November 23, 2005 A PRIMEDIA Property Vol. III No. 22



CONTENTS
Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits, Part VI. Listing Requirements
725.82 Listing and Marking of Class 2 and Class 3 Cables

Wishy-Washy Installation

What's Wrong Here?

Code Q&A

Code Quiz

NFPA World Safety Conference and Exposition


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    Top 2005 Code Changes
    Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits, Part VI. Listing Requirements
    725.82 Listing and Marking of Class 2 and Class 3 Cables

    By Mike Holt
    New subsections were added to recognize the use of raceways designed for Class 2 and Class 3 cables. (Note: Code text has been paraphrased.)

    What the Code says:
    (I) Plenum Signaling Raceways. Listed plenum raceways can be installed in other environmental air spaces in accordance with 725.61(A).
    (Text new to the Code is underlined.)

    Behind the change: Listed plenum signaling raceways must contain plenum-rated Class 2 or Class 3 cables when installed above a suspended ceiling or below a raised floor used for environmental air [725.61(A)].

    What the Code says:
    (J) Riser Signaling Raceway. Riser signaling raceways must be listed as preventing the carrying of fire from floor to floor.
    (K) General-Purpose Signaling Raceway. General-purpose signaling raceways must be listed to resist the spread of fire.
    (Text new to the Code is underlined.)



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    Nightmare Installations
    Wishy-Washy Installation
    After completing the wiring for a clothes dryer and plugging the cord into the receptacle, I placed one hand on the dryer and one on the washer to climb out from behind the unit. In doing so, I received a terrible shock. I pulled out my meter and measured 120V between appliances. I knew the washer was bonded to the copper water line so I double-checked my wiring. My work looked good. Additional measurements showed 120V receptacles measuring 120V (white wire) and 240V (black wire) to remote earth.

    Although it was a rainy night, I wanted to check the outdoor service entrance (SE) panel. A shock from the SE panel convinced me it could wait. Morning light revealed no ground rod at the SE panel. The triplex SE cable was terminated correctly on the pole-mounted transformer, and the transformer tank was bonded to the pole ground. However, there was no ground strap from the transformer neutral bushing to the tank.

    A lack of ground at either end of the SE triplex created a floating neutral. Also, one transformer secondary line bushing was cracked. I reasoned that during wet weather the cracked bushing would short to the transformer tank establishing a ground. The floating neutral went to 120V, and the other side went to 240V. Replacement of the transformer and installation of a ground rod solved the problem.

    Terry Johnson
    Iowa City, Iowa

    Send your 200-word story to us, and it may appear in a future issue of CodeWatch. Authors of stories chosen will receive $25.


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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: This gives new meaning to the phrase "adjustable light fixture."


    Code Q&A
    By Mike Holt
    Q. Electricians in our area ground the metal conduit that runs up a utility pole to a local ground rod. Is this a Code-compliant installation?

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


    Code Quiz
    By Steven Owen
    Q. What is the maximum number of multi-conductor cables (for control circuits only) permitted in an 18-inch-wide by 4-inch-deep ladder type cable tray? The outer diameter of each conductor is 0.5 inches, and there will be no equipment-grounding conductor installed within the cable tray. Does the number of allowed cables change if the cable tray has a solid bottom? If so, what is the new number?

    A) 144 / 144
    B) 183 / 146
    C) 184 / 147
    D) 366 / 366

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


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    Shows and Events
    NFPA World Safety Conference and Exposition
    The NFPA World Safety Conference and Exposition will take place June 4-8, 2006 at the Orlando County Convention Center in Orlando, Fla. The conference typically consists of more than 100 education sessions and brings together thousands of fire protection, life safety, and electrical professionals. The conference is supported by a exposition floor where you can view the latest product and service offerings from several hundred manufacturers and service companies. For more information, visit the NFPA Web site.


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