NEC weighs cables on the ceiling system

The August 2000 Ask Donna column reported on National Electrical Code 2002--the work in progress-and promised to keep you updated. The following are recent notable changes.

Feb 1st, 2001
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The August 2000 Ask Donna column reported on National Electrical Code 2002--the work in progress-and promised to keep you updated. The following are recent notable changes.

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The Technical Committee on NEC Panel 16 has added a new section titled "Installation of Circuits" to Article 800, which now reads: "Communications circuits shall be installed in compliance with A or B.

A. New Ceiling Construction. The installation of cables in new ceiling construction shall comply with Section 300-11.

B. Existing Ceilings.
1. Fire-Rated Ceilings. The installation of cables in the cavity of an existing fire-rated ceiling assembly shall comply with Section 300-11

2. Non-Fire-Rated-Ceilings. For installations in the cavity of an existing non-fire-rated ceiling assembly, cables less than 6 mm (0.25 in) in diameter shall be permitted to be installed unsupported from the building structure in accordance with the following:

a. Fixed or Hard Ceilings. In areas having fixed or hard ceilings with access points or access panels, a combined total of three cables from Article 640, 650, 725, 760, 770, 800, 820 and 830, shall be permitted to be placed between access points or access panels in the ceiling. Additional cables shall be in accordance with 300.11.

b. Suspended Lay-In Ceilings. In areas having suspended lay-in ceilings, in any 3 m by 3 m (10 ft x 10 ft) ceiling area, a combined total of three cables from Article 640, 650, 725, 760, 770, 800, 820 and 830, shall be permitted to be installed directly on the ceiling grid. Additional cables shall be installed in accordance with 300.11 FPN. Cables of all types are included in the total limit of three cables, not three cables from each article."

No cables, or a few?

All this came about because a strong lobby for the regulated telephone companies was looking for some "wiggle room" in the interpretation of Section 800-5. As with most contentious issues, there are at least two (opposing, of course) views of what 800-5 really means.

Lobbying for cable support

In the "no cables on the ceiling system" camp-manufacturers. Cable support hardware manufacturers vigorously support no cables resting on the ceiling panels, because they will sell more cable supports. But not all cabling supports currently available are designed to provide the "independent means of support" that 300-11 requires.

Cable manufacturers also support no cables on the ceiling, because their cable is less likely to be disturbed when the various tradespersons open the ceiling tiles or access panels to perform normal building maintenance.

Suspended lay-in ceiling system manufacturers round out the no-cables-on-the-ceiling camp, because their ceiling systems are not designed to support telecommunications cables. Not that they couldn't support the weight of three 0.25-inch cables, but that the telecommunications cables are not being tested as part of the ceiling system in accordance with Section 300-11(a)(1). Section 300-11(a)(1) allows the ceiling support system to support only that wiring and equipment which is tested as part of the fire-rated assembly.

In the "a few cables on the ceiling system" camp-regulated access providers, who are always needing to install just a few more cables to the tenant space and don't see why they should have to install cable supports. Why? Because they are "The Telephone Company."

Installer ramifications

What does this mean to you as a designer or installer? Until such time as the ceiling systems manufacturers decide to get into the telecommunications structured cabling business (like the open-office furniture manufacturers have in recent years) for new construction, all telecommunications cabling must be supported per Section 300-11. The currently proposed wording also provides a reasonable, safe and practical solution to placing a limited number of unsupported telecommunications cables in existing construction-maximum of three 0.25-inch cables per 10 foot x 10 foot area.

Section 300-11(a)(1) was revised in NEC 1999. For those of you not familiar with the current Section 300-11, I suggest that you study it carefully. Presently, if you choose to use support wires within the fire-rated ceiling cavity, the support wires you install must be distinguishable from those that are part of the ceiling support system, and they must be secured at both ends.

OK, so they have to be tagged or a different color, but why attached at both ends? To prevent horizontal movement or sway, which could cause loss of grounding continuity provided by the raceway.

But what if you are installing a non-conductive raceway or individually attached cable supports? This is where things begin to get messy, because 300-11 focuses on conductors that carry power and leaves the exceptions to the other articles. Hence, with no exception in Article 800 allowing the support wires to swing freely at the bottom, the 2002 NEC code will leave us with few options-use threaded rod or attach support wires to the ceiling grid.

Threaded rod is more expensive and attaching the support wires to the ceiling grid will serve to further complicate adding cables. As for cable placement, you will likely have to lay-in rather than pull through and risk bending the attached ceiling grid should a cable snag.

Abandoned cable redefined

Panel 16 has also refined its definition of "Abandoned Communications Cable" to now read, "Installed communications cable that is not terminated at both ends at a connector or other equipment and not identified for future use with a tag." Which means that the 25-pair cables with cans attached can still be simply tossed above the ceiling as long as they are not resting on the ceiling system (grid and panels) itself.

Hopefully, Panel 16 will address this issue in a future edition of the code, but until then, it remains the designer's responsibility to specify removal of such cabling within the project requirements.

Panel 16 also received many comments regarding the inclusion of limited combustible (CMP-50) cable, and if the cable should be allowed to remain in place even after abandonment. Currently, CMP-50 will be included in NEC 2002, and because limited combustible material can still burn, and a build-up of such material increases the fire load (hence, the fire hazard or risk unnecessarily), CPM-50 cables must be removed after abandonment.

For more information on how we can participate in the NFPA process, see www.nfpa.org

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: ballast@utexas.edu.




What about toxicity and irritancy produced by burning cables?

I have just reviewed a paper entitled "Combustion Atmosphere Toxicity of Polymeric Materials intended for Internal Cables." The paper was written by Bernt-Ake Sultan, Filip Samson and James Robinson of Borealis, and recently presented at the 49th International Wire and Cable Symposium.

The following is a quote from the abstract:
"There is no doubt that the inhalation of toxic products formed during the combustion process is the major cause of fatalities that occur during fire catastrophes. There is, however, considerable dispute as to the best means to mitigate these hazards.

Essentially two approaches are currently adopted-the American and the European. In summary, the U.S. approach is that heat release is all-important. Toxicity is directly linked to carbon monoxide, which in flashover fires is proportional to heat release. In Europe, the fire hazard model is different. Fire deaths are believed due to a two-stage process-incapacitation followed by carbon monoxide poisoning. Therefore, the focus is on controlling the smoke and irritant gases which cause incapacitation."

I remember back in the mid-'70s when an environmental air expert and friend sarcastically told me how wonderful it was that I was now using the CMP-rated cables. He explained that now anyone in a burning building would be able to see their exit door through the light smoke as they lay dying on the floor from the toxic gas produced by the burning cable. To which I sheepishly nodded and said, "Yes, but we are code-compliant."

Today, not much has changed. Even the new "gee whiz" CMP-50 rating still does not address the toxicity and irritancy of combustion fumes produced from the burning of plastics.

For information on the International Wire and Cable Symposium, see www.iwcs.org

(My thanks to Amir Yaari, with TELDOR Wires & Cables for hosting the TELDOR Technical Cabling Forum.)

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