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March 19, 2009 A Penton Media Publication Vol. VII No. 6

CONTENTS
Editorial Clarification

702.5 Capacity and Rating for Optional Standby Systems

What's Wrong Here?

Code Q&A

Code Quiz

Comments Sought on Proposed TIA

Enroll In EC&M University's Online Arc Flash Courses


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    Editorial Correction
    Editorial Clarification
    The Top 2008 Code Change item from the last issue (700.9 Wiring for Emergency Power Systems) has caused some confusion. To rectify this situation, we offer the following text to help clarify when and where these requirements apply.

    These wiring requirements apply to single or multiple (two or more) generators connected in parallel configurations.

    An Exception to 700.9(B)(5)(b) states, "Overcurrent protection shall be permitted at the source or for the equipment, provided the overcurrent protection is selectively coordinated with the downstream overcurrent protection."

    In addition to a "generator source", the new subsection (5) applies to other power sources such as storage batteries, uninterruptible power supplies, a separate service (i.e., redundant utility feeder), fuel cell systems, and unit equipment.

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    Top 2008 Code Changes















    702.5 Capacity and Rating for Optional Standby Systems
    By Mike Holt
     The sizing for optional standby power systems is now based on the type of transfer switch used: manual versus automatic. This Code section was extensively revised and new subsections were added in response to the growth of generator installations — and the concern about the sizing of an optional standby source that uses automatic transfer switching.

    (A) Available Short Circuit Current. Optional standby system equipment shall be rated for the maximum available short circuit current at its terminals.

    (B) System Capacity. The calculated load on the standby source shall be in accordance with Art. 220 or by a method approved by the Authority Having Jurisdiction (AHJ).

    (1) Manual Transfer Equipment. The optional standby power source shall have adequate capacity for all equipment intended to operate at one time. The user of the optional standby system selects the loads to be connected to the system.

    When a manual transfer switch is used, the user of the optional standby system selects the loads to be connected to the system, which determines the system size.

    (2) Automatic Transfer Equipment.
    (a) Full Load.     The optional standby power source shall have adequate capacity to supply the full load transferred.

    If an automatic transfer switch is used in an optional system, the power source — typically a generator — must be capable of supplying the full load transferred. The load is determined by using Art. 220 as a basis on system sizing or an alternate method approved by the AHJ.

    For existing facilities, the optional standby source can be sized to the maximum demand data available for one year or the average power demand of a 15-min. period over a minimum of 30 days [220.87].

    However, the conditions are not the same for optional standby power supply when a manual transfer switch is used. In this case, the user of the optional standby system selects the loads to be connected to the system, which determines the system size.

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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: A shining example of poor construction
    Code Q&A
    By Mike Holt
     Q. Can the ground wire from a ground rod terminate in the meter socket enclosure, or must it terminate in the service disconnect?

    Visit EC&M's Web site to see the answer.
    Code Quiz
    By Steven Owen
     When grounding network interface units containing protectors, network interface units with metallic enclosures, primary protectors, and the metallic members of the network-powered broadband communications cables that are intended to be grounded, which of the following requirements apply to the grounding conductor?

    1. The grounding conductor shall be insulated. The grounding conductor shall be copper or other corrosion-resistant conductive material, stranded or solid.
    2. The grounding conductor shall not be smaller than 14 AWG copper, and have a current-carrying capacity approximately equal to that of the grounded metallic members and protected conductors of the network-powered broadband communications cable. In addition, the grounding conductor shall not be required to exceed 6 AWG.
    3. The grounding conductor shall be as short a practicable, be run in a straight line, and be protected where exposed to physical damage.
    4. All of the above requirements apply.

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

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    Code News Update
    Comments Sought on Proposed TIA
    As published in the March issue of NFPA News, the following Tentative Interim Amendment (TIA) has been proposed to the NFPA.

    NFPA 70-2008 and proposed 2011 Edition, National Electrical Code
    TIA Log No. 941
    Reference: 250.104
    Submitter: Robert Torbin, Cutting Edge Solutions LLC

    Revise 250.104 to read as follows:

    250.104 Bonding of Piping Systems and Exposed Structural Steel.
    (B) Other Metal Piping.     Where installed in or attached to a building or structure, a metal piping system(s), including gas piping, that is likely to become energized shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or the one or more grounding electrodes used. The bonding jumper(s) shall be sized in accordance with 250.122, using the rating of the circuit that is likely to energize the piping system(s). The equipment grounding conductor for the circuit that is likely to energize the piping shall be permitted to serve as the bonding means. The points of attachment of the bonding jumper(s) shall be accessible.

    (1) Other than Corrugated Stainless Steel Tubing (CSST). The bonding jumper(s) shall be sized in accordance with 250.122, using the rating of the circuit that is likely to energize the piping system(s). The equipment grounding conductor for the circuit that is likely to energize the piping shall be permitted to serve as the bonding means.

    (2) CSST. Corrugated stainless steel tubing gas piping systems shall be bonded by connection to a metallic piping segment or fitting, either outside or inside the building, between the individual gas meter and the first CSST fitting. The bonding jumper shall be sized in accordance with Table 250.66 based on the size of the service-entrance conductor or feeder supplying each occupancy and as permitted in 250.66(A), (B), and (C), but not smaller than 6 AWG copper (or equivalent).

    FPN (unchanged)

    To review the submitter's reason (substantiation and technical merit) and emergency nature text for this change, click here and review the text on pages 1, 2, and 3.

    This TIA has been published for public review and comment. Comments should be filed with the Secretary, Standards Council by April 17, 2009. You should identify the TIA number when submitting your comments. The Standards Council will review the technical committees’ ballot results, the public comments, and any other information that has been submitted when it considers the issuance of the TIA at its meeting on August 4-6, 2009.
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    • Clarifying NFPA 70E and IEEE 1584 Requirements
      April 9, 2009
    • Impact of System and Operating Conditions on Arc Flash Energy Levels
      April 21, 2009
    • High Resistance Grounding and Arc Flash Accident Prevention
      May 7, 2009
    • Mitigation of Arc Flash Hazards Using Fuses
      May 12, 2009
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      June 16, 2009
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      June 25, 2009
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