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November 27, 2006 A Prism Business Media Publication Vol. IV No. 22

250.52 Grounding (Earthing) Electrodes

What's Wrong Here?

Code Q&A

Code Quiz


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    Top 50 NEC Rules

    250.52 Grounding (Earthing) Electrodes

    By Mike Holt

    Electrodes permitted for grounding include:
    • An underground metal water pipe in direct contact with earth for 10 feet or more
    • The metal frame of a building or structure, where any of the following methods exist:
      (a) 10 feet or more of a single structural metal member is in direct contact with the earth or encased in concrete that is in direct contact with the earth.
      (b) The structural metal is bonded to an electrode as defined in 250.52(A)(1), (3), or (4).
      (c) The structural metal is bonded to two ground rods if the ground resistance of a single ground rod exceeds 25 ohms [250.52(A)(5) and 250.56].
      (d) Other means approved by the authority having jurisdiction.
    • A concrete-encased grounding electrode. Steel reinforcing bars not smaller than 1/2-inch in diameter or 4 AWG copper conductor can serve as a grounding electrode if the steel or copper conductor has a total conductive length of 20 feet, is encased in not less than 2 inches of concrete, and is located near the bottom of a foundation or footer that is in direct contact with earth.
    • A ground ring encircling a building or structure, in direct contact with earth consisting of not less than 20 feet of bare copper conductor not smaller than 2 AWG copper.
    • A ground rod not less than 8 feet long, with no less than 8 feet of length in contact with the soil.
    • A grounding plate. A buried iron or steel plate with not less than 1/4-inch of thickness, or a nonferrous (copper) metal plate not less than 0.06 inch thick, with an exposed surface area not less than 2 square feet.
    • A metal underground system such as piping systems, underground tanks, or an underground metal well casing that isn't effectively bonded to a metal water pipe system.
    Electrodes not permitted for grounding include:
    • Underground metal gas piping systems or structures.
    • Aluminum electrodes. Aluminum can't be used as a grounding electrode because it corrodes more quickly than copper.
    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: Is this a new faux wood-approved electrical barrier?

    Code Q&A
    By Mike Holt
    Q. What are the limitations on the use of rigid nonmetallic conduit in an underground application serving a gasoline dispenser?

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

    Code Quiz
    By Steven Owen
    Q. In a Class 1 location of a spray application (Art. 516) area, portable equipment such as portable electric lamps or other utilization equipment shall be permitted in which of the following situations?

    A) Never permitted.
    B) Portable electric lamps identified for Class 1, Division 1 or Class 1, Zone 1 locations where readily ignitable residues may be present. This is intended for operations in spaces not readily illuminated by fixed lighting within the spraying area.
    C) Where portable electric drying apparatus is used in automobile refinishing spray booths, and the additional requirements of 516.4(D), Exception No. 2, (a) through (d) are met.
    D) Both B and C.

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

    Cool Electronic Cabinets
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    Shows and Events

    Check out this list of gems, all free of charge in the "On-Demand Library and Viewing Room" across from Conference Room A within the virtual trade show:
    • Preparing a Claim: Bolstering Your Case Through Good Project Management
    • Harmonics: Causes, Symptoms, and Remediation Techniques
    • Power Outages: Preventive Electrical Designs and Product Solutions
    • Electrical Power Engineering: Industry Shortcomings and Possible Solutions
    • MV Cable Basics: Construction, Testing, Ground Fault Coordination
    • Ten Trends That Will Shock the Electrical Market
    • Good Project Management: Enhancing the Bottom Line
    • Insulation Resistance Testing
    • Short Term, Long Term Energy Storage Methods for Standby Power Systems
    • 2007 Construction Market Forecast

    Before accessing the archives, 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. Free access and all the information you need are available at

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