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December 11, 2006 A Prism Business Media Publication Vol. IV No. 23

250.53 Installation of Grounding Electrode System

What's Wrong Here?

Code Q&A

Code Quiz

Changes in Store for Electrical Code in Northwest Missouri Town?

Get In-Depth Information on Code Changes & Standards

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    Top 50 NEC Rules

    250.53 Installation of Grounding Electrode System

    By Mike Holt
    Where practicable, ground rods must be embedded below permanent moisture level and must be free from nonconductive coatings such as paint or enamel [250.12]. Ground rod electrodes must be installed so that not less than 8 feet of length is in contact with the soil. Where rock bottom is encountered, the ground rod must be driven at an angle not to exceed 45 degrees from vertical. If rock bottom is encountered at an angle up to 45 degrees from vertical, the ground rod can be buried in a minimum 30-inch-deep trench.

    The upper end of the ground rod must be flush with or underground unless the grounding electrode conductor attachment is protected against physical damage as specified in 250.10. See 250.52(A)(5) and 250.53(A) for additional details. When the grounding electrode attachment fitting is located underground, it must be listed for direct soil burial [250.68(a) Ex. 1, and 250.70].

    Where more than one grounding electrode system exists at a building or structure, they must be separated by at least 6 feet.

    Where within 18 inches of earth, the conductor used to bond grounding electrodes together to form the grounding electrode system must be copper [250.64(A)], securely fastened to the surface on which it's carried, and be protected if exposed to physical damage [250.64(B)]. The bonding jumper to each electrode must be sized in accordance with 250.66.

    In addition, the grounding electrode bonding jumpers must terminate to the grounding electrode by exothermic welding, listed lugs, listed pressure connectors, listed clamps, or other listed means [250.8]. When the termination is encased in concrete or buried, the termination fittings must be listed and identified for this purpose [250.70].

    The bonding connection to the interior metal water piping system, as required by 250.104(A), must not be dependent on water meters, filtering devices, or similar equipment likely to be disconnected for repairs or replacement. When necessary, a bonding jumper must be installed around insulated joints and equipment likely to be disconnected for repairs or replacement to assist in clearing and removing dangerous voltage on metal parts because of a ground fault. See 250.68(B) and 250.104 for additional details.

    The underground metal water pipe grounding electrode, if present [250.52(A)(1)], must be supplemented by one of the following electrodes:

    • Metal frame of the building or structure [250.52(A)(2)]
    • Concrete-encased steel [250.52(A)(3)]
    • Ground ring [250.52(A)(4)
    Where none of the above electrodes are available, one of the following electrodes must be used:
    • Ground rod in accordance with 250.56 [250.52(A)(5)
    • Grounding plate [250.52(A)(6)]
    • Metal underground systems [250.52(A)(7)]
    The underground water pipe supplemental electrode must terminate to one of the following:
    • Grounding electrode conductor
    • Grounded neutral service conductor
    • Metal service raceway
    • Service equipment enclosure
    Where the supplemental electrode is a ground rod, that portion that is the sole connection to a ground rod isn't required to be larger than 6 AWG copper. The bonding jumper for the underground metal water pipe supplemental electrode is sized in accordance with 250.66, including Table 250.66, where applicable.

    If working with a ground ring, it must encircle the building or structure, consist of at least 20 feet of bare copper conductor not smaller than 2 AWG, and be buried at a depth not less than 30 inches. See 250.52(A)(4) for additional details.

    If working with a plate electrode, it must not have less than 2 square feet of surface exposed to exterior soils and installed so that it's at least 30 inches below the surface of the earth [250.52(A)(6)].

    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: Seems a little tight here, doesn't it?

    Code Q&A
    By Mike Holt
    Q. Can Table 310.15(B)(6) be used to size service conductors to a duplex, where there is no firewall separating the units?

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

    Code Quiz
    By Steven Owen
    Q. Where more than one equipment grounding or bonding conductor of a branch circuit enters a box, all such conductors shall be in good electrical contact with each other, and the arrangement shall be such that the disconnection or removal of a receptacle, luminaire (fixture), or other device fed from the box will not interfere with or interrupt the grounding continuity. Where is this section found in the 2005 NEC?

    A) 110.12(C)
    B) 250.148
    C) 300.13(B)
    D) 551.55(E)

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

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    Code News Update
    Changes in Store for Electrical Code in Northwest Missouri Town?
    Based on a report in the Dec. 6th edition of the St. Joseph News-Press, the city's Electrical Standards and Appeals Board and city building development staff have been working for years to come up with changes to its electrical code. According to the article, "Master electricians must pass a third-party test to earn their licenses. One of the changes would require master electrician applicants to appear before the board for a second, brief test to evaluate their experience."

    But the article goes on to point out that the board only meets quarterly, which potentially sets up a three-month waiting period for qualified electricians to get a license. Opponents of this change say it will create a barrier for out-of-town competition. Supporters of this change say there are plenty of local electric companies to meet the city's needs.

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    Shows and Events
    Get In-Depth Information on Code Changes & Standards
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    Click here for information on accessing the EC&M e-Tradeshow, a virtual online exhibition and live conference center. Also available on the site is an archive of various past presentations, such as Claim Litigation and Harmonics: Causes, Symptoms, and Remedial Solutions.

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