April 8, 2005 A PRIMEDIA Property Vol. III No. 7

310.15 -- Conductor Ampacity

A Polarity Pickle

What's Wrong Here?

Code Q&A

Code Committee Call-Up

What's Your Code?

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    Top 2005 Code Changes
    310.15 -- Conductor Ampacity
    By Mike Holt
    Text was added to clarify how each current-carrying conductor of a parallel conductor set is to be treated when applying the ampacity adjustment factors of Table 310.15(B)(2)(a). (Note: Code text has been paraphrased.)

    What the Code says:
    (B) Ampacity Table. The allowable conductor ampacities listed in Table 310.16 are based on conditions where the ambient temperature isn't over 86°F and no more than three current-carrying conductors are bundled together.
    (2) Ampacity Adjustment
    (a) Conductor Bundle. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are stacked or bundled in lengths exceeding 24 in., the allowable ampacity of each conductor, as listed in Table 310.16, must be adjusted in accordance with the adjustment factors contained in Table 310.15(B)(2)(a). Each current-carrying conductor of a paralleled set of conductors must be counted as a current-carrying conductor.
    (Text new to the Code is underlined.)

    Behind the change: The change was intended to resolve the misconception presented by the language in 310.4 that paralleled conductors are counted as a single conductor when applying the provisions of 310.15(B)(2)(a).

    Big Features, Small Package
    The Fluke 321 and 322 are designed to verify the presence of load current, AC voltage and continuity of circuits, switches, fuses and contacts. These small and rugged clamp meters are ideally suited for current measurements up to 400 A in tight cable compartments. The Fluke 322 also offers DC voltage measurements and has a higher resolution for loads below 40 A.

    Nightmare Installations
    A Polarity Pickle
    Several years ago I made a service call to an old two-story house where the upstairs tenant reported that his new window air conditioner kept causing fuses to blow. Not only that, he got shocked every time he tried to replace them. I found that all the lighting and receptacles in the apartment were wired to one circuit. But the real horror story was the fuse box in the basement. I found a 30A, 250V safety switch (with two plug fuses) mounted upside down. That alone wasn't a problem, but the installer had fed the line side into the top terminals (which were really the load terminals) and the load to the bottom (which was really the line side). He also fused the neutral side as well as the hot wire, presenting several opportunities for electrocution. The threaded shell of the fuse would have been hot as it was screwed into the hot side holder, the switch blades would have been hot when the hot fuse was installed, and the wiring and devices upstairs would have been hot even if the neutral side fuse blew. The only thing that probably saved the tenant's life was that he had to stand on a wooden chair on the damp basement floor to reach the fuse box.
    Michael Reed
    Viburnum, Mo.

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

    Cool Electronic Cabinets
    Stop electronic control downtime due to heat, dirt and moisture. UL Listed Cabinet Coolers produce 20 degree Fahrenheit air from an ordinary supply of compressed air to cool electrical controls. Thermostat control minimizes air usage. Maintains the NEMA 4, 4X (stainless steel) and 12 rating of the enclosure. Web site offers detailed information, downloadable drawings and PDF literature.

    Code Challenge
    What's Wrong Here?
    By Joe Tedesco
    How does this installation violate the NEC?

    Hint: The key word is "access."

    Code Q&A
    By Mike Holt
    Q. What's the maximum number of circuit breakers permitted to be installed in a panel?
    See the answer.

    The National Electrical Code Internet Connection, the No. 1 rated Code Web site in the world, offers the following FREE products:
    Books, Code Quiz, DVDs, Graphics for PowerPoint, Newsletter, Online Training, Posters, Simulated Exams, Software, Video clips, and Videos
    Visit www.NECcode.com and stay current with important industry issues.

    Code News Updates
    Code Committee Call-Up
    Got some extra time on your hands? Looking to put some of your vast knowledge of the electrical field to use? NFPA is looking for new members for several of its committees, including the following:

    • Committee on Electrical Systems Maintenance (special experts excluded)
    • Committee on Health-Care Facilities -- Electrical Equipment (users excluded)
    • Committee on Health-Care Facilities -- Electrical Systems (special experts excluded)
    • Committee on Electrical Systems for Manufactured Housing (manufacturers and enforcers excluded)

    Anyone interested in serving can download the application form at NFPA's Web site.

    Speak Out
    What's Your Code?
    CodeWatch readers' opinions on what to do about the current state of Code adoption are almost as varied as the Code rules from one state to the next. Three-fourths of you agree that something needs to be done, but you're split on what it should be.

    To give your fellow readers a better understanding of why you voted the way you did, it helps to put it into context. What version of the Code are you required to follow? Visit EC&M's Web site to tell us.

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