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October 25, 2006 A Prism Business Media Publication Vol. IV No. 20

250.32 Buildings or Structures Supplied by a Feeder or Branch Circuit

What's Wrong Here?

Code Q&A

Code Quiz

Code Quiz Correction

Code Committee Call-Up

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    Top 50 NEC Rules

    250.32 Buildings or Structures Supplied by a Feeder or Branch Circuit

    By Mike Holt
    (A) Grounding Electrode. To provide a path to earth for lightning, each building or structure must have its disconnecting means [225.31] grounded (earthed) to one of the following electrodes [250.50 and 250.52(A)]:
    • Underground metal water pipe [250.52(A)(1)]
    • Metal frame of the building or structure [250.52(A)(2)]
    • Concrete-encased steel [250(A)(3)]
    • Ground ring [250.52(A)(4)]
    Where none of the above grounding electrodes are available at a building or structure, then one or more of the following must be used:
    • Ground rod [250.52(A)(5)]
    • Metal underground systems [250.52(A)(7)]
    Exception: A grounding electrode isn't required where only one branch circuit serves the building or structure. For the purpose of this section, a multiwire branch circuit is considered to be a single branch circuit.

    Bonding Requirements. To quickly clear a ground fault and remove dangerous voltage from metal parts, the building or structure disconnecting means must be grounded (bonded) to an effective ground-fault current path in accordance with (1) or (2) [250.4(A)(3)].

    (1) Equipment Grounding (Bonding) Conductor. The building or structure disconnecting means can be bonded to an equipment grounding (bonding) conductor, as described in 250.118, installed with the feeder conductors. The equipment grounding (bonding) conductor, if of the wire type, must be sized in accordance with 250.122, based on the rating of the feeder protection device.

    Caution: To prevent dangerous objectionable current from flowing onto metal parts of the electrical installation, as well as metal piping and structural steel [250.6(A)], a building or structure disconnecting means supplied by a feeder must not have the grounded neutral conductor bonded to the building or structure disconnecting means.

    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: Was this installer color blind?

    Code Q&A
    By Mike Holt
    Q. Do I have to use bonding jumpers around listed reducing washers?

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

    Code Quiz
    By Steven Owen
    Q. What is the proper size overload, and branch-circuit, short-circuit, ground-fault protective device permitted for a hermetic compressor with a nameplate rated-load of 38A, and a branch-circuit selection current of 40A? The fusible disconnect is going to serve as the disconnecting means, the overload protective device, and the branch-circuit, short-circuit, ground-fault protective device. A) 47.5A
    B) 50A
    C) 70A
    D) 90A

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

    Code Quiz Correction
    By Steven Owen
    Although the answer to the question in the last issue was correctly shown as: C) 70A, the ampere ratings in the question were inadvertently reversed. The nameplate rated-load current should have been shown as 38A, and the branch-circuit selection current should have been listed as 40A.

    We apologize for any confusion this may have caused.

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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. 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 Systems Maintenance (special experts excluded). 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.

    Cool Electronic Cabinets
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    Shows and Events
    Visit the 2006 EC&M E-TradeShow, a Year-Long Virtual Business Event

    Don't miss these scheduled seminars on November 16 in the EC&M e-TradeShow:
    • "Energy Storage Methods for Electric Power Systems," presented by John DeDad (11:00 a.m. EDT and PDT). Learn about all the new energy storage technologies now available, including ultracapacitors, fuel cells, and flywheels by attending this live conference.
    • Find out how to size residential electrical generators by sitting in on Generac's live conference scheduled for 9 a.m. EDT and PDT. If you can't make these times, catch a special contractor's night live conference at 8 p.m. EDT.
    • If you're looking for information to include in your business forecast for 2007, you'll certainly want to attend the 2007 electrical market sales forecast, presented by Jim Lucy, Electrical Wholesaling's chief editor and scheduled for 10 a.m. EDT and PDT. You'll see forecasting statistics for residential, commercial, institutional, and industrial construction market segments. This yearly presentation has become a MUST for electrical equipment manufacturers, contractors, distributors, and engineers.
    Before attending these events, make sure you visit the 2006 EC&M e-TradeShow, a year-long virtual business event. In addition to attending live activities at conference sessions scheduled throughout the year, you can meet with exhibitors in virtual exhibit halls. You can also access past presentations that are archived in the e-Tradeshow. Employing the latest interactive 3D technology, sponsors use online trade-show booths to generate leads on a continuous basis throughout the year, while interacting live with customers and prospects during scheduled events. Free access and all the information you need are available at the event's Web site.

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