Issue link: https://www.e-digitaleditions.com/i/1066130
January/February 2019 I 23 a +20°C adjustment factor over a 25°C normal ambient to the temperature results. NEC Article 725.144(B) permits the use of Class 2-LP or Class 3-LP cables with no bundle size limits. However, LP-rated cables are not required; non-LP rated Class 2 and 3 cables with 22-26 AWG sizes should follow the ampacity table for temperature ratings and bundle sizes not to exceed 192 cables. Each standard and code might have different definitions of a cable bundle, but most of them standardize around multiple cables, contact between the cables and proximity (or distance limits) between cables. When to limit maximum bundle size to 24 cables. This easy-to- remember practice addresses most media, environmental and application scenarios. Since there is no easy method to monitor temperature or cool pathways, the recommended approach to minimize the risks associated with elevated temperatures is to select cabling media that is rated for operation in higher ambient temperature environments. Cables rated for operation at temperatures higher than the ISO/IEC and TIA specified upper operating temperature of 60°C (140°F) offer additional flexibility for deployment of greater than 60 W remote powering applications, and shielded cables offer much better heat dissipation over unshielded cables. For example, shielded category 6A and category 7A cables that are mechanically rated for operation up to 75°C (167°F) are ideal for support of up to 100 W (1A per pair) in bundle configurations of up to 192 cables. CONNECTING OUTSIDE THE BOX Another consideration when installing devices in an intelligent building is the different connection configurations. The term "EO" is used by TIA to indicate an equipment outlet for facility or building applications outside the definition of telecommunications outlets (TOs) that are used to connect to computers, printers or phones. FIGURE 5: ANSI/BICSI-007: Building system horizontal cabling elements within a star topology. planned properly, heat build-up and signal loss can be minimized or mitigated. Here are some of the techniques recommended by TIA: • Derating the cable by reducing the horizontal channel length. (See Figure 4 showing that the insertion loss increases in proportion to temperature.) This requires length derating at temperatures above 40°C (68°F). Installers need to make certain that they do not exceed the channel length that matches the cable type, depending on the rise of the temperature. • Unbundle cable in the cable tray to allow for improved heat dissipation. • In a pathway, mix cables carrying PoE power with those only carrying data signals. When in doubt about cable, mechanical or heat dissipation capability, installation environment, or remote powering application, a conservative practice is FIGURE 6: A modular plug terminated link (MPTL) is a field-terminated plug for connecting directly to intelligent building devices and is recognized by TIA-568.2-D.