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lar cover. Raceways approved for burial only where concrete encased shall require a concrete envelope not less than 50 mm (2 in.) thick. Lesser depths shall be permitted where cables and conductors rise for terminations or splices or where access is otherwise required. Where one of the wiring metho...

lar cover. Raceways approved for burial only where concrete encased shall require a concrete envelope not less than 50 mm (2 in.) thick. Lesser depths shall be permitted where cables and conductors rise for terminations or splices or where access is otherwise required. Where one of the wiring method types listed in Columns 1 through 3 is used for one of the circuit types in Columns 4 and 5, the shallowest depth of burial shall be permitted. Where solid rock prevents compliance with the cover depths specified in this table, the wiring shall be installed in a metal raceway, or a nonmetallic raceway permitted for direct burial. The raceways shall be covered by a minimum of 50 mm (2 in.) of concrete extending down to rock. Directly buried electrical metallic tubing (EMT) shall comply with 358.10. ENHANCED CONTENT Collapse Table 300.5(A) requires conductors under residential driveways to be at least 18 inches below grade. However, if the conductors are protected by an overcurrent device rated at not more than 20 amperes and provided with GFCI protection for personnel, column 4 permits the burial depth to be reduced to 12 inches. The exhibit below show examples of underground installations of 18 inches and 12 inches, respectively. Footnote 1 in column 5 permits wiring at depths less than the minimum if it is specified by the manufacturer’s instructions. Footnote 2 permits column 5 to apply to circuits for pool, spa, and fountain lighting provided that the circuit voltage is 30 volts or less and it is installed in a nonmetallic raceway. Wet Locations. The interior of enclosures or raceways installed underground shall be considered to be a wet location. Insulated conductors and cables installed in these enclosures or raceways in underground installations shall comply with 310.10(C). ENHANCED CONTENT Collapse The inside of all raceways and enclosures installed underground is classified as a wet location. Conductors installed in such underground locations must meet one of the following criteria: Be moisture-impervious, metal-sheathed Be Type MTW, RHW, RHW-2, TW, THW, THW-2, THHW, THWN, THWN-2, XHHW, XHHW-2, or ZW Be of a type listed for use in wet locations (C) Underground Cables and Conductors Under Buildings. Underground cable and conductors installed under a building shall be in a raceway. Exception No. 1: Type MI cable shall be permitted under a building without installation in a raceway where embedded in concrete, fill, or other masonry in accordance with 332.10(6) or in underground runs where suitably protected against physical damage and corrosive conditions in accordance with 332.10(10). Exception No. 2: Type MC cable listed for direct burial or concrete encasement shall be permitted under a building without installation in a raceway in accordance with 330.10(A)(5) and in wet locations in accordance with 330.10(A)(11). (D) Protection from Damage. Conductors and cables shall be protected from damage in accordance with 300.5(D)(1) through (D)(4). Emerging from Grade. Direct-buried conductors and cables emerging from grade and specified in Columns 1 and 4 of Table 300.5(A) shall be protected by enclosures or raceways extending from the minimum cover distance below grade required by 300.5(A) to a point at least 2.5 m (8 ft) above finished grade. In no case shall the protection be required to exceed 450 mm (18 in.) below finished grade. Conductors Entering Buildings. Conductors entering a building shall be protected to the point of entrance. Service Conductors. Underground service conductors that are not encased in concrete and that are buried 450 mm (18 in.) or more below grade shall have their location identified by a warning ribbon that is placed in the trench at least 300 mm (12 in.) above the underground installation. ENHANCED CONTENT Collapse The warning ribbon reduces the risk of an accident, such as an electrocution or an arc-flash incident, during excavation near underground service conductors that are not encased in concrete, because these circuits are not protected from short circuit and overload. Enclosure or Raceway Damage. Where the enclosure or raceway is subject to physical damage, the conductors shall be installed in electrical metallic tubing, rigid metal conduit, intermediate metal conduit, RTRC-XW, Schedule 80 PVC conduit, or equivalent. Splices and Taps. Direct-buried conductors or cables shall be permitted to be spliced or tapped without the use of splice boxes. The splices or taps shall be made in accordance with 110.14(B). ENHANCED CONTENT Collapse Underground splices are not required to be in a box if they are made in accordance with 110.14(B), which requires the splicing means to be listed for underground use. Listed sealed wire connector systems restore the insulation integrity of the spliced conductors in a permanent joint. Sealed wire connectors are used where future access to the splices will not be necessary. The difference between multiconductor cables labeled for direct burial and single conductors labeled for direct burial is that direct-burial multiconductor cables might or might not contain individual conductors labeled for direct burial. The overall cable jacket might be the only underground protection technique for the contained conductors. Although the direct-burial splicing techniques used on multiconductor cables can differ widely from the techniques used on direct-burial single-conductor cables, the NEC requirements are generally the same. The splicing technique must be listed for the cable type and listed for direct burial. An example of a listed heat-shrink underground splice kit being utilized with a multiconductor cable is shown below. (Courtesy of Ideal Industries, Inc.) Backfill. Backfill that contains large rocks, paving materials, cinders, large or sharply angular substances, or corrosive material shall not be placed in an excavation where materials might damage raceways, cables, conductors, or other substructures or prevent adequate compaction of fill or contribute to corrosion of raceways, cables, or other substructures. Where necessary to prevent physical damage to the raceway, cable, or conductor, protection shall be provided in the form of granular or selected material, suitable running boards, suitable sleeves, or other approved means. Raceway Seals. Conduits or raceways through which moisture might contact live parts shall be sealed or plugged at either or both ends. Spare or unused raceways shall also be sealed. Sealants shall be identified for use with the cable insulation, conductor insulation, bare conductor, shield, or other components. Informational Note: Presence of hazardous gases or vapors might also necessitate the sealing of underground conduits or raceways entering buildings. ENHANCED CONTENT Collapse A conduit sealing bushing, shown below, is one method that prevents the entrance of gas or moisture. See 230.8 for sealing service raceways. Bushing. A bushing, or terminal fitting, with an integral bushed opening shall be used at the end of a conduit or other raceway that terminates underground where the conductors or cables emerge as a direct burial wiring method. A seal incorporating the physical protection characteristics of a bushing shall be permitted to be used in lieu of a bushing. Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors shall be installed in the same raceway or cable or shall be installed in close proximity in the same trench. Exception No. 1: Conductors shall be permitted to be installed in parallel in raceways, multiconductor cables, or direct-buried single conductor cables. Each raceway or multiconductor cable shall contain all conductors of the same circuit, including equipment grounding conductors. Each direct-buried single conductor cable shall be located in close proximity in the trench to the other single conductor cables in the same parallel set of conductors in the circuit, including equipment grounding conductors. Exception No. 2: Isolated phase, polarity, grounded conductor, and equipment grounding and bonding conductor installations shall be permitted in nonmetallic raceways or cables with a nonmetallic covering or nonmagnetic sheath in close proximity where conductors are paralleled as permitted in 310.10(G), and where the conditions of 300.20(B) are met. ENHANCED CONTENT Collapse Isolated phase installations contain only one phase per raceway or cable. In an ac circuit installation, the spacing between isolated phase raceways and cables should be as small as possible and the length of the run limited to avoid increased circuit impedance and the resulting increase in voltage drop. Isolated phase installations can be used in ac circuits to limit available fault current at downstream equipment. Isolated phase installations present an inherent hazard of overheating, which is a risk that must be understood and carefully controlled. This hazard results from induced currents in metal raceways that contain only one phase conductor. The surrounding metal acts as a shorted transformer turn. In underground installations, a single conductor is unlikely to be installed in a metal raceway; if it is installed, it is unlikely to present a fire hazard. This is not true for aboveground raceways, which is the reason isolated phase installations have limited application for aboveground installations. See also 300.20(A) and (B) for more information on induced currents in raceways. Earth Movement. Where direct-buried conductors, raceways, or cables are subject to movement by settlement or frost, direct-buried conductors, raceways, or cables shall be arranged so as to prevent damage to the enclosed conductors or to equipment connected to the raceways. Informational Note: This section recognizes “S” loops in underground direct burial cables and conductors to raceway transitions, expansion fittings in raceway risers to fixed equipment, and, generally, the provision of flexible connections to equipment subject to settlement or frost heaves. (K) Directional Boring. Cables or raceways installed using directional boring equipment shall be approved for the purpose. 300.6 Protection Against Corrosion and Deterioration. Raceways, cable trays, cablebus, auxiliary gutters, cable armor, boxes, cable sheathing, cabinets, enclosures (other than surrounding fences and walls), elbows, couplings, fittings, supports, and support hardware shall be of materials suitable for the environment in which they are to be installed. Ferrous Metal Equipment. Ferrous metal raceways, cable trays, cablebus, auxiliary gutters, cable armor, boxes, cable sheathing, cabinets, enclosures (other than surrounding fences and walls), elbows, couplings, nipples, fittings, supports, and support hardware shall be suitably protected against corrosion inside and outside (except threads at joints) by a coating of approved corrosion-resistant material. Where corrosion protection is necessary and the conduit is threaded anywhere other than at the factory where the product is listed, the threads shall be coated with an approved electrically conductive, corrosion-resistant compound. Exception: Stainless steel shall not be required to have protective coatings. ENHANCED CONTENT Collapse Ferrous metal equipment must be protected from corrosion with an approved anti-corrosion compound, an example of which is shown below. (Courtesy of Thomas and Betts, A Member of the ABB Group) Protected from Corrosion Solely by Enamel. Where protected from corrosion solely by enamel, ferrous metal raceways, cable trays, cablebus, auxiliary gutters, cable armor, boxes, cable sheathing, cabinets, enclosures (other than surrounding fences and walls), elbows, couplings, nipples, fittings, supports, and support hardware shall not be used outdoors or in wet locations as described in 300.6(D). Organic Coatings on Boxes or Cabinets. Where boxes, cabinets, or enclosures (other than surrounding fences and walls) have an approved system of organic coatings and are marked “Raintight,” “Rainproof,” or “Outdoor Type,” they shall be permitted outdoors. In Concrete or in Direct Contact with the Earth. Ferrous metal raceways, cable armor, boxes, cable sheathing, cabinets, enclosures (other than surrounding fences and walls), elbows, couplings, nipples, fittings, supports, and support hardware shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where made of material approved for the condition or where provided with corrosion protection approved for the condition. ENHANCED CONTENT Collapse Metal raceways installed in the earth can be coated with an asphalt compound, plastic sheath, or other equivalent protection to help prevent deterioration. Also, metal raceways are available with a bonded PVC coating. Galvanized steel RMC and steel IMC generally do not require supplementary corrosion protection. Aluminum Metal Equipment. Aluminum raceways, cable trays, cablebus, auxiliary gutters, cable armor, boxes, cable sheathing, cabinets, enclosures (other than surrounding fences and walls), elbows, couplings, nipples, fittings, supports, and support hardware embedded or encased in concrete or in direct contact with the earth shall be provided with supplementary corrosion protection. Nonmetallic Equipment. Nonmetallic raceways, cable trays, cablebus, auxiliary gutters, boxes, cables with a nonmetallic outer jacket and internal metal armor or jacket, cable sheathing, cabinets, enclosures (other than surrounding fences and walls), elbows, couplings, nipples, fittings, supports, and support hardware shall be made of material approved for the condition and shall comply with 300.6(C)(1) and (C)(2) as applicable to the specific installation. Exposed to Sunlight. Where exposed to sunlight, the materials shall be listed as sunlight resistant or shall be identified as sunlight resistant. Chemical Exposure. Where subject to exposure to chemical solvents, vapors, splashing, or immersion, materials or coatings shall either be inherently resistant to chemicals based on their listing or be identified for the specific chemical reagent. Indoor Wet Locations. In portions of dairy processing facilities, laundries, canneries, and other indoor wet locations, and in locations where walls are frequently washed or where there are surfaces of absorbent materials, such as damp paper or wood, the entire wiring system, where installed exposed, including all boxes, cabinets, enclosures (other than surrounding fences and walls), fittings, raceways, and cable used therewith, shall be mounted so that there is at least a 6 mm (1⁄4in.) airspace between it and the wall or supporting surface. Exception: Nonmetallic raceways, boxes, and fittings shall be permitted to be installed without the airspace on a concrete, masonry, tile, or similar surface. Informational Note: In general, areas where acids and alkali chemicals are handled and stored might present such corrosive conditions, particularly when wet or damp. Severe corrosive conditions might also be present in portions of meatpacking plants, tanneries, glue houses, and some stables; in installations immediately adjacent to a seashore and swimming pool areas; in areas where chemical deicers are used; and in storage cellars or rooms for hides, casings, fertilizer, salt, and bulk chemicals. 300.7 Raceways Exposed to Different Temperatures. (A) Sealing. Where portions of a raceway or sleeve are known to be subjected to different temperatures, and where condensation is known to be a problem, as in cold storage areas of buildings or where passing from the interior to the exterior of a building, the raceway or sleeve shall be sealed to prevent the circulation of warm air to a colder section of the raceway or sleeve. Sealants shall be identified for use with cable insulation, conductor insulation, a bare conductor, a shield, or other components. An explosionproof seal shall not be required for this purpose. ENHANCED CONTENT Collapse Condensation can form in raceways or sleeves that are subjected to temperature differences as a result of air circulating through the raceway from a warmer to a colder section. Condensation could accumulate, for example, in a raceway used to supply lighting or branch-circuit conductors within a walk-in refrigerator or freezer. Circulation of air can be prevented by sealing the raceway with a suitable pliable compound at a conduit body or junction box, usually installed in the raceway before it enters the colder section. Special sealing fittings such as those used in hazardous (classified) locations are not necessary. Expansion, Expansion-Deflection, and Deflection Fittings. Raceways shall be provided with expansion, expansion-deflection, or deflection fittings where necessary to compensate for thermal expansion, deflection, and contraction. Informational Note No. 1: Table 352.44(A) and Table 355.44 provide the expansion information for polyvinyl chloride (PVC) and for reinforced thermosetting resin conduit (RTRC), respectively. A nominal number for steel conduit can be determined by multiplying the expansion length in Table 352.44(A) by 0.20. The coefficient of expansion for steel electrical metallic tubing, intermediate metal conduit, and rigid metal conduit is 1.170 × 10-5 (0.0000117 mm per mm of conduit for each °C in temperature change) [0.650 × 10-5 (0.0000065 in. per in. of conduit for each °F in temperature change)]. A nominal number for aluminum conduit and aluminum electrical metallic tubing can be determined by multiplying the expansion length in Table 352.44(A) by 0.40. The coefficient of expansion for aluminum electrical metallic tubing and aluminum rigid metal conduit is 2.34 × 10-5 (0.0000234 mm per mm of conduit for each °C in temperature change) [1.30 × 10-5 (0.000013 in. per in. of conduit for each °F in temperature change)]. Informational Note No. 2: See NEMA FB 2.40-2019, Installation Guidelines for Expansion and Expansion/Deflection Fittings, for further information on expansion and expansion deflection fittings. ENHANCED CONTENT Collapse Substantial changes in temperature cause destructive amounts of expansion, deflection, and contraction in a raceway system. Properly designed and installed expansion and deflection fittings allow expansion, deflection, and contraction without damage to enclosures, raceways, and their conductors. The informational note addresses expansion of aluminum RMC and reinforced thermosetting resin conduit (RTRC). The note also provides a few simple relationships (or ratios) of linear expansion in length of PVC conduit to other types of conduit. The key to determining any temperature-related change in conduit length is understanding that the change in length is equal to the coefficient of expansion of the conduit material times the change in temperature times the initial length of the conduit. The table below provides the coefficient of expansion for various conduit types, showing the variances of different raceway types due to thermal expansion with a 55°F change. 300.8 Installation of Conductors With Other Systems. Raceways or cable trays containing electrical conductors shall not contain any pipe, tube, or equal for steam, water, air, gas, drainage, or any service other than electrical. 300.9 Raceways in Wet Locations Above Grade. Where raceways are installed in wet locations above grade, the interior of these raceways shall be considered to be a wet location. Insulated conductors and cables installed in raceways in wet locations above grade shall comply with 310.10(C). 300.10 Electrical Continuity of Metal Raceways, Cable Armor, and Enclosures. Metal raceways, cable armor, and other metal enclosures for conductors shall be metallically joined together into a continuous electrical conductor and shall be connected to all boxes, fittings, and cabinets to provide effective electrical continuity. Unless specifically permitted elsewhere in this Code, raceways and cable assemblies shall be mechanically secured to boxes, fittings, cabinets, and other enclosures. 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 made electrically continuous. Exception No. 2: Equipment enclosures to be isolated, as permitted by 250.96(B), shall not be required to be metallically joined to the metal raceway. ENHANCED CONTENT Collapse Sections 250.4(A) and (B) require that the metal parts form an effective low-impedance path to ground. This safely conducts any fault current and facilitates the operation of overcurrent devices protecting the enclosed circuit conductors. 300.11 Securing and Supporting. (A) Secured in Place. Raceways, cable assemblies, boxes, cabinets, and fittings shall be securely fastened in place. Wiring Systems Installed Above Suspended Ceilings. Support wires that do not provide secure support shall not be the sole support. Support wires and associated fittings that provide secure support and that are installed in addition to the ceiling grid support wires shall be permitted as the sole support. Where independent support wires are used, they shall be secured at both ends. Cables and raceways shall not be supported by ceiling grids. Fire-Rated Assemblies. Wiring located within the cavity of a 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 from those that are part of the fire-rated design. Exception: The ceiling support system shall be permitted to support wiring and equipment that have been tested as part of the fire-rated assembly. Informational Note: See ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials, for one method of testing to determine fire rating. ENHANCED CONTENT Collapse Wiring methods and luminaires are not allowed to be supported or secured to the support wires or T-bars of a fire-rated ceiling-assembly unless the assembly has been tested and listed for that use. If wire is selected as the supporting means for the electrical system within a fire-rated ceiling cavity, it must be distinguishable from the ceiling support wires by color, tagging, or other effective means and must be secured at both ends. Independent support and securing both ends of the support wire do preclude a connection to the ceiling grid on one end. Generally, the rule for supporting electrical equipment is that the equipment must be “securely fastened in place.” This phrase means not only that vertical support for the weight of the equipment must be provided but also that the equipment must be secured to prevent horizontal movement or sway. The intention is to prevent the loss of grounding continuity provided by the raceway that could result from horizontal movement. Sections 300.11(B)(1) and (B)(2) are quite similar. Unless the exceptions apply, these sections prohibit all types of wiring from being attached in any way to the support wires of a ceiling assembly or ceiling grid not part of the building structure. Refer to the appropriate wiring method article in Chapter 3 for cable and raceway supporting requirements. See also… Article 410, Part IV, for the proper support of luminaires 314.23 for the support of outlet boxes 760.24 and 770.24 for various low-voltage fire alarm and optical-fiber cable supports 800.110(C) for requirements on communications systems cable supports (2) Non-Fire-Rated Assemblies. Wiring located within the c