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act by persons, shall be bonded to the grounding electrode systems in the area. ENHANCED CONTENT Collapse Metal fences around substations must be grounded to limit the rise of hazardous voltage on the fence. For situations where considerations of step potential and touch potential indicate that addi...

act by persons, shall be bonded to the grounding electrode systems in the area. ENHANCED CONTENT Collapse Metal fences around substations must be grounded to limit the rise of hazardous voltage on the fence. For situations where considerations of step potential and touch potential indicate that additional grounding and bonding design is required, alternative designs performed under engineering supervision are permitted. Article 300 General Requirements for Wiring Methods and Materials 300.1 Scope. (A) All Wiring Installations. This article covers general requirements for wiring methods and materials for all wiring installations unless modified by other articles in Chapter 3. Integral Parts of Equipment. The requirements of this article are not intended to apply to the conductors that form an integral part of equipment, such as motors, controllers, motor control centers, or factory-assembled control equipment or listed utilization equipment. ENHANCED CONTENT Collapse Requirements for specific wiring methods can be found in the Chapter 3 article governing that particular wiring method, but the overarching requirements for wiring methods are covered in this first article of Chapter 3. Chapters 5 through 7 modify some of the requirements of Article 300. Chapter 8 is not subject to the requirements of Article 300, except where specifically referenced. Article 300 also covers wiring requirements within boxes, conduit bodies, and fittings. Metric Designators and Trade Sizes. Metric designators and trade sizes for conduit, tubing, and associated fittings and accessories shall be in accordance with Table 300.1(C). Table 300.1(C) Metric Designators and Trade Sizes Metric Designator Trade Size 12 3⁄ 8 16 1⁄ 2 21 3⁄ 4 27 1 35 11⁄4 41 11⁄2 53 2 63 21⁄2 78 3 91 31⁄2 103 4 129 5 155 6 Note: The metric designators and trade sizes are for identification purposes only and are not actual dimensions. ENHANCED CONTENT Collapse Metric designators are used for traditional trade size threaded conduit. They do not change the physical dimensions or the traditional “NPT-type” threads of the conduit. Metric designators are simply another method of identifying the size of a circular raceway. Table 300.1(C) identifies a distinct metric designator for each circular raceway trade size. The unit of measure has not been included because it reflects a modular or relative measure rather than an exact dimension. As stated in the table footnote, the metric designators and trade sizes are not actual dimensions. Each metric designator-sized circular raceway is identical in dimension (including manufacturing tolerances) to its trade size counterpart in Table 4 of Chapter 9. Therefore, the Informative Annex C wire fill tables are applicable to both metric designator and trade size circular raceways. Threaded joints on circular raceways are a concern. For example, 344.6 requires rigid metal conduit (RMC) to be listed, and the appropriate product standard is ANSI/UL 6, Electrical Rigid Metal Conduit — Steel. Listed conduit must be threaded in accordance with ANSI/ASME B.1.20.1-1983, Pipe Threads, General Purpose (Inch). Therefore, only conduit threaded to the traditional dimension of ¾-inch taper per foot is acceptable. Simply stated, although conduit with a metric designator is permitted, metric-threaded conduit is not permitted by the NEC. This aligns with 500.8(E)(2), for example, which states that although metric threads are permitted on equipment, an adapter must be used for connection to conduit. 300.2 Limitations. (A) Voltage. Wiring methods specified in Chapter 3 shall be used for 1000 volts ac, 1500 volts dc, nominal, or less where not specifically limited elsewhere in Chapter 3. They shall be permitted for over 1000 volts ac, 1500 volts dc, nominal, where specifically permitted elsewhere in this Code. ENHANCED CONTENT Collapse Where an installation involves requirements using different voltage range limits, the limits within each applicable article must be observed. Temperature. Temperature limitation of conductors shall be in accordance with 310.14(A)(3). 300.3 Conductors. (A) Single Conductors. Single conductors specified in Table 310.4(1) shall only be permitted where installed as part of a recognized wiring method specified in Chapter 3. Exception: Individual conductors shall be permitted where installed as separate overhead conductors in accordance with 225.6. ENHANCED CONTENT Collapse Individual insulated conductors, such as THHN, are prohibited from use in other than recognized wiring methods. The exception points out two long-time permissions that allow individual conductors as overhead spans and as festoon lighting. Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, conduit body, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4). ENHANCED CONTENT Collapse All conductors of an individual circuit must be grouped in order to reduce inductive heating and to avoid increases in overall circuit impedance. See also 300.5(I) for a similar requirement pertaining to underground installations. Paralleled Installations. Conductors shall be permitted to be run in parallel in accordance with 310.10(G). The requirement to run all circuit conductors within the same raceway, auxiliary gutter, cable tray, trench, cable, or cord shall apply separately to each portion of the paralleled installation, and the equipment grounding conductors shall comply with 250.122. Connections, taps, or extensions made from paralleled conductors shall connect to all conductors of the paralleled set, grounded and ungrounded, as applicable. Parallel runs in cable trays shall comply with 392.20(C). Exception: Conductors installed in nonmetallic raceways run underground shall be permitted to be arranged as isolated phase, neutral, and grounded conductor installations. The raceways shall be installed in close proximity, and the isolated phase, neutral, and grounded conductors shall comply with 300.20(B). Grounding and Bonding Conductors. Equipment grounding conductors shall be permitted to be installed outside a raceway or cable assembly in accordance with 250.130(C) for certain existing installations or in accordance with 250.134, Exception No. 2, for dc circuits. Equipment bonding conductors shall be permitted to be installed on the outside of raceways in accordance with 250.102(E). Nonferrous Wiring Methods. Conductors in wiring methods with a nonmetallic or other nonmagnetic sheath, where run in different raceways, auxiliary gutters, cable trays, trenches, cables, or cords, shall comply with 300.20(B). Conductors in single-conductor Type MI cable with a nonmagnetic sheath shall comply with 332.31. Conductors of single-conductor Type MC cable with a nonmagnetic sheath shall comply with 330.31, 330.116, and 300.20(B). Column-Width Panelboard Enclosures. Where an auxiliary gutter runs between a column-width panelboard and a pull box, and the pull box includes neutral terminations, the neutral conductors of circuits supplied from the panelboard shall be permitted to originate in the pull box. Conductors of Different Systems. 1000 Volts ac, 1500 volts dc, Nominal, or Less. Conductors of ac and dc circuits rated 1000 volts ac, 1500 volts dc, nominal, or less shall be permitted to occupy the same equipment wiring enclosure, cable, or raceway. All conductors shall have an insulation rating equal to at least the maximum circuit voltage applied to any conductor within the enclosure, cable, or raceway. Secondary wiring to electric-discharge lamps of 1000 volts ac, 1500 volts dc, or less, if insulated for the secondary voltage involved, shall be permitted to occupy the same luminaire, sign, or outline lighting enclosure as the branch-circuit conductors. Informational Note No. 1: See 725.136(A) for Class 2 and Class 3 circuit conductors. Informational Note No. 2: See 690.31(B) for photovoltaic source and output circuits. ENHANCED CONTENT Collapse For systems of 1000 volts or less, the maximum circuit voltage in the raceway is what determines the minimum voltage rating required for the insulation of conductors, not the maximum insulation voltage rating of the conductors in the raceway. Specific systems with requirements elsewhere in the NEC have modifications to this allowance. See also 690.31(B), which prohibits the location of solar photovoltaic dc circuits within the same enclosure as conductors of other systems unless separated by a partition. See 700.10(B), which requires that circuit wiring for emergency systems be kept entirely independent of all other wiring and equipment. Over 1000 Volts ac, 1500 Volts dc, Nominal. Conductors of circuits rated over 1000 volts ac, 1500 volts dc, nominal, shall not occupy the same equipment wiring enclosure, cable, or raceway with conductors of circuits rated 1000 volts ac, 1500 volts dc, nominal, or less unless permitted in accordance with 305.4. 300.4 Protection Against Physical Damage. Where subject to physical damage, conductors, raceways, and cables shall be protected. Cables and Raceways Through Wood Members. Bored Holes. In both exposed and concealed locations, where a cable- or raceway-type wiring method is installed through bored holes in joists, rafters, or wood members, holes shall be bored so that the edge of the hole is not less than 32 mm (11⁄4 in.) from the edges of the wood member. Where this distance cannot be maintained, the cable or raceway shall be protected from penetration by screws or nails by a steel plate(s) or bushing(s) at least 1.6 mm (1⁄16 in.) thick, and of appropriate length and width, installed to cover the area of the wiring. Exception No. 1: Steel plates shall not be required to protect rigid metal conduit, intermediate metal conduit, rigid PVC conduit, RTRC, or electrical metallic tubing. Exception No. 2: A listed and marked steel plate less than 1.6 mm (1⁄16 in.) thick that provides equal or better protection against nail or screw penetration shall be permitted. ENHANCED CONTENT Collapse The intent is to prevent nails and screws from being driven into conductors, cables, and raceways. If the edge of a drilled hole is less than 1¼ inch from the nearest edge of a wood stud, a plate is required to prevent screws or nails from penetrating the stud far enough to injure a cable. Building codes limit the maximum size of bored or notched holes in studs, and 300.4(A)(2) indicates that consideration should be given to the size of notches in studs, so as not to affect the strength of the structure. (Courtesy of Hubbell Incorporated) Notches in Wood. Where there is no objection because of weakening the building structure, in both exposed and concealed locations, cables or raceways shall be permitted to be laid in notches in wood studs, joists, rafters, or other wood members where the cable or raceway at those points is protected from penetration by nails or screws by a steel plate at least 1.6 mm (1⁄16 in.) thick, and of appropriate length and width, installed to cover the area of the wiring. The steel plate shall be installed before the building finish is applied. Exception No. 1: Steel plates shall not be required to protect rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, or electrical metallic tubing. Exception No. 2: A listed and marked steel plate less than 1.6 mm (1⁄16 in.) thick that provides equal or better protection against nail or screw penetration shall be permitted. (B) Nonmetallic-Sheathed Cables and Electrical Nonmetallic Tubing Through Metal Framing Members. (1) Nonmetallic-Sheathed Cable. In both exposed and concealed locations where nonmetallic-sheathed cables pass through either factory- or field-punched, cut, or drilled slots or holes in metal members, the cable shall be protected by listed bushings or listed grommets covering all metal edges that are securely fastened in the opening prior to installation of the cable. Nonmetallic-Sheathed Cable and Electrical Nonmetallic Tubing. Where nails or screws are likely to penetrate nonmetallic-sheathed cable or electrical nonmetallic tubing, a steel sleeve, steel plate, or steel clip not less than 1.6 mm (1⁄16 in.) in thickness shall be used to protect the cable or tubing. Exception: A listed and marked steel plate less than 1.6 mm (1⁄16 in.) thick that provides equal or better protection against nail or screw penetration shall be permitted. Cables Through Spaces Behind Panels Designed to Allow Access. Cables or raceway-type wiring methods, installed behind panels designed to allow access shall be supported according to their applicable articles. ENHANCED CONTENT Collapse Cable- or raceway-type wiring installed above suspended ceilings with lift-up panels must not be laid on the suspended ceiling, which would inhibit access. Such wiring is required to be supported according to 300.11(B), 300.23, and the requirements of the Chapter 3 article applicable to the particular wiring method. Similarly, low-voltage, optical fiber, broadband, and communications cables also are not permitted to block access to equipment above a suspended ceiling. Cables and Raceways Parallel to Framing Members and Furring Strips. In both exposed and concealed locations, where a cable- or raceway-type wiring method is installed parallel to framing members, such as joists, rafters, or studs, or is installed parallel to furring strips, the cable or raceway shall be installed and supported so that the nearest outside surface of the cable or raceway is not less than 32 mm (11⁄4 in.) from the nearest edge of the framing member or furring strips where nails or screws are likely to penetrate. Where this distance cannot be maintained, the cable or raceway shall be protected from penetration by nails or screws by a steel plate, sleeve, or equivalent at least 1.6 mm (1⁄16 in.) thick. Exception No. 1: Steel plates, sleeves, or the equivalent shall not be required to protect rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, or electrical metallic tubing. Exception No. 2: For concealed work in finished buildings, or finished panels for prefabricated buildings where such supporting is impracticable, it shall be permissible to fish the cables between access points. Exception No. 3: A listed and marked steel plate less than 1.6 mm (1⁄16 in.) thick that provides equal or better protection against nail or screw penetration shall be permitted. ENHANCED CONTENT Collapse To prevent mechanical damage to cables and raceways from nails and screws, the raceways need the same level of physical protection at furring strips as they do at framing members. Two means of protection that generally apply to exposed or concealed work are described. The first method, shown below, is to position the nonmetallic-sheathed cables a clear distance from the nearest edge of the furring strip. The exhibit below illustrates the NM cable installed parallel to framing members and fastened to maintain clearance from the edge. The second method requires physical protection, such as a steel plate or a sleeve, if the 1¼-inch clearance cannot be maintained. Cables, Raceways, or Boxes Installed in or Under Metal-Corrugated Roof Decking. A cable, raceway, or box, installed in exposed or concealed locations under metal-corrugated sheet roof decking, shall be installed and supported so there is not less than 38 mm (11⁄2 in.) measured from the lowest surface of the roof decking to the top of the cable, raceway, or box. A cable, raceway, or box shall not be installed in concealed locations in metal-corrugated, sheet decking–type roof. Informational Note: Roof decking material is often repaired or replaced after the initial raceway or cabling and roofing installation and might be penetrated by screws or other mechanical devices designed to provide “hold down” strength of the waterproof membrane or roof insulating material. Exception No. 1: Rigid metal conduit and intermediate metal conduit, with listed steel or malleable iron fittings and boxes, shall not be required to comply with 300.4(E). Exception No. 2: The 38 mm (11⁄2in.) spacing is not required where metal-corrugated sheet roof decking is covered with a minimum thickness 50 mm (2 in.) concrete slab, measured from the top of the corrugated roofing. ENHANCED CONTENT Collapse For cables, raceways, and boxes installed below a metal-corrugated sheet roof decking installation, 300.4(E) requires at least 1½ inches of separation from any of the roof decking surface, as illustrated below. The 1½-inch dimension is measured from the lowest point of the roof deck to the top surface of the cable, raceway, or box. This section prohibits cables, raceways, or boxes from being installed in the space between the metal deck and the roofing material. Roof replacement materials are fastened in place with long screws, which penetrate the roof decking installation and could continue into cables and raceways installed below. Adequate space between the corrugated sheet metal roof deck installation and the cables and raceways below the deck will prevent future damage to the cable or raceway installation. The exception clarifies that this requirement does not apply to more robust metal raceways such as RMC and IMC. See also 410.10(F) for similar requirements for luminaires. Cables and Raceways Installed in Shallow Grooves. Cable- or raceway-type wiring methods installed in a groove, to be covered by wallboard, siding, paneling, carpeting, or similar finish, shall be protected by 1.6 mm (1⁄16 in.) thick steel plate, sleeve, or equivalent or by not less than 32-mm (11⁄4-in.) free space for the full length of the groove in which the cable or raceway is installed. Exception No. 1: Steel plates, sleeves, or the equivalent shall not be required to protect rigid metal conduit, intermediate metal conduit, rigid PVC conduit, RTRC, or electrical metallic tubing. Exception No. 2: A listed and marked steel plate less than 1.6 mm (1⁄16 in.) thick that provides equal or better protection against nail or screw penetration shall be permitted. (G) Fittings. Where raceways contain 4 AWG or larger insulated circuit conductors, and these conductors enter a cabinet, a box, an enclosure, or a raceway, prior to the installation of conductors, the conductors shall be protected in accordance with any of the following: (1) An identified fitting providing a smoothly rounded insulating surface A listed metal fitting that has smoothly rounded edges Separation from the fitting or raceway using an identified insulating material that is securely fastened in place Threaded hubs or bosses that are an integral part of a cabinet, box, enclosure, or raceway providing a smoothly rounded or flared entry for conductors Conduit bushings constructed wholly of insulating material shall not be used to secure a fitting or raceway. The insulating fitting or insulating material shall have a temperature rating not less than the insulation temperature rating of the installed conductors. ENHANCED CONTENT Collapse Heavy conductors and cables tend to stress the conductor insulation at raceway terminating points. Care must be taken at raceway and cable terminations to reduce the risk of insulation failure at conductor insulation stress points. This is often done by using insulating bushings or fittings with rounded edges; however, there are multiple options to achieve the desired protection of the insulation. The temperature ratings of the insulating bushing must coordinate with the insulation of the conductor to ensure that the conductor is protected for its entire life cycle. Whether provided separately or as part of a fitting, listed insulating bushings are colored black or brown to indicate a temperature rating of 150°C and any other color to indicate a rating of 90°C unless specifically marked for a higher temperature. The exhibit below shows an insulated thermoplastic or fiber bushing used to protect the conductors from chafing against a metal conduit fitting. Note the use of a double locknut, with one on the inside and one on the outside of the enclosure. The locknuts are necessary because the raceway cannot be secured by the fiber or plastic bushing. See also 342.46, 344.46, and 352.46 for further information relating to bushings. Structural Joints. A listed expansion/deflection fitting or other approved means shall be used where a raceway crosses a structural joint intended for expansion, contraction, or deflection, used in buildings, bridges, parking garages, or other structures. ENHANCED CONTENT Collapse Raceways can be damaged if improperly installed in structural construction joints, leaving conductors or cables exposed. Structural construction joints can experience shear and lateral loads due to gravity, expansion and contraction, and movement of the structure. Listed expansion/deflection fittings are available for use at structural joints. However, other approved means of protecting the integrity of the raceways system are permitted. 300.5 Underground Installations. (A) Minimum Cover Requirements. Direct-buried cable, conduit, or other raceways shall be installed to meet the minimum cover requirements of Table 300.5(A). Table 300.5(A) Minimum Cover Requirements, 0 to 1000 Volts ac, 1500 Volts dc, Nominal, Burial in Millimeters (Inches) Type of Wiring Method or Circuit Location of Wiring Method or Circuit Column 1 Direct Burial Cables or Conductors Column 2 Rigid Metal Conduit or Intermediate Metal Conduit Column 3 Electrical Metallic Tubing, Nonmetallic Raceways Listed for Direct Burial Without Concrete Encasement, or Other Approved Raceways Column 4 Residential Branch Circuits Rated 120 Volts or Less with GFCI Protection and Maximum Overcurrent Protection of 20 Amperes Column 5 Circuits for Control of Irrigation and Landscape Lighting Limited to Not More Than 30 Volts and Installed with Type UF or in Other Identified Cable or Raceway mm in. mm in. mm in. mm in. mm in. All locations not specified below 600 24 150 6 450 18 300 12 1501,2 61,2 In trench below 50 mm (2 in.) thick concrete or equivalent 450 18 150 6 300 12 150 6 150 6 Under a building 0 0 0 0 0 0 0 0 0 0 (in raceway or Type MC or Type MI cable identified for direct burial) (in raceway or Type MC or Type MI cable identified for direct burial) (in raceway or Type MC or Type MI cable identified for direct burial) Under minimum of 102 mm (4 in.) thick concrete exterior slab with no vehicular traffic and the slab extending not less than 152 mm (6 in.) beyond the underground installation 450 18 100 4 100 4 150 6 150 6 (direct burial) (direct burial) 100 4 100 4 (in raceway) (in raceway) Under streets, highways, roads, alleys, driveways, and parking lots 600 24 600 24 600 24 600 24 600 24 One- and two-family dwelling driveways and outdoor parking areas, and used only for dwelling-related purposes 450 18 450 18 450 18 300 12 450 18 In or under airport runways, including adjacent areas where trespassing is prohibited 450 18 450 18 450 18 450 18 450 18 1 A lesser depth shall be permitted where specified in the installation instructions of a listed low-voltage lighting system. 2 A depth of 150 mm (6 in.) shall be permitted for pool, spa, and fountain lighting, installed in a nonmetallic raceway, limited to not more than 30 volts where part of a listed low-voltage lighting system. Notes: Cover shall be defined as the shortest distance in mm (in.) measured between a point on the top surface of any direct-buried conductor, cable, conduit, or other raceway and the top surface of finished grade, concrete, or simi