300.22 Wiring in Ducts, Plenums, and Other Air-Handling Spaces
The provisions of this section apply to the installation and uses of electric wiring and equipment in ducts, plenums, and other air-handling spaces.
© 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 does not include habitable rooms or areas of buildings, the prime purpose of which is not air handling.
FPN: The space over a hung ceiling used for environmental air-handling purposes is an example of the type of other space to which this section applies.
Section 300.22© applies to other spaces that are used to transport environmental air and that are not specifically manufactured as ducts or plenums, such as the space or cavity between a structural floor or roof and a suspended (hung) ceiling. Many spaces above suspended ceilings are intended to transport return air. Some spaces are also used for supply air, but they are far less common than those used for return air. This section does not apply to habitable rooms and other areas whose prime purpose is other than air handling. Such an area is shown in Exhibit 300.20. If the prime purpose of the room or space is air handling as depicted in Exhibit 300.20, then the restrictions in 300.22© apply, whether or not electrical equipment is located in the room.
Exception: This section shall not apply to the joist or stud spaces of dwelling units where the wiring passes through such spaces perpendicular to the long dimension of such spaces.
The exception to 300.22© permits cable to pass through joist or stud spaces of a dwelling unit, as illustrated in Exhibit 300.21. The joist space is covered with sheet metal and used as a cold-air return for a forced warm-air central heating system. Equipment such as junction boxes or device enclosures is not permitted in this location.
(1) Wiring Methods The wiring methods for such other space shall be limited to totally enclosed, nonventilated, insulated busway having no provisions for plug-in connections, Type MI cable, Type MC cable without an overall nonmetallic covering, Type AC cable, or other factory-assembled multiconductor control or power cable that is specifically listed for the use, or listed prefabricated cable assemblies of metallic manufactured wiring systems without nonmetallic sheath. Other types of cables and conductors shall be installed in electrical metallic tubing, flexible metallic tubing, intermediate metal conduit, rigid metal conduit without an overall nonmetallic covering, flexible metal conduit, or, where accessible, surface metal raceway or metal wireway with metal covers or solid bottom metal cable tray with solid metal covers.
Revised for the 2002 Code, 300.22©(1) no longer permits liquidtight flexible metal conduit as covered in Article 350 to be installed within ``other spaces used for environmental air.’’ The previous exception permitting this application for single lengths up to 6 ft was removed.
(2) Equipment Electrical equipment with a metal enclosure, or with a nonmetallic enclosure listed for the use and having adequate fire-resistant and low-smoke-producing characteristics, and associated wiring material suitable for the ambient temperature shall be permitted to be installed in such other space unless prohibited elsewhere in this Code.
Electrical equipment with metal enclosures is allowed within spaces used for environmental air. However, nonmetallic enclosures must be listed for this use.
Exception: Integral fan systems shall be permitted where specifically identified for such use.
It is not intended that the requirements of 300.22(B) or 300.22© apply to air-handling areas beneath raised floors in information technology rooms. See Article 645, Information Technology Equipment.
(D) Information Technology Equipment Electric wiring in air-handling areas beneath raised floors for information technology equipment shall be permitted in accordance with Article 645.