking the twisted-pair cable may cause only poor performance.

The fiber optic industry has come a long way in developing easy and quick fiber terminations that can be made in the field. The cons for fiber is the cost of the electronics to convert the optical signal back into an electrical signal. Another consideration is that the optical industry has been working with 10G Ethernet speeds longer, and it has a mature product line for 10G Ethernet. You also can stretch beyond the 100 meter channel distance limitation set out by the cabling standard. Still, the downside is that the optical network interface cards typically cost more than the twisted-pair variety. Even with an all optical data network, some twisted-pair copper cabling may be required for telephones and power of Ethernet devices.

The industrial environment

The industrial environment doesn’t see the same turnover in bandwidth-greedy network applications as in commercial and office environments. Too much turnover in applications used in manufacturing or processing can lead to costly disruptions. The industrial environment has a different mentality regarding the type of data being networked. It will still have an office network susceptible to the bandwidth issues faced in a commercial environment, but the industrial networks are more purposeful in traffic. Network traffic is planned: A network designed to communicate between a server and programmable logic controllers (PLCs) in a batch plant won’t arbitrarily decide to download a video from the Internet.

With this in mind, an environment that has a moderate to minimum amount of EMI can operate with Cat 5e cable. This is assuming that in this environment the cabling will most likely be routed in electrical metallic tubing conduit or, if necessary, a ventilated cable tray. A solid bottom tray with a cover may add additional EMI protection to the unshielded twisted-pair cable.

The alternative to the Cat 5e cable is the fiber optic cable for industrial environments. It is not susceptible to the effects of EMI and it can go much longer distances. Where there are PLCs located throughout a manufacturing or processing area, it is not always feasible to locate a network switch to provide coverage for 100-meter limited twisted-pair cable. As noted before, the commercial building standard does not allow extending beyond 100 meters. For an industrial environment, as long as engineers don’t extend beyond the Ethernet protocol for distance over the fiber optic cable, it is within good engineering judgment to step beyond the commercial building standard.

In either environment, it is important to choose a quality cable manufacturer or a certified installer. The commercial environment isn’t as harsh as the industrial environment, but you will likely start pushing the bandwidth limitation of the cable plant in a commercial environment. For very harsh industrial environments, some cabling manufacturers manufacture cable components designed to keep the cable connectors clean and free of contaminates.

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