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November 13, 2007 A Penton Media Publication Vol. V No. 21

314.16 Number of 6 AWG and Smaller Conductors in Boxes and Conduit Bodies

What's Wrong Here?

Code Q&A

Code Quiz

EC&M Code Change Conferences

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    Top 50 NEC Rules

    314.16 Number of 6 AWG and Smaller Conductors in Boxes and Conduit Bodies

    By Mike Holt
    Boxes containing 6 AWG and smaller conductors must be sized to provide sufficient free space for all conductors, devices, and fittings. In no case can the volume of that box, as calculated in 314.16(A), be less than the volume requirement as calculated in 314.6(B). Conduit bodies must be sized in accordance with 314.16(C). Note: The requirements for sizing boxes and conduit bodies containing conductors 4 AWG and larger are contained in 314.28.

    The volume of a box includes the total volume of its assembled parts, including plaster rings, extension rings, and domed covers that are either marked with their volume in cubic inches or are made from boxes listed in Table 314.16(A).

    The calculated conductor volume determined by (1) through (5) and Table 314.16(B) are added together to determine the total volume of the conductors, devices, and fittings. Raceway and cable fittings, including locknuts and bushings, are not counted for box fill calculations.

    Each conductor that runs through a box and does not have 6 inches of free conductor for splices or terminations in accordance with 300.14, and each conductor that terminates in a box is counted as a single conductor volume in accordance with Table 310.16(B). Conductors that originate and terminate within the box, such as pigtails, aren't counted at all. An Exception notes: Equipment grounding (bonding) conductors, and not more than four 16 AWG and smaller fixture wires, can be omitted from box fill calculations if they enter the box from a domed luminaire or similar canopy, such as a ceiling paddle fan canopy. Caution: Conductor loops occupy space and a box can be excessively filled if we do not take into consideration the increased conductor volume. This can create a serious fire hazard, especially when an electronic device is installed in an outlet box without adequate room for heat dissipation.

    One or more internal cable clamps count as a single conductor volume in accordance with Table 310.16(B), based on the largest conductor that enters the box. Cable connectors that have their clamping mechanism outside the box aren't counted.

    Each luminaire stud or luminaire hickey counts as a single conductor volume in accordance with Table 310.16(B), based on the largest conductor that enters the box.

    Each device yoke (regardless of the ampere rating of the device) counts as two conductor volumes in accordance with Table 310.16(B), based on the largest conductor that terminates on the device.

    All equipment grounding (bonding) conductors in a box count as a single conductor volume in accordance with Table 310.16(B), based on the largest equipment grounding (bonding) conductor that enters the box. Equipment grounding (bonding) conductors for isolated ground circuits count as a single conductor volume in accordance with Table 310.16(B).

    Splices are only permitted in conduit bodies that are legibly marked, by the manufacturer, with their volume. The maximum number of conductors permitted in a conduit body is limited in accordance with 314.16(B).

    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: Indecent exposure.

    Code Q&A
    By Mike Holt
    Q. When a conduit leaves a Class I, Division 1 classified paint spray room and goes under the concrete floor into a cabinet in the motor control room that is non-classified, is one sealing fitting in the paint mix room sufficient, or is an additional sealing fitting required in the non-classified area as well?

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

    Code Quiz
    By Steven Owen
    Q. When installing cable- or raceway-type wiring methods, installed in exposed or concealed locations under metal-corrugated sheet roof decking, the cable- or raceway-type wiring method shall be installed and supported so that the nearest outside surface of the cable or raceway is not less than 1 1/2 inches from the nearest surface of the roof decking. This rule applies to all cable- or raceway-type wiring methods except which one of the following?

    1. No exceptions. It applies to all cable- or raceway-type wiring methods.
    2. MI cable. It does not apply to MI cable with a 2-hour fire rating.
    3. Type TC -- ER cable as noted in 336.10(7).
    4. Rigid metal conduit (RMC) and intermediate metal conduit (IMC).

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

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    For additional information on the dates and locations of these events, click here.

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