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e, it is cadmium hydroxide. The electrolyte is potassium hydroxide (an alkali). In stationary installations, nickel-cadmium cells generally are of the vented type and liberate hydrogen and oxygen during normal charging. Hermetically sealed nickel-cadmium cells are sometimes used, but they require sp...

e, it is cadmium hydroxide. The electrolyte is potassium hydroxide (an alkali). In stationary installations, nickel-cadmium cells generally are of the vented type and liberate hydrogen and oxygen during normal charging. Hermetically sealed nickel-cadmium cells are sometimes used, but they require special charging equipment to prevent gas emissions. Although some of the newer-technology batteries do not ventilate hydrogen under normal operation, they can generate hydrogen during fault conditions. For energy storage systems, see Article 706. 480.3 Equipment. Storage batteries and battery management equipment shall be listed. This requirement shall not apply to lead-acid batteries. ENHANCED CONTENT Collapse As energy demands increase, many stationary battery types will be introduced into the electrical infrastructure. Standards exist for stationary batteries to support a practical and reasonable implementation of these technologies within the electrical infrastructure. This requirement does not require listing of battery systems in Article 480 — it only addresses listing of the batteries themselves, other than the lead-acid type, and battery management equipment (such as charge controllers). 480.4 Battery and Cell Terminations. (A) Corrosion Prevention. Where mating dissimilar metals, antioxidant material suitable for the battery connection shall be used where recommended by the battery manufacturer’s installation and instruction manual. Intercell and Intertier Conductors and Connections. The ampacity of field-assembled intercell and intertier connectors and conductors shall be of such cross-sectional area that the temperature rise under maximum load conditions and at maximum ambient temperature shall not exceed the safe operating temperature of the conductor insulation or of the material of the conductor supports. Informational Note: Conductors sized to prevent a voltage drop exceeding 3 percent of maximum anticipated load, and where the maximum total voltage drop to the furthest point of connection does not exceed 5 percent, may not be appropriate for all battery applications. IEEE 1375-2003, Guide for the Protection of Stationary Battery Systems, provides guidance for overcurrent protection and associated cable sizing. (C) Battery Terminals. Electrical connections to the battery, and the cable(s) between cells on separate levels or racks, shall not put mechanical strain on the battery terminals. Terminal plates shall be used where practicable. Informational Note: Conductors are commonly pre-formed to eliminate stress on battery terminations. Fine stranded cables may also eliminate the stress on battery terminations. See the manufacturer’s instructions for guidance. (D) Accessibility. The terminals of all cells or multicell units shall be readily accessible for readings, inspections, and cleaning where required by the equipment design. One side of transparent battery containers shall be readily accessible for inspection of the internal components. 480.5 Wiring and Equipment Supplied from Batteries. Wiring and equipment supplied from storage batteries shall be subject to the applicable provisions of this Code applying to wiring and equipment operating at the same voltage, unless otherwise permitted by 480.6. 480.6 Overcurrent Protection for Prime Movers. Overcurrent protection shall not be required for conductors from a battery with a voltage of 60 volts dc or less if the battery provides power for starting, ignition, or control of prime movers. Section 300.3 shall not apply to these conductors. ENHANCED CONTENT Collapse The requirement to use Chapter 3 wiring methods is not applicable to battery-powered single conductors used to perform certain operational functions associated with a prime mover, such as for starting a stationary combustion engine that drives an electric generator. For example, if it is necessary to extend the conductors from the battery to the prime mover starting solenoid at a generator location, battery-powered conductors would not be required to have overcurrent protection and could be run as open, single conductors. 480.7 DC Disconnect Methods. Disconnecting Means. A disconnecting means shall be provided for all ungrounded conductors derived from a stationary standby battery with a voltage over 60 volts dc. A disconnecting means shall be readily accessible and located within sight of the stationary standby battery. Informational Note: See 240.21(H) for information on the location of the overcurrent device for battery conductors. ENHANCED CONTENT Collapse Battery systems need maintenance to remain functional. In some cases, such as in 700.3(C), the NEC requires battery system maintenance. For maintenance to be performed safely on a stationary battery system, a readily accessible disconnect means located within sight of the battery system is required. It should be noted that the disconnecting means only isolates the batteries from the equipment and loads being supplied by the battery system. Similar to disconnecting means requirements in Article 690 for photovoltaic electric systems, it is recognized that the batteries, like the photovoltaic modules, cannot be shut down or de-energized. However, having a disconnecting means within sight of the power source minimizes the amount of line-side conductor that remains energized after the disconnecting means is turned off or put into the open position. See also 240.21(H), which addresses the location of overcurrent protection devices for battery conductors. Emergency Disconnect. For one-family and two-family dwellings, a disconnecting means or its remote control for a stationary standby battery shall be located at a readily accessible location outside the building for emergency use. The disconnect shall be labeled as follows: EMERGENCY DISCONNECT ENHANCED CONTENT Collapse This requirement applies only to the battery systems covered under the scope of Article 480 that are installed as a primary or standby power source at one- and two-family dwellings. If a battery-type energy storage system (ESS) is installed as a power source for a one- or two-family dwelling, the requirements of Article 706 apply to the installation. See also 706.15 for the requirements on ESS disconnecting means at one- and two-family dwellings. Disconnection of Series Battery Circuits. Battery circuits exceeding 240 volts dc nominal between conductors or to ground and subject to field servicing shall have provisions to disconnect the series-connected strings into segments not exceeding 240 volts dc nominal for maintenance by qualified persons. Non-load-break bolted or plug-in disconnects shall be permitted. Remote Actuation. Where a disconnecting means, located in accordance with 480.7(A), is provided with remote controls to activate the disconnecting means and the controls for the disconnecting means are not located within sight of the stationary standby battery, the disconnecting means shall be capable of being locked in the open position, in accordance with 110.25, and the location of the controls shall be field marked on the disconnecting means. Busway. Where a dc busway system is installed, the disconnecting means shall be permitted to be incorporated into the busway. Notification. The disconnecting means shall be legibly marked in the field. A label with the marking shall be placed in a conspicuous location near the battery if a disconnecting means is not provided. The marking shall be of sufficient durability to withstand the environment involved and shall include the following: Nominal battery voltage Available fault current derived from the stationary standby battery Informational Note No. 1: Battery equipment suppliers can provide information about available fault current on specific battery models. An arc flash label in accordance with acceptable industry practice Informational Note No. 2: See NFPA 70E-2021, Standard for Electrical Safety in the Workplace, for assistance in determining the severity of potential exposure, planning safe work practices, arc flash labeling, and selecting personal protective equipment. Date the calculation was performed Exception: List items (2), (3), and (4) shall not apply to one- and two-family dwellings. Identification of Power Sources. Stationary standby batteries shall be indicated by 480.7(G)(1) and (G)(2). Facilities with Utility Services and Stationary Standby Batteries. Plaques or directories shall be installed in accordance with 705.10. Exception: This requirement does not apply where a disconnect in 480.7(A) is not required. (2) Facilities with Stand-Alone Systems. A permanent plaque or directory shall be installed in accordance with 710.10. 480.8 Insulation of Batteries. Batteries constructed of an electrically conductive container shall have insulating support if a voltage is present between the container and ground. 480.9 Battery Support Systems. For battery chemistries with corrosive electrolyte, the structure that supports the battery shall be resistant to deteriorating action by the electrolyte. Metallic structures shall be provided with nonconducting support members for the cells, or shall be constructed with a continuous insulating material. Paint alone shall not be considered as an insulating material. 480.10 Battery Locations. Battery locations shall conform to 480.10(A) through (G). ENHANCED CONTENT Collapse Batteries should be located in clean, dry rooms and be arranged to provide sufficient work space for inspection and maintenance. The voltage of the battery system, rather than the voltage of the individual batteries or cells, is to be used in determining the work space requirements in 110.26 for systems rated 1000 volts and less and 110.34 for systems rated over 1000 volts. Adequate ventilation is necessary to prevent an accumulation of an explosive mixture of the gases from batteries that generate hydrogen. The fumes given off by some storage batteries are very corrosive; therefore, wiring and its insulation must be of a type that withstands corrosion, as required by 110.11 and 310.10(F). Special precautions are necessary to ensure that all metalwork (such as metal raceways and metal racks) is designed or treated to be corrosion resistant. The battery racks pictured below are coated with a nonmetallic outer covering as required by 480.9. The covering insulates and provides protection against the corrosive action of fumes from batteries being charged and any electrolyte that might escape from the cells. (Courtesy of the International Association of Electrical Inspectors) Manufacturers sometimes suggest that aluminum or plastic conduit be used to withstand corrosive battery fumes or, if steel conduit is used, that it be zinc coated and corrosion protected with a coating of an asphaltum-type (asphalt-based) paint. See 300.6 for more on protection against corrosion and deterioration. Overcharging heats a battery and causes gassing and loss of water. A battery should not be allowed to reach temperatures over 110°F, because heat causes a shedding of active materials from the plates, which will eventually form a sediment buildup in the bottom of the case and short circuit the plates and the cell. Because mixtures of oxygen and hydrogen are highly explosive, flame or sparks should never be allowed near a cell, especially if the filler cap is removed. Ventilation. Provisions appropriate to the battery technology shall be made for sufficient diffusion and ventilation of gases from the battery, if present, to prevent the accumulation of an explosive mixture. Informational Note No. 1: See NFPA 1-2021, Fire Code, Chapter 52, for ventilation considerations for specific battery chemistries. Informational Note No. 2: Some battery technologies do not require ventilation. Informational Note No. 3: See IEEE Std 1635-2012/ASHRAE Guideline 21-2012, Guide for the Ventilation and Thermal Management of Batteries for Stationary Applications, for additional information on the ventilation of stationary battery systems. ENHANCED CONTENT Collapse Ventilation is necessary to prevent classification of a battery location as a hazardous (classified) location, in accordance with Article 500. Mechanical ventilation is not mandated. Hydrogen disperses rapidly and requires little air movement to prevent accumulation. Unrestricted natural air movement in the vicinity of the battery, together with normal air changes for occupied spaces or heat removal, normally is sufficient. If the space is confined, mechanical ventilation might be required in the vicinity of the battery. Hydrogen is lighter than air and tends to concentrate at ceiling level, so some form of ventilation should be provided at the upper portion of the structure. Ventilation can be a fan, a roof ridge vent, or a louvered area. Although valve-regulated batteries often are referred to as “sealed,” they actually emit very small quantities of hydrogen gas under normal operation and are capable of liberating large quantities of explosive gases if overcharged. These batteries, therefore, require the same amount of ventilation as their vented counterparts. Of the primary types of battery chemistries used in storage battery systems and energy storage systems, only lithium-ion and sodium-nickel chloride batteries do not require ventilation under normal or abnormal charging conditions. Live Parts. Guarding of live parts shall comply with 110.27. Spaces About Stationary Standby Batteries. Spaces about stationary standby batteries shall comply with 110.26 and 110.34. Working space shall be measured from the edge of the battery cabinet, racks, or trays. For battery racks, there shall be a minimum clearance of 25 mm (1 in.) between a cell container and any wall or structure on the side not requiring access for maintenance. Battery stands shall be permitted to contact adjacent walls or structures, provided that the battery shelf has a free air space for not less than 90 percent of its length. Informational Note: Additional space is often needed to accommodate battery hoisting equipment, tray removal, or spill containment. (D) Top Terminal Batteries. Where top terminal batteries are installed on tiered racks or on shelves of battery cabinets, working space in accordance with the battery manufacturer’s instructions shall be provided between the highest point on a cell and the row, shelf, or ceiling above that point. Informational Note: See IEEE 1187-2013, IEEE Recommended Practice for Installation Design and Installation of Valve-Regulated Lead-Acid Batteries for Stationary Applications, for guidance for top clearance of valve-regulated lead-acid batteries, which are commonly used in battery cabinets. (E) Egress. Personnel doors intended for entrance to, and egress from, rooms designated as battery rooms shall open at least 90 degrees in the direction of egress and shall be equipped with listed panic or listed fire exit hardware. Piping in Battery Rooms. Gas piping shall not be permitted in dedicated battery rooms. Illumination. Illumination shall be provided for working spaces containing stationary standby batteries. The lighting outlets shall not be controlled by automatic means only. Additional lighting outlets shall not be required where the work space is illuminated by an adjacent light source. The location of luminaires shall not result in the following: Expose personnel to energized battery components while performing maintenance on the luminaires in the battery space Create a hazard to the battery upon failure of the luminaire 480.11 Vents. (A) Vented Cells. Each vented cell shall be equipped with a flame arrester. Informational Note: A flame arrester prevents destruction of the cell due to ignition of gases within the cell by an external spark or flame. (B) Sealed Cells. Where the battery is constructed such that an excessive accumulation of pressure could occur within the cell during operation, a pressure-release vent shall be provided. 480.12 Battery Interconnections. Flexible cables, as identified in Table 400.4, in sizes 2/0 AWG and larger shall be permitted within the battery enclosure from battery terminals to a nearby junction box where they shall be connected to an approved wiring method. Flexible battery cables shall also be permitted between batteries and cells within the battery enclosure. Such cables shall be listed and identified for the environmental conditions. Flexible, fine-stranded cables shall only be used with terminals, lugs, devices, or connectors in accordance with 110.14. 480.13 Ground-Fault Detection. Battery circuits exceeding 100 volts between the conductors or to ground shall be permitted to operate with ungrounded conductors, provided a ground-fault detector and indicator is installed to monitor for ground faults.Article 495 Equipment Over 1000 Volts ac, 1500 Volts dc, Nominal Part I. General 495.1 Scope. This article covers the general requirements for equipment operating at more than 1000 volts ac, 1500 volts dc, nominal. Informational Note No. 1: See NFPA 70E-2021, Standard for Electrical Safety in the Workplace, for electrical safety requirements for employee workplaces. Informational Note No. 2: See ANSI Z535.4-2011, Product Signs and Safety Labels, for further information on hazard signs and labels. Informational Note No. 3: See IEEE 3001.5-2013, Recommended Practice for the Application of Power Distribution Apparatus in Industrial and Commercial Power Systems, for information regarding power distribution apparatus. ENHANCED CONTENT Collapse In developing the 2023 edition of the NEC, areas of former Article 490, Equipment Over 1000 Volts, Nominal, were modified and relocated to new Article 495, Equipment Over 1000 Volts ac, 1500 Volts dc, Nominal. Some portions of former Article 490 have also been relocated into other areas of the NEC. For example, former 490.21, which deals with circuit-interrupter devices, has been relocated to 245.21 of new Article 245, Overcurrent Protection for Systems Rated Over 1000 Volts ac, 1500 Volts dc. The threshold voltage for the requirements covering higher voltage equipment has been revised from 600 volts to 1000 volts beginning in the 2014 edition of the NEC to recognize that standard configurations commonly used in alternative energy systems operate at over 600 volts for increased efficiency and performance. One of the most impactful effects of those changes throughout the NEC was revision of former Article 490 to apply to equipment rated over 1000 volts rather than over 600 volts, and with that change, product certification standards were able to be modified. One of the best examples of how that change affected products is the availability of disconnecting means (safety switches) that are rated for 1000 volts dc, rather than that class of equipment being limited to 600-volt applications because it did not meet the product safety requirements in former Article 490. Prior to the change, switches to interrupt ac or dc circuits rated over 600 volts would have had to meet the “medium voltage” equipment requirements contained in former Article 490. The construction differences between two classes of equipment are illustrated below: a 5000-volt disconnecting means and a 1000-volt disconnecting means. 495.2 Reconditioned Equipment. Except as modified within this article, reconditioned equipment shall not be permitted. 495.3 Other Articles. Oil-Filled Equipment. Installation of electrical equipment containing more than 38 L (10 gal) of flammable oil per unit shall meet the requirements of Parts II and III of Article 450. Enclosures in Damp or Wet Locations. Enclosures in damp or wet locations shall meet the requirements of 312.2. Part II. Equipment — Specific Provisions 495.22 Isolating Means. Means shall be provided to completely isolate an item of equipment from all ungrounded conductors. The use of isolating switches shall not be required where there are other ways of de-energizing the equipment for inspection and repairs, such as draw-out-type switchgear units and removable truck panels. Isolating switches not interlocked with an approved circuit-interrupting device shall be provided with a sign warning against opening them under load. The warning sign(s) or label(s) shall comply with 110.21(B). An identified fuseholder and fuse shall be permitted as an isolating switch. 495.23 Voltage Regulators. Proper switching sequence for regulators shall be ensured by use of one of the following: (1) Mechanically sequenced regulator bypass switch(es) Mechanical interlocks Switching procedure prominently displayed at the switching location 495.24 Minimum Space Separation. In field-fabricated installations, the minimum air separation between bare live conductors and between such conductors and adjacent grounded surfaces shall not be less than the values given in Table 495.24. These values shall not apply to interior portions or exterior terminals of equipment designed, manufactured, and tested in accordance with accepted national standards. Table 495.24 Minimum Clearance of Live Parts Nominal Voltage Rating (kV) Impulse Withstand, Basic Impulse Level (BIL) (kV) Minimum Clearance of Live Parts Phase-to-Phase Phase-to-Ground Indoors Outdoors Indoors Outdoors Indoors Outdoors mm in. mm in. mm in. mm in. 2.4–4.16 60 95 115 4.5 180 7 80 3.0 155 6 7.2 75 95 140 5.5 180 7 105 4.0 155 6 13.8 95 110 195 7.5 305 12 130 5.0 180 7 14.4 110 110 230 9.0 305 12 170 6.5 180 7 23 125 150 270 10.5 385 15 190 7.5 255 10 34.5 150 150 320 12.5 385 15 245 9.5 255 10 200 200 460 18.0 460 18 335 13.0 335 13 46 — 200 — — 460 18 — — 335 13 — 250 — — 535 21 — — 435 17 69 — 250 — — 535 21 — — 435 17 — 350 — — 790 31 — — 635 25 115 — 550 — — 1350 53 — — 1070 42 138 — 550 — — 1350 53 — — 1070 42 — 650 — — 1605 63 — — 1270 50 161 — 650 — — 1605 63 — — 1270 50 — 750 — — 1830 72 — — 1475 58 230 — 750 — — 1830 72 — — 1475 58 — 900 — — 2265 89 — — 1805 71 — 1050 — — 2670 105 — — 2110 83 Note: The values given are the minimum clearance for rigid parts and bare conductors under favorable service conditions. They shall be increased for conductor movement or under unfavorable service conditions or wherever space limitations permit. The selection of the associated impulse withstand voltage for a particular system voltage is determined by the characteristics of the overvoltage(surge) protective equipment. 495.25 Backfeed. Installations where the possibility of backfeed exists shall comply with 495.25(A) and (B). Sign. A permanent sign in accordance with 110.21(B) shall be installed on the disconnecting means enclosure or immediately adjacent to open disconnecting means with the following words or equivalent: DANGER — CONTACTS ON EITHER SIDE OF THIS DEVICE MAY BE ENERGIZED BY BACKFEED. Diagram. A permanent and legible single-line diagram of the local switching arrangement, clearly identifying each point of connection to the high-voltage section, shall be provided within sight of each point of connection. Part III. Equipment — Switchgear and Industrial Control Assemblies 495.30 General. Part III covers assemblies of switchgear and industrial control equipment, including, but not l