This article Is based on the newly issued 2002 National Electrical Code (NEC). The NEC style has been changed for the 2002 edition. It may take awhile for those who are familiar with previous issues of the Code to become accustomed to using it, but this new style should make it much easier to use.

Within the individual articles, parts have been changed from capital letters to Roman numerals. For example, former Part A will now be Part I, Part B will now be Part II, and old Part D will now be Part IV.

The “dash” has been changed to a “dot.” For example, Section 300-21 will now be 300.21.

The hierarchy within the individual sections has been changed from (a)(1)(a) to (A)(1)(a) with titles added to most major subsections. The new 2002 NEC style is to place metric measurements first with English inch-pound units in parenthesis. Differences between the 1999 NEC and the 2002 text will be noted very clearly within this article.

Last month, we found that NEC installation requirements for ducts, plenums, and other air-handling spaces can be difficult to understand and apply. These air-handling systems have the potential to convey smoke, hot gases, and flames from one area of a building into another, and provide the air supply for a potential fire.

We concentrated primarily on understanding the requirements stated in Section 300.21 for the spread of fire and products of combustion and Section 300.22 for wiring in ducts, plenums, and other air-handling spaces. It would be nice if all of the requirements for a particular installation could be in one location in the NEC.

However, most installations require many different types of electrical equipment and a corresponding number of wiring methods to connect it.

Sections 300.21 and 300.22 provide the general requirements for these installations, but there are many other sections of the NEC that permit use of equipment and wiring methods in these air handling ducts, plenums, or other spaces. Other sections in the NEC may restrict methods of wiring that may be used or may provide additional requirements for special applications within these spaces.

Sections 300.11(A)(1) and 300.11(A)(2) provide requirements for support of wiring methods, such as electrical metallic tubing and flexible metal conduit, within the cavities of both fire-rated and nonfire-rated floor-ceiling or roof-ceiling assemblies. These floor-ceiling and roof-ceiling assemblies include those ceilings that are also used as other spaces for environmental air (suspended ceilings).

Notice these two subsections only cover wiring methods installed in these areas and not the actual electrical equipment.

Section 410.16(C) covers the installation requirements in suspended ceilings (both “other spaces for environmental air” and those ceiling spaces not used for environmental air) for lighting fixtures, now called “luminaires” in the 2002 NEC.

This section requires framing members of suspended ceiling systems used to support “luminaires” (fixtures) to be securely fastened to each other. The “luminaires” must be then securely fastened to the ceiling-framing member by some mechanical means, such as bolts, screws, or rivets.

The luminaires can also be connected to the framing members with listed clips that are identified for use with the type of ceiling framing member and the specific luminaire(s).

Article 370 in the 1999 NEC has been moved to Article 314 in the 2002 NEC as part of a major rewrite of Chapter 3 to make the NEC more user friendly. Boxes and enclosures have been moved to the front of Chapter 3.

All of the various cable wiring methods, such as Type Armored Cables (AC), Nonmetallic-Sheathed (NM) cable, and others are located immediately after Article 314 covering boxes. Conduit articles start with Intermediate Metal Conduit (IMC) in Article 342.

Section 314.23(D) provides the requirements for outlet, device, pull, and junction boxes installed in suspended ceilings. For example, an enclosure or box can be mounted to the structural or supporting elements of a suspended ceiling, provided the enclosure is not more than 1,650 cubic centimeters (100 cubic inches).

Ceiling support wires can also support the enclosure (box). Additional support wires may be installed to help support the enclosure (box), provided the installation complies with Section 300.11(A).

Section 725.61(A) permits listed Class 2P and Class 3P cables to be installed in ducts, plenums, and other spaces for environmental air. These cables have been listed for their low smoke-producing characteristics and fire resistance.

The same is true in Sections 760.30 and 760.61 for plenum rated fire alarm cable, such as non-power limited fire alarm plenum (NPLFP) cables and power-limited fire alarm plenum (PLFP) cable.

Since these wiring methods are not specifically found in Sections 300.22(B) and (C), it is necessary to first understand the layout of the NEC. Section 90.3 permits Chapters 5, 6, and 7 to supplement or amend the requirements in Chapters 1 through 4.

As can be seen, it is not enough to just read and apply the requirements in Section 300.22. One should become familiar with and apply all parts of the NEC that are applicable to a specific installation.

ODE is staff engineering associate at Underwriters Laboratories, Inc., in Research Triangle Park, N.C. He can be reached at (919) 549-1726 or via e-mail at