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August 14, 2006 A Prism Business Media Publication Vol. IV No. 15

Introducing the EC&M

240.6 Standard Ampere Ratings

What's Wrong Here?

Code Q&A

Code Quiz

Call for Comments

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    Top 50 NEC Rules

    240.6 Standard Ampere Ratings

    By Mike Holt
    The standard ratings in amperes for fuses and inverse-time breakers are: 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1,000, 1,200, 1,600, 2,000, 2,500, 3,000, 4,000, 5,000 and 6,000. Additional standard ampere ratings for fuses include 1, 3, 6, 10, and 601.

    Fuses rated less than 15A are sometimes required for the protection of fractional horsepower motor circuits [430.52], motor control circuits [430.72], small transformers [450.3(B)], and remote-control circuit conductors [725.23].

    The ampere rating of an adjustable circuit breaker is equal to its maximum long-time pickup current setting.

    The ampere rating of adjustable-trip circuit breakers that have restricted access to the adjusting means is equal to their adjusted long-time pickup current settings.

    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: Something seems to be missing here.

    Code Q&A
    By Mike Holt
    Q. What type of fitting can I use to terminate ground wires in a metal box?

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

    Code Quiz
    By Steven Owen
    Q. What is the maximum number of 12 AWG THHN insulated conductors permitted in a strut-type channel raceway that is 1 1/2 inches by 1 1/2 inches and of unlimited length? The channel location is defined as indoors and dry. The ambient temperature does not exceed 30°C. The raceway sections of this strut-type channel are joined with external joiners.

    A) 54
    B) 55
    C) 34
    D) 35

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

    Cool Electronic Cabinets
    Stop electronic control downtime due to heat, dirt and moisture. UL Listed Cabinet Coolers from EXAIR 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.

    Speak Out
    Call for Comments
    The following Tentative Interim Amendment (TIA Log No. 822) to the 2005 NEC has been proposed to the NFPA. The TIA is now open for public review and comment. All comments on this proposed change should be filed with the Secretary, Standards Council, by September 20, 2006. The Standards Council will review any and all information submitted and then determine whether or not to issue the TIA at its November 3, 2006 meeting.

    The TIA proposes new wording for the ampacity of conductors in cellular metal floor raceways. The existing wording and proposed wording are shown here for your benefit.

    Existing Wording:
    "374.17 Ampacity of Conductors. The ampacity adjustment factors in 310.15(B)(2) shall apply to conductors installed in cellular metal floor raceways."

    Proposed Wording:
    "374.17 Ampacity of Conductors. In addition to all other requirements of Article 374 of the NEC, the ampacity adjustment factors in 310.15(B)(2) shall apply to current-carrying conductors installed in headers with internal dimensions of less than 9 square inches.
    "The ampacity adjustment factors in 310.15(B)(2) shall also apply to current-carrying conductors installed in cells, except that cells having internal dimensions in excess of 5.5 square inches shall be permitted to contain up to 30 current-carrying conductors of #10 size without ampacity reduction, and cells having internal dimensions in excess of 15 square inches shall be permitted to contain up to 75 current-carrying conductors of #10 size without ampacity reduction."

    The submitter's reason behind this proposed change is noted in the August 2006 issue of NFPA News (page 3).

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