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February 27, 2007 A Prism Business Media Publication Vol. V No. 4

250.92 Service Bonding

What's Wrong Here?

Code Q&A

Code Quiz

Eliminating Confusion Over Rod Size

EC&M Code Change Conferences

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    Top 50 NEC Rules

    250.92 Service Bonding

    By Mike Holt
    As per section A of this requirement, the following metal parts must be service bonded to an effective ground-fault current path in accordance with 250.92(B):
    1. Metal raceways containing service conductors.
    2. Enclosures containing service conductors.
    3. A metal raceway containing the grounding electrode conductor.
    The metal raceway containing the grounding electrode conductor must be effectively bonded in accordance with 250.64(E). Raceways or enclosures containing feeder and branch-circuit conductors are not required to be service bonded in accordance with 250.92(B).

    As per section B of this requirement, enclosures and raceways containing service conductors must be bonded to an effective ground-fault current path by one of the following methods:

    1. Grounded Neutral Conductor. Enclosures and raceways containing service conductors are considered bonded to an effective ground-fault current path by bonding to the grounded neutral service conductor via the main bonding jumper. The bonding must be by exothermic welding, listed pressure connectors, listed clamps, or other listed fittings [250.8].

      A main bonding jumper is required to bond the service disconnect to the grounded neutral service conductor [250.24(B) and 250.28]. At service equipment, the grounded neutral service conductor is used to provide the effective ground-fault current path to the power source [250.24(C)]. Therefore, an equipment grounding (bonding) conductor isn't required to be installed within a non-metallic raceway containing service-entrance conductors [250.142(A)(1) and 352.60, Ex. 2] (see Figure).

    2. Threaded Fittings or Entries. Raceways containing service conductors are considered bonded to an effective ground-fault current path by threaded couplings or threaded entries on enclosures where made up wrenchtight.

    3. Threadless Fitting. Raceways containing service conductors are considered bonded to an effective ground-fault current path by threadless raceway couplings and connectors where made up tight.

    4. Bonding Fitting. When a metal service raceway terminates to an enclosure with a ringed knockout, a listed bonding device, such as a bonding wedge or bushing, must bond one end of the service raceway with a bonding jumper sized in accordance with Table 250.66 [250.92(B)(4) and 250.102(C)].

      When a metal raceway containing service conductors terminates to an enclosure without a ringed knockout, a bonding-type locknut can be used instead of a bonding wedge or bushing. A bonding-type locknut differs from a standard-type locknut in that it has a bonding screw with a sharp point that drives into the metal enclosure to ensure a solid termination. Bonding one end of a service raceway in accordance with 250.92(B) provides the low-impedance fault-current path to the utility electrical supply source.

    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: Do you hear a fire truck siren?

    Code Q&A
    By Mike Holt
    Q. If the secondary conductors of a transformer are less than 10 feet in length, do the secondary conductors have to terminate in a main breaker?

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

    Code Quiz
    By Steven Owen
    Q. When cutting and threading rigid metal conduit, intermediate metal conduit and stainless steel conduit in the "field", which one of the aforementioned conduits is not required to have its threads protected with an approved electrically conductive corrosion-resistant compound?
    A) Rigid metal conduit.
    B) Intermediate metal conduit.
    C) Stainless steel conduit.
    D) None of these conduit types are required to be protected with an approved electrically conductive corrosion-resistant compound.

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

    One-touch automated design and one-touch automated protective device coordination options, available in EasyPower 8.0, will be introduced in the Hands-On training in Portland, OR April 30 -- May 4, 2007! Streamline the implementation of your Arc Flash and Electrical Safety Program. What used to take hours, now takes mere seconds! EasyPower delivers Windows®-based tools for designing, analyzing, and monitoring electrical power systems.

    Code News Update
    Eliminating Confusion Over Rod Size
    Installers and inspectors alike have been confused over the requirements of 250.52(A)(5) -- more specifically with regard to the diameter of the rod. In an effort to eliminate this confusion, Code-Making Panel 5 has accepted in principle proposal 5-160 for the 2008 NEC. If adopted, the new section would read as follows:

    "Rod and pipe electrodes shall not be less than 2.44 m (8 ft) in length and shall consist of the following materials.

    (a) Grounding electrodes of pipe or conduit shall not be smaller than metric designator 21 (trade size 3/4), and where of steel, shall have the outer surface galvanized or otherwise metal-coated for corrosion protection.

    (b) Grounding electrodes of stainless steel, copper, or zinc-coated steel shall be at least 15.87 mm (5/8 in.) in diameter unless listed and not less than 12.70 mm (1/2 in.) in diameter."

    Cool Electronic Cabinets
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    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. Plans are currently underway to present seven Code change conferences 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.

    Hotel and registration information will be announced soon!

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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.