power distribution - Siemens

Busway SystemsNational Electric CodeI.General Requirements368.1 Scope. This article covers serviceentrance,feeder and branch-circuitbusways and associated fittings.368.2 Definition.Busway. A grounded metal enclosurecontaining factory-mounted, bare orinsulated conductors, which are usuallycopper or aluminum bars, rods or tubes.FPN: For cables, refer to article 370.II. Installation368.10 Uses Permitted. Busways shallbe permitted to be installed where theyare located in accordance with 368.10(A)through (C).(A) Exposed. Busways shall bepermitted to be located in the openwhere visible, except as permitted in368.10 (C).(B) Concealed. Busways shall bepermitted to be installed behind accesspanels, provided the busways are totallyenclosed, of non-ventilating-typeconstruction and installed so that thejoints between sections and at fittingsare accessible for maintenancepurposes. Where installed behind accesspanels, means of access shall beprovided and either of the followingconditions shall be met:(1) The space behind the access panelsshall not be used for air-handlingpurposes.(2) Where the space behind the accesspanels is used for environmental air,other than ducts and plenums, thereshall be no provisions for plug-inconnections and the conductors shall beinsulated.(C) Through walls and Floors.Busways shall be permitted to beinstalled through walls and floors inaccordance with (C)(1) and (C)(2).(1) Walls. Unbroken lengths of buswayshall be permitted to be extendedthrough dry walls.(2) Floors. Floor penetrations shallcomply with (a) and (b).(a) Busways shall be permitted to beextended vertically through dry floors iftotally enclosed (unventilated) wherepassing through and for a minimumdistance of 1.8m (6ft) above the floor toprovide adequate protection fromphysical damage.(b) In other than industrialestablishments, where a vertical riserpenetrates two or more dry floors, aminimum 100mm (4 in) high curb shallbe installed around all floor openings forriser busway to prevent liquids fromentering the opening. Electricalequipment shall be located so that it willnot be damaged by liquids that areretained by the curb.FPN: See 300.21 for informationconcerning the spread of fire or productsof combustion.368.12 Uses Not Permitted.(A) Physical Damage. Busways shallnot be installed where subject to severephysical damage or corrosive vapors.(B) Hoist ways. Busways shall not binstalled in Hoist ways.(C) Hazardous Locations. Buswaysshall not be installed in any hazardous(Classified) location, unless specificallyapproved for such use.FPN: See 501.10(B)(D) Wet Locations. Busway shall not beinstalled outdoors or in wet damplocations unless identified for such use.(E) Working Platform. Lighting buswayand trolley busway shall not be installedless than 2.5 m (8 ft) above the floor orworking platform unless provided with acover identified for the purpose.368.17 Over current Protection. Overcurrent protection shall be provided inaccordance with 368.17(A) through (D).(A) Rating of over current protection –Feeders. A busway shall be protectedagainst over current in accordance withthe allowable current rating of thebusway.Exception No. 1: The applicableprovisions of 240.4 shall be permitted.Exception No. 2: Where used astransformer secondary ties, theprovisions of 450.6(A)(3) shall bepermitted.(B) Reduction in Ampacity Size ofBusway. Over current protection shallbe required where busways are reducedin ampacity.Exception: For industrial establishmentsonly, omission of over current protectionshall be permitted at points wherebusway are reduced in ampacity,provided that the length of the buswayhaving the smaller ampacity does notexceed 15m(50ft) and has ampacity atleast equal to one-third the rating orsetting of the over current device nextback on the line, and provided that suchbusway is free from contact withcombustible material.(C) Feeder or Branch Circuits. Where abusway is used as a feeder, devices orplug-in connections for tapping offTechnicalfeeder or branch circuits from thebusway shall contain the over currentdevices required for the protection ofthe feeder or branch circuits. Theplug0in device shall consist of anexternally operable circuit breaker or anexternally operable fusible switch.Where such devices are mounted out ofreach and contain disconnecting means,suitable means such as ropes, chains orsticks shall be provided for operating thedisconnecting means from the floor.Exception No.1: As permitted in 240.21.Exception No. 2: For fixed or semi fixedluminaries (light fixtures), where thebranch circuit over current device is partof the luminaries (fixture) cord plug oncord-connected luminaries (fixtures).Exception No.3: Where luminaries(fixtures) without cords are plugged indirectly into busway and the over currentdevice is mounted on the luminaries(fixture).(D) Rating of Over Current Protection– Branch Circuits. A busway used as abranch circuit shall be protected againstover current in accordance with 210.20.368.30 Support. Busways shall besecurely supported at intervals notexceeding 1.5 m (5 ft) unless otherwisedesigned and marked.368.50 Branches from Busways.Branches from busways shall bepermitted to be made in accordancewith 368.56(A), (B) and (C).(A)General. Branches from buswaysshall be permitted to use any of thefollowing wiring methods:(1) Type AC Armored Cable(2) Type MC metal-clad Cable(3) Type MI mineral-insulated, metalsheathed cable(4) Type IMC intermediate metal conduit(5) Type RMC rigid metal conduit(6) Type FMC flexible metal conduit(7) Type LFMC liquid tight flexible metalconduit(8) Type RNC rigid nonmetallic conduit(9) Type LFNC liquid tight flexiblenonmetal conduit(10 Type EMT electrical metallic tubing(11) Type ENT electrical nonmetallictubing(12) Busways(13) Strut-type channel raceway(14) Surface Metal raceways(15) Surface nonmetallic raceways14 BUSWAYSYSTEMSSiemens Power Distribution & Control, SPEEDFAX 2007-2008 Product Catalog 14-19