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November 13, 2006 A Prism Business Media Publication Vol. IV No. 21

250.50 Grounding Electrode System

What's Wrong Here?

Code Q&A

Code Quiz

EC&M E-TradeShow

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    Top 50 NEC Rules

    250.50 Grounding Electrode System

    By Mike Holt
    All grounding electrodes as described in 250.52(A)(1) through (A)(6) that are present at each building or structure must be bonded together to form the grounding electrode (earthing) system.
    • 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)]
    • Ground rod [250.52(A)(5)]
    • Grounding plate [250.52(A)(6)]
    Exception: Concrete-encased electrodes are not required for existing buildings or structures where the conductive steel reinforcing bars aren't accessible without disturbing the concrete.

    Where an underground metal water pipe electrode, metal building or structure frame electrode, or concrete-encased electrode is not present, one or more of the following electrodes specified in 250.52(A)(4) through (A)(7) must be installed to create the grounding electrode (earthing) system.

    • Ground rod [250.52(A)(5)]
    • Grounding plate [250.52(A)(6)]
    • Metal underground systems [250.52(A)(7)
    Editor's note: This information was extracted from Mike Holt's textbook, Understanding the National Electrical Code.

    Fluke 1735 Three-Phase Power Logger
    Power quality logging, electrical load studies and energy consumption testing. The Fluke 1735 Power Logger is the ideal electrician or technician's power meter for conducting energy studies and basic power quality logging. Set the Power Logger up in seconds with the included flexible current probes and color display. The power quality meter measures most electrical power parameters, harmonics, and captures voltage events.

    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: Fill 'er up!

    Code Q&A
    By Mike Holt
    Q. Can Table 310.15(B)(6) (reduced size wire for dwelling unit service) be used to size the service neutral conductor for a single-family dwelling?

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

    Code Quiz
    By Steven Owen
    Q. The wiring of the emergency system in hospitals shall be mechanically protected. Where installed as branch circuits in patient care areas, the installation shall comply with the requirements of 517.13(A) and 517.13(B). Which of the following wiring methods is permitted?

    1. Nonflexible metal raceways, Type MI cable, Schedule 80 rigid nonmetallic conduit. Nonmetallic raceways shall not be used for branch circuits that supply patient care areas.
    2. Where encased in not less than 2 inches of concrete. Schedule 40 nonmetallic conduit, flexible nonmetallic or jacketed metallic raceways, or jacketed metallic cable assemblies listed for installation in concrete. Nonmetallic raceways shall not be used for branch circuits that supply patient care areas.
    3. Listed flexible metal raceways and listed metal sheathed cable assemblies in any of the following:
      • a. Where used in listed prefabricated medical headwalls.
      • b. In listed office furnishings.
      • c. Where fished into existing walls or ceilings, not otherwise accessible and not subject to physical damage.
      • d. Where necessary for flexible connection to equipment.
    4. Flexible power cords of appliances and other utilization equipment connected to the emergency system.
    5. Secondary circuits of Class 2 and Class 3 communication or signaling systems.
    A) 1 and 2 only
    B) 2 and 3 only
    C) 1, 2 and 3 only
    D) All of the above

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

    Cool Electronic Cabinets
    Stop electronic control downtime due to heat, dirt and moisture. UL Listed Cabinet Coolers from EXAIR produce 20 degree Fahrenheit air from an ordinary supply of compressed air to cool electrical controls. Thermostat control minimizes air usage. Maintains the NEMA 4, 4X (stainless steel) and 12 rating of the enclosure. Web site offers detailed information, downloadable drawings and PDF literature.

    Shows and Events
    EC&M E-TradeShow

    Free Live Conferences in November
    Mark Nov. 16 on your schedule to attend these highly informative live conferences:
    • Learn about all the new energy-storage technologies -- including ultracapacitors, fuel cells, and flywheels -- now available by attending the live conference "Energy Storage Methods for Standby Electric Power Systems," presented by John DeDad at 11 a.m. EDT and PDT.
    • 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, we're having a special Contractor's Night live conference at 8 p.m. EDT.
    • If you're looking for construction industry information to include in your business forecast for 2007, you'll certainly want to attend Jim Lucy's 2007 Electrical Market Sales Forecast, 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-see for electrical equipment manufacturers, contractors, distributors, and engineers.
    But 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, which are archived in the E-TradeShow. Employing the latest interactive 3D technology, sponsors use online tradeshow 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

    One Gets It Done.
    Feel the difference with the Twister® Wire Connector. A comfortable swept wing design provides added leverage, while the durable polypropylene shell expands for a smooth application. The patented live-action, square-wire spring locks onto the wire for safe, secure connections. Don't settle for just any wire connector. Insist on the Twister. Visit for a free sample.

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    Copyright 2006, Prism Business Media. All rights reserved. This article is protected by United States copyright and other intellectual property laws and may not be reproduced, rewritten, distributed, re-disseminated, transmitted, displayed, published or broadcast, directly or indirectly, in any medium without the prior written permission of Prism Business Media.