Article 490

Equipment Over 1000 Volts, Nominal

Part I. General

Scope. This article covers the general requirements for equipment operating at more than 1000 volts, nominal.Informational Note No. 1: See NFPA 70E -2015, Standard for Elec‐ trical Safety in the Workplace, for electrical safety requirements for employee workplaces.Informational Note No. 2: For further information on hazard signs and labels, see ANSI Z535.4-2011, Product Signs and Safety Labels.
Definition.High Voltage. For the purposes of this article, more than 1000 volts, nominal.
Other Articles.

Oil-Filled Equipment. Installation of electrical equip‐ ment, other than transformers covered in Article 450, contain‐ ing more than 38 L (10 gal) of flammable oil per unit shall meet the requirements of Parts II and III of Article 450.N
Enclosures in Damp or Wet Locations. Enclosures in damp or wet locations shall meet the requirements of 312.2.

Part II. Equipment — Specific Provisions

Circuit-Interrupting Devices.
1. Circuit Breakers.
  1. Location.
    1. Circuit breakers installed indoors shall be mounted either in metal-enclosed units or fire-resistant cell-mounted units, or they shall be permitted to be open-mounted in loca‐ tions accessible to qualified persons only.
    2. Circuit breakers used to control oil-filled transform‐ ers in a vault shall either be located outside the transformer vault or be capable of operation from outside the vault.
    3. Oil circuit breakers shall be arranged or located so that adjacent readily combustible structures or materials are safeguarded in an approved manner.
  2. Operating Characteristics. Circuit breakers shall have the following equipment or operating characteristics:
    1. An accessible mechanical or other identified means for manual tripping, independent of control power
    2. Be release free (trip free)
    3. If capable of being opened or closed manually while energized, main contacts that operate independently of the speed of the manual operation
    4. A mechanical position indicator at the circuit breaker to show the open or closed position of the main contacts
    5. A means of indicating the open and closed position of the breaker at the point(s) from which they may be oper‐ ated
    1. Nameplate. A circuit breaker shall have a permanent and legible nameplate showing manufacturer’s name or trademark, manufacturer’s type or identification number, continuous current rating, interrupting rating in megavolt-amperes (MVA) or amperes, and maximum voltage rating. Modification of a circuit breaker affecting its rating(s) shall be accompanied by an appropriate change of nameplate information.
    2. Rating. Circuit breakers shall have the following ratings:
    1. The continuous current rating of a circuit breaker shall not be less than the maximum continuous current through the circuit breaker.
    2. The interrupting rating of a circuit breaker shall not be less than the maximum fault current the circuit breaker will be required to interrupt, including contributions from all connected sources of energy.
    3. The closing rating of a circuit breaker shall not be less than the maximum asymmetrical fault current into which the circuit breaker can be closed.
    4. The momentary rating of a circuit breaker shall not be less than the maximum asymmetrical fault current at the point of installation.
    5. The rated maximum voltage of a circuit breaker shall not be less than the maximum circuit voltage.
2. Power Fuses and Fuseholders.
  1. Use. Where fuses are used to protect conductors and equipment, a fuse shall be placed in each ungrounded conduc‐ tor. Two power fuses shall be permitted to be used in parallel to protect the same load if both fuses have identical ratings and both fuses are installed in an identified common mounting with electrical connections that divide the current equally. Power fuses of the vented type shall not be used indoors,
    underground, or in metal enclosures unless identified for the use.
  2. Interrupting Rating. The interrupting rating of power fuses shall not be less than the maximum fault current the fuse is required to interrupt, including contributions from all connected sources of energy.
  3. Voltage Rating. The maximum voltage rating of power fuses shall not be less than the maximum circuit voltage. Fuses having a minimum recommended operating voltage shall not be applied below this voltage.
  4. Identification of Fuse Mountings and Fuse Units. Fuse mountings and fuse units shall have permanent and legible nameplates showing the manufacturer’s type or designation, continuous current rating, interrupting current rating, and maximum voltage rating.
  5. Fuses. Fuses that expel flame in opening the circuit shall be designed or arranged so that they function properly without hazard to persons or property.
  6. Fuseholders. Fuseholders shall be designed or installed so that they are de-energized while a fuse is being replaced. A field-applied permanent and legible sign, in accordance with 110.21(B), shall be installed immediately adjacent to the fuse‐ holders and shall be worded as follows:DANGER — DISCONNECT CIRCUIT BEFORE REPLAC‐ ING FUSES.Exception: Fuses and fuseholders designed to permit fuse replacement by qualified persons using identified equipment without de-energizing the fuseholder shall be permitted.
  7. High-Voltage Fuses. Switchgear and substations that utilize high-voltage fuses shall be provided with a gang- operated disconnecting switch. Isolation of the fuses from the circuit shall be provided by either connecting a switch between the source and the fuses or providing roll-out switch and fuse- type construction. The switch shall be of the load-interrupter type, unless mechanically or electrically interlocked with a load- interrupting device arranged to reduce the load to the inter‐ rupting capability of the switch.Exception: More than one switch shall be permitted as the disconnecting means for one set of fuses where the switches are installed to provide connection to more than one set of supply conductors. The switches shall be mechanically or electrically interlocked to permit access to the fuses only when all switches are open. A conspicuous sign shall be placed at the fuses identifying the presence of more than one source.
3. Distribution Cutouts and Fuse Links — Expulsion Type.
  1. Installation. Cutouts shall be located so that they may be readily and safely operated and re-fused, and so that the exhaust of the fuses does not endanger persons. Distribution cutouts shall not be used indoors, underground, or in metal enclosures.
  2. Operation. Where fused cutouts are not suitable to inter‐ rupt the circuit manually while carrying full load, an approved means shall be installed to interrupt the entire load. Unless the fused cutouts are interlocked with the switch to prevent open‐ ing of the cutouts under load, a conspicuous sign shall be placed at such cutouts identifying that they shall not be oper‐ ated under load.
  3. Interrupting Rating. The interrupting rating of distribu‐ tion cutouts shall not be less than the maximum fault current the cutout is required to interrupt, including contributions from all connected sources of energy.
  4. Voltage Rating. The maximum voltage rating of cutouts shall not be less than the maximum circuit voltage.
  5. Identification. Distribution cutouts shall have on their body, door, or fuse tube a permanent and legible nameplate or identification showing the manufacturer’s type or designation, continuous current rating, maximum voltage rating, and inter‐ rupting rating.
  6. Fuse Links. Fuse links shall have a permanent and legible identification showing continuous current rating and type.
  7. Structure Mounted Outdoors. The height of cutouts mounted outdoors on structures shall provide safe clearance between lowest energized parts (open or closed position) and standing surfaces, in accordance with 110.34(E).
4. Oil-Filled Cutouts.
  1. Continuous Current Rating. The continuous current rating of oil-filled cutouts shall not be less than the maximum continuous current through the cutout.
  2. Interrupting Rating. The interrupting rating of oil-filled cutouts shall not be less than the maximum fault current the oil-filled cutout is required to interrupt, including contribu‐ tions from all connected sources of energy.
  3. Voltage Rating. The maximum voltage rating of oil-filled cutouts shall not be less than the maximum circuit voltage.
  4. Fault Closing Rating. Oil-filled cutouts shall have a fault closing rating not less than the maximum asymmetrical fault current that can occur at the cutout location, unless suitable interlocks or operating procedures preclude the possibility of closing into a fault.
  5. Identification. Oil-filled cutouts shall have a permanent and legible nameplate showing the rated continuous current, rated maximum voltage, and rated interrupting current.
  6. Fuse Links. Fuse links shall have a permanent and legible identification showing the rated continuous current.
  7. Location. Cutouts shall be located so that they are readily and safely accessible for re-fusing, with the top of the cutout not over 1.5 m (5 ft) above the floor or platform.
  8. Enclosure. Suitable barriers or enclosures shall be provi‐ ded to prevent contact with nonshielded cables or energized parts of oil-filled cutouts.
5. Load Interrupters. Load-interrupter switches shall be permitted if suitable fuses or circuit breakers are used in conjunction with these devices to interrupt fault currents. Where these devices are used in combination, they shall be coordinated electrically so that they will safely withstand the effects of closing, carrying, or interrupting all possible currents up to the assigned maximum short-circuit rating.Where more than one switch is installed with interconnected load terminals to provide for alternate connection to different supply conductors, each switch shall be provided with a conspicuous sign identifying this hazard.
  1. Continuous Current Rating. The continuous current rating of interrupter switches shall equal or exceed the maxi‐ mum continuous current at the point of installation.
  2. Voltage Rating. The maximum voltage rating of inter‐ rupter switches shall equal or exceed the maximum circuit volt‐ age.
  3. Identification. Interrupter switches shall have a perma‐ nent and legible nameplate including the following informa‐ tion: manufacturer’s type or designation, continuous current rating, interrupting current rating, fault closing rating, maxi‐ mum voltage rating.
  4. Switching of Conductors. The switching mechanism shall be arranged to be operated from a location 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 arranged to be locked in the open position. Metal-enclosed switches shall be operable from outside the enclosure.
  5. 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.
  6. Supply Terminals. The supply terminals of fused inter‐ rupter switches shall be installed at the top of the switch enclo‐ sure, or, if the terminals are located elsewhere, the equipment shall have barriers installed so as to prevent persons from acci‐ dentally contacting energized parts or dropping tools or fuses into energized parts.
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.
Voltage Regulators. Proper switching sequence for regulators shall be ensured by use of one of the following:
1. Mechanically sequenced regulator bypass switch(es)
2. Mechanical interlocks
3. Switching procedure prominently displayed at the switch‐ ing location
Minimum Space Separation. In field-fabricated instal‐ lations, the minimum air separation between bare live conduc‐ tors and between such conductors and adjacent grounded surfaces shall not be less than the values given in Table 490.24. These values shall not apply to interior portions or exterior terminals of equipment designed, manufactured, and tested in accordance with accepted national standards.
Backfeed. Installations where the possibility of back‐ feed exists shall comply with (a) and (b), which follow.
1. A permanent sign in accordance with 110.21(B) shall be installed on the disconnecting means enclosure or immedi‐ ately adjacent to open disconnecting means with the followingwords or equivalent: DANGER — CONTACTS ON EITHER SIDE OF THIS DEVICE MAY BE ENERGIZED BY BACKFEED.
2. 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

General. Part III covers assemblies of switchgear and industrial control equipment including, but not limited to, switches and interrupting devices and their control, metering, protection, and regulating equipment where they are an inte‐ gral part of the assembly, with associated interconnections and supporting structures.
Arrangement of Devices in Assemblies. Arrangement of devices in assemblies shall be such that individual compo‐ nents can safely perform their intended function without adversely affecting the safe operation of other components in the assembly.
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 compart‐ ments 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.
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.
Clearance for Cable Conductors Entering Enclosure. The unobstructed space opposite terminals or opposite race‐ ways or cables entering a switchgear or control assembly shall be approved for the type of conductor and method of termina‐ tion.
Accessibility of Energized Parts.
1. 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.
2. Control Equipment. Where operating at 1000 volts, nomi‐ nal, or less, control equipment, relays, motors, and the like shall not be installed in compartments with exposed high- voltage energized parts or high-voltage wiring, unless either of the following conditions is met:
  1. The access means is interlocked with the high-voltage switch or disconnecting means to prevent the access means from being opened or removed.
  2. The high-voltage switch or disconnecting means is in the isolating position.
3. High-Voltage Instruments or Control Transformers and Space Heaters. High-voltage instrument or control transform‐ ers 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.
Grounding. Frames of switchgear and control assem‐ blies shall be connected to an equipment grounding conductor or, where permitted, the grounded conductor.
Grounding of Devices. The metal cases or frames, or both, such as those of instruments, relays, meters, and instru‐ ment and control transformers, located in or on switchgear or control assemblies, shall be connected to an equipment grounding conductor or, where permitted, the grounded conductor.
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.
Gas Discharge from Interrupting Devices. Gas discharged during operating of interrupting devices shall be directed so as not to endanger personnel.
Visual Inspection Windows. Windows intended for visual inspection of disconnecting switches or other devices shall be of suitable transparent material.
Location of Industrial Control Equipment. Routinely operated industrial control equipment shall meet the require‐ ments of (A) unless infrequently operated, as covered in 490.41(B).
1. 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.
2. 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.
Interlocks — Interrupter Switches. Interrupter switches equipped with stored energy mechanisms shall have mechanical interlocks to prevent access to the switch compart‐ ment unless the stored energy mechanism is in the discharged or blocked position.
Stored Energy for Opening. The stored energy opera‐ tor shall be permitted to be left in the uncharged position after the switch has been closed if a single movement of the operat‐ ing handle charges the operator and opens the switch.
Fused Interrupter Switches.
1. Supply Terminals. The supply terminals of fused inter‐ rupter switches shall be installed at the top of the switch enclo‐ sure or, if the terminals are located elsewhere, the equipment shall have barriers installed so as to prevent persons from acci‐ dentally contacting energized parts or dropping tools or fuses into energized parts.
  Table 490.24 Minimum Clearance of Live Parts
  
  Nominal Voltage
  Impulse Withstand, Basic Impulse Level B.I.L (kV)Minimum Clearance of Live PartsPhase-to-Phase Phase-to-Ground Indoors Outdoors Indoors OutdoorsRating (kV)IndoorsOutdoorsmmin.mmin.mmin.mmin.2.4–4.1660951154.51807803.015567.275951405.518071054.0155613.8951101957.5305121305.0180714.41101102309.0305121706.518072312515027010.5385151907.52551034.515015032012.5385152459.525510
  20020046018.04601833513.03351346—200——46018——33513
  —250——53521——4351769—250——53521——43517
  —350——79031——63525115—550——135053——107042138—550——135053——107042
  —650——160563——127050161—650——160563——127050
  —750——183072——147558230—750——183072——147558
  —900——226589——180571
  —1050——2670105——211083Note: 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 surge protective equipment.
2. Backfeed. Where fuses can be energized by backfeed, a sign shall be placed on the enclosure door identifying this hazard.
3. 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 in accordance with 110.25.
Circuit Breakers — Interlocks.
1. 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.
2. 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.
Circuit Breaker Locking. Circuit breakers shall be capable of being locked in the open position or, if they are installed in a drawout 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 in accordance with 110.25.
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 490.35(A) shall include a notice that access is limited to the serving utility or is permitted only following an authorization of the serving utility.
Substation Design, Documentation, and Required Diagram.

Design and Documentation. Substations shall be designed by a qualified licensed professional engineer. Where compo‐ nents or the entirety of the substation are 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.
1. Clearances and exits
2. Electrical enclosures
3. Securing and support of electrical equipment
4. Fire protection
5. Safety ground connection provisions
6. Guarding live parts
7. Transformers and voltage regulation equipment
8. Conductor insulation, electrical and mechanical protec‐ tion, isolation, and terminations
9. Application, arrangement, and disconnection of circuit breakers, switches, and fuses
10. Provisions for oil filled equipment
11. Switchgear
12. Surge arresters
Diagram. A permanent, single-line diagram of the switch‐ gear shall be provided in a readily visible location within the same room or enclosed area with the switchgear, and this diagram shall clearly identify interlocks, isolation means, and all possible sources of voltage to the installation under normal or emergency conditions and the marking on the switchgear shall cross-reference the diagram.

Exception: Where the equipment consists solely of a single cubicle or metal-enclosed unit substation containing only one set of high-voltage switching devices, diagrams shall not be required.

Part IV. Mobile and Portable Equipment

General.
1. Covered. The provisions of this part shall apply to installa‐ tions and use of high-voltage power distribution and utilization equipment that is portable, mobile, or both, such as substations and switch houses mounted on skids, trailers, or cars; mobile shovels; draglines; cranes; hoists; drills; dredges; compressors; pumps; conveyors; underground excavators; and the like.
2. Other Requirements. The requirements of this part shall be additional to, or amendatory of, those prescribed in Arti‐ cles 100 through 725 of this Code. Special attention shall be paid to Article 250.
3. Protection. Approved enclosures or guarding, or both, shall be provided to protect portable and mobile equipment from physical damage.
4. 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.
Overcurrent Protection. Motors driving single or multiple dc generators supplying a system operating on a cyclic load basis do not require overload protection, provided that 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 protec‐ tion and shall be permitted to be external to the equipment.
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.
Collector Rings. The collector ring assemblies on revolving-type machines (shovels, draglines, etc.) shall be guar‐ ded to prevent accidental contact with energized parts by personnel on or off the machine.
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 ground‐ ing 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 connec‐ tions. The enclosure shall have provision for locking so that only authorized and qualified persons may 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).
High-Voltage Portable Cable for Main Power Supply. Flexible high-voltage cable supplying power to portable or mobile equipment shall comply with Article 250 and Arti‐ cle 400, Part III.

Part V. Electrode-Type Boilers

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.
Electrical Supply System. Electrode-type 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.
Branch-Circuit Requirements.
1. Rating. Each boiler shall be supplied from an individual branch circuit rated not less than 100 percent of the total load.
2. 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 thecircuit upon removal of an overload condition but shall not reclose after a fault condition.
3. 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.
4. 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 71∕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.
5. Grounded Neutral Conductor. The grounded neutral conductor shall be as follows:
1. Connected to the pressure vessel containing the electro‐ des
2. Insulated for not less than 1000 volts
3. Have not less than the ampacity of the largest ungrounded branch-circuit conductor
4. 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
5. Not used for any other circuit
Pressure and Temperature Limit Control. Each boiler shall be equipped with a means to limit the maximum tempera‐ ture, pressure, or both, by directly or indirectly interrupting all current flow through the electrodes. Such means shall be in addition to the temperature, pressure, or both, regulating systems and pressure relief or safety valves.
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 accord‐ ance with 250.102, except the ampacity of the bonding jumper shall not be less than the ampacity of the neutral conductor.

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