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imited to, switches and interrupting devices and their control, metering, protection, and regulating equipment where they are an integral part of the assembly, with associated interconnections and supporting structures. ENHANCED CONTENT Collapse Indicator instruments, such as voltmeters, ammeters, w...

imited to, switches and interrupting devices and their control, metering, protection, and regulating equipment where they are an integral part of the assembly, with associated interconnections and supporting structures. ENHANCED CONTENT Collapse Indicator instruments, such as voltmeters, ammeters, wattmeters, and protective relays, can be mounted on the panel doors as desired. This switchgear affords a high degree of safety because all live parts are metal-enclosed, and interlocks are provided for safe operation. 495.31 Arrangement of Devices in Assemblies. Arrangement of devices in assemblies shall be such that individual components can safely perform their intended function without adversely affecting the safe operation of other components in the assembly. 495.32 Guarding of High-Voltage Energized Parts Within a Compartment. Where access for other than visual inspection is required to a compartment that contains energized high-voltage parts, barriers shall be provided to prevent accidental contact by persons, tools, or other equipment with energized parts. Exposed live parts shall only be permitted in compartments accessible to qualified persons. Fuses and fuseholders designed to enable future replacement without de-energizing the fuseholder shall only be permitted for use by qualified persons. ENHANCED CONTENT Collapse An example of a high-voltage pad-mounted transformer and enclosure that may contain primary and secondary switches or circuit breakers is pictured below. The high-voltage compartment on the left of the exhibit has bayonet fusing and a load-break transformer on/off switch, which are both hot-stick operated. (Courtesy of Schneider Electric) 495.33 Guarding of Energized Parts Operating at 1000 Volts, Nominal, or Less Within Compartments. Energized bare parts mounted on doors shall be guarded where the door must be opened for maintenance of equipment or removal of draw-out equipment. 495.34 Clearance for Cable Conductors Entering Enclosure. The unobstructed space opposite terminals or opposite raceways or cables entering a switchgear or control assembly shall be approved for the type of conductor and method of termination. 495.35 Accessibility of Energized Parts. High-Voltage Equipment. Doors that would provide unqualified persons access to high-voltage energized parts shall be locked. Permanent signs in accordance with 110.21(B) shall be installed on panels or doors that provide access to live parts over 1000 volts and shall read DANGER — HIGH VOLTAGE — KEEP OUT. Control Equipment. Where operating at 1000 volts, nominal, or less, control equipment, relays, motors, and the like shall not be installed in compartments with high-voltage parts or high-voltage wiring, unless both of the following apply: The access means is interlocked with the high-voltage switch or disconnecting means to prevent the access means from being opened or removed when the high-voltage switch is in the closed position or a withdrawable disconnecting means is in the connected position. All high-voltage parts or high-voltage wiring in the compartment that remains energized when a fixed mounted high-voltage switch is in the open position or a withdrawable disconnecting means is in the isolating (fully withdrawn) position are protected by insulating or grounded metal barriers to prevent accidental contact with energized high-voltage parts or wiring. High-Voltage Instruments or Control Transformers and Space Heaters. High-voltage instrument or control transformers and space heaters shall be permitted to be installed in the high-voltage compartment without access restrictions beyond those that apply to the high-voltage compartment generally. 495.37 Equipment Grounding Connections. The metal cases or frames, or both, such as those of instruments, relays, meters, and instrument and control transformers, located in or on switchgear or control assemblies, and the frames of switchgear and control assemblies shall be connected to an equipment grounding conductor or, where permitted, the grounded conductor, in accordance with 250.190. 495.38 Door Stops and Cover Plates. External hinged doors or covers shall be provided with stops to hold them in the open position. Cover plates intended to be removed for inspection of energized parts or wiring shall be equipped with lifting handles and shall not exceed 1.1 m2 (12 ft2) in area or 27 kg (60 lb) in weight, unless they are hinged and bolted or locked. 495.39 Gas Discharge from Interrupting Devices. Gas discharged during operating of interrupting devices shall be directed so as not to endanger personnel. 495.40 Visual Inspection Windows. Windows intended for visual inspection of disconnecting switches or other devices shall be of suitable transparent material. 495.41 Location of Industrial Control Equipment. Routinely operated industrial control equipment shall meet the requirements of 495.41(A) unless infrequently operated, as covered in 495.41(B). Control and Instrument Transfer Switch Handles or Push Buttons. Control and instrument transfer switch handles or push buttons shall be in a readily accessible location at an elevation of not over 2.0 m (6 ft 7 in.). Exception: Operating handles requiring more than 23 kg (50 lb) of force shall be located no higher than 1.7 m (66 in.) in either the open or closed position. Infrequently Operated Devices. Where operating handles for such devices as draw-out fuses, fused potential or control transformers and their primary disconnects, and bus transfer and isolating switches are only operated infrequently, the handles shall be permitted to be located where they are safely operable and serviceable from a portable platform. 495.42 Interlocks — Interrupter Switches. Interrupter switches equipped with stored energy mechanisms shall have mechanical interlocks to prevent access to the switch compartment unless the stored energy mechanism is in the discharged or blocked position. 495.43 Stored Energy for Opening. The stored energy operator shall be permitted to be left in the uncharged position after the switch has been closed if a single movement of the operating handle charges the operator and opens the switch. 495.44 Fused Interrupter Switches. Supply Terminals. The supply terminals of fused interrupter switches shall be installed at the top of the switch enclosure or, if the terminals are located elsewhere, the equipment shall have barriers installed to prevent persons from accidentally contacting energized parts or dropping tools or fuses into energized parts. Backfeed. Where fuses can be energized by backfeed, a sign shall be placed on the enclosure door identifying this hazard. Switching Mechanism. The switching mechanism shall be arranged to be operated from a location outside the enclosure where the operator is not exposed to energized parts and shall be arranged to open all ungrounded conductors of the circuit simultaneously with one operation. Switches shall be lockable open in accordance with 110.25. 495.45 Circuit Breakers — Interlocks. Circuit Breakers. Circuit breakers equipped with stored energy mechanisms shall be designed to prevent the release of the stored energy unless the mechanism has been fully charged. Mechanical Interlocks. Mechanical interlocks shall be provided in the housing to prevent the complete withdrawal of the circuit breaker from the housing when the stored energy mechanism is in the fully charged position, unless a suitable device is provided to block the closing function of the circuit breaker before complete withdrawal. 495.46 Circuit Breaker Locking. Circuit breakers shall be capable of being locked in the open position or, if they are installed in a draw-out mechanism, that mechanism shall be capable of being locked in such a position that the mechanism cannot be moved into the connected position. In either case, the provision for locking shall be lockable open in accordance with 110.25. 495.47 Switchgear Used as Service Equipment. Switchgear installed as high-voltage service equipment shall include a ground bus for the connection of service cable shields and to facilitate the attachment of safety grounds for personnel protection. This bus shall be extended into the compartment where the service conductors are terminated. Where the compartment door or panel provides access to parts that can only be de-energized and visibly isolated by the serving utility, the warning sign required by 495.35(A) shall include a notice that access is limited to the serving utility or is permitted only following an authorization of the serving utility. ENHANCED CONTENT Collapse Switchgear must include a ground bus for the service cable shields. The bus must extend to the compartment where the service conductor terminals are located. It also provides a location for the connection of temporary protective grounding equipment for protection of personnel during servicing of the equipment. See also 120.5 of NFPA 70E®, Standard for Electrical Safety in the Workplace®, 2021 edition, for temporary protective grounding equipment requirements, as it relates to establishing an electrically safe work condition (ESWC). 495.48 Substation Design, Documentation, and Required Diagram. Design and Documentation. Substations shall be designed by a qualified licensed professional engineer. Where components or the entirety of the substation is listed by a qualified electrical testing laboratory, documentation of internal design features subject to the listing investigation shall not be required. The design shall address but not be limited to the following topics, and the documentation of this design shall be made available to the authority having jurisdiction: Clearances and exits Electrical enclosures Securing and support of electrical equipment Fire protection Safety ground connection provisions Guarding live parts Transformers and voltage regulation equipment Conductor insulation, electrical and mechanical protection, isolation, and terminations Application, arrangement, and disconnection of circuit breakers, switches, and fuses Provisions for oil-filled equipment Switchgear Overvoltage (surge) protection equipment Diagram. A permanent, single-line diagram of the switchgear shall be provided in a readily visible location within the same room or enclosed area with the switchgear and shall clearly identify the following: Interlocks Isolation means All possible sources of voltage to the installation under normal or emergency conditions The marking on the switchgear shall cross-reference the diagram. Exception: Where the equipment consists solely of a single cubicle or metal-enclosed substation containing only one high-voltage switching device, diagrams shall not be required. 495.49 Reconditioned Switchgear. Reconditioned switchgear, or sections of switchgear, shall be permitted. If equipment has been damaged by fire, products of combustion, or water, it shall be specifically evaluated by its manufacturer or a qualified testing laboratory prior to being returned to service. Part IV. Mobile and Portable Equipment 495.61 General. Covered. The provisions of this part shall apply to installations and use of high-voltage power distribution and utilization equipment that is portable, mobile, or both, and include but not be limited to the following: Substations and switch houses mounted on skids Trailers or cars Mobile shovels Draglines Cranes Hoists Drills Dredges Compressors Pumps Conveyors Underground excavators Grounding and Bonding. Grounding and bonding shall be in accordance with Part X of Article 250. Protection. Approved enclosures or guarding, or both, shall be provided to protect portable and mobile equipment from physical damage. Disconnecting Means. Disconnecting means shall be installed for mobile and portable high-voltage equipment according to the requirements of Part VIII of Article 230 and shall disconnect all ungrounded conductors. 495.62 Overcurrent Protection. Motors driving single or multiple dc generators supplying a system operating on a cyclic load basis shall not require overload protection if the thermal rating of the ac drive motor cannot be exceeded under any operating condition. The branch-circuit protective device(s) shall provide short-circuit and locked-rotor protection and shall be permitted to be external to the equipment. 495.63 Enclosures. All energized switching and control parts shall be enclosed in grounded metal cabinets or enclosures. These cabinets or enclosures shall be marked DANGER — HIGH VOLTAGE — KEEP OUT and shall be locked so that only authorized and qualified persons can enter. The danger marking(s) or label(s) shall comply with 110.21(B). Circuit breakers and protective equipment shall have the operating means projecting through the metal cabinet or enclosure so these units can be reset without opening locked doors. With doors closed, safe access for normal operation of these units shall be provided. 495.64 Collector Rings. The collector ring assemblies on revolving-type machines (shovels, draglines, etc.) shall be guarded to prevent accidental contact with energized parts by personnel on or off the machine. 495.65 Power Cable Connections to Mobile Machines. A metallic enclosure shall be provided on the mobile machine for enclosing the terminals of the power cable. The enclosure shall include terminal connections to the machine frame for the equipment grounding conductor. Ungrounded conductors shall be attached to insulators or be terminated in approved high-voltage cable couplers (which include equipment grounding conductor connectors) of proper voltage and ampere rating. The method of cable termination used shall prevent any strain or pull on the cable from stressing the electrical connections. The enclosure shall have provision for locking so that only authorized and qualified persons can open it and shall be marked as follows: DANGER — HIGH VOLTAGE — KEEP OUT. The danger marking(s) or label(s) shall comply with 110.21(B). 495.66 High-Voltage Portable Cable for Main Power Supply. Flexible high-voltage cable supplying power to portable or mobile equipment shall comply with the grounding and bonding requirements in Parts V, VI, and X of Article 250 and the flexible cable requirements in Part III of Article 400. Part V. Boilers 495.70 General. The provisions of Part V shall apply to boilers operating over 1000 volts, nominal, in which heat is generated by the passage of current between electrodes through the liquid being heated. 495.71 Electrical Supply System. Boilers shall be supplied only from a 3-phase, 4-wire solidly grounded wye system, or from isolating transformers arranged to provide such a system. Control circuit voltages shall not exceed 150 volts, shall be supplied from a grounded system, and shall have the controls in the ungrounded conductor. 495.72 Branch-Circuit Requirements. Rating. Each boiler shall be supplied from an individual branch circuit rated not less than 100 percent of the total load. Common-Trip Fault-Interrupting Device. The circuit shall be protected by a 3-phase, common-trip fault-interrupting device, which shall be permitted to automatically reclose the circuit upon removal of an overload condition but shall not reclose after a fault condition. Phase-Fault Protection. Phase-fault protection shall be provided in each phase, consisting of a separate phase-overcurrent relay connected to a separate current transformer in the phase. Ground Current Detection. Means shall be provided for detection of the sum of the neutral conductor and equipment grounding conductor currents and shall trip the circuit-interrupting device if the sum of those currents exceeds the greater of 5 amperes or 7 1⁄2 percent of the boiler full-load current for 10 seconds or exceeds an instantaneous value of 25 percent of the boiler full-load current. Grounded Neutral Conductor. The grounded neutral conductor shall be as follows: Connected to the pressure vessel containing the heating elements Insulated for not less than 1000 volts Have not less than the ampacity of the largest ungrounded branch-circuit conductor Installed with the ungrounded conductors in the same raceway, cable, or cable tray, or, where installed as open conductors, in close proximity to the ungrounded conductors Not used for any other circuit 495.73 Pressure and Temperature Limit Control. Each boiler shall be equipped with a means to limit the maximum temperature, pressure, or both, by directly or indirectly interrupting all current flow through the heating elements. Such means shall be in addition to the temperature, pressure, or both, regulating systems and pressure relief or safety valves. 495.74 Bonding. All exposed non-current-carrying metal parts of the boiler and associated exposed metal structures or equipment shall be bonded to the pressure vessel or to the neutral conductor to which the vessel is connected in accordance with 250.102, except the ampacity of the bonding jumper shall not be less than the ampacity of the neutral conductor. Article 500 Hazardous (Classified) Locations, Classes I, II, and III, Divisions 1 and 2 ENHANCED CONTENT Collapse Articles 500 through 516 cover the requirements for electrical installations in locations classified as hazardous due to the materials handled, processed, or stored in those locations. Hazardous (classified) locations, if properly treated, are not necessarily any more dangerous to work in than other areas or locations. Hazardous locations are sometimes referred to as classified locations. As used in other NFPA codes and standards and the NEC, the terms are interchangeable. Some of the most common materials encountered in hazardous locations are flammable and combustible liquids. A flammable liquid is one that has a flash point below 100°F, while a combustible liquid has a flash point at or above 100°F. A flammable or combustible liquid must be at its flash point before an explosion can occur. For example, No. 1-D diesel fuel oil and kerosene, with flash points higher than 100°F, are combustible liquids and do not emit flammable vapors unless heated above their flash points. Article 500 is limited to locations classified as Class I, Class II, or Class III, which are further addressed in Articles 501, 502, and 503, respectively. Articles 505 and 506 contain the requirements for using the classification by Zones. Article 504 on intrinsically safe systems is used for both methods (Division and Zone) of area classification. 500.1 Scope. ENHANCED CONTENT Collapse It is outside the scope of the NEC to classify hazardous locations. The NEC provides the requirements for installing electrical equipment within locations classified as hazardous through compliance with other standards. The NEC does not classify areas where explosive materials, such as ammunition, dynamite, and blasting powder, are present. Areas where such materials are present are not considered hazardous locations in accordance with Article 500. However, many organizations responsible for the safety of such areas require equipment and wiring methods suitable for hazardous locations as part of many safety precautions, even though the equipment and wiring have not been investigated for such locations. Further information on these locations can be found in NFPA 495, Explosive Materials Code. Covered. This article covers area classification and general requirements for electrical and electronic equipment and wiring rated at all voltages where fire or explosion hazards might exist due to flammable gases, flammable liquid–produced vapors, combustible liquid–produced vapors, combustible dusts, combustible fibers/flyings, or ignitible fibers/flyings in the following: Class I, Division 1 or Class I, Division 2 hazardous (classified) locations Class II, Division 1 or Class II, Division 2 hazardous (classified) locations Class III, Division 1 or Class III, Division 2 hazardous (classified) locations Informational Note No. 1: See NFPA 497, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, and NFPA 499, Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, for extracted information referenced in brackets. Only editorial changes were made to the extracted text to make it consistent with this Code. Informational Note No. 2: See Article 100 for the definition of restricted industrial establishment [as applied to hazardous (classified) locations]. Not Covered. This article does not cover electrical and electronic equipment and wiring rated at all voltages for the following: Zone 0, Zone 1, or Zone 2 hazardous (classified) locations Zone 20, Zone 21, or Zone 22 hazardous (classified) locations Locations subject to the unique risk and explosion hazards associated with explosives, pyrotechnics, and blasting agents Locations where pyrophoric materials are the only materials used or handled Features of equipment that involve nonelectrical potential sources of ignition (e.g., couplings, pumps, gearboxes, brakes, hydraulic and pneumatic motors, fans, engines, compressors) Informational Note No. 1: Common nonelectrical potential sources of ignition include hot surfaces and mechanically generated sparks. Informational Note No. 2: See ANSI/UL 80079-36, Explosive Atmospheres — Part 36: Non-Electrical Equipment for Explosive Atmospheres — Basic Method and Requirements, and ANSI/UL 80079-37, Explosive Atmospheres — Part 37: Non-Electrical Equipment for Explosive Atmospheres — Non-Electrical Type of Protection Constructional Safety “c” Control of Ignition Source “b”, Liquid Immersion “k”, for additional information. ENHANCED CONTENT Collapse Because pyrophoric materials ignite spontaneously upon contact with air, the use of electrical equipment suitable for hazardous locations will not prevent ignition of such materials. Instead, the process containment system should be designed to prevent contact between pyrophoric material and air. 500.4 Documentation. Areas designated as hazardous (classified) locations or determined to be unclassified shall be documented on an area classification drawing and other associated documentation. This documentation shall be available to the authority having jurisdiction (AHJ) and those authorized to design, install, inspect, maintain, or operate electrical equipment at the location. Informational Note No. 1: See the following standards for additional information on the classification of locations: (1) NFPA 30, Flammable and Combustible Liquids Code (2) NFPA 32, Standard for Drycleaning Facilities (3) NFPA 33, Standard for Spray Application Using Flammable or Combustible Materials (4) NFPA 34, Standard for Dipping, Coating, and Printing Processes Using Flammable or Combustible Liquids (5) NFPA 35, Standard for the Manufacture of Organic Coatings (6) NFPA 36, Standard for Solvent Extraction Plants (7) NFPA 45, Standard on Fire Protection for Laboratories Using Chemicals (8) NFPA 55, Compressed Gases and Cryogenic Fluids Code (9) NFPA 58, Liquefied Petroleum Gas Code (10) NFPA 59, Utility LP-Gas Plant Code (11) NFPA 497, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas (12) NFPA 499, Recommended Practice for the Class