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avity of a non-fire-rated floor–ceiling or roof–ceiling assembly shall not be secured to, or supported by, the ceiling assembly, including the ceiling support wires. An independent means of secure support shall be provided and shall be permitted to be attached to the assembly. Where independent...

avity of a non-fire-rated floor–ceiling or roof–ceiling assembly shall not be secured to, or supported by, the ceiling assembly, including the ceiling support wires. An independent means of secure support shall be provided and shall be permitted to be attached to the assembly. Where independent support wires are used, they shall be distinguishable by color, tagging, or other effective means. Exception: The ceiling support system shall be permitted to support branch-circuit wiring and associated equipment where installed in accordance with the ceiling system manufacturer’s instructions. (C) Raceways Used as Means of Support. Raceways shall be used only as a means of support for other raceways, cables, or nonelectrical equipment under any of the following conditions: (1) Where the raceway or means of support is identified as a means of support Where the raceway contains power supply conductors for electrically controlled equipment and is used to support Class 2 or Class 3 circuit conductors or cables that are solely for the purpose of connection to the equipment control circuits Where the raceway is used to support boxes or conduit bodies in accordance with 314.23 or to support luminaires in accordance with 410.36(E) ENHANCED CONTENT Collapse As a general rule, this section prohibits supporting cables by securing them to the exterior of a raceway. Electrical, telephone, and data cables wrapped around a raceway can impede dissipation of heat from the raceway, thus affecting the temperature of the conductors contained in the raceway. The weight from large bundles of cables can compromise the mechanical integrity of the raceway system. For those reasons, this section also prohibits the use of a raceway as a means of support for nonelectrical equipment, such as suspended ceilings, water pipes, and signs. Class 2 conductors or cables are allowed to be supported by a raceway as long as the power supply conductors are inside the raceway or functionally associated with the attached Class 2 circuit conductors. For example, the thermostat conductors for heating or air-conditioning units are permitted to be supported by the conduit supplying power to the unit. Cables Not Used as Means of Support. Cable wiring methods shall not be used as a means of support for other cables, raceways, or nonelectrical equipment. 300.12 Mechanical Continuity — Raceways and Cables. Raceways, cable armors, and cable sheaths shall be continuous between cabinets, boxes, conduit bodies, fittings, or other enclosures or outlets. Exception No. 1: Short sections of raceways used to provide support or protection of cable assemblies from physical damage shall not be required to be mechanically continuous. Exception No. 2: Raceways and cables installed into the bottom of open bottom equipment, such as switchboards, motor control centers, and floor or pad-mounted transformers, shall not be required to be mechanically secured to the equipment. 300.13 Mechanical and Electrical Continuity — Conductors. (A) General. Conductors in raceways shall be continuous between outlets, boxes, devices, and so forth. There shall be no splice or tap within a raceway unless permitted by 300.15, 368.56(A), 376.56, 378.56, 384.56, 386.56, 388.56, or 390.56. Device Removal. In multiwire branch circuits, the continuity of a grounded conductor shall not depend on device connections such as lampholders, receptacles, and so forth where the removal of such devices would interrupt the continuity. ENHANCED CONTENT Collapse Grounded conductors (neutrals) of multiwire branch circuits supplying receptacles, lampholders, or other devices are not permitted to depend on terminal connections for continuity between devices. For multiwire installations, a splice can be made with a jumper connected to the terminal or the neutral can be looped. This allows a receptacle or device to be replaced without interrupting the continuity of energized downstream line-to-neutral loads. Opening the neutral could cause unbalanced voltages, and a considerably higher voltage would be impressed on one part of a multiwire branch circuit, especially if the downstream line-to-neutral loads were appreciably unbalanced. 300.14 Length of Free Conductors at Outlets, Junctions, and Switch Points. At least 150 mm (6 in.) of free conductor, measured from the point in the box where it emerges from its raceway or cable sheath, shall be left at each outlet, junction, and switch point for splices or the connection of luminaires or devices. The 150 mm (6 in.) free conductor shall be permitted to be spliced or unspliced. Where the opening to an outlet, junction, or switch point is less than 200 mm (8 in.) in any dimension, each conductor shall be long enough to extend at least 75 mm (3 in.) outside the opening. Exception: Conductors that are not spliced or terminated at the outlet, junction, or switch point shall not be required to comply with 300.14. ENHANCED CONTENT Collapse A conductor must have enough slack for the connections to be made easily. The length of slack (free conductor) required for the box size is illustrated below. The exception excludes conductors running through a box, which should have sufficient slack to prevent physical damage from the insertion of devices or from the use of luminaire studs, hickeys, or other luminaire supports within the box. 300.15 Boxes, Conduit Bodies, or Fittings — Where Required. A box shall be installed at each outlet and switch point for concealed knob-and-tube wiring. Fittings and connectors shall be used only with the specific wiring methods for which they are designed and listed. Where the wiring method is conduit, tubing, Type AC cable, Type MC cable, Type MI cable, nonmetallic-sheathed cable, or other cables, a box or conduit body shall be installed at each outlet point, switch point, conductor splice point, conductor junction point, conductor termination point, wiring method transition point, or conductor pull point, unless otherwise permitted in 300.15(A) through (L). Wiring Methods with Interior Access. A box or conduit body shall not be required for each splice, junction, switch, pull, termination, or outlet points in wiring methods with removable covers, such as wireways, multioutlet assemblies, auxiliary gutters, and surface raceways. The covers shall be accessible after installation. Equipment. An integral junction box or wiring compartment as part of approved equipment shall be permitted in lieu of a box. Protection. A box or conduit body shall not be required where cables enter or exit from conduit or tubing that is used to provide cable support or protection against physical damage. A fitting shall be provided on the end(s) of the conduit or tubing to protect the cable from abrasion. Type MI Cable. A box or conduit body shall not be required where accessible fittings are used for straight-through splices in mineral-insulated metal-sheathed cable. Integral Enclosure. A wiring device with integral enclosure identified for the use, having brackets that securely fasten the device to walls or ceilings of conventional on-site frame construction, for use with nonmetallic-sheathed cable, shall be permitted in lieu of a box or conduit body. Informational Note: See 334.30(C); 545.10; 550.15(I); 551.47(E), Exception No. 1; and 552.48(E), Exception No. 1. ENHANCED CONTENT Collapse This requirement applies to a device with an integral enclosure (boxless device), examples of which are pictured below. (Courtesy of Legrand®) (Courtesy of Sillites®) Fitting. A fitting identified for the use shall be permitted in lieu of a box or conduit body where conductors are not spliced or terminated within the fitting. The fitting shall be accessible after installation, unless listed for concealed installation. Direct-Buried Conductors and Cables. As permitted in 300.5(E), a box or conduit body shall not be required for splices and taps in direct-buried conductors and cables. Insulated Devices. As permitted in 334.40(B), a box or conduit body shall not be required for insulated devices supplied by nonmetallic-sheathed cable. Enclosures. A box or conduit body shall not be required where a splice, switch, terminal, or pull point is in a cabinet or cutout box, in an enclosure for a switch or overcurrent device as permitted in 312.8, in a motor controller as permitted in 430.10(A), or in a motor control center. Luminaires. A box or conduit body shall not be required where a luminaire is used as a raceway as permitted in 410.64. Embedded. A box or conduit body shall not be required for splices where conductors are embedded as permitted in 424.40, 424.41(D), 426.22(C), 426.24(A), and 427.19(A). Manholes and Handhole Enclosures. A box or conduit body shall not be required for conductors in manholes or handhole enclosures, except where connecting to electrical equipment. The installation shall comply with Part V of Article 110 for manholes, and 314.30 for handhole enclosures. 300.16 Raceway or Cable to Open or Concealed Wiring. Box, Conduit Body, or Fitting. A box, conduit body, or terminal fitting having a separately bushed hole for each conductor shall be used wherever a change is made from conduit, electrical metallic tubing, electrical nonmetallic tubing, nonmetallic-sheathed cable, Type AC cable, Type MC cable, or mineral-insulated, metal-sheathed cable and surface raceway wiring to open wiring or to concealed knob-and-tube wiring. A fitting used for this purpose shall contain no taps or splices and shall not be used at luminaire outlets. A conduit body used for this purpose shall contain no taps or splices unless it complies with 314.16(C)(2). ENHANCED CONTENT Collapse A fitting is permitted instead of a box where a cable system transitions to a raceway to protect it against physical damage. For example, when a nonmetallic-sheathed cable runs overhead on floor joists, then needs protection where it drops down on a masonry wall to supply a receptacle, a short length of raceway is installed to the outlet device box. The cable is then inserted into the raceway and secured by a combination fitting that is fastened to the end of the raceway. Bushing. A bushing shall be permitted in lieu of a box or terminal where the conductors emerge from a raceway and enter or terminate at equipment, such as open switchboards, unenclosed control equipment, or similar equipment. The bushing shall be of the insulating type for other than lead-sheathed conductors. 300.17 Number and Size of Conductors and Cables in Raceway. The number and size of conductors and cables in any raceway shall not be more than will permit dissipation of the heat and ready installation or withdrawal of the conductors or cables without damage to the conductors or cables, or to their insulation. Informational Note: See the following sections of this Code: intermediate metal conduit, 342.22; rigid metal conduit, 344.22; flexible metal conduit, 348.22; liquidtight flexible metal conduit, 350.22; PVC conduit, 352.22; HDPE conduit, 353.22; RTRC, 355.22; liquidtight nonmetallic flexible conduit, 356.22; electrical metallic tubing, 358.22; flexible metallic tubing, 360.22; electrical nonmetallic tubing, 362.22; cellular concrete floor raceways, 372.22; cellular metal floor raceways, 374.22; metal wireways, 376.22; nonmetallic wireways, 378.22; surface metal raceways, 386.22; surface nonmetallic raceways, 388.22; underfloor raceways, 390.22; fixture wire, 402.7; theaters, 520.6; signs, 600.31(C); elevators, 620.33; audio signal processing, amplification, and reproduction equipment, 640.23(A) and 640.24; Class 1 circuits, 724.3(A); Class 2, Class 3, Class 4, and power-limited fire alarm (PLFA) circuits, 722.3(A); non-power-limited fire alarm (NPLFA) circuits, 760.3(H); and optical fiber cables and raceways, 770.110(B). 300.18 Raceway Installations. Complete Runs. Raceways other than busways, listed manufactured assemblies in accordance with 604.100, or exposed raceways having hinged or removable covers shall be installed complete between outlet, junction, or splicing points prior to the installation of conductors or cables. Where required to facilitate the installation of utilization equipment, the raceway shall be permitted to be initially installed without a terminating connection at the equipment. Prewired raceway assemblies shall be permitted only where specifically permitted in this Code for the applicable wiring method. Exception: Short sections of raceways used to contain conductors or cable assemblies for protection from physical damage shall not be required to be installed complete between outlet, junction, or splicing points. ENHANCED CONTENT Collapse One of the primary functions of a raceway is to provide physical protection for conductors. If raceways are incomplete at the time of conductor installation, a greater possibility of damage to the conductors exists. The installation of conductors in an incomplete raceway is permitted for connection of utilization equipment. The motor installation illustrated below is a typical example, in which the motor will be supplied through liquidtight flexible metal conduit (LFMC) that terminates in the motor terminal box through a 90-degree angle connector. Wiring a luminaire whip prior to connecting a luminaire is also permitted by this section. Welding. Metal raceways shall not be supported, terminated, or connected by welding to the raceway unless specifically designed to be or otherwise specifically permitted to be in this Code. 300.19 Supporting Conductors in Vertical Raceways. (A) Spacing Intervals — Maximum. Conductors in vertical raceways shall be supported if the vertical rise exceeds the values in Table 300.19(A). At least one support method shall be provided for each conductor at the top of the vertical raceway or as close to the top as practical. Intermediate supports shall be provided as necessary to limit supported conductor lengths to not greater than those values specified in Table 300.19(A). Exception: Steel wire armor cable shall be supported at the top of the riser with a cable support that clamps the steel wire armor. A safety device shall be permitted at the lower end of the riser to hold the cable in the event there is slippage of the cable in the wire-armored cable support. Additional wedge-type supports shall be permitted to relieve the strain on the equipment terminals caused by expansion of the cable under load. Table 300.19(A) Spacings for Conductor Supports Conductors Conductor Size Support of Conductors in Vertical Raceways Aluminum or Copper-Clad Aluminum Copper m ft m ft 18 AWG through 8 AWG Not greater than 30 100 30 100 6 AWG through 1/0 AWG Not greater than 60 200 30 100 2/0 AWG through 4/0 AWG Not greater than 55 180 25 80 Over 4/0 AWG through 350 kcmil Not greater than 41 135 18 60 Over 350 kcmil through 500 kcmil Not greater than 36 120 15 50 Over 500 kcmil through 750 kcmil Not greater than 28 95 12 40 Over 750 kcmil Not greater than 26 85 11 35 ENHANCED CONTENT Collapse This requirement prevents the weight of the conductors from damaging the insulation where they leave the conduit and prevents the conductors from being pulled out of the terminals. Support bushings or cleats such as those shown below may be used, in addition to many other types of grips manufactured for this purpose. Fire-Resistive Cables and Conductors. Support methods and spacing intervals for fire-resistive cables and conductors shall comply with any restrictions provided in the listing of the electrical circuit protective system or fire-resistive cable system used and in no case shall exceed the values in Table 300.19(A). Support Methods. One of the following methods of support shall be used: Clamping devices constructed of or employing insulating wedges inserted in the ends of the raceways. Where clamping of insulation does not adequately support the cable, the conductor also shall be clamped. Inserting boxes at the required intervals in which insulating supports are installed and secured in an approved manner to withstand the weight of the conductors attached thereto, the boxes being provided with covers. In junction boxes, deflecting the cables not less than 90 degrees and carrying them horizontally to a distance not less than twice the diameter of the cable, with the cables being carried on two or more insulating supports and additionally secured thereto by tie wires, if desired. Where this method is used, cables shall be supported at intervals not greater than 20 percent of the support spacing in Table 300.19(A). Other approved means. 300.20 Induced Currents in Ferrous Metal Enclosures or Ferrous Metal Raceways. Conductors Grouped Together. Where conductors carrying alternating current are installed in ferrous metal enclosures or ferrous metal raceways, they shall be arranged so as to avoid heating the surrounding ferrous metal by induction. To accomplish this, all phase conductors and, where used, the grounded conductor and all equipment grounding conductors shall be grouped together. Exception No. 1: Equipment grounding conductors for certain existing installations shall be permitted to be installed separate from their associated circuit conductors where run in accordance with 250.130(C). Exception No. 2: A single conductor shall be permitted to be installed in a ferromagnetic enclosure and used for skin-effect heating in accordance with 426.42 and 427.47. ENHANCED CONTENT Collapse Nonferrous metals are defined as those with little or no iron in their composition. Some of the more common nonferrous (nonmagnetic) metals include aluminum, brass, bronze, copper, lead, tin, and zinc. Section 300.20(A) addresses the problem of induction from ac conductors into ferrous (magnetic) metal enclosures and ferrous raceways. Induction into raceways and enclosures can lead to overheating and is also a shock hazard. Individual Conductors. Where a single conductor carrying alternating current passes through metal with magnetic properties, the inductive effect shall be minimized by either cutting slots in the metal between the individual holes through which the individual conductors pass or passing all the conductors in the circuit through an insulating wall sufficiently large for all of the conductors of the circuit. Exception: In the case of circuits supplying vacuum or electric-discharge lighting systems or signs or X-ray apparatus, the currents carried by the conductors are so small that the inductive heating effect can be ignored where these conductors are placed in metal enclosures or pass through metal. Informational Note: Because aluminum is not a magnetic metal, there will be no heating due to hysteresis; however, induced currents will be present. They will not be of sufficient magnitude to require grouping of conductors or special treatment in passing conductors through aluminum wall sections. 300.21 Spread of Fire or Products of Combustion. Electrical installations in hollow spaces, vertical shafts, and ventilation or air-handling ducts shall be made so that the possible spread of fire or products of combustion will not be substantially increased. Openings around electrical penetrations into or through fire-resistant-rated walls, partitions, floors, or ceilings shall be firestopped using approved methods to maintain the fire resistance rating. Informational Note: Directories of electrical construction materials published by qualified testing laboratories contain many listing installation restrictions necessary to maintain the fire-resistive rating of assemblies where penetrations or openings are made. Building codes also contain restrictions on membrane penetrations on opposite sides of a fire-resistance-rated wall assembly. An example is the 600-mm (24-in.) minimum horizontal separation that usually applies between boxes installed on opposite sides of the wall. Assistance in complying with the requirements of 300.21 can be found in building codes, fire resistance directories, and product listings. ENHANCED CONTENT Collapse Cables, cable trays, and raceways must be installed through fire-rated walls, floors, and ceiling assemblies using an approved firestop method so they do not contribute to the spread of fire or the products of combustion. In the UL Guide Information for Electrical Equipment, which can be found at productspec.ul.com, Category XHEZ covers through-penetration firestop systems, and Category XHJI covers firestop devices. These two category sections provide valuable information concerning application, installation, and use of firestop systems and firestop devices. A firestop system, the seals for which are pictured below, meets the requirements of 300.21. (Courtesy of O-Z/Gedney, a division of EGS Electrical Group) Using the proper protection techniques is crucial in limiting or stopping flame, excessive temperature, and smoke from passing through fire-rated construction. Sleeves for the protection of cables passing through fire-rated construction must be fire-stopped to the original rating of the assembly both around the sleeve and around the cables inside the sleeve. The structural integrity of the floor or wall assembly needs to be evaluated when openings for the penetrating items are being provided. The rating of the building assembly being penetrated by electrical cables or conduits must also be determined. This information is available from construction documents or building codes. Once the fire resistance rating has been determined, the properties and types of electrical penetration required [whether metal or nonmetallic cable(s), conduit(s), or even cable trays] must be determined. Next, the selected method of firestopping must be approved by the AHJ. Building codes generally require that a firestop system or device be tested. ASTM E814- 2013, Standard Test Method for Fire Tests of Penetration Firestop Systems, and ANSI/UL 1479-2015, Fire Tests of Penetration Firestops, are two examples of such test methods. Certain construction practices can be used in lieu of tested systems or devices. NFPA 221, Standard for High Challenge Fire Walls, Fire Walls, and Fire Barrier Walls, as well as some building codes, contains a statement somewhat similar to the following: Where concrete, grout, or mortar has been used to fill the annular spaces around . . . steel conduit or tubing that penetrates one or more concrete or masonry walls, the nominal diameter of each penetrating item shall not exceed 6 in., the opening size shall not exceed 144 in.2, and the thickness of the concrete, grout, or mortar shall be the full thickness of the assembly. 300.22 Wiring in Ducts Not Used for Air Handling, Fabricated Ducts for Environmental Air, and Other Spaces for Environmental Air (Plenums). The requirements of this section shall apply to the installation and uses of electrical wiring and equipment in ducts used for dust, loose stock, or vapor removal; ducts specifically fabricated for environmental air; and other spaces used for environmental air (plenums). Informational Note: See Part VI of Article 424 for requirements on duct heaters. ENHANCED CONTENT Collapse Other codes and standards refer to all spaces that move air as plenums, including spaces that the NEC identifies as “other spaces.” Some of the terms used to describe this space include plenum, ceiling cavity plenum, and raised floor plenum. Products are often required to be marked as “suitable for use in other spaces for environmental air” or equivalent language to comply with requirements in the NEC. Section 300.22(B) addresses ducts and spaces used solely for the movement of environmental air. In 300.22(C), the term plenum appears with other spaces used for environmental air to make it clear that it applies to structures that are not fabricated specifically to handle environmental air as the primary purpose but that handle the air, nonetheless. Ducts for Dust, Loose Stock, or Vapor Removal. No wiring systems of any type shall be installed in ducts used to transport dust, loose stock, or flammable vapors. No wiring system of any type shall be installed in any duct, or shaft containing only such ducts, used for vapor removal or for ventilation of commercial-type cooking equipment. Ducts Specifically Fabricated for Environmental Air. Equipment, devices, and the wiring methods specified in this section shall be permitted within such duc