View this email as a Web page Please add Code Watch to your Safe Sender list.

July 25, 2006 A Prism Business Media Publication Vol. IV No. 14

240.4 Protection of Conductors

What's Wrong Here?

Code Q&A

Code Quiz

About this Newsletter
This twice-a-month
e-newsletter is brought to you from the publisher of EC&M magazine.

CodeWatch will:

  • Let you know what could be changing in the Code®.
  • Help you brush up on your ability to apply the Code®.
  • Test your knowledge of the Code® with a Q&A format.
  • Provide information on upcoming Code® seminars and shows.
  • Give you an opportunity to sound off on Code®-related issues.

    We want to make sure we're providing you with the content you need to better manage your business or enhance your technical skills. E-mail us and let us know what you want to see in future issues of this e-newsletter. We will do our best to address your request in a future issue of CodeWatch.

  • Subscriptions
    To unsubscribe from this newsletter go to: Unsubscribe

    To subscribe to this newsletter, go to: Subscribe

    To get this newsletter in a different format (Text or HTML), or to change your e-mail address, please visit your profile page to change your delivery preferences.

    Back Issues
    Missed an issue? Visit the CodeWatch archive on EC&M's Web site.

    Tell a friend about CodeWatch
    Do you know of someone who'd like to receive CodeWatch? Visit the subscriber site, enter their e-mail address and spread the wealth!

    To find out how to advertise in this newsletter, e-mail David Miller or call him at (312) 840-8497.

    The designations "National Electrical Code” and “NEC” refer to the National Electrical Code®, which is a registered trademark of the National Fire Protection Association.



    Top 50 NEC Rules

    240.4 Protection of Conductors

    By Mike Holt
    Except as permitted by (A) through (G), conductors must be protected against overcurrent in accordance with their ampacity after ampacity adjustment, as specified in 310.15.

    (A) Power Loss Hazard. Conductor overload protection is not required, but short-circuit protection is required where the interruption of the circuit would create a hazard, such as in a material-handling electromagnet circuit or fire pump circuit.

    (B) Overcurrent Protection Not Over 800A. The next higher standard rating overcurrent device (above the ampacity of the ungrounded conductors being protected) is permitted, provided all of the following conditions are met:

    1. The conductors do not supply multi-outlet receptacle branch circuits.
    2. The ampacity of a conductor, after ampacity adjustment and/or correction, doesn't correspond with the standard rating of a fuse or circuit breaker in 240.6(A).
    3. The protection device rating doesn't exceed 800A.
    This "next size up rule" doesn't apply to feeder tap conductors [240.21(B)], or secondary transformer conductors [240.21(C)].

    (C) Overcurrent Protection Over 800A. If the circuit's overcurrent protection device exceeds 800A, the conductor ampacity, after ampacity adjustment and/or correction, must have a rating not less than the rating of the overcurrent device.

    (D) Small Conductors. Unless specifically permitted in 240.4(E) or (G), overcurrent protection must not exceed 15A for 14AWG, 20A for 12 AWG, and 30A for 10 AWG copper, or 15A for 12 AWG and 25A for 10 AWG aluminum, after ampacity adjustment and/or correction.

    (E) Tap Conductors. Tap conductors must be protected against overcurrent as follows:

    1. Household Ranges and Cooking Appliances and Other Loads -- 210.19(A)(3) and (4)
    2. Fixture Wire -- 240.5(B)(2)
    3. Location in Circuit -- 240.21
    4. Reduction in Ampacity Size of Busway -- 368.17(B)
    5. Feeder or Branch Circuits (busway taps) -- 368.17(C)
    6. Single Motor Taps -- 430.53(D)

    (F) Transformer Secondary Conductors. The primary overcurrent protection device sized in accordance with 450.3(B) can protect the secondary conductors of a 2-wire system or a 3-wire, 3-phase, delta/delta connected system, provided the primary protection device does not exceed the value determined by multiplying the secondary conductor ampacity by the secondary-to-primary transformer voltage ratio.

    (G) Overcurrent for Specific Applications. Overcurrent protection for specific equipment and conductors must comply with that referenced in Table 240.4(G).

    • Air-conditioning and refrigeration equipment and circuit conductors must be protected against overcurrent in accordance with 440.22. Typically, the branch-circuit conductor and protection size is marked on the equipment nameplate [440.4(A)].
    • Motor circuit conductors must be protected against short circuits and ground faults in accordance with 430.52 and 430.62 [430.51].
    • Motor control circuit conductors must be sized and protected in accordance with 430.72.
    • Remote-control, signaling, and power-limited circuit conductors must be protected against overcurrent according to 725.23 and 725.41.
    Editor's note: This information was extracted from Mike Holt's textbook, Understanding the National Electrical Code.

    Achieve Your
    Performance Goals

    Anticipate, prevent and troubleshoot motors, electrical and equipment maintenance with fast, accurate non-contact temperature measurements with Fluke infrared thermometers.

    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: Disturbed by this mix and match arrangement.

    Code Q&A
    By Mike Holt
    Q. Is liquidtight flexible metal conduit (LFMC) permitted under the raised floor of a computer room? If yes, must it be secured?

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

    Code Quiz
    By Steven Owen
    Q. What is the minimum size NM cable required for an electric space-heating branch circuit installed 3 inches above a heated ceiling (with no thermal insulation) in a dwelling unit? The branch circuit will supply a calculated load of 12A.

    A) 14 AWG NM
    B) 12 AWG NM
    C) 10 AWG NM
    D) 12 AWG Type TC

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

    Cool Electronic Cabinets
    EXAIR's low cost Cabinet Coolers prevent hot weather failures by keeping electrical enclosures cool. 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.

    You are subscribed to this newsletter as #email#

    For questions concerning delivery of this newsletter, please contact our Customer Service Department at:
    Customer Service Department
    A Prism Business Media publication
    US Toll Free: 866-505-7173
    International: 847-763-9504

    Prism Business Media
    9800 Metcalf Avenue
    Overland Park, KS 66212

    Copyright 2006, Prism Business Media. All rights reserved. This article is protected by United States copyright and other intellectual property laws and may not be reproduced, rewritten, distributed, re-disseminated, transmitted, displayed, published or broadcast, directly or indirectly, in any medium without the prior written permission of Prism Business Media.