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March 20, 2008 A Penton Media Publication Vol. VI No. 6
CONTENTS
440.32 Conductor Size for A/C and Refrigeration Equipment -- One Motor Compressor

What's Wrong Here?

Code Q&A

Code Quiz

Comments Sought on Proposed TIA

VISIT THE EC&M e-TRADESHOW


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    440.32 Conductor Size for A/C and Refrigeration Equipment -- One Motor Compressor
    By Mike Holt
     The branch-circuit conductors for air-conditioning and refrigeration equipment must be sized not smaller than identified on the equipment's nameplate. If the equipment doesn't have a nameplate specifying the branch-circuit conductors, the conductors must be sized in accordance with 440.32.

    If equipment doesn't have a nameplate identifying the minimum circuit ampacity, the branch-circuit conductors to a single motor-compressor must have an ampacity not less than 125% of the motor-compressor rated load current or the branch-circuit selection current, whichever is greater.

    In accordance with 440.22(A), branch-circuit conductors must have branch-circuit protection sized between 175% and 225% of the rated load current to provide protection against short circuits and ground faults. Let's review an example to better explain these requirements.

    What size conductor and protection device is required for an 18A motor-compressor?

    Step 1. Refer to Table 310.16 to determine the proper size branch-circuit conductor.
    18A x 1.25 = 22.5A
    Therefore, you should use a 12AWG conductor, rated 25A at 75°C.

    Step 2. Refer to Sections 240.6(A) and 440.22(A) to determine the proper size protection device.
    18A x 1.75 = 31.5A
    Use the next size down device, rated 30A.
    If the 30A protection device isn't capable of carrying the starting current, then the protection device can be sized up to 225% of the equipment load current rating.
    18A x 2.25 = 40.5A
    Use the next size down device, rated 40A.

    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: 7th floor problems.
    Code Q&A
    By Mike Holt
     Q. Is GFCI protection required for drinking water fountains in office buildings?

    Visit EC&M's Web site to see the answer.
    Code Quiz
    By Steven Owen
     Q. Which of the following methods for connecting grounding and bonding conductors to equipment is the only one not permitted by the NEC?

    1. listed pressure connectors
    2. exothermic welding process
    3. green-colored "tapcon" self-tapping concrete anchors drilled directly through a metal box (no threads engaged), and used to connect the grounding and bonding conductors
    4. thread-forming machine screws that engage not less than two threads in the enclosure

    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 79-2007, Electrical Standard for Industrial Machinery
    TIA Log No. 901
    Reference: 13.2.4.1
    Submitter: Christine Livingston, Ford Motor Co.
    1. Revise 13.2.4.1 to read as follows: "The color ORANGE or YELLOW shall be used to identify ungrounded conductors that remain energized when the main supply circuit disconnecting means is in the off position. This color identification shall be strictly reserved for this application only."
    2. Revise A.13.2.4.1 by removing the first sentence only.

    Substantiation: Add the color yellow as an additional color option for ungrounded conductors that remain energized when the main disconnect is in the off position. This option was allowed in the 2002 edition, but was removed from the 2007 publication. Traditionally, U.S.-based manufacturing has used the yellow color option exclusively for excepted circuits so there is a large installation base using this color.

    Emergency Nature: By removing the yellow option from the list of colors designated for excepted circuits in the standard, we have opened the door for use of this color in other applications, creating confusion and dangerous conditions.

    This TIA has been published for public review and comment. Comments should be filed with the Secretary, Standards Council by May 2, 2008. 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 July 22-24, 2008 meeting.

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    Shows and Events


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    Look for these FREE live conferences, scheduled for THIS MONTH:

    Monday, March 24, 10 a.m. EST and PST: "Harmonic Solutions: Side-by-Side Comparisons" presented by Dan Carnovale, P.E., Eaton Corp.
    Learn about side-by-side comparisons of various harmonic mitigation technologies, based on testing conducted in a test lab specially constructed to evaluate all of the major categories of harmonic solutions for industrial and commercial power systems. See the results of this testing, including considerations for generator applications, harmonic resonance, and the application of phase shifting. Energy savings observations will also be discussed. Video recordings of the testing will be included.

    Coming soon:

    • "Understanding Electrical Safety and PPE Selection"
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    • "Preparing an Arc Flash Hazard Study"

    Visit the many exhibitors in this virtual tradeshow and take a look at the On-Demand Theater, where you can view past online conferences 24/7/365. Go to www.ecmweb.com for information on accessing the EC&M e-Tradeshow and visiting the On-Demand Library.

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