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December 26, 2006 A Prism Business Media Publication Vol. IV No. 24

CONTENTS
250.54 Supplementary Electrodes

What's Wrong Here?

Code Q&A

Code Quiz

Code Committee Call-Up

Get In-Depth Information on Code Changes & Standards


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    250.54 Supplementary Electrodes
    By Mike Holt
     A supplementary electrode is an electrode that is not required by the NEC. This electrode is not required to be bonded to the building or structure grounding electrode (earthing) system. In addition, the supplementary electrode is not required to be sized to 250.66, and is not required to comply with the 25-ohm resistance requirement of 250.56. However, the earth cannot be used as an effective ground-fault current path as required by 250.4(A)(4). Because the resistance of the earth is so high, very little current will return to the electrical supply source via the earth. If a ground rod is used as the ground-fault current path, the circuit overcurrent protection device will not open, and metal parts will remain energized.

    It's important to note that the requirements contained in 250.54 for a "supplementary" electrode should not be confused with the requirements contained in 250.53(D)(2) for the underground metal water pipe "supplemental" electrode. Typically, a supplementary electrode serves no useful purpose. In some cases, it may actually create equipment or performance failure. However, in a few cases, the supplementary electrode is used to help reduce static charges on metal parts. For information on protection against static electricity in hazardous (classified) locations, see NFPA 77, Recommended Practice on Static Electricity.

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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: If it works, it's not a problem, right?
    Code Q&A
    By Mike Holt
     Q. Can I install a panel in a residential bathroom? What about in a bedroom?

    Visit EC&M's Web site to see the answer.
    Code Quiz
    By Steven Owen
     Q. The wiring of each mobile home shall be subjected to a ____ minute, ____ volt dielectric strength test (with all switches closed) between live parts (including neutral) and the mobile home ground. Alternatively, the test shall be permitted to be performed at ___ volts for ___ second(s). This test shall be performed after branch circuits, luminaires (fixtures), and appliances are installed.
    A) 10, 240 and 550, 10
    B) 5, 480 and 600, 2
    C) 1, 900 and 1,080, 1
    D) There are no required tests for mobile homes, RVs, or any type of structure.

    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. 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 of Industrial Machinery (seeking members in all categories except end users or manufacturers). This committee is responsible for NFPA 79, Electrical Standard for Industrial Machinery.
    • Committee on Electrical Systems Maintenance (special experts excluded). This committee is responsible for NFPA 73, Electrical Inspection Code for Existing Dwellings.
    • Committee on Health Care Facilities -- Electrical Systems. This committee is responsible for chapters within NFPA 99, Standard for Health Care Facilities
    Anyone interested in serving can download the application form at NFPA's Web site.

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    Shows and Events
    Get In-Depth Information on Code Changes & Standards
    Are you a residential, industrial, commercial, or institutional electrical contractor? Do you specify equipment or review construction plans? Do you maintain electrical systems in a facility? If you answered "yes" to any of these questions then you have to make plans to attend the Electric West conference program next year in Long Beach, Calif. Attend one of 12 fact-filled seminars, three of which offer CEUs. Or make plans to attend one of two update sessions on the 2005 NEC, led by top trainer Mike Holt. These Code sessions will also offer a sneak preview of proposed changes to the 2008 NEC. Check out this event's 40+ seminars and make plans to meet 200+ leading suppliers. Or register now.

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