Article 368

Busways

Part I. General Requirements

1. Scope. This article covers service-entrance, feeder, and branch-circuit busways and associated fittings.
2. Definition.

Busway. A raceway consisting of a metal enclosure containing factory-mounted, bare or insulated conductors, which are usually copper or aluminum bars, rods, or tubes.

Informational Note: For cablebus, refer to Article 370.

Part II. Installation

368.10 Uses Permitted. Busways shall be permitted to be installed where they are located in accordance with 368.10(A) through (C).

Informational Note: See 300.21 for information concerning the spread of fire or products of combustion.

1. Exposed. Busways shall be permitted to be located in the open where visible, except as permitted in 368.10(C).
2. Behind Access Panels. Busways shall be permitted to be installed behind access panels, provided the busways are totally enclosed, of nonventilating-type construction, and installed so that the joints between sections and at fittings are accessible for maintenance purposes. Where installed behind access panels, means of access shall be provided, and either of the following conditions shall be met:
   1. The space behind the access panels shall not be used for air-handling purposes.
   2. Where the space behind the access panels is used for environmental air, other than ducts and plenums, there shall be no provisions for plug-in connections, and the conductors shall be insulated.
3. Through Walls and Floors. Busways shall be permitted to be installed through walls or floors in accordance with (C)(1) and (C)(2).
   1. Walls. Unbroken lengths of busway shall be permitted to be extended through dry walls.
   2. Floors. Floor penetrations shall comply with (a) and (b):
      1. Busways shall be permitted to be extended vertically through dry floors if totally enclosed (unventilated) where passing through and for a minimum distance of 1.8 m (6 ft) above the floor to provide adequate protection from physical damage.368.12 ARTICLE 368 — BUSWAYS
      2. In other than industrial establishments, where a verti‐ cal riser penetrates two or more dry floors, a minimum 100-mm (4-in.) high curb shall be installed around all floor openings for riser busways to prevent liquids from entering the opening. The curb shall be installed within 300 mm (12 in.) of the floor opening. Electrical equipment shall be located so that it will not be damaged by liquids that are retained by the curb.

368.12 Uses Not Permitted.

1. Physical Damage. Busways shall not be installed where subject to severe physical damage or corrosive vapors.
2. Hoistways. Busways shall not be installed in hoistways.
3. Hazardous Locations. Busways shall not be installed in any hazardous (classified) location, unless specifically approved for such use.Informational Note: See 501.10(B).
4. Wet Locations. Busways shall not be installed outdoors or in wet or damp locations unless identified for such use.
5. Working Platform. Lighting busway and trolley busway shall not be installed less than 2.5 m (8 ft) above the floor or working platform unless provided with an identified cover.

368.17 Overcurrent Protection. Overcurrent protection shall be provided in accordance with 368.17(A) through (D).

1. Rating of Overcurrent Protection — Feeders. A busway shall be protected against overcurrent in accordance with the allowable current rating of the busway.Exception No. 1: The applicable provisions of 240.4 shall be permitted.Exception No. 2: Where used as transformer secondary ties, the provi‐ sions of 450.6(A)(3) shall be permitted.
2. Reduction in Ampacity Size of Busway. Overcurrent protection shall be required where busways are reduced in ampacity.Exception: For industrial establishments only, omission of overcurrent protection shall be permitted at points where busways are reduced in ampacity, provided that the length of the busway having the smaller ampacity does not exceed 15 m (50 ft) and has an ampacity at least equal to one-third the rating or setting of the overcurrent device next back on the line, and provided that such busway is free from contact with combustible material.
3. Feeder or Branch Circuits. Where a busway is used as a feeder, devices or plug-in connections for tapping off feeder or branch circuits from the busway shall contain the overcurrent devices required for the protection of the feeder or branch circuits. The plug-in device shall consist of an externally opera‐ ble circuit breaker or an externally operable fusible switch. Where such devices are mounted out of reach and contain disconnecting means, suitable means such as ropes, chains, or sticks shall be provided for operating the disconnecting means from the floor.Exception No. 1: As permitted in 240.21.Exception No. 2: For fixed or semifixed luminaires, where the branch- circuit overcurrent device is part of the luminaire cord plug on cord- connected luminaires.Exception No. 3: Where luminaires without cords are plugged directly into the busway and the overcurrent device is mounted on the lumin‐ aire.
   Exception No. 4: Where the branch-circuit overcurrent plug-in device isdirectly supplying a readily accessible disconnect, a method of floor oper‐ ation shall not be required.
4. Rating of Overcurrent Protection — Branch Circuits. A busway used as a branch circuit shall be protected against over‐ current in accordance with 210.20.

368.30 Support. Busways shall be securely supported at inter‐ vals not exceeding 1.5 m (5 ft) unless otherwise designed and marked.

368.56 Branches from Busways. Branches from busways shall be permitted to be made in accordance with 368.56(A), (B), and (C).

1. General. Branches from busways shall be permitted to use any of the following wiring methods:
   1. Type AC armored cable
   2. Type MC metal-clad cable
   3. Type MI mineral-insulated, metal-sheathed cable
   4. Type IMC intermediate metal conduit
   5. Type RMC rigid metal conduit
   6. Type FMC flexible metal conduit
   7. Type LFMC liquidtight flexible metal conduit
   8. Type PVC rigid polyvinyl chloride conduit
   9. Type RTRC reinforced thermosetting resin conduit
   10. Type LFNC liquidtight flexible nonmetallic conduit
   11. Type EMT electrical metallic tubing
   12. Type ENT electrical nonmetallic tubing
   13. Busways
   14. Strut-type channel raceway
   15. Surface metal raceway
   16. Surface nonmetallic racewayWhere a separate equipment grounding conductor is used, connection of the equipment grounding conductor to the busway shall comply with 250.8 and 250.12.
2. Cord and Cable Assemblies. Suitable cord and cable assemblies approved for extra-hard usage or hard usage and listed bus drop cable shall be permitted as branches from busways for the connection of portable equipment or the connection of stationary equipment to facilitate their inter‐ change in accordance with 400.10 and 400.12 and the follow‐ ing conditions:
   1. The cord or cable shall be attached to the building by an approved means.
   2. The length of the cord or cable from a busway plug-in device to a suitable tension take-up support device shall not exceed 1.8 m (6 ft).
   3. The cord and cable shall be installed as a vertical riser from the tension take-up support device to the equip‐ ment served.
   4. Strain relief cable grips shall be provided for the cord or cable at the busway plug-in device and equipment termi‐ nations.
   Exception to (B)(2): In industrial establishments only, where the condi‐ tions of maintenance and supervision ensure that only qualified persons service the installation, lengths exceeding 1.8 m (6 ft) shall be permitted between the busway plug-in device and the tension take-up support device where the cord or cable is supported at intervals not exceeding 2.5 m (8 ft).
3. Branches from Trolley-Type Busways. Suitable cord and cable assemblies approved for extra-hard usage or hard usage

ARTICLE 370 — CABLEBUS 370.10

and listed bus drop cable shall be permitted as branches from trolley-type busways for the connection of movable equipment in accordance with 400.10 and 400.12.

368.58 Dead Ends. A dead end of a busway shall be closed.

368.60 Grounding. Busway shall be connected to an equip‐ ment grounding conductor(s), to an equipment bonding jumper, or to the grounded conductor where permitted or required by 250.92(B)(1) or 250.142.

Part III. Construction

368.120 Marking. Busways shall be marked with the voltage and current rating for which they are designed, and with the manufacturer’s name or trademark in such a manner as to be visible after installation.

Part IV. Requirements for Over 1000 Volts, Nominal

368.214 Adjacent and Supporting Structures. Metal-enclosed busways shall be installed so that temperature rise from induced circulating currents in adjacent ferrous metal parts will not be hazardous to personnel or constitute a fire hazard.

368.234 Barriers and Seals.

1. Vapor Seals. Busway runs that have sections located both inside and outside of buildings shall have a vapor seal at the building wall to prevent interchange of air between indoor and outdoor sections.Exception: Vapor seals shall not be required in forced-cooled bus.
2. Fire Barriers. Fire barriers shall be provided where fire walls, floors, or ceilings are penetrated.

Informational Note: See 300.21 for information concerning the spread of fire or products of combustion.

1. Drain Facilities. Drain plugs, filter drains, or similar methods shall be provided to remove condensed moisture from low points in busway run.
2. Ventilated Bus Enclosures. Ventilated busway enclo‐ sures shall be installed in accordance with Article 110, Part III, and 490.24.
3. Terminations and Connections. Where bus enclo‐ sures terminate at machines cooled by flammable gas, seal-off bushings, baffles, or other means shall be provided to prevent accumulation of flammable gas in the busway enclosures.All conductor termination and connection hardware shall be accessible for installation, connection, and maintenance.
4. Switches. Switching devices or disconnecting links provided in the busway run shall have the same momentary rating as the busway. Disconnecting links shall be plainly marked to be removable only when bus is de-energized. Switch‐ ing devices that are not load-break shall be interlocked to prevent operation under load, and disconnecting link enclo‐ sures shall be interlocked to prevent access to energized parts.
5. Wiring 1000 Volts or Less, Nominal. Secondary control devices and wiring that are provided as part of the metal-enclosed bus run shall be insulated by fire-retardant barriers from all primary circuit elements with the exception of

short lengths of wire, such as at instrument transformer termi‐ nals.

368.244 Expansion Fittings. Flexible or expansion connec‐ tions shall be provided in long, straight runs of bus to allow for temperature expansion or contraction, or where the busway run crosses building vibration insulation joints.

368.258 Neutral Conductor. Neutral bus, where required, shall be sized to carry all neutral load current, including harmonic currents, and shall have adequate momentary and short-circuit rating consistent with system requirements.

368.260 Grounding. Metal-enclosed busway shall be groun‐ ded.

368.320 Marking. Each busway run shall be provided with a permanent nameplate on which the following information shall be provided:

1. Rated voltage.
2. Rated continuous current; if bus is forced-cooled, both the normal forced-cooled rating and the self-cooled (not forced-cooled) rating for the same temperature rise shall be given.
3. Rated frequency.
4. Rated impulse withstand voltage.
5. Rated 60-Hz withstand voltage (dry).
6. Rated momentary current.
7. Manufacturer’s name or trademark.

Informational Note: See ANSI C37.23-1987 (R1991), Guide for Metal-Enclosed Bus and Calculating Losses in Isolated-Phase Bus, for construction and testing requirements for metal-enclosed buses.