SWITCHBOARDS AND PANELBOARDS

384-1. Scope. This article covers (1) all switchboards, panelboards, and distribution boards installed for the control of light and power circuits, and (2) battery-charging panels supplied from light or power circuits. Exception: Switchboards or portions thereof used exclusively to control signaling circuits operated by batteries. 384-2. Other Articles. Switches, circuit breakers, and overcurrent devices used on switchboards, panelboards, and distribution boards, and their enclosures, shall comply with this article and also with the requirements of Articles 240, 250, 370, 373, 380, and other articles that apply. Switchboards and panelboards in hazardous (classified) locations shall comply with the requirements of Articles 500 through 517. 384-3. Support and Arrangement of Busbars and Conductors. (a) Conductors and Busbars on a Switchboard, Panelboard, or Control Board. Conductors and busbars on a switchboard, panelboard, or control board shall be so located as to be free from physical damage and shall be held firmly in place. Other than the required interconnections and control wiring, only those conductors that are intended for termination in a vertical section of a switchboard shall be located in that section. Barriers shall be placed in all service switchboards that will isolate the service busbars and terminals from the remainder of the switchboard. Exception: Conductors shall be permitted to travel horizontally through vertical sections of switchboards where such conductors are isolated from busbars by a barrier. (b) Overheating and Inductive Effects. The arrangement of busbars and conductors shall be such as to avoid overheating due to inductive effects. (c) Used As Service Equipment. Each switchboard, or panelboard, if used as service equipment shall be provided with a main bonding jumper sized in accordance with Section 250-79(d) or the equivalent placed within the panelboard or one of the sections of the switchboard for connecting the grounded service conductor on its supply side to the switchboard or panelboard frame. All sections of a switchboard shall be bonded together using an equipment grounding conductor sized in accordance with Table 250-95. Exception: As covered in Section 250-27 for high-impedance. grounded neutral system connections. (d) Terminals. Terminals in switchboards and panelboards shall be so located that it will not be necessary to reach across or beyond an ungrounded line bus in order to make connections. ARTICLE 384 - SWITCHBOARDS AND PANELBOARDS 70-301 (e) High-Leg Marking. On a switchboard or panelboard supplied from a 4-wire delta-connected system, where the midpoint of one phase is grounded, that phase busbar or conductor having the higher voltage to ground shall be durably and permanently marked by an outer finish that is orange in color, or by other effective means. (f) Phase Arrangement. The phase arrangement on 3-phase buses shall be A, B, C from front to back, top to bottom, or left to right, as viewed from the front of the switchboard or panelboard. The B phase shall be that phase having the higher voltage to ground on 3-phase, 4-wire deltaconnected systems. Other busbar arrangements shall be permitted for additions to existing installations and shall be marked. Exception: Equipment within the same single section or multisection switchboard or panelboard as the meter on 3-phase, 4-wire deltaconnected systems shall be permitted to have the same phase configuration as the metering equipment. (g) Minimum Wire Bending Space. The minimum wire bending space at terminals and minimum gutter space provided in panelboards and switchboards shall be as required in Section 373-6. 384-4. Installation. Equipment within the scope of Article 384 shall be located in rooms or spaces dedicated to such equipment. Such space shall include that space described in Section 110-16 and, in addition, shall include an exclusively dedicated space extending 25 feet (7.62 m) from the floor or to the structural ceiling with a width and depth that of the equipment. No piping, ducts, or equipment foreign to the electrical equipment or architectural appurtenances shall be permitted to be installed in, enter, or pass through such spaces or rooms. (FPN No. 1): It is not the intent to mandate a dedicated room. (FPN No. 2): This section is not intended to prohibit sprinkler protection for the electrical installation. (FPN No. 3): For the purpose of this section, dropped, suspended, and similar ceilings not intended to add strength to the building structure are not structural ceilings. (FPN No. 4): It is not the intent that any of the provisions of this rule or the exceptions thereto allow any equipment to be located in the working space described in Section 110-16. Exception No. 1: Control equipment that by its very nature or because of other rules of this Code must be adjacent to or within sight of its operating machinery. Exception No. 2: Ventilating, heating, or cooling equipment that serves the electrical rooms or spaces. Exception No. 3: Equipment located throughout industrial plants that is isolated from foreign equipment by height or physical enclosures or covers that will afford adequate mechanical protection from vehicular traffic, accidental contact by unauthorized personnel, or accidental spillage or leakage from piping systems. Exception No. 4: Outdoor electrical equipment located in weatherproof enclosures protected from accidental contact by unauthorized personnel or vehicular traffic or accidental spillage or leakage from piping systems. 70-302 NATIONAL ELECTRICAL CODE A. Switchboards 384-5. Location of Switchboards. Switchboards that have any exposed live parts shall be located in permanently dry locations and then only where under competent supervision and accessible only to qualified persons. Switchboards shall be so located that the probability of damage from equipment or processes is reduced to a minimum. 384-6. Switchboards in Damp or Wet Locations. Switchboards in damp or wet locations shall be installed to comply with Section 373-2(a). 384-7. Location Relative to Easily Ignitible Material. Switchboards shall be so placed as to reduce to a minimum the probability of communicating fire to adjacent combustible materials. Where installed over a combustible floor, suitable protection thereto shall be provided. 384-8. Clearances. (a) From Ceiling. A space of 3 feet (914 mm) or more shall be provided between the top of any switchboard and any combustible ceiling. Exception No. 1: Where a noncombustible shield is provided between the switchboard and the ceiling. Exception No. 2: Totally enclosed switchboards. (b) Around Switchboards. Clearances around switchboards shall comply with the provisions of Section 110-16. 384-9. Conductor Insulation. An insulated conductor used within a switchboard shall be listed, flame-retardant, and shall be rated not less than the voltage applied to it and not less than the voltage applied to other conductors or busbars with which it may come in contact. 384-10. Clearance for Conductors Entering Bus Enclosures. Where conduits or other raceways enter a switchboard, floor standing panelboard, or similar enclosure at the bottom, sufficient space shall be provided to permit installation of conductors in the enclosure. The wiring space shall not be less than shown in the following table where the conduit or raceways enter or leave the enclosure below the busbars, their supports, or other obstructions. The conduit or raceways, including their end fittings, shall not rise more than 3 inches (76 mm) above the bottom of the enclosure. Minimum Spacing Between Bottom of Enclosure and Busbars, Their Supports, or Other Obstructions (Inches) Conductor Insulated busbars, their supports, or other obstructions 8 (203 mm) Noninsulated busbars 10 (254 mm) ARTICLE 384 - SWITCHBOARDS AND PANELBOARDS 70-303 384-11. Grounding Switchboard Frames. Switchboard frames and structures supporting switching equipment shall be grounded. Exception: Frames of 2-wire, direct-current switchboards shall not be required to be grounded if effectively insulated from ground. 384-12. Grounding of Instruments, Relays, Meters, and Instrument Transformers on Switchboards. Instruments, relays, meters, and instrument transformers located on switchboards shall be grounded as specified in Sections 250-121 through 250-125. B. Panelboards 384-13. General. All panelboards shall have a rating not less than the minimum feeder capacity required for the load computed in accordance with Article 220. Panelboards shall be durably marked by the manufacturer with the voltage and the current rating and the number of phases for which they are designed and with the manufacturer's name or trademark in such a manner as to be visible after installation, without disturbing the interior parts or wiring. All panelboard circuits and circuit modifications shall be legibly identified as to purpose or use on a circuit directory located on the face or inside of the panel doors. (FPN): See Section 110-22 for additional requirements. 384-14. Lighting and Appliance Branch-Circuit Panelboard. For the purposes of this article, a lighting and appliance branch-circuit panelboard is one having more than 10 percent of its overcurrent devices rated 30 amperes or less, for which neutral connections are provided. 384-15. Number of Overcurrent Devices on One Panelboard. Not more than forty-two overcurrent devices (other than those provided for in the mains) of a lighting and appliance branch-circuit panelboard shall be installed in any one cabinet or cutout box. A lighting and appliance branch-circuit panelboard shall be provided with physical means to prevent the installation of more overcurrent devices than that number for which the panelboard was designed, rated, and approved. For the purposes of this article, a 2-pole circuit breaker shall be considered two overcurrent devices; a 3-pole breaker shall be considered three overcurrent devices. 384-16. Overcurrent Protection. (a) Lighting and Appliance Branch-Circuit Panelboard Individually Protected. Each lighting and appliance branch-circuit panelboard shall be individually protected on the supply side by not more than two main circuit breakers or two sets of fuses having a combined rating not greater than that of the panelboard. Exception No. 1: Individual protection for a lighting and appliance panelboard shall not be required if the panelboard feeder has overcurrent protection not greater than the rating of the panelboard. 70-304 NATIONAL ELECTRICAL CODE Exception No. 2: For existing installations, individual protection for lighting and appliance branch-circuit panelboards shall not be required where such panelboards are used as service equipment in supplying an individual residential occupancy. (b) Snap Switches Rated at 30 Amperes or Less. Panelboards equipped with snap switches rated at 30 amperes or less shall have overcurrent protection not in excess of 200 amperes. (c) Continuous Load. The total load on any overcurrent device located in a panelboard shall not exceed 80 percent of its rating where, in normal operation, the load will continue for three hours or more. Exception: Where the assembly, including the overcurrent device, is listed for continuous operation at 100 percent of its rating. (d) Supplied through a Transformer. Where a panelboard is supplied through a transformer, the overcurrent protection required in (a) and (b) above shall be located on the secondary side of the transformer. Exception: A panelboard supplied by the secondary side of a singlephase transformer having a 2-wire (single-voltage) secondary shall be considered as protected by overcurrent protection provided on the primary (supply) side of the transformer, provided this protection is in accordance with Section 450-3(b)(1) and does not exceed the value determined by multiplying the panelboard rating by the secondary-to-primary voltage ratio. (e) Delta Breakers. A 3-phase disconnect or overcurrent device shall not be connected to the bus of any panelboard that has less than 3-phase buses. (FPN): This is intended to prohibit the use of "delta breakers" in panelboards. (f) Back-Fed Devices. Plug-in-type overcurrent protection devices or plug-in-type main lug assemblies that are back fed shall be secured in place by an additional fastener that requires other than a pull to release the device from the mounting means on the panel. 384-17. Panelboards in Damp or Wet Locations. Panelboards in damp or wet locations shall be installed to comply with Section 373-2(a). 384-18. Enclosure. Panelboards shall be mounted in cabinets, cutout boxes, or enclosures designed for the purpose and shall be dead front. Exception: Panelboards other than of the dead-front externally operable type shall be permitted where accessible only to qualified persons. 384-19. Relative Arrangement of Switches and Fuses. In panelboards, fuses of any type shall be installed on the load side of any switches. Exception: As provided in Section 230-94 for use as service equipment. 384-20. Grounding of Panelboards. Panelboard cabinets and panelboard frames, if of metal, shall be in physical contact with each other and shall be grounded in accordance with Article 250 or Section 384-3(c). Where the panelboard is used with nonmetallic raceway or cable or where separate ARTICLE 384 - SWITCHBOARDS AND PANELBOARDS 70-305 grounding conductors are provided, a terminal bar for the grounding conductors shall be secured inside the cabinet. The terminal bar shall be bonded to the cabinet and panelboard frame, if of metal, otherwise it shall be connected to the grounding conductor that is run with the conductors feeding the panelboard. Grounding conductors shall not be connected to a terminal bar provided for grounded conductors (may be a neutral) unless the bar is identified for the purpose and is located where connection is made from the grounded conductor to a grounding electrode as permitted or required by Article 250. Exception: Where an isolated equipment grounding conductor is provided as permitted by Section 250-74, Exception No. 4, this insulated equipment grounding conductor that is run with the circuit conductors shall be permitted to pass through the panelboard without being connected to the panelboard's equipment grounding terminal bar. C. Construction Specifications 384-30. Panels. The panels of switchboards shall be made of moistureresistant, noncombustible material. 384-31. Busbars. Insulated or bare busbars shall be rigidly mounted. 384-32. Protection of Instrument Circuits. Instruments, pilot lights, potential transformers, and other switchboard devices with potential coils shall be supplied by a circuit that is protected by standard overcurrent devices rated 15 amperes or less. Exception No. 1: Where the operation of the overcurrent device might introduce a hazard in the operation of devices. Exception No. 2: For ratings of 2 amperes or less, special types of enclosed fuses shall be permitted. 384-33. Component Parts. Switches, fuses, and fuseholders used on panelboards shall comply with the applicable requirements of Articles 240 and 380. 384-34. Knife Switches. Exposed blades of knife switches shall be deenergized when open. 384-35. Wire Bending Space in Panelboards. The enclosure for a panelboard shall have the top and bottom wire bending space sized in accordance with Table 373-6(b) for the largest conductor entering or leaving the enclosure. Side wire bending space shall be in accordance with Table 373- 6(a) for the largest conductor to be terminated in that space. Exception No. 1: Either the top or bottom wire bending space shall be permitted to be sized in accordance with Table 373-6(a) for a lighting and appliance branch-circuit panelboard rated 225 amperes or less. 70-306 NATIONAL ELECTRICAL CODE Exception No. 2: Either the top or bottom wire bending space for any panelboard shall be permitted to be sized in accordance with Table 373-6(a) where at least one side wire bending space is sized in accordance with Table 373-6(b) for the largest conductor to be terminated in any side wire bending space. Exception No. 3: The top and bottom wire bending space shall be permitted to be sized in accordance with Table 373-6(a) spacings if the panelboard is designed and constructed for wiring using only one single 90-degree bend for each conductor, including the neutral, and the wiring diagram shows and specifies the method of wiring that shall be used. Exception No. 4: Either the top or the bottom wire bending space, but not both, shall be permitted to be sized in accordance with Table 373-6(a) where there are no conductors terminated in that space. 384-36. Minimum Spacings. The distance between bare metal parts, busbars, etc., shall not be less than specified in Table 384-36. Exception No. 1: At switches or circuit breakers. Exception No. 2: Inherent spacings in listed components. Where close proximity does not cause excessive heating, parts of the same polarity at switches, enclosed fuses, etc., shall be permitted to be placed as close together as convenience in handling will allow. Table 384-36. Minimum Spacings Between Bare Metal Parts Opposite Opposite Polarity Polarity Where Where Mounted on Held the Same Free Live Parts Surface in Air to Ground* Not over 125 volts, nominal 3/4 inch ½ inch ½ inch Not over 250 volts, nominal 1½ inch 3/4 inch ½ inch Not over 600 volts, nominal 2 inches 1 inch 1 inch For SI units: one inch = 25.4 millimeters. *For spacing between live parts and doors of cabinets, see Sections 373-11(a) (1), (2), and (3). 70-307 Chapter 4. Equipment for General Use