Thread: Romex in Return Air plenum

Romex routed through return air or supply air plenums? Ok, I am having a senior moment here. I know I was told, heard, saw, read, something about Romex, NMC, etc not routing through a return air or supply air plenum.....but I cannot find a single source to verify that.

Does anyone have any information to verify or deny that this is not acceptable?

Thanks
Michael

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It's 300.22(B), but I don't have the NEC on on my home PC. You can probably GOOGLE it.

- 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.
- - - FPN: See Article 424, Part VI, for duct heaters.
- - (B) Ducts or Plenums Used for Environmental Air. Only wiring methods consisting of Type MI cable, Type MC cable employing a smooth or corrugated impervious metal sheath without an overall nonmetallic covering, electrical metallic tubing, flexible metallic tubing, intermediate metal conduit, or rigid metal conduit without an overall nonmetallic covering shall be installed in ducts or plenums specifically fabricated to transport environmental air. Flexible metal conduit and liquidtight flexible metal conduit shall be permitted, in lengths not to exceed 1.2 m (4 ft), to connect physically adjustable equipment and devices permitted to be in these ducts and plenum chambers. The connectors used with flexible metal conduit shall effectively close any openings in the connection. Equipment and devices shall be permitted within such ducts or plenum chambers only if necessary for their direct action upon, or sensing of, the contained air. Where equipment or devices are installed and illumination is necessary to facilitate maintenance and repair, enclosed gasketed-type luminaires (fixtures) shall be permitted.
- - (C) 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.
- - - 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.
- - - (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.
- - - (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.
Exception: Integral fan systems shall be permitted where specifically identified for such use.

And of course, thanks all. Answered my question. <S>

So NM can cross it, but can't follow it???

Originally Posted by Erby Crofutt

So NM can cross it, but can't follow it???

Erby,

I must be on a different wave length tonight - I have no idea what you are referring to?

Here, you go Mr. Style.

You can use this to tune your wave length.

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.

Originally Posted by Erby Crofutt

So NM can cross it, but can't follow it???

Oh, now I see (said the blind man) ... "IT" was referring to ...

Originally Posted by Erby Crofutt

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.

... "joist or stud spaces"?

Notice that the "Exception" is not for "(B) Ducts or Plenums Used for Environmental Air.", but is applicable to "(C) Other Space Used for Environmental Air." And that "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." excludes what you said (i.e., 'allows other types of wiring methods'): "So NM can cross it, but can't follow it???" in "dwelling units" ... provided that all openings around those cables are properly sealed with fire caulk. The end result being that the return air plenum is subjected to 16" or 24" long pieces of NM cable, nothing longer, and that the holes around the NM cables are sealed with an intumescent caulk/sealant.

From the 2006 IRC.

- SECTION M1601
- - DUCT CONSTRUCTION

- - - M1601.1 Duct design.

- - - - M1601.1.1 Above-ground duct systems.

Above-ground duct systems shall conform to the following:

- - - - - 7. Stud wall cavities and the spaces between solid floor joists to be used as air plenums shall comply with the following conditions:
- - - - - - 7.1. These cavities or spaces shall not be used as a plenum for supply air.
- - - - - - 7.2. These cavities or spaces shall not be part of a required fire-resistance-rated assembly.
- - - - - - 7.3. Stud wall cavities shall not convey air from more than one floor level.

- - - - - - 7.4. Stud wall cavities and joist-space plenums shall be isolated from adjacent concealed spaces by tight-fitting fire blocking in accordance with Section R602.8.

- R602.8 Fireblocking required. Fireblocking shall be provided to cut off all concealed draft openings (both vertical and horizontal) and to form an effective fire barrier between stories, and between a top story and the roof space. Fireblocking shall be provided in wood-frame construction in the following locations.

- - 1. In concealed spaces of stud walls and partitions, including furred spaces and parallel rows of studs or staggered studs; as follows:
- - - 1.1. Vertically at the ceiling and floor levels.
- - - 1.2. Horizontally at intervals not exceeding 10 feet (3048 mm).

- - 2. At all interconnections between concealed vertical and horizontal spaces such as occur at soffits, drop ceilings and cove ceilings.
- - 3. In concealed spaces between stair stringers at the top and bottom of the run. Enclosed spaces under stairs shall comply with Section R311.2.2.
- - 4. At openings around vents, pipes, ducts, cables and wires at ceiling and floor level, with an approved material to resist the free passage of flame and products of combustion.
- - 5. For the fireblocking of chimneys and fireplaces, see Section R1003.19.
- - 6. Fireblocking of cornices of a two-family dwelling is required at the line of dwelling unit separation.

You got it, Stylish!