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May 14, 2007 A Penton Media Publication Vol. V No. 9



CONTENTS
Cast Your Vote Now!

250.122 Sizing Equipment Grounding (Bonding) Conductor

What's Wrong Here?

Code Q&A

Code Quiz

California Codes

EC&M Code Change Conferences

Don't Miss This FREE Live Session Scheduled for May 17th in the EC&M e-Tradeshow


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    Top 50 NEC Rules















    250.122 Sizing Equipment Grounding (Bonding) Conductor

    By Mike Holt
    The equipment grounding (bonding) conductor must be sized in accordance with Table 250.122, based on the ampere rating of the circuit-protection device, but in no case is it required to be larger than the circuit conductors. Equipment grounding (bonding) conductors must be capable of safely conducting any ground-fault current likely to be imposed on them [110.10]. If the equipment grounding (bonding) conductor isn't sized to withstand the ground-fault current, the conductor may burn clear before the protective device responds.

    When ungrounded circuit conductors are increased in size for any reason, the equipment grounding (bonding) conductor must be proportionately increased in size. Ungrounded conductors could be increased in size to accommodate voltage drop, because of excessive heating from harmonic currents, fault current studies, or future capacity.

    When multiple circuits are installed in the same raceway or cable, only one equipment grounding (bonding) conductor is required. This conductor must be sized in accordance with Table 250.122, based on the largest overcurrent device protecting the circuit conductors.

    When circuit conductors are run in parallel [310.4], an equipment grounding (bonding) conductor must be installed with each parallel conductor set -- and it must be sized in accordance with (1) or (2).

    1. Based on the ampere rating of the circuit-protection device in accordance with Table 250.122.
    2. Based on the ampere rating of the ground-fault protection in accordance with Table 250.122 where ground-fault protection of equipment is installed if:
      • Maintenance and supervision ensure that only qualified persons will service the installation.
      • Ground-fault protection is set to trip at not more than the ampacity of a single ungrounded conductor.
    Equipment grounding (bonding) conductors for feeder taps must be sized in accordance with Table 250.122, based on the ampere rating of the circuit-protection device ahead of the feeder, but in no case is it required to be larger than the circuit conductors.

    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: You've got mail


    Code Q&A
    By Mike Holt
    Q. Can I connect a range hood in a dwelling unit kitchen to the small appliance circuit?

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


    Code Quiz
    By Steven Owen
    Q. A contractor installed a 2,000A, 480V, 3-phase feeder in six separate raceways, consisting of a total of six 500kcmil XHHW insulated conductors per phase. Four of the raceways are 3-inch trade size EMT. The other two raceways are 3 1/2-inch RMC. All conductors are exactly the same length, per paralleled phase, and feature the same insulation type and conductor material. In addition, all are terminated in the same manner and have the same cross-sectional area. The inspector has turned this installation down. What could possibility make this installation non-Code compliant?

    1. Nothing. This installation is Code compliant.
    2. The raceways are not the same. You must change all raceway sizes to either 3 1/2-inch EMT or 3 1/2-inch RMC.
    3. The raceways are not the same. You must change all raceways to either EMT or RMC of the proper trade size.
    4. The installation has an incorrect number of conductors paralleled. Change the number of conductors per phase from six to five.

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


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    Code News Update
    California Codes
    According to the April 2007 issue of NEMA's electroindustry, the California Building Standards Commission (CBSC) recently announced that all pertinent state agencies have completed their review of the appropriate model codes and have submitted their recommendations for amendments. The new 2007 California Electrical Code will be based on the 2005 NEC. The new code is scheduled to be published by July 1 2007, with enforcement taking place on January 1 2008.


    Shows and Events
    EC&M Code Change Conferences
    Where do you turn when you need accurate information on changes to the National Electrical Code? Acknowledged as the leaders in providing information on the NEC, EC&M magazine and EC&M Seminars have been the preferred sources of this information for more than 60 years. Seven Code change conferences have been scheduled in the fall of 2007. Host cities include: Atlanta, Boston, Dallas, Orlando, Philadelphia, St. Louis, and Seattle.

    As an approved provider with the National Council of Examiners for Engineering and Surveying (NCEES), through its Registered Continuing Education provider Program (RCEPP), professional engineers attending any of our 2008 Code change conferences will receive Professional Development Hours (PDHs), a requirement for re-licensing in many states. The conferences are also approved by every state that has a continuing education requirement for contractors and electricians.

    For additional information on the dates and locations of these events, click here.



    Don't Miss This FREE Live Session
    Scheduled for May 17th in the EC&M e-Tradeshow

    • "Understanding Ground Resistance Testing" presented by John Olobri, AEMC Instruments, 10:00 a.m. Eastern and Pacific time

    In today's rapidly changing world of technological advances, good grounding is more important than ever to prevent costly damage and downtime due to service interruptions and inoperative surge protection caused by poor grounds. Attend this live conference and learn about soil resistivity, ground resistance, 3- and 4-point measurements, and clamp-on measurements. This conference is a must for professional engineers, plant/facility electrical maintenance technicians, and electrical contractors and field technicians. Bring Your Questions!

    Before and after the conference session, visit the many exhibitors in this virtual tradeshow and take a look at the On-Demand Theater, where you can view past online webcasts 24/7/365.

    Go to http://www.ecmweb.com/etradeshow/index.html for information on accessing the EC&M e-Tradeshow and attending this FREE live event.

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