370.3Article 370 — Cablebus

shall be accessible for installation, connection, and mainte- ARTICLE 370nance. Cablebus368.239 Switches

ContentsSwitching devices or disconnecting links provided in thebusway run shall have the same momentary rating as the 370.1 Scopebusway. Disconnecting links shall be plainly marked to be 370.2 Definitionremovable only when bus is de-energized. Switching devices 370.3 Usethat are not load-break shall be interlocked to prevent opera- 370.4 Conductorstion under load, and disconnecting link enclosures shall be (A) Types of Conductorsinterlocked to prevent access to energized parts. (B) Ampacity of Conductors

(C) Size and Number of Conductors(D) Conductor Supports368.240 Wiring 600 Volts or Less, Nominal

370.5 Overcurrent ProtectionSecondary control devices and wiring that are provided as370.6 Support and Extension Through Walls and Floorspart of the metal-enclosed bus run shall be insulated by fire-(A) Supportretardant barriers from all primary circuit elements with the(B) Transversely Routedexception of short lengths of wire, such as at instrument(C) Through Dry Floors and Platformstransformer terminals.(D) Through Floors and Platforms in Wet Locations

370.7 Fittings368.244 Expansion Fittings370.8 Conductor Terminations

Flexible or expansion connections shall be provided in long, 370.9 Groundingstraight runs of bus to allow for temperature expansion or 370.10 Markingcontraction, or where the busway run crosses building vibra-tion insulation joints.

370.1 Scope368.258 Neutral This article covers the use and installation requirements of

cablebus and associated fittings.Neutral bus, where required, shall be sized to carry all neutralload current, including harmonic currents, and shall have

370.2 Definitionadequate momentary and short-circuit rating consistent withsystem requirements. Cablebus. An assembly of insulated conductors with fit-

tings and conductor terminations in a completely enclosed,368.260 Grounding ventilated protective metal housing. Cablebus is ordinarily

assembled at the point of installation from the componentsMetal-enclosed busway shall be grounded.furnished or specified by the manufacturer in accordancewith instructions for the specific job. This assembly is de-368.320 Markingsigned to carry fault current and to withstand the magnetic

Each busway run shall be provided with a permanent name- forces of such current.plate on which the following information shall be provided:

(1) Rated voltage. As shown in Exhibit 370.1, cablebus consists of a metal(2) Rated continuous current; if bus is forced-cooled, both structure or framework installed in a manner similar to that

the normal forced-cooled rating and the self-cooled (not for a cable tray support system. Insulated conductors, 1/0forced-cooled) rating for the same temperature rise shall AWG or larger, are field installed within the framework onbe given. special insulating blocks at specified intervals to provide

(3) Rated frequency. controlled spacing between conductors. To completely en-(4) Rated impulse withstand voltage. close the conductors, a ventilated top cover is attached to(5) Rated 60-Hz withstand voltage (dry). the framework.(6) Rated momentary current.(7) Manufacturer’s name or trademark.

370.3 UseFPN: See ANSI C37.23-1987 (R1991),Guide for Metal-

Approved cablebus shall be permitted at any voltage orEnclosed Bus and Calculating Losses in Isolated-Phasecurrent for which spaced conductors are rated and shall beBus, for construction and testing requirements for metal-

enclosed buses. installed only for exposedwork, except as permitted in 370.6.

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370.4 Article 370 — Cablebus

ported at intervals not greater than 900 mm (3 ft) for hori-zontal runs and 450 mm (11⁄2 ft) for vertical runs. Verticaland horizontal spacing between supported conductors shallnot be less than one conductor diameter at the points ofsupport.

370.5 Overcurrent ProtectionCablebus shall be protected against overcurrent in accor-dance with the allowable ampacity of the cablebus conduc-tors in accordance with 240.4.

Exception: Overcurrent protection shall be permitted inaccordance with 240.100 and 240.101 for over 600 volts,nominal.

370.6 Support and Extension Through Wallsand Floors(A) Support Cablebus shall be securely supported at inter-vals not exceeding 3.7 m (12 ft).

Exception: Where spans longer than 3.7 m (12 ft) are re-quired, the structure shall be specifically designed for the

Exhibit 370.1 A section of cablebus with conductors in place required span length.and the ventilated top cover ready to be attached to the buswayframe. (Courtesy of MPHusky Corp.) (B) Transversely Routed Cablebus shall be permitted to

extend transversely through partitions or walls, other thanfire walls, provided the section within the wall is continuous,protected against physical damage, and unventilated.Cablebus installed outdoors or in corrosive, wet, or damp

locations shall be identified for such use. Cablebus shall not(C) Through Dry Floors and Platforms Except wherebe installed in hoistways or hazardous (classified) locationsfirestops are required, cablebus shall be permitted to extendunless specifically approved for such use. Cablebus shallvertically through dry floors and platforms, provided thebe permitted to be used for branch circuits, feeders, andcablebus is totally enclosed at the point where it passesservices.through the floor or platform and for a distance of 1.8 mCablebus framework, where bonded, shall be permitted(6 ft) above the floor or platform.to be used as the equipment grounding conductor for branch

circuits and feeders. (D) Through Floors and Platforms inWet Locations Ex-cept where firestops are required, cablebus shall be permitted

370.4 Conductors to extend vertically through floors and platforms in wet(A) Types of Conductors The current-carrying conductors locations where (1) there are curbs or other suitable meansin cablebus shall have an insulation rating of 75�C (167�F) or to prevent waterflow through the floor or platform opening,higher and be an approved type suitable for the application. and (2) where the cablebus is totally enclosed at the point

where it passes through the floor or platform and for a(B) Ampacity of Conductors The ampacity of conductors distance of 1.8 m (6 ft) above the floor or platform.in cablebus shall be in accordance with Tables 310.17 and310.19, or with Tables 310.69 and 310.70 for installations 370.7 Fittingsover 600 volts.

A cablebus system shall include approved fittings for the(C) Size and Number of Conductors The size and number following:of conductors shall be that for which the cablebus is de-

(1) Changes in horizontal or vertical direction of the runsigned, and in no case smaller than 1/0 AWG.(2) Dead ends(3) Terminations in or on connected apparatus or equipment(D) Conductor Supports The insulated conductors shall

be supported on blocks or other mounting means designed or the enclosures for such equipment(4) Additional physical protection where required, such asfor the purpose.

The individual conductors in a cablebus shall be sup- guards where subject to severe physical damage

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372.6Article 372 — Cellular Concrete Floor Raceways

This construction method is very similar in design, applica-370.8 Conductor Terminationstion, and adaptation to cellular metal floor raceways. Basi-Approved terminating means shall be used for connectionscally, this wiring method consists of floor cells (that are partto cablebus conductors.of the structural floor system), header ducts laid at rightangles to the cells and used to carry conductors from cabinets370.9 Groundingto cells, and junction boxes.

A cablebus installation shall be grounded and bonded inaccordance with Article 250, excluding 250.86, ExceptionNo. 2. 372.2 Definitions

Cell. A single, enclosed tubular space in a floor made of370.10 Markingprecast cellular concrete slabs, the direction of the cell being

Each section of cablebus shall be marked with the manufac- parallel to the direction of the floor member.turer’s name or trade designation and themaximumdiameter,

Header. Transverse metal raceways for electric conductors,number, voltage rating, and ampacity of the conductors toproviding access to predetermined cells of a precast cellularbe installed. Markings shall be located so as to be visibleconcrete floor, thereby permitting the installation of electricafter installation.conductors from a distribution center to the floor cells.

ARTICLE 372 372.4 Uses Not PermittedConductors shall not be installed in precast cellular concreteCellular Concrete Floor Racewaysfloor raceways as follows:

(1) Where subject to corrosive vaporSummary of Changes(2) In any hazardous (classified) locations except as permit-• 372.17: Added requirement that the ampacity adjustment

ted by 504.20, and in Class I, Division 2 locations asfactors of 310.15(B)(2) apply to the installed conductors.permitted in 501.10(B)(3)

(3) In commercial garages, other than for supplying ceilingoutlets or extensions to the area below the floor but notaboveContents

372.1 Scope FPN: See 300.8 for installation of conductors with othersystems.372.2 Definitions

372.4 Uses Not Permitted372.5 Header Section 300.8 prohibits the installation of electric conductors372.6 Connection to Cabinets and Other Enclosures in raceways or cable trays containing any pipes, tubes, or372.7 Junction Boxes other means for carrying steam, water, air, gas, or drainage372.8 Markers or for any service other than electrical.372.9 Inserts372.10 Size of Conductors372.11 Maximum Number of Conductors 372.5 Header372.12 Splices and Taps

The header shall be installed in a straight line at right angles372.13 Discontinued Outlets

to the cells. The header shall be mechanically secured to372.17 Ampacity of Conductors

the top of the precast cellular concrete floor. The end jointsshall be closed by a metal closure fitting and sealed againstthe entrance of concrete. The header shall be electrically372.1 Scopecontinuous throughout its entire length and shall be electri-

This article covers cellular concrete floor raceways, the hol- cally bonded to the enclosure of the distribution center.low spaces in floors constructed of precast cellular concreteslabs, together with suitable metal fittings designed to pro-

372.6 Connection to Cabinets andvide access to the floor cells.Other EnclosuresConnections from headers to cabinets and other enclosuresCellular concrete floor raceways are a form of floor deckshall be made by means of listed metal raceways and listedconstruction commonly used in high-rise office buildings.fittings.

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