Donna Ballast
When you are writing specifications, make certain you know what is covered and what is not in the codes and standards that you are referencing. Recently, I heard an interesting "war story" from someone in charge of information technology for a large school district and who wishes to remain anonymous.
Rather than installing a cable tray or separate support wires to support the cable hangers, the cabling-installation contractor in this case had secured the bundles of telecommunications cables to the ceiling support wires, and the ceiling nearest to the telecommunications room fell. Having learned of the incident during the blame-placing phase of the project, I began wading through contract documents. Most designers assume that if their specifications comply with the National Electrical Code (NEC) and the standards of the Telecommunications Industry Association and Electronic Industries Alliance (TIA/EIA--Arlington, VA) and something goes wrong, then the installation contractor must not have followed the specifications.
Not true. Neither the 1999 NEC nor ansi/TIA/EIA-569a prohibits the practice just referenced.
1999 NEC, Chapter 3, Article 300, Section 11, clearly states that wiring located within the cavity floor-ceiling or roof-ceiling assembly shall not be secured to, or supported by, the ceiling assembly, including the ceiling support wires. An independent means of secure support shall be provided. There is an exception permitting use of the ceiling support system to support wiring and equipment that have been tested as part of the fire-rated assembly. So the contractor is in violation of the NEC, right?
Wrong. NEC 300-11 does not apply to telecommunications cabling because 300-11 is not specifically referenced in Article 800 Communications Circuits. There is a parallel gap in Article 725-3 Class 1, Class 2, and Class 3--Remote Control, Signaling, and Power-Limited Circuits, and Article 770-3 Optical Fiber Cables and Raceways, which says that "only those sections of Article 300 referenced in this article shall apply." In each case, only 300-21 and 300-22 are referenced.
ANSI/TIA/EIA-569a 4.6.5 states that where zone conduit or cable tray is not available in a suspended ceiling, adequate open-top cable supports shall be provided. Where larger quantities of cables (50 to 75 cables) are bunched together in the ceiling in a congested area, special supports shall be designed and installed to carry the additional weight. Translation: If there is no cable tray, use J-hooks. Got a lot of cable? Then use special J-hooks that will not bend under the weight of the cables.
So if the contractor purchased a lot of J-hooks, attached multiple J-hooks to a ceiling support wire, and filled each J-hook to capacity, he was within the requirements of TIA/EIA-569a. But the ceiling still fell.
Most of us would agree that a falling ceiling is not only a cable-performance issue, but also a life-safety issue. Life-safety--that`s NEC, right? Maybe not. Speaking offline with several members of NEC Panel 16, I described a scenario where a ceiling support wire, which is also supporting a large bundle of telecommunications cables, fails, and the ceiling falls on a child. To which I was asked, "Was the child crushed or electrocuted?" This may seem a cold view, but the NEC addresses life-safety from electrocution only.
So until this issue has been addressed elsewhere, cabling-system designers must answer these questions:
•Are you going to allow the telecommunications cables to be supported by J-hooks secured to the ceiling support wires?
•If so, how many cables per J-hook?
•How many J-hooks per ceiling support wire?
•How much weight beyond that of the ceiling t-bars and tiles can the ceiling support wire support?
Donna Ballast is a communications analyst at the University of Texas at Austin and a bicsi 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].