Issue link: https://www.e-digitaleditions.com/i/1081695
March/April 2019 I 23 Although this is the best solution, it is not always practical or feasible. It can be a daunting task to determine all these potential difference values, and industrial environments can also be very dynamic with electrical system changes. As machines and equipment are moved, added, replaced, and upgraded, just one of these changes can immediately change potential differences previously identified and have a detrimental effect on the integrity of the communications infrastructure. Since shielded cabling solutions are more susceptible to detrimental effects from this scenario, industry installers use a single ended bonding technique that has proven successful for mitigation. The cable shields are bonded at their source and isolated at their destination. Although this is not technically standards compliant, it offers a viable and proven solution to this issue. If this method is chosen, there are further considerations when selecting infrastructure system components. Specify a patch panel that is designed for shielded cabling and stipulate that each patch panel must be individually bonded to the rack bonding busbar with a #12AWG copper conductor. If using a modular solution, specify shielded modular jacks for all shielded cables terminating at these patch panels. Specify unshielded jacks for the device/field ends and that heat shrink tubing be installed to maintain shield isolation. Most IP- enabled end devices have shielded ports, so it may be necessary to specify a voltage rated and shielded patch cable to connect the end device to the jack outlet, depending on whether it needs to run in close proximity to or share a wire way with power wiring within the enclosure. This patch cord will then attain a single ended bond through the shielded jack in the equipment, but it will remain isolated where it connects to the unshielded jack, thus protecting the integrity of the single ended bonding solution while every section of noise susceptible cable remains effectively shielded. Following are some examples of critical design information needed for specific environment types: Food & Beverage • Are areas washed down regularly? • Are there food safety regulations that prohibit the use of typical infrastructure support components? • Are there food safety or corporate standards that dictate the type and material for pathways and enclosures used within the facility? Conduit example: schedule 40 stainless steel Cable tray example: non-ventilated (solid), aluminum, with cover Enclosure example: NEMA 4X, non-metallic, with sloped top. Gas and Oil, Grain Handling, Chemical Processing, Painting, and Waste Water All of these facilities include hazardous areas as defined by NEC/CEC, which are classified using a Class & Division or a Zone rating system. • Which areas hold a hazardous designation as specified in the NEC/CEC? • What are the physical boundaries of the classified area(s)? • Are any telecommunications outlets required in these areas? • Is air purging for enclosures an option? If so, it is typically acceptable only if the purge is monitored and includes a safety shutdown feature in the event that purge pressure is lost. • NEC/CEC compliant pathways, enclosures, outlet/terminations, and devices must be part of the infrastructure when terminating in or passing through any hazardous area. Many industrial spaces, though technically inside, are not environmentally controlled and are subject to temperature and humidity extremes that can be more severe than outdoor installations.