True, the National Electrical Code (NEC), Article 90-3 "Code Arrangement," states that "Chapter 8 covers communications systems and is independent of the other chapters except where they are specifically referenced therein." But what about the optical fiber in Article 770 and the Class 1, Class 2, and Class 3 remote-control, signaling, and power-limited circuits in Article 725? Yes, they must meet guidelines specified in Chapter 3, "Wiring Methods and Materials", Section 300-11, which specifically addresses securing and supporting raceways, cable assemblies, boxes, cabinets, and fittings.
Suppose that we are installing a small bundle of unshielded twisted-pair (utp) 4-pair cables, and we decide that in order to meet the "support-the-cable-every-48-to-60-inches" rule, we will use clips designed especially for this purpose. We secure the cables to the ceiling support wires from the work area back to the cable tray. A few months pass, and someone tracing a cable in the cable tray mistakenly pulls harder and harder on the cable, waiting for his partner to detect any movement down line. Nothing--it must be stuck. Another good tug bends the ceiling support wires, and up goes the ceiling grid!
Now suppose that we are "value engineering" this job and we don`t want to install a cable tray at all. But we still have all this cable to get back to the telecommunications closet and we can`t lay it on the ceiling tile. In the newly published ansi/tia/eia-569a standard, we can install cable fasteners directly on the T-bar. For example, we are cabling 10 offices along a corridor 6 feet wide by 50 feet long, with four locations in each office, with eight utp cables to each location. Three-hundred-twenty cables without a cable tray--no problem. We will just install cable fasteners directly on the T-bar; they can support up to 0.45 pound per foot of cable. The corridor ceiling is 6 feet wide, so using a 2 x 4 grid, we now have four rows of ceiling rails that we can use. Ironically, tia/eia-569a instructs the designer of these fasteners regarding obstruction of tiles, but gives no guidance to the installer.
My fear is that the architects and project managers will see this as another candidate for "value engineering" in their future projects.
eia/tia-569, Section 4.6.2.1, states: "The design shall provide a suitable means and method for supporting cables and wires from the telecommunications closet to the workstation. The suspended ceiling support wire or rod shall not be used for this purpose. Wire or cable shall not be laid directly on the ceiling tile or rails."
tia/eia-569a, Section 4.6.2.1, states: "The design shall provide a suitable means and method for supporting cables from the telecommunications closet to the work area to be served. Cable shall not be laid directly on the ceiling tile or rails."
A new section was also added to tia/eia-569a, Section 4.6.2.1, which says: "A suspended ceiling support rod or wire may be used to mount appropriate cable fasteners loaded with multiple cables up to the total weight for which the fastener is approved. The T-bar rail of a suspended ceiling may be used to mount appropriate cable fasteners loaded with cable up to a total weight of 0.45 lb per foot."
Donna Ballast is a communications analyst at The University of Texas at Austin and a BISCI registered communications distribution designer (RCDD). Questions can be sent to her at:
Cabling Installation & Maintenance or at PO Drawer 7580,
The University of Texas,
Austin, TX 78713;
tel: (512) 471-0112,
fax: (512) 471-8883,
e-mail: [email protected].