Switchboards, Switchgear, and Panelboards
Part I. General
- Scope. This article covers switchboards, switchgear, and panelboards. It does not apply to equipment operating at over 1000 volts, except as specifically referenced elsewhere in the Code.
- Other Articles. Switches, circuit breakers, and overcur‐ rent devices used on switchboards, switchgear, and panelboards and their enclosures shall comply with this article and also with the requirements of Articles 240, 250, 312, 404, and other arti‐ cles that apply. Switchboards, switchgear, and panelboards in hazardous (classified) locations shall comply with the applica‐ ble provisions of Articles 500 through 517.
- Support and Arrangement of Busbars and Conductors.
- Conductors and Busbars on a Switchboard, Switchgear, or Panelboard. Conductors and busbars on a switchboard, switchgear, or panelboard shall comply with 408.3(A)(1), (A)(2), and (A)(3) as applicable.
- Location. Conductors and busbars shall be located so as to be free from physical damage and shall be held firmly in place.
- Service Panelboards, Switchboards, and Switchgear. Barri‐ ers shall be placed in all service panelboards, switchboards, and switchgear such that no uninsulated, ungrounded service busbar or service terminal is exposed to inadvertent contact by persons or maintenance equipment while servicing load termi‐ nations.
Exception: This requirement shall not apply to service panelboards withprovisions for more than one service disconnect within a single enclo‐ sure as permitted in 408.36, Exceptions 1, 2, and 3.
- Same Vertical Section. Other than the required intercon‐ nections and control wiring, only those conductors that are intended for termination in a vertical section of a switchboard or switchgear shall be located in that section.Exception: Conductors shall be permitted to travel horizontally through vertical sections of switchboards and switchgear where such conductors are isolated from busbars by a barrier.
- Overheating and Inductive Effects. The arrangement of busbars and conductors shall be such as to avoid overheating due to inductive effects.
- Used as Service Equipment. Each switchboard, switch‐ gear, or panelboard, if used as service equipment, shall be provided with a main bonding jumper sized in accordance with 250.28(D) or the equivalent placed within the panelboard or one of the sections of the switchboard or switchgear for connecting the grounded service conductor on its supply side to the switchboard, switchgear, or panelboard frame. All sections of a switchboard or switchgear shall be bonded together using an equipment-bonding jumper or a supply-side bonding jumper sized in accordance with 250.122 or 250.102(C)(1) as applicable.Exception: Switchboards, switchgear, and panelboards used as service equipment on high-impedance grounded neutral systems in accordance with 250.36 shall not be required to be provided with a main bonding jumper.
- Terminals. In switchboards, switchgear, and panelboards, load terminals for field wiring, including grounded circuit conductor load terminals and connections to the equipment grounding conductor bus for load equipment grounding conductors, shall be so located that it is not necessary to reach across or beyond an uninsulated ungrounded bus in order to make connections.
- Bus Arrangement.
- AC Phase Arrangement. Alternating-current 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, switchgear, or panelboard. The B phase shall be that phase having the higher voltage to ground on 3-phase, 4-wire, delta-connected 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, switchgear, or panelboard as the meter on 3-phase, 4-wire, delta-connected systems shall be permitted to have the same phase config‐ uration as the metering equipment.Informational Note: See 110.15 for requirements on marking the busbar or phase conductor having the higher voltage to ground where supplied from a 4-wire, delta-connected system.
- DC Bus Arrangement. Direct-current ungrounded buses shall be permitted to be in any order. Arrangement of dc buses shall be field marked as to polarity, grounding system, and nominal voltage.
- Switchboard, Switchgear, or Panelboard Identification. A caution sign(s) or a label(s) provided in accordance with 408.3(F)(1) through (F)(5) shall comply with 110.21(B).
- High-Leg Identification. A switchboard, switchgear, or panelboard containing a 4-wire, delta-connected system where the midpoint of one phase winding is grounded shall be legibly and permanently field marked as follows:“Caution Phase Has Volts to Ground”
- Ungrounded AC Systems. A switchboard, switchgear, or panelboard containing an ungrounded ac electrical system as permitted in 250.21 shall be legibly and permanently field marked as follows:“Caution Ungrounded System Operating — Volts Between Conductors”ARTICLE 408 — SWITCHBOARDS, SWITCHGEAR, AND PANELBOARDS 408.22
- High-Impedance Grounded Neutral AC System. A switch‐ board, switchgear, or panelboard containing a high-impedanceTable 408.5 Clearance for Conductors Entering Bus Enclosuresgrounded neutral ac system in accordance with 250.36 shall be legibly and permanently field marked as follows:CAUTION: HIGH-IMPEDANCE GROUNDED NEUTRAL AC SYSTEM OPERATING — VOLTS BETWEEN CONDUCTORS AND MAY OPERATE — VOLTS TO GROUND FOR INDEFINITE PERIODS UNDER FAULT CONDITIONS
- Ungrounded DC Systems. A switchboard, switchgear, or
ConductorInsulated busbars, their supports, or other obstructionsMinimum Spacing Between Bottom of Enclosure and Busbars, Their Supports, or Other Obstructionsmm in.200 8panelboard containing an ungrounded dc electrical system in accordance with 250.169 shall be legibly and permanently field marked as follows:CAUTION: UNGROUNDED DC SYSTEM OPERATING — VOLTS BETWEEN CONDUCTORS
- Resistively Grounded DC Systems. A switchboard, switch‐ gear, or panelboard containing a resistive connection between current-carrying conductors and the grounding system to stabi‐ lize voltage to ground shall be legibly and permanently field marked as follows:CAUTION: DC SYSTEM OPERATING — VOLTS BETWEEN CONDUCTORS ANDMAY OPERATE — VOLTS TO GROUND FOR INDEFI‐ NITE PERIODS UNDER FAULT CONDITIONS
- Minimum Wire-Bending Space. The minimum wire- bending space at terminals and minimum gutter space provi‐ ded in switchboards, switchgear, and panelboards shall be as required in 312.6.
- Conductors and Busbars on a Switchboard, Switchgear, or Panelboard. Conductors and busbars on a switchboard, switchgear, or panelboard shall comply with 408.3(A)(1), (A)(2), and (A)(3) as applicable.
- Field Identification Required.
- Circuit Directory or Circuit Identification. Every circuit and circuit modification shall be legibly identified as to its clear, evident, and specific purpose or use. The identification shall include an approved degree of detail that allows each circuit to be distinguished from all others. Spare positions that contain unused overcurrent devices or switches shall be descri‐ bed accordingly. The identification shall be included in a circuit directory that is located on the face or inside of the panel door in the case of a panelboard and at each switch or circuit breaker in a switchboard or switchgear. No circuit shall be described in a manner that depends on transient conditions of occupancy.
- Source of Supply. All switchboards, switchgear, and panel‐ boards supplied by a feeder(s) in other than one- or two-family dwellings shall be permanently marked to indicate each device or equipment where the power originates. The label shall be permanently affixed, of sufficient durability to withstand the environment involved, and not handwritten.
- Clearance for Conductor Entering Bus Enclosures. Where conduits or other raceways enter a switchboard, switch‐ gear, floor-standing panelboard, or similar enclosure at the bottom, approved space shall be provided to permit installation of conductors in the enclosure. The wiring space shall not be less than shown in Table 408.5 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 75 mm (3 in.) above the bottom of the enclosure.
Noninsulated busbars 250 10
408.7 Unused Openings. Unused openings for circuit break‐ ers and switches shall be closed using identified closures, or other approved means that provide protection substantially equivalent to the wall of the enclosure.
Part II. Switchboards and Switchgear
- Switchboards and Switchgear in Damp or Wet Loca‐ tions. Switchboards and switchgear in damp or wet locations shall be installed in accordance with 312.2.
- Location Relative to Easily Ignitible Material. Switch‐ boards and switchgear shall be placed so as to reduce to a mini‐ mum the probability of communicating fire to adjacent combustible materials. Where installed over a combustible floor, suitable protection thereto shall be provided.
- From Ceiling. For other than a totally enclosed switch‐ board or switchgear, a space not less than 900 mm (3 ft) shall be provided between the top of the switchboard or switchgear and any combustible ceiling, unless a noncombustible shield is provided between the switchboard or switchgear and the ceil‐ ing.
- Around Switchboards and Switchgear. Clearances around switchboards and switchgear shall comply with the provisions of 110.26.
- Conductor Insulation. An insulated conductor used within a switchboard or switchgear shall be listed, shall be 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 into contact.
- Location of Switchboards and Switchgear. Switch‐ boards and switchgear 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 and switchgear shall be located such that the probability of damage from equipment or processes is reduced to a minimum.
408.22 Grounding of Instruments, Relays, Meters, and Instru‐ ment Transformers on Switchboards and Switchgear. Instru‐ ments, relays, meters, and instrument transformers located on switchboards and switchgear shall be grounded as specified in
250.170 through 250.178.
Part III. Panelboards
408.30 General. All panelboards shall have a rating not less than the minimum feeder capacity required for the load calcu‐ lated in accordance with Part III, IV, or V of Article 220, as applicable.
- Overcurrent Protection. In addition to the require‐ ment of 408.30, a panelboard shall be protected by an overcur‐ rent protective device having a rating not greater than that of the panelboard. This overcurrent protective device shall be located within or at any point on the supply side of the panel‐ board.Exception No. 1: Individual protection shall not be required for a panelboard used as service equipment with multiple disconnecting means in accordance with 230.71. In panelboards protected by three or more main circuit breakers or sets of fuses, the circuit breakers or sets of fuses shall not supply a second bus structure within the same panel‐ board assembly.Exception No. 2: Individual protection shall not be required for a panelboard protected on its supply side by two main circuit breakers or two sets of fuses having a combined rating not greater than that of the panelboard. A panelboard constructed or wired under this exception shall not contain more than 42 overcurrent devices. For the purposes of determining the maximum of 42 overcurrent devices, a 2-pole or a 3-pole circuit breaker shall be considered as two or three overcurrent devices, respectively.Exception No. 3: For existing panelboards, individual protection shall not be required for a panelboard used as service equipment for an indi‐ vidual residential occupancy.
- Snap Switches Rated at 30 Amperes or Less. Panelboards equipped with snap switches rated at 30 amperes or less shall have overcurrent protection of 200 amperes or less.
- Supplied Through a Transformer. Where a panelboard is supplied through a transformer, the overcurrent protection required by 408.36 shall be located on the secondary side of the transformer.Exception: A panelboard supplied by the secondary side of a transformer shall be considered as protected by the overcurrent protection provided on the primary side of the transformer where that protection is in accord‐ ance with 240.21(C)(1).
- 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. Delta breakers shall not be instal‐ led in panelboards.
- Back-Fed Devices. Plug-in-type overcurrent protection devices or plug-in type main lug assemblies that are backfed and used to terminate field-installed ungrounded supply conductors 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.
- Panelboards in Damp or Wet Locations. Panelboards in damp or wet locations shall be installed to comply with 312.2.
- Enclosure. Panelboards shall be mounted in cabinets, cutout boxes, or identified enclosures 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.
- Relative Arrangement of Switches and Fuses. In panel‐ boards, fuses of any type shall be installed on the load side of any switches.Exception: Fuses installed as part of service equipment in accordance with the provisions of 230.94 shall be permitted on the line side of the service switch.
- Grounding of Panelboards. Panelboard cabinets and panelboard frames, if of metal, shall be in physical contact with each other and shall be connected to an equipment grounding conductor. Where the panelboard is used with nonmetallic raceway or cable or where separate equipment grounding conductors are provided, a terminal bar for the equipment 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 equip‐ ment grounding conductor that is run with the conductors feeding the panelboard.Exception: Where an isolated equipment grounding conductor is provi‐ ded as permitted by 250.146(D), the insulated equipment grounding conductor that is run with the circuit conductors shall be permitted to pass through the panelboard without being connected to the panel‐ board’s equipment grounding terminal bar.Equipment grounding conductors shall not be connected to a terminal bar provided for grounded conductors or neutral conductors unless the bar is identified for the purpose and is located where interconnection between equipment grounding conductors and grounded circuit conductors is permitted or required by Article 250.
- Grounded Conductor Terminations. Each grounded conductor shall terminate within the panelboard in an individ‐ ual terminal that is not also used for another conductor.
Exception: Grounded conductors of circuits with parallel conductors shall be permitted to terminate in a single terminal if the terminal is identified for connection of more than one conductor.
Part IV. Construction Specifications
- Panels. The panels of switchboards and switchgear shall be made of moisture-resistant, noncombustible material.
- Busbars. Insulated or bare busbars shall be rigidly mounted.
- Protection of Instrument Circuits. Instruments, pilot lights, voltage (potential) transformers, and other switchboard or switchgear 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: Overcurrent devices rated more than 15 amperes shall be permitted where the interruption of the circuit could create a hazard. Short-circuit protection shall be provided.Exception No. 2: For ratings of 2 amperes or less, special types of enclosed fuses shall be permitted.
- Component Parts. Switches, fuses, and fuseholders used on panelboards shall comply with the applicable require‐ ments of Articles 240 and 404.
- Maximum Number of Overcurrent Devices. A panel‐ board shall be provided with physical means to prevent theARTICLE 409 — INDUSTRIAL CONTROL PANELS 409.21
installation of more overcurrent devices than that number for which the panelboard was designed, rated, and listed.For the purposes of this section, a 2-pole circuit breaker or fusible switch shall be considered two overcurrent devices; a 3- pole circuit breaker or fusible switch shall be considered three overcurrent devices.
- Wire-Bending Space Within an Enclosure Containing a Panelboard.
- Top and Bottom Wire-Bending Space. The enclosure for a panelboard shall have the top and bottom wire-bending space sized in accordance with Table 312.6(B) for the largest conduc‐ tor entering or leaving the enclosure.Exception No. 1: Either the top or bottom wire-bending space shall be permitted to be sized in accordance with Table 312.6(A) for a panel‐ board rated 225 amperes or less and designed to contain not over 42 overcurrent devices. For the purposes of this exception, a 2-pole or a 3-pole circuit breaker shall be considered as two or three overcurrent devices, respectively.Exception No. 2: Either the top or bottom wire-bending space for any panelboard shall be permitted to be sized in accordance with Table 312.6(A) where at least one side wire-bending space is sized in accordance with Table 312.6(B) for the largest conductor to be termina‐ ted 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 312.6(A) spacings if the panelboard is designed and constructed for wiring using only a single 90-degree bend for each conductor, including the grounded circuit conductor, 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 312.6(A) where there are no conductors terminated in that space.
- Side Wire-Bending Space. Side wire-bending space shall be in accordance with Table 312.6(A) for the largest conductor to be terminated in that space.
- Back Wire-Bending Space. Where a raceway or cable entry is in the wall of the enclosure opposite a removable cover, the distance from that wall to the cover shall be permitted to comply with the distance required for one wire per terminal in Table 312.6(A). The distance between the center of the rear entry and the nearest termination for the entering conductors shall not be less than the distance given in Table 312.6(B).
- Minimum Spacings. The distance between bare metal parts, busbars, and so forth shall not be less than specified in Table 408.56.
Where close proximity does not cause excessive heating, parts of the same polarity at switches, enclosed fuses, and so forth shall be permitted to be placed as close together as convenience in handling will allow.
Exception: The distance shall be permitted to be less than that specified in Table 408.56 at circuit breakers and switches and in listed compo‐ nents installed in switchboards, switchgear, and panelboards.
Table 408.56 Minimum Spacings Between Bare Metal Parts
AC or DC Voltage
|Opposite Polarity Where Mounted on the Same Surface
|Opposite Polarity Where Held Free in Air
Live Parts to Ground*
|Not over 125 volts, nominalNot over 250 volts, nominalNot over 1000 volts, nominal
*For spacing between live parts and doors of cabinets, see 312.11(A) (1), (2), and (3).
408.58 Panelboard Marking. Panelboards shall be durably marked by the manufacturer with the voltage and the current rating and the number of ac phases or dc buses for which they are designed and with the manufacturer’s name or trademark in such a manner so as to be visible after installation, without disturbing the interior parts or wiring.