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April 13, 2007 A Penton Media Publication Vol. V No. 7

250.104 Bonding of Piping Systems and Exposed Structural Metal

What's Wrong Here?

Code Q&A

Code Quiz

Flame-Resistant Garments

EC&M Code Change Conferences

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    Top 50 NEC Rules

    250.104 Bonding of Piping Systems and Exposed Structural Metal

    By Mike Holt
    To remove dangerous voltage on metal parts from a ground fault, electrically conductive metal water piping systems, metal sprinkler piping, metal gas piping, and other metal piping systems, as well as exposed structural steel members that are likely to become energized, must be bonded to an effective ground-fault current path [250.4(A)(4)]. Although bonding isn't required for isolated sections of metal water piping connected to a nonmetallic water piping system, metal water piping systems must be bonded in accordance with the following:
    1. Building Supplied by a Service. The metal water piping system of a building or structure must be bonded to one of the following: service equipment enclosure; grounded neutral service conductor; grounding electrode conductor where the grounding electrode conductor is sized in accordance with Table 250.66; or one of the electrodes of the grounding electrode system. The metal water pipe bonding jumper must be sized in accordance with Table 250.66, based on the largest ungrounded service conductor. Where hot and cold water pipes are electrically connected, only one bonding jumper is required, either to the cold or hot water pipe. Otherwise, a single bonding jumper, sized in accordance with 250.104(A)(1), must be used to bond the hot and cold water piping together.
    2. Multiple Occupancy Building. When the metal water piping system in an individual occupancy is metallically isolated from other occupancies, the metal water piping system for that occupancy can be bonded to the equipment grounding terminal of the occupancy's panelboard. The bonding jumper used for this purpose must be sized to the ampere rating of the occupancy's feeder overcurrent protection device in accordance with Table 250.122.
    3. Building or Structure Supplied by a Feeder. The metal water piping system of a building or structure that is supplied by a feeder must be bonded to: the equipment grounding terminal of the building disconnect enclosure; the feeder equipment grounding (bonding) conductor; or one of the electrodes of the grounding electrode system. The bonding jumper for the metal water piping system must be sized to the feeder circuit conductors that supply the building or structure in accordance with Table 250.66. The bonding jumper is not required to be larger than the ungrounded feeder conductors. Note: It makes no sense to size the metal water piping bonding jumper in accordance with Table 250.66, based on the feeder circuit conductor size. The bonding jumper should be sized in accordance with Table 250.122, based on the building or structure feeder overcurrent protection device.
    Click here to read the rest of this article.

    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: What is physical damage?

    Code Q&A
    By Mike Holt
    Q. Can I secure signal or communications cables to ceiling-support wires or ceiling grid?

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

    Code Quiz
    By Steven Owen
    Q. In general, a disconnecting means is required for each sign and outline lighting system or feeder circuit and branch circuit supplying a sign or outline lighting system per 600.6. When is a disconnecting means not required per 600.6?

    1. When the sign is an exit directional sign supplied by batteries.
    2. When the sign is cord-connected with an attachment plug.
    3. When the sign is an exit directional sign located within a building.
    4. Both B and C.

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

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    Code News Update
    Flame-Resistant Garments
    According to the April 2007 issue of NFPA News, the NFPA Standards Council recently approved the development of one or two new documents related to flame-resistant garments. The Flash Fire Protective Garments Committee will address: 1) the design, manufacturing, testing, and certification of new single-use or limited-use flame-resistant garments; and 2) the selection, care, maintenance, and use of single-use or limited-use flame-resistant garments. If this topic piques your interest, and you'd like to join in on the development process, then download a Technical Committee form from the NFPA Web site or request one from the Codes and Standards Administration, NFPA, One Batterymarch Park, Quincy, MA 02169-7471.

    Cool Electronic Cabinets
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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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