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March 6, 2008 A Penton Media Publication Vol. VI No. 5

CONTENTS
440.22 Short-Circuit and Ground-Fault Protection Devices for A/C and Refrigeration Equipment

What's Wrong Here?

Code Q&A

Code Quiz

Deadline Fast Approaching

Visit The EC&M e-Tradeshow


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    440.22 Short-Circuit and Ground-Fault Protection Devices for A/C and Refrigeration Equipment

    By Mike Holt
    Short-circuit and ground-fault protection for air-conditioning and refrigeration equipment must be sized no larger than identified on the equipment's nameplate. If the equipment doesn't have a nameplate specifying the size and type of protection device, then the protection device must be sized in accordance with (A) or (B).

    (A) One Motor Compressor. The short-circuit and ground-fault protection device must not be greater than 175% of the motor-compressor current rating. If the protection device sized at 175% isn't capable of carrying the starting current of the motor-compressor, the next size larger protection device can be used, but in no case can it exceed 225% of the motor-compressor current rating.

    (B) Rating for Equipment. Where the equipment incorporates more than one hermetic refrigerant motor-compressor, or a hermetic refrigerant motor-compressor and other motors or other loads, the equipment short-circuit and ground-fault protection must be sized as follows:
    (1) Motor-Compressor Largest Load. The rating of the branch-circuit short-circuit and ground-fault protective device must not be greater than the largest motor-compressor short-circuit ground-fault protection device, plus the sum of the rated load currents of the other compressors.

    The branch-circuit conductors are sized at 125% of the larger motor-compressor current, plus the sum of the rated load currents of the other compressors [440.33].

    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: Damaged equipment in Las Vegas.


    Code Q&A
    By Mike Holt
    Q. A 400A service is made up of two 200A main breaker panelboards that are nippled together. Can the service conductors pass through one of the cabinets to supply the other panelboard?

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


    Code Quiz
    By Steven Owen
    Q. What is the allowable ampacity of any one of the current-carrying 12 AWG THHN insulated conductors installed in a cellular concrete floor raceway with 29 other current-carrying 12 AWG THHN conductors and five equipment grounding conductors? Disregard the terminals in your calculations.

    1. 30A
    2. 20A
    3. 13.5A
    4. 11.25A

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


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    Code News Update
    Deadline Fast Approaching
    The Notice of Intent to Make a Motion closing date for the next revision of NFPA 70E: Standard for Electrical Safety in the Workplace is April 4, 2008. This standard addresses "electrical safety requirements for employee workplaces that are necessary for the practical safeguarding of employees in their pursuit of gainful employment." The posting of certified Notice of Intent to Make an NEC Motions (NITMAMs) is scheduled to take place on May 4, 2008.


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    Shows and Events


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    Look for these FREE live conferences, scheduled for 2008:

    • Using the Electrical Designer's Reference Software Program
    • The NEC in Construction Litigation
    • Understanding Electrical Safety and PPE Selection
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    • Preparing an Arc Flash Hazard Study
    • Proper Working Drawings: An Engineer's Perspective
    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 e-tradeshow for information on accessing the EC&M e-Tradeshow and visiting the On-Demand Library.



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