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Part 1 of this article on changes in the 2011 National Electrical Code (NEC) addressed significant revisions to Article 90 and Chapter 1. Part 2 of this series reviewed significant revisions in NEC Chapter 2. Part 3 picks up with changes in NEC Chapter 3, which provides the requirements for electrical wiring methods and materials.
Chapter 3 Wiring Methods and Materials
Section 300.4(E) (Revision)
Section 300.4(E) was new in the 2008 NEC and only addressed protection for cables and raceways installed under roof decking. This current revision provides protection for boxes and makes clear that the minimum distance from the “lowest” point (bottom) of the decking material to the top of the wiring method or box is not permitted to be less than 1 inches. The previous rule required the measurement to be from the “nearest” surface of the decking material. This section has also been revised to restrict wiring from being installed in concealed spaces above the roof decking between the insulation and roofing material. Wiring installed in such locations is subject to physical damage during roofing and reroofing operations.
Section 300.11(A)(2) (Revision)
The revision in Section 300.11(A)(2) was to include an identification requirement for support wires that are installed in accordance with approved wiring methods and are located above a nonfire-rated floor-ceiling or roof-ceiling assembly. The change aligns this identification requirement with an identical requirement in 300.11(A)(1) for identification of additional support wires for wiring methods installed above a fire-rated floor-ceiling or roof-ceiling assemblies. The revision improves consistency for identical installations covered in different Code sections.
Section 310.10(E) (Revision and Renumbering)
Section 310.6 was renumbered as 310.10(E) as a result of action by Code-Making Panel 6 to more logically reorganize Article 310. In addition to the renumbering, 310.10(E) was revised to with two technical changes. The first sentence was revised to clarify that nonshielded, ozone-resistant insulated conductors having a maximum phase-to-phase voltage of 5,000 volts are permitted in Type MC (metal-clad) cables in industrial establishments under controlled conditions that include qualified people servicing the installation. The words “equipment grounding conductor” have been added to the second sentence of the requirement. This revision clarifies that the shielding of medium- and high-voltage cables can be connected to an equipment-grounding conductor in addition to a grounding electrode, grounding-electrode conductor, or grounding busbar within equipment. The second revision incorporates a new Exception No. 2 to allow listed nonshielded cables up to 5,000 volts to be used as replacements on existing equipment under restrictive conditions and only in industrial establishments.
Section 310.15(B) Tables (Revision)
The tables in Article 310 have been renumbered, and the previous number for each table has been added to follow in parentheses for the 2011 NEC cycle. The second sentence is new and provides a significant correlation to Section 110.14(C). This revision clarifies that the ampacity for a conductor’s temperature rating may be used for application of the temperature correction and adjustment factors, but the lower of the corrected and adjusted ampacity or the ampacity for the temperature rating of the conductor must be used. The actual temperature rating of the conductor can be used as the starting point for ampacity adjustment or conductor-correction factors as long as the resultant ampacity does not exceed the temperature limitations of the termination (60 or 75 degrees). The tie to Section 110.14(C) and the additional text help to promote more consistent application of conductor ampacity adjustment and correction factors.
Section 312.8 Switch and Overcurrent Device Enclosures With Splices, Taps, and Feed-Through Conductors (Revision)
The revisions to this section improve clarity and usability and change the driving language from restrictive to permissive text with conditions. The section is now presented in list format, with list items (1) and (2) addressing fill capacity of cross--sectional areas of enclosures previously covered by this rule. New list item (3) incorporates a requirement for a warning label that identifies the closest disconnecting means for conductors that pass through an enclosure. This revision is an improvement in worker safety because it draws attention to the possibilities of the presence of energized conductors in the enclosure even when the supply circuit is de-energized, because the feed-through conductors could be supplied from another source. The warning label provides workers with direction to the disconnecting means for the conductors feeding through the equipment, so they can be de-energized as may be necessary so that certain work tasks can be performed in a safe manner.
Section 314.70 Pull and Junction Boxes, Conduit Bodies, and Handhole Enclosures for Use on Systems Over 600 Volts, Nominal (Revision)
The title and text of 314.70 have been revised to incorporate conduit bodies into the requirements of Part IV of Article 314. The applicable requirements for conduit bodies in Parts I and II of the article differ from those for conduit bodies used for installations over 600 volts, and thus, need to be listed separately. The revisions to this section incorporate conduit bodies under the applicable rules. Where conduit bodies are used in installations over 600 volts, they are required to meet the applicable requirements contained in Part IV or Article 314. A new subdivision (C) now addresses handhole enclosures within the requirements of Part IV, which was inadvertently overlooked when handholes were added to Article 314. The result is requirements that address conduit bodies and handholes used in over 600-volt installations where none previously existed.
Section 314.71 Size of Pull and Junction Boxes, Conduit Bodies, and Handhole Enclosures (Revision)
Section 314.71 has been revised to include conduit bodies in the sizing requirements of this rule. Where conduit bodies are used in installations over 600 volts, they are required to meet the applicable requirements contained in Part IV or Article 314.
Section 328.14 Installation (New)
This new section has been added to Article 328 to require that the installation of Type MV (medium-voltage) cables be performed only by qualified people. Proper installation of any raceway with conductors or cable assembly requires a certain amount of expertise and experience. The installation of medium-voltage cable is very often misunderstood, in that installers are often under the misconception that these cables can be installed like any other conductor or cable. Manufacturers of Type MV cable provide various recommendations on cable-pulling tensions, sidewall bearing pressures, and bending radius for the cable that must be followed when medium-voltage cables are installed. These recommendations ensure the cable is not damaged during the installation. This new requirement mandates that only qualified people install Type MV cable. A new informational note has also been added to reference IEEE 576, which is the recommended practice for installing, terminating and splicing medium-voltage power cables in commercial and industrial locations.
Sections 348.30(A) and 350.30(A) Securely Fastened (Revision)
This revision applies to the support requirements for flexible-metal conduit (FMC) and liquidtight flexible-metal conduit (LFMC). New text has been added to Exception No. 2 that permits support in excess of 12 inches of conduit termination where flexibility is required after installation. This new text requires that the distance permitted be measured from the last point of support. This revision clarifies that the length of unsupported flexible-metal conduit or liquidtight flexible-metal conduit may be measured only from the last point it was securely fastened in place.
Sections 348.60 and 350.60 Grounding and Bonding (Revision)
This revised text clearly states where an equipment-grounding conductor is required in short lengths of FMC and LFMC that are permitted to be used without an equipment-grounding conductor under the conditions Section 250.118 outlines. This requirement is intended to offset the movement of flexible-metal conduits connected to equipment from vibration or movement that could compromise continuity of the ground-fault path. This revised text now clarifies that, where FMC or LFMC is used for one of the following reasons, an equipment-grounding conductor is required:
1. Flexibility is necessary to minimize the transmission of vibration from equipment, for example, as a connection to a motor or transformer.
2. Flexibility is necessary for equipment that requires movement after installation, for example, an industrial control panel mounted to a hinged panel to allow equipment access.
Article 399 Outdoor, Overhead Conductors, Over 600 Volts (New)
This new article addresses outdoor overhead conductors rated over 600 volts. Its requirements apply to overhead conductors installed as services, feeders or branch circuits. This new article is part of an effort to improve requirements in the NEC where services, feeders and branch circuits over 600 volts are installed outdoors. As such, it includes requirements for high-voltage outdoor installations. All conductors on the load side of the “service point” are “premises wiring” installations over which the NEC has jurisdiction and should be applied.
This concludes Part 3 in this series on 2011 NEC changes. Part 4 will be in the January issue of Electrical Contractor magazine. For more detailed information about these or any other important NEC changes, refer to the textbook, “2011 NEC Significant Changes,” published by the National Joint Apprenticeship and Training Committee. Additional detailed information about each proposal and comment resulting in NEC changes is provided in the NFPA Report on Proposals and Report on Comments for the 2011 NEC. It is also highly recommended that a copy of the 2011 NEC be referred to for complete information about the rules that have been added or revised in this edition.
JOHNSTON is NECA’s executive director of standards and safety. He is former director of education, codes and standards for IAEI; a member of the IBEW; and an active member of the NFPA Electrical Section, Education Section, and the UL Electrical Council. Reach him at [email protected].
About The Author
JOHNSTON is NECA’s executive director of codes and standards. He is a member of the NEC Correlating Committee, NFPA Standards Council, IBEW, UL Electrical Council and NFPA’s Electrical Section. Reach him at [email protected].