Subtle NEC tweaks may change plenum classifications, down the road

Nov. 1, 2002
Last month, I said I would cover some proposed subtle changes in National Electrical Code (NEC) language that, if adopted, will have a huge effect on telecommunications cabling designs and specifications in the future.

Last month, I said I would cover some proposed subtle changes in National Electrical Code (NEC) language that, if adopted, will have a huge effect on telecommunications cabling designs and specifications in the future.

First order of business: meet the players. The National Fire Protection Association Technical Committee on Air Conditioning (TCAC) authors NFPA 90A, the Standard for Air Conditioning and Ventilation Systems. Within NFPA, this committee has jurisdiction for the limitations of combustible materials used in air ducts and plenum spaces. These combustible materials include wire, cable, and nonmetallic raceway. Translation: if it is installed in ducts, plenums, or other spaces for environmental air, this group develops maximum allowable potential heat (fuel load), flame-spread index, and smoke-developed index for the materials.

The NFPA NEC Committee is primarily responsible for preparing documents on minimizing the risk of electricity as a source of electric shock and as an ignition source of fires and explosions. The committee is also responsible for developing requirements to minimize the propagation of fire and explosions due to electrical installations. Telecommunications cabling falls under this domain. So, it is this committee's responsibility to address the concerns of the NFPA TCAC regarding telecommunications cable in plenum spaces.

Cable buildup, task force analysis

The TCAC has been monitoring the buildup of telecommunications cabling in plenum spaces since 1991. That was about the same time we began the big push for structured cabling, and then recabling, to meet high-performance requirements—stepping through the categories in the process.

In 1993, NFPA 90A established a task force to formally review the proliferation of telecommunications and computer networks in commercial use, and in 1997, the task force presented its report. Brief summary: there is a lot of telecommunications cable piling up in the plenums. Rarely did our rapid deployment of high-performance cabling include removal of the existing cable. Depending on the age of the building, some of that cable predates the established performance criteria for cables used in plenum spaces—CMP.

In January 1998, the NFPA TCAC accepted its own proposal, (Log #CP14) 90A-28 for revision of Standard for Installation of Air Conditioning and Ventilating Systems. The proposal called for the deletion of

2-3.10.1(a) Exception No. 1 (a), which addresses electrical wires, as well as cables that meet NFPA 262, Standard Method of Test for Fire and Smoke Characteristics of Wires and Cables.

This deletion would have meant that only noncombustible or limited-combustible cable would have met the requirements of NFPA 90A. Ironically, there were no noncombustible or limited-combustible cable constructions available or used prior to or during the 1999 code revision cycle. The initiative failed.

Not easily discouraged, proponents of limited-combustible cable proposed in November 1999 that a limited-combustible listing be included in NEC 2002. This initiative also failed, because there was not a unique use requirement for the cable.

A new, old proposal

Fast forward to this month (November), and it is happening again. The listing will likely have a new name, but this is the same initiative as before.

NFPA TCAC has reviewed the NEC 2002 with respect to wiring and cable methods used in ducts and plenums that move environmental air, and has made a series of proposed changes for NEC 2005.

As with most standards initiatives, they begin with definitions. Both NFPA 90A 2002 and NEC 2002 define plenum as "a compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system." But NFPA TCAC divides "plenum" into various subsets. Ceiling-cavity plenum, raised-floor plenum, duct-distribution plenum, apparatus-casing plenum, and air-handling room plenum are among the subsets.

NFPA TCAC is proposing to define ceiling-cavity plenum and raised-floor plenum for NEC 2005 based on NFPA 90A 2002.

The result is that we will likely have a couple of new definitions. This is not exactly a monumental occurrence, but it sets the stage for proposed changes in NEC section 300.22 to have a significant effect.

NEC 2002 section 300.22 states, "The provisions of this section apply to the installation and uses of electric wiring and equipment in ducts, plenums, and other air-handling spaces."

NEC 2002 300.22 subsections more specifically address:

  1. Ducts for Dust, Loose Stock, or Vapor Removal;
  2. Ducts or Plenums Used for Environmental Air;
  3. Other Space Used for Environmental Air;
  4. Information Technology Equipment.

NFPA TCAC is proposing to change NEC section 300.22(B) from "Ducts or Plenums Used for Environmental Air" to "Ducts or Plenums (other than above-ceiling or raised-floor plenums)", and to add the sentence, "It includes ceiling-cavity plenums and raised-floor plenums" to 300.22(C).

NEC 2005 section 300.22(C) would then read "Other Space Used for Environmental Air. This section applies to space used for environmental air-handling purposes other than ducts and plenums as specified in 300.22(A) and (B). It includes ceiling-cavity plenums and raised-floor plenums. It does not include habitable rooms or areas of buildings, the prime purpose of which is not air handling."

Result: no cable could be installed in ducts, or in plenums (other than above-ceiling or raised-floor plenums)—unless, of course, there was a listing for limited-combustible cable to meet this now unique requirement.


One of the perks of turning 50 is that you have been alive long enough to know the game and the rules of engagement. You can watch the players and predict their moves. NEC 2002 and NFPA 90A 2002 both published with the flame-retardant-chemical and fluoropolymer manufacturers in a stalemate. NEC 2005 is a new game, but with the same players. I predict that limited-combustible, by some other, yet-to-be-determined name, will be listed in NEC 2005, and that CMP will be in a very precarious position by the publication of NEC 2008.

How this affects you depends on your role. If you are a cable manufacturer, after a few engineering tweaks to ensure performance, you order the appropriate beads and dump them into your new extruder. If you are the designer or installer, you would simply specify and install the newly listed cable. But if you are the guy that pays the bills, it will be costing you a lot more dollars to provide the same quality and quantity of cabling.

Or, the way most new-building projects are managed, the same money will provide less cabling, which would then have a big effect on the designers and installers (less work) and on the cable manufacturers (less product sold).

...and forward thinking

So, how can we provide the same or more services, and install less cable in the plenums? TIA is busy working on a solution. Ironically, most of the participants aren't realizing the ultimate effect of their actions—less cable will be needed, hence, less cable will be sold.

Remember when the TIA came out with the consolidation point (CP)—an interconnect installed somewhere between two pieces of horizontal cable linking the TR and the work area? Remember that everyone was either excited or worried about having active equipment installed at the CP, even though forbidden within the standard?

Enter the telecommunications enclosure (TE), formerly known as the "tiny TR." The TE is somewhat like a CP, only with active equipment. And how convenient—the cable from the TR to the TE is called "backbone." That means there is no cable-for-cable matching requirement between the TR and the TE. So, you can reduce the fuel load in the plenum even further by installing a single backbone cable from the TR to the TE, active equipment in the TE and, if you are not using the ceiling or under-floor plenum for cable distribution, you can use even less-expensive CMR cable from the TE to the outlet/connector in the work area.

Hence, you will still be designing and installing the same number of outlet/ connectors in the work area; you will just be using shorter cables.

Building owners and property managers will want to make the provisioning and removal of telecommunications cabling a contractual item, specifically stating who puts it in and who takes it out. Using a design formula of a floor-serving TR (during construction) with multiple TEs (installed during client build-out), there will be a much-reduced fuel load going into the plenum, and much less to remove when the client vacates.

Click here to enlarge image

Donna Ballast is BICSI's standards representative, and a BICSI registered communications distribution designer (RCDD). Send your questions to Donna via e-mail: [email protected].

New terms

NFPA 90A 2002 section 2-3.10.2 describes a ceiling-cavity plenum as the space between the top of the finished ceiling and the underside of the floor or roof above used to supply air to the occupied area, or return or exhaust air from, or return and exhaust air from the occupied area, provided that certain conditions are met.

NFPA 90A 2002 section 2-3.10.6 describes a raised-floor plenum as the space between the top of the finished floor and the underside of a raised floor to supply air to the occupied area, or return or exhaust air from, or return and exhaust air from the occupied area, provided that certain conditions are met.

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