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ts only if necessary for the direct action upon, or sensing of, the contained air. Where equipment or devices are installed and illumination is necessary to facilitate maintenance and repair, enclosed gasketed-type luminaires shall be permitted. Only wiring methods consisting of Type MI cable withou...

ts only if necessary for the direct action upon, or sensing of, the contained air. Where equipment or devices are installed and illumination is necessary to facilitate maintenance and repair, enclosed gasketed-type luminaires shall be permitted. Only wiring methods consisting of Type MI cable without an overall nonmetallic covering, Type MC cable employing a smooth or corrugated impervious metal sheath without an overall nonmetallic covering, electrical metallic tubing, flexible metallic tubing, intermediate metal conduit, or rigid metal conduit without an overall nonmetallic covering shall be instal⁠led in ducts specifically fabricated to transport environmental air. Flexible metal conduit shall be permitted, in lengths not to exceed 1.2 m (4 ft), to connect physically adjustable equipment and devices permitted to be in these fabricated ducts. The connectors used with flexible metal conduit shall effectively close any openings in the connection. Exception: Wiring methods and cabling systems, listed for use in other spaces used for environmental air (plenums), shall be permitted to be installed in ducts specifically fabricated for environmental air-handling purposes under both of the following conditions: (1) The wiring methods or cabling systems shall be permitted only if necessary to connect to equipment or devices associated with the direct action upon or sensing of the contained air. (2) The total length of such wiring methods or cabling systems shall not exceed 1.2 m (4 ft). ENHANCED CONTENT Collapse The use of wiring methods within ducts is limited to minimize the contribution of smoke and products of combustion during a fire in an area that handles environmental air. Other Spaces Used for Environmental Air (Plenums). This section shall apply to spaces not specifically fabricated for environmental air-handling purposes but used for air-handling purposes as a plenum. This section shall not apply to habitable rooms or areas of buildings, the prime purpose of which is not air handling. Informational Note No. 1: The space over a hung ceiling used for environmental air-handling purposes is an example of the type of other space to which this section applies. Informational Note No. 2: See NFPA 90A, Standard for the Installation of Air-Conditioning and Ventilating Systems, and other mechanical codes for information on how the term other spaces used for environmental air (plenum), as used in this section, correlates with the use of the term plenumwhere the plenum is used for return air purposes, as well as some other air-handling spaces. Exception: This section shall not apply to the joist or stud spaces of dwelling units where the wiring passes through such spaces perpendicular to the long dimension of such spaces. ENHANCED CONTENT Collapse Other spaces or plenums — such as the space or cavity between a structural floor or roof and a suspended (hung) ceiling — are used to transport environmental air and are not specifically manufactured as ducts. Many spaces above suspended ceilings are intended to transport return air. Informational Note No. 2 correlates the phrase other spaces used for environmental air with the term plenum as used in NFPA 90A, Standard for the Installation of Air-Conditioning and Ventilating Systems. The distinction between a habitable room and one used for air handling is illustrated below. If the prime purpose of the room or space is air handling, the restrictions in 300.22(C) apply. The exception permits cable to pass through joist or stud spaces of a dwelling unit where the joist space is used as a return for a forced-air central heating or air-conditioning system. The joist space is covered with appropriate material, and the cable passes through the space perpendicular to the vertical run, as illustrated below,. Wiring Methods. The wiring methods for other spaces used for environmental air shall be limited to totally enclosed, nonventilated, insulated busway having no provisions for plug-in connections, Type MI cable without an overall nonmetallic covering, Type MC cable without an overall nonmetallic covering, Type AC cable, or other factory-assembled multiconductor control or power cable that is specifically listed for use within an air-handling space, or listed prefabricated cable assemblies of metallic manufactured wiring systems without nonmetallic sheath. Other types of cables, conductors, and raceways shall be permitted to be installed in electrical metallic tubing, flexible metallic tubing, intermediate metal conduit, rigid metal conduit without an overall nonmetallic covering, flexible metal conduit, or, where accessible, surface metal raceway or metal wireway with metal covers. Nonmetallic cable ties and other nonmetallic cable accessories used to secure and support cables shall be listed as having low smoke and heat release properties. Informational Note: See UL 2043, Fire Test for Heat and Visible Smoke Release for Discrete Products and Their Accessories Installed in Air-Handling Spaces, for one method of testing low smoke and heat release properties for nonmetallic cable ties and other nonmetallic cable accessories to determine a maximum peak optical density of 0.50 or less, an average optical density of 0.15 or less, and a peak heat release rate of 100 kW or less. Cable Tray Systems. The requirements in 300.22(C)(2)(a) or (C)(2)(b) shall apply to the use of metallic cable tray systems in other spaces used for environmental air (plenums), where accessible. Metal Cable Tray Systems. Metal cable tray systems shall be permitted to support the wiring methods specified in 300.22(C)(1). Solid Side and Bottom Metal Cable Tray Systems. Solid side and bottom metal cable tray systems with solid metal covers shall be permitted to enclose wiring methods and cables not already covered in 300.22(C)(1) in accordance with 392.10(A) and (B). Equipment. Electrical equipment with a metal enclosure, or electrical equipment with a nonmetallic enclosure listed for use within an air-handling space and having low smoke and heat release properties, and associated wiring material suitable for the ambient temperature shall be permitted to be installed in such other spaces unless prohibited elsewhere in this Code. Informational Note: See UL 2043, Fire Test for Heat and Visible Smoke Release for Discrete Products and Their Accessories Installed in Air-Handling Spaces, for one method of testing low smoke and heat release properties to determine that the equipment exhibits a maximum peak optical density of 0.50 or less, an average optical density of 0.15 or less, and a peak heat release rate of 100 kW or less. Exception: Integral fan systems shall be permitted where specifically identified for use within an air-handling space. (D) Information Technology Equipment. Where the installation complies with the special requirements specified in 645.4, electrical wiring in air-handling areas beneath raised floors for information technology equipment shall be permitted in accordance with 645.5(E). 300.23 Panels Designed to Allow Access. Cables, raceways, and equipment installed behind panels designed to allow access, including suspended ceiling panels, shall be arranged and secured to allow the removal of panels and access to the equipment. 300.25 Exit Enclosures (Stair Towers). Where an exit enclosure is required to have a fire resistance rating, only electrical wiring methods serving equipment permitted by the authority having jurisdiction in the exit enclosure shall be installed within the exit enclosure. Exception: Where egress lighting is required on outside exterior doorways from the exit enclosure, luminaires shall be permitted to be supplied from the inside of the exit enclosure. Informational Note: See NFPA 101-2021, Life Safety Code, 7.1.3.2.1(10)(b), for more information. ENHANCED CONTENT Collapse NFPA 101®, Life Safety Code®, requires certain stairways, those defined as “exit enclosures,” to be separated from the building by fire-rated walls or other means. A critical function of these stairways is to provide safe passage out of the building in the event of an emergency. It is the intent of the requirements in NFPA 101 to limit the materials contained within an exit enclosure to only those needed to serve the intended function of the exit enclosure. 300.26 Remote-Control and Signaling Circuits Classification. Remote-control and signaling circuits shall be classified as either power-limited or non-power-limited and comply with 300.26(A) through (C). Class 1 Power-Limited Remote-Control and Signaling Circuits. Class 1 power-limited remote-control and signaling circuits shall comply with 724.3. Class 2 and Class 3 Power-Limited Remote-Control and Signaling Circuits. Class 2 and Class 3 power-limited remote-control and signaling circuits shall comply with 725.3. Non-Power-Limited Remote-Control and Signaling Circuits. Non-power-limited remote-control and signaling circuits shall be installed in accordance with 300.2 through 300.25 and comply with 300.26(C)(1) through (C)(3). Sizes and Use. Conductors that are 18 AWG and 16 AWG copper shall be permitted to be used if they supply loads that do not exceed the ampacities specified in 402.5 and are installed in a raceway, an approved enclosure, or a listed cable. Conductors that are 14 AWG copper-clad aluminum shall be permitted to be used in Type MC cable and Type TC cable. The continuous load shall not exceed 8 amperes. Conductors larger than 16 AWG copper or 14 AWG copper-clad aluminum shall not supply loads greater than the ampacities specified in 310.14. Flexible cords shall comply with the applicable general requirements, applications, and construction specifications for flexible cords and flexible cables in accordance with Article 400 Parts I and II. Insulation. Insulation on conductors shall be rated for the system voltage and not less than 600 volts. Conductors larger than 16 AWG copper or 14 AWG copper-clad aluminum shall comply with the applicable general requirements for conductors rated up to and including 2000 volt for type designations, insulations, markings, ampacity ratings, and uses in accordance with 310.3, 310.4, 310.6, 310.8, 310.10, and 310.14. Conductors that are 18 AWG copper, 16 AWG copper, or 14 AWG copper-clad aluminum shall be Type FFH-2, Type KF-2, Type KFF-2, Type PAF, Type PAFF, Type PF, Type PFF, Type PGF, Type PGFF, Type PTF, Type PTFF, Type RFH-2, Type RFHH-2, Type RFHH-3, Type SF-2, SFF-2, Type TF, Type TFF, Type TFFN, Type TFN, Type ZF, or Type ZFF. Conductors with other types and thicknesses of insulation shall be permitted if listed for Class 1 circuit use. Overcurrent Protection. Overcurrent protection for conductors 14 AWG copper and larger shall be provided in accordance with the conductor ampacity, without applying the ampacity adjustment and correction factors specified in 310.15 to the ampacity calculation. Overcurrent protection shall not exceed 7 amperes for 18 AWG copper conductors and 10 amperes for 16 AWG copper and 14 AWG copper-clad aluminum. Exception: The overcurrent protection specified in 300.26(C)(3)(a) and 300.26(C)(3)(b) shall not be required where this Code requires or permits other overcurrent protection ratings. Article 305 General Requirements for Wiring Methods and Materials for Systems Rated Over 1000 Volts ac, 1500 Volts dc, Nominal 305.1 Scope. This article covers wiring methods and materials for systems rated over 1000 volts ac, 1500 volts dc, nominal. 305.3 Other Articles. Conductors shall be permitted to be installed in accordance with any of the wiring methods identified in Table 305.3. Table 305.3 Wiring Methods Permitted for Use in Systems Rated Over 1000 Volts ac, 1500 Volts dc, Nominal Wiring Methods Permitted for Use Above 1000 Volts ac, 1500 Volts dc Voltage Levels Reference Pull and junction boxes, conduit bodies, and handhole enclosures Over 1000 Article 314, Part IV Metal-clad cable (Type MC) 1000–35,000 Article 330 Type P cable 1000–2000 Article 337 Intermediate metal conduit (IMC) Over 1000 Article 342 Rigid metal conduit (RMC) Over 1000 Article 344 Rigid polyvinyl chloride conduit (PVC) Over 1000 Article 352 Reinforced thermosetting resin conduit (RTRC) Over 1000 Article 355 Electrical metallic tubing (EMT) Over 1000 Article 358 Auxiliary gutters Over 1000 Article 366 Busway Over 1000 Article 368, Part IV Cablebus 1000–35,000 Article 370 Cable trays 1000–35,000 Article 392 Messenger-supported wiring 1000–35,000 Article 396 Outdoor overhead conductors Over 1000 Article 395 Insulated bus pipe (IBP) 1000–35,000 ac Article 369 Exposed runs of Type MV cables, bare conductors, and bare busbars shall be permitted in locations accessible only to qualified persons. Busbars shall be permitted to be either copper or aluminum. Exception: Airfield lighting cable used in series circuits that are powered by regulators and installed in restricted airport lighting vaults shall be permitted as exposed cable installations. Informational Note: An example of a common application is FAA L-824 cables installed as exposed runs within a restricted vault area. 305.4 Conductors of Different Systems. 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 otherwise permitted as follows: (1) Where contained within the individual wiring enclosure, primary leads of electric-discharge lamp ballasts insulated for the primary voltage of the ballast shall be permitted to occupy the same luminaire, sign, or outline lighting enclosure as the branch-circuit conductors. Excitation, control, relay, and ammeter conductors used in connection with any individual motor or starter shall be permitted to occupy the same enclosure as the motor-circuit conductors. Conductors of different voltage ratings shall be permitted in motors, transformers, switchgear, switchboards, control assemblies, and similar equipment. If the conductors of each system in a manhole are permanently and effectively separated from the conductors of the other systems and securely fastened to racks, insulators, or other approved supports, conductors of different voltage ratings shall be permitted. Conductors having nonshielded insulation and operating at different voltage levels shall not occupy the same enclosure, cable, or raceway. 305.5 Conductor Bending Radius. The conductor shall not be bent to a radius less than 8 times the overall diameter for nonshielded conductors or 12 times the overall diameter for shielded or lead-covered conductors during or after installation. For multiconductor or multiplexed single-conductor cables having individually shielded conductors, the minimum bending radius shall be 12 times the diameter of the individually shielded conductors or 7 times the overall diameter, whichever is greater. 305.6 Protection Against Induction Heating. Metallic raceways and associated conductors shall be arranged to avoid heating of the raceway in accordance with 300.20. 305.7 Covers Required. Suitable covers shall be installed on all boxes, fittings, and similar enclosures to prevent accidental contact with energized parts or physical damage to parts or insulation. 305.8 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 be either moisture-impervious metal-sheathed or of a type listed for use in wet locations. 305.9 Braid-Covered Insulated Conductors — Exposed Installation. Exposed runs of braid-covered insulated conductors shall have a flame-retardant braid. If the conductors used do not have this protection, a flame-retardant saturant shall be applied to the braid covering after installation. This treated braid covering shall be stripped back a safe distance at conductor terminals, according to the operating voltage. Where practicable, this distance shall not be less than 25 mm (1 in.) for each kilovolt of the conductor-to-ground voltage of the circuit. 305.10 Insulation Shielding. Metallic and semiconducting insulation shielding components of shielded cables shall be removed for a distance dependent on the circuit voltage and insulation. Stress reduction means shall be provided at all terminations of factory-applied shielding. Metallic shielding components such as tapes, wires, or braids, or combinations of them, shall be connected to an equipment grounding conductor, an equipment grounding busbar, or a grounding electrode. 305.11 Moisture or Mechanical Protection for Metal-Sheathed Cables. Where cable conductors emerge from a metal sheath and where protection against moisture or physical damage is necessary, the insulation of the conductors shall be protected by a cable sheath terminating device. 305.12 Danger Signs. Danger signs shall be conspicuously posted at points of access to conductors in all raceway systems and cable systems. The sign(s) shall meet the requirements in 110.21(B), shall be readily visible, and shall state the following: DANGER—HIGH VOLTAGE—KEEP OUT 305.15 Underground Installations. General. Underground conductors shall be identified for the voltage and conditions under which they are installed. Conductors used for direct-burial applications shall be of a type identified for such use. Underground cables shall be installed in accordance with 305.15(A)(1), (A)(2), or (A)(3), and the installation shall meet the depth requirements of Table 305.15(A). Table 305.15(A) Minimum Cover Requirements General Conditions (not otherwise specified) Special Conditions (use if applicable) Column 1 Column 2 Column 3 Column 4 Column 5 Column 6 Direct-Buried Cables1 Electrical Metallic Tubing, RTRC, PVC, and HDPE Conduit2 Rigid Metal Conduit and Intermediate Metal Conduit Raceways Under Buildings or Exterior Concrete Slabs, 100 mm (4 in.) Minimum Thickness3 Cables in Airport Runways or Adjacent Areas Where Trespass Is Prohibited Areas Subject to Vehicular Traffic, Such as Thoroughfares and Commercial Parking Areas Circuit Voltage mm in. mm in. mm in. mm in. mm in. mm in. Over 1000 V ac, 1500 V dc, through 22 kV 750 30 450 18 150 6 100 4 450 18 600 24 Over 22 kV through 40 kV 900 36 600 24 150 6 100 4 450 18 600 24 Over 40 kV 1000 42 750 30 150 6 100 4 450 18 600 24 Notes: Cover shall be defined as the shortest distance in millimeters (inches) 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 similar cover. Lesser depths shall be permitted where cables and conductors rise for terminations or splices or where access is otherwise required. Where solid rock prevents compliance with the cover depths specified in this table, the wiring shall be installed in a metal or 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. In industrial establishments, where conditions of maintenance and supervision ensure that qualified persons will service the installation, the minimum cover requirements for other than rigid metal conduit and intermediate metal conduit shall be permitted to be reduced 150 mm (6 in.) for each 50 mm (2 in.) of concrete or equivalent placed entirely within the trench over the underground installation. 1 Underground direct-buried cables that are not encased or protected by concrete and are buried 750 mm (30 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 cables. 2 Listed by a qualified testing agency as suitable for direct burial without encasement. All other nonmetallic systems shall require 50 mm (2 in.) of concrete or equivalent above conduit in addition to the table depth. 3 The slab shall extend a minimum of 150 mm (6 in.) beyond the underground installation, and a warning ribbon or other effective means suitable for the conditions shall be placed above the underground installation. ENHANCED CONTENT Collapse Prior to backfilling a ditch or trench, a warning ribbon must be placed near underground direct-buried conductors over 1000 volts, nominal, that are not encased in concrete, in accordance with Table 305.15(A), Footnote 1. This requirement is intended to reduce the risk of an accident, electrocution, or arc-flash incident during excavation. Shielded Cables and Nonshielded Cables in Metal-Sheathed Cable Assemblies. Underground cables, including nonshielded, Type MC and moisture-impervious metal sheath cables, shall have those sheaths grounded through an effective grounding path meeting the requirements of 250.4(A)(5) or 250.4(B)(4). They shall be direct buried or installed in raceways identified for the use. Industrial Establishments. In industrial establishments, where conditions of maintenance and supervision ensure that only qualified persons service the installed cable, nonshielded single-conductor cables with insulation types up to 2000 volts that are listed for direct burial shall be permitted to be directly buried. Other Nonshielded Cables. Other nonshielded cables not covered in 305.15(A)(1) or (A)(2) shall be installed in rigid metal conduit, intermediate metal conduit, or rigid nonmetallic conduit encased in not less than 75 mm (3 in.) of concrete. 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 be listed for use in wet locations and shall be either moisture-impervious metal-sheathed or of a type listed for use in wet locations. Any connections or splices in an underground installation shall be approved for wet locations. 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 be listed for use in wet locations and comply with 310.10(C). Protection from Damage. Conductors emerging from the ground shall be enclosed in listed raceways. Raceways installed on poles shall be of rigid metal conduit, intermediate metal conduit, RTRC-XW, Schedule 80 PVC conduit, or equivalent, extending from the minimum cover depth specified in Table 305.15(A) to a point 2.5 m (8 ft) above finished grade. Conductors entering a building shall be protected by an approved enclosure or raceway from the minimum cover depth to the point of entrance. Where direct-buried conductors, raceways, or cables are subject to movement by settlement or frost, they shall be installed to prevent damage to the enclosed conductors or to the equipment connected to the raceways. Metallic enclosures shall be grounded. Splices. Direct burial cables shall be permitted to be spliced or tapped without the use of splice boxes if they are installed using materials suitable for the application. The taps and splices shall be watertight and protected from mechanical damage. Where cables are shielded, the shielding shall be continuous across the splice or tap. Exception: At splices of an engineered cabling system, metallic shields of direct-buried single-conductor cables with maintained spacing between phases shall be permitted to be interrupted and overlapped. Where shields are interrupted and overlapped, each shield section shall be grounded at one point. (E) Backfill. Backfill containing large rocks, paving materials, cinders, large or sharply angular substances, or corrosive materials shall not be placed in an excavation where materials can damage or contribute to the corrosion of raceways, cables, or other substructures or where it might prevent adequate compaction of fill. Protection in the form of granular or selected material or suitable sleeves shall be provided to prevent physical damage to the raceway or cable. Raceway Seal. Where a raceway enters from an underground system, the end within the building shall be sealed with an identified compound to prevent the entrance of moisture. Informational No