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September 27, 2007 A Penton Media Publication Vol. V No. 18

300.22 Ducts, Plenums, and Air-Handling Spaces

What's Wrong Here?

Code Q&A

Code Quiz

Code Committee Call-Up

EC&M Code Change Conferences

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    Top 50 NEC Rules

    300.22 Ducts, Plenums, and Air-Handling Spaces

    By Mike Holt
    Ducts that transport dust, loose stock, or vapors must not have any wiring method installed within them. What about ducts or plenums used for environmental air?

    Where necessary for the direct action upon, or sensing of, the contained air, Type MI cable, Type MC cable that has 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 can be installed in ducts or plenums specifically fabricated to transport environmental air.

    Flexible metal conduit in lengths not exceeding 4 feet can be used to connect physically adjustable equipment and devices, provided any openings are effectively closed.

    Where equipment or devices are installed and illumination is necessary to facilitate maintenance and repair, enclosed gasketed-type luminaires are permitted.

    What about space used for environmental air? Wiring and equipment in spaces used for environmental air-handling purposes must comply with 300.22(C)(1) and (2). This requirement doesn't apply to habitable rooms or areas of buildings, the prime purpose of which isn't air handling.
    FPN: The spaces above a suspended ceiling or below a raised floor that are used for environmental air are examples of the type of space to which this section applies.

    As per 300.22(C)(1), electrical metallic tubing, rigid metal conduit, intermediate metal conduit, armored cable, metal-clad cable without a nonmetallic cover, and flexible metal conduit can be installed in other environmental air spaces. Where accessible, surface metal raceways, metal wireways with metal covers, or solid bottom metal cable tray with solid metal covers can be installed in other environmental air spaces.

    Control, signaling, and communication cables installed in surface metal raceways, metal wireways with solid metal covers, or solid bottom metal cable trays with solid metal covers are not required to be plenum-rated.

    Rigid nonmetallic conduit (Art. 352), electrical nonmetallic tubing (Art. 362), and nonmetallic cables are not permitted to be installed in spaces used for environmental air because they give off deadly toxic fumes when burned or super heated.

    However, control, signaling, and communications cables, and nonmetallic raceways installed in spaces used for environmental air must be plenum rated. A space not used for environmental air-handling purposes has no wiring method restrictions.

    As per 300.22(C)(2), electrical equipment with a metal enclosure is permitted in other environmental air spaces, unless prohibited elsewhere in the Code. For example, dry-type transformers with a metal enclosure, rated not over 50kVA, can be installed above suspended ceilings used for environmental air [450.13(B)].

    What are the requirements when working in an information technology equipment room? Wiring under a raised floor in an information technology room must comply with 645.5(D). Signal and communications cables under a raised floor are not required to be plenum rated [645.5(D)(5)(c)], because ventilation is restricted to that room/space [645.5(D)(3)].

    Editor's note: This information was extracted from Mike Holt's textbook, Understanding the National Electrical Code

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    Code Challenge
    What's Wrong Here?
    By Joe Tedesco
    Think you know how this installation violates the NEC? Visit EC&M's Web site to see the answer.

    Hint: Pull the plug!

    Code Q&A
    By Mike Holt
    Q. A conductor passing through a box unbroken counts as one conductor, so if I loop a conductor through the box unbroken and strip off enough insulation to terminate on a receptacle without cutting the wire, does the conductor count as one or two conductors for box sizing?

    Visit EC&M's Web site to see the answer.

    Code Quiz
    By Steven Owen
    Q. A 60-foot metal pole supporting luminaires is found to be deficient with respect to the 2005 version of the NEC. The installation consists of the following: The interior of the pole is being used as a raceway. A properly sized handhole has been provided. A grounding terminal within the pole has been provided. The size of the branch-circuit equipment-grounding conductor, which also serves to bond the metal pole to the metal raceway supporting the branch circuit conductors, is 12 AWG. The branch circuit rating is 30A. What could possibly be the deficiency in this particular installation?

    1. There is no raceway inside the pole.
    2. The pole does not feature a hinged base.
    3. There is a lack of vertical conductor support per 300.19.
    4. Improperly sized equipment grounding and bonding conductor.

    Visit EC&M's Web site for the answer and explanation.

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    Code News Update
    Code Committee Call-Up
    Got some extra time on your hands? Looking to put some of your vast knowledge of the electrical field to use? NFPA is looking for new members for several of its committees, including the following:
    • Committee on Electrical Equipment in Chemical Atmospheres(seeking members in all categories). This committee is responsible for NFPA 496, Standard for Purged and Pressurized Enclosures for Electrical Equipment; NFPA 497, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas; and NFPA 499, Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas
    • Committee on Electrical Equipment Evaluation (seeking members in all categories)
    • Committee on Electrical Systems Maintenance (seeking members in all categories, except special experts). This committee is responsible for NFPA 73, Electrical Inspection Code for Existing Dwellings.
    Anyone interested in serving can download the application form at NFPA's Web site.

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    Shows and Events
    EC&M Code Change Conferences
    Where do you turn when you need accurate information on changes to the National Electrical Code? Acknowledged as the leaders in providing information on the NEC, EC&M magazine and EC&M Seminars have been the preferred sources of this information for more than 60 years. Seven Code change conferences have been scheduled in the fall of 2007. Host cities include: Atlanta, Boston, Dallas, Orlando, Philadelphia, St. Louis, and Seattle.

    As an approved provider with the National Council of Examiners for Engineering and Surveying (NCEES), through its Registered Continuing Education provider Program (RCEPP), professional engineers attending any of our 2008 Code change conferences will receive Professional Development Hours (PDHs), a requirement for re-licensing in many states. The conferences are also approved by every state that has a continuing education requirement for contractors and electricians.

    For additional information on the dates and locations of these events, click here.

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