Safely Installing, Maintaining and Inspecting Cable Trays

1 Department of LaborOccupational Safety and Health AdministrationDirectorate of Technical Support & Emergency ManagementOffice of Technical Programs and Coordination ActivitiesSHIB 01-16-2008 Safety and Health Information BulletinSafely Installing, Maintaining and Inspecting Cable TraysThis Safety and Health Information Bulletin (SHIB) isnot a standard or regulation, and it creates no newlegal obligations. The Bulletin is advisory in nature,informational in content, and is intended to assistemployers in providing a safe and healthfulworkplace. The Occupational Safety and Health Actrequires employers to comply with safety and healthstandards promulgated by OSHA or by a state withan OSHA-approved state plan. In addition, pursuantto Section 5(a)(1), the General Duty Clause of theAct, employers must provide their employees with aworkplace free from recognized hazards likely tocause death or serious physical harm. Employers canbe cited for violating the General Duty Clause if thereis a recognized hazard and they do not takereasonable steps to prevent or abate the , failure to implement any recommendationsin this SHIB is not, in itself, a violation of the GeneralDuty Clause.

2 Citations can only be based onstandards, regulations, and the General Duty purpose of this Safety and Health InformationBulletin is to:Review the proper methods for safelyinstalling, Maintaining and Inspecting electricalcable Trays ;Provide information regarding the hazards ofoverloaded Cable Trays ;Identify specific Occupational Safety andHealth Administration (OSHA) regulatoryrequirements and National Electrical Code (NEC) guidance that address the properinstallation and maintenance of Cable Trays ;Recognize electrical Cable tray misuse thatcan lead to electric shock and arc-flash/blastevents and fires caused by Regulations and Industry ConsensusStandards that Apply to Cable TraysThe use and installation of Cable Trays is covered bylegally enforceable OSHA regulations in 29 (a)(3), or comparable standardspromulgated by States operating OSHA-approvedState plans. In addition, this document containsseveral references to provisions of the NationalElectric Code (NEC), which is published by theNational Fire Protection Association (NFPA).

3 The2005 edition of NEC is listed as a reference inAppendix A Reference Documents of OSHAS ubpart S, Electrical ( through ).While these references provide nonmandatoryinformation that can be helpful in understanding andcomplying with Subpart S, compliance with thereferenced provisions of the NEC is not required andis not a substitute for compliance with any applicableOSHA the recently promulgated electricalstandards for general industry at 29 CFR 1910 Subpart S (72 FR 7136 7221, February 14, 2007)are based on the 2002 edition of the NEC, OSHAhas not conducted rulemaking to adopt all of therequirements of the NEC (or subsequent revisions)and, therefore, cannot enforce those , industry consensus standards such as theNEC and others referenced throughout this Bulletincan be used by employers as guidance for conductinghazard analyses and selecting effective National Electrical Manufacturers Association(NEMA) also publishes three consensus standardsthat apply to the proper manufacture and installationof Cable Trays : ANSI/NEMA-VE 1-1998, Metal 2 Cable Tray Systems.

4 NEMA-VE 2-1996, MetalCable Tray Installation Guidelines; and NEMA-FG-1998, Nonmetallic Cable Tray TraysAccording to OSHA , a Cable tray system is [a] unit or assembly of units or sections andassociated fittings forming a rigid structural systemused to securely fasten or support cables andraceways. Cable tray systems include ladders,troughs, channels, solid bottom Trays , and other similarstructures. Cable Trays are not raceways, but theyare treated as a structural component of a facility selectrical system. Cable Trays are a part of a plannedcable management system to support, route, protectand provide a pathway for Cable systems. Cable trayssupport cables across open spans in the same waythat roadway bridges support Trays can provide a safe component of a power,low voltage control, data or telecommunications wiringdistribution system. Cables in Trays can be easy tomark, find, and remove. Their flexibility makes cabletrays a good choice for installation situations thatrequire upgrading, reconfiguring, or Trays are available in a number of differentconfigurations, including ladder, ventilated trough,ventilated channel, solid bottom, wire mesh, single railand other configurations.

5 They come in a wide varietyof shapes and sizes, with a host of hanging options thatare able to meet almost any installation need. Cabletrays are manufactured of steel, stainless steel,aluminum and fiber reinforced plastic (FRP). Theyalso are available with special finishes includingpolyvinylchloride (PVC) coated and galvanized significant portion of Cable Trays used in industrytoday are aluminum. Aluminum, steel and coated-steelcable Trays , all being metallic, may be used asequipment grounding conductors in accordance withOSHA (a)(3)(iii). This requirement ismirrored by the guidance provided by NEC (C). Depending on the need, covers andventilated louvers or slats are available for all physically protect the cables as well asshielding the Cable jackets from the sun s ultravioletradiation when used outdoors. Suitable guards orcovers must be installed to a minimum height of (8 ft.) above grade such as where Cable Trays areexposed to physical damage from vehicular louvers also protect the cables andfacilitate cooling by allowing natural convection (heatdissipation) to Tray UseCable Trays can be used in a variety of Trays can be rated for outdoors, indoors,corrosive and classified hazardous locations, andareas with high electrical noise and vibration.

6 Aswith any electrical equipment, Cable Trays and thewiring contained in the Trays must be listed, labeledor otherwise approved, pursuant to the requirementsof 29 CFR (a). The National ElectricalManufacturers Association (NEMA) Standard VE1-2002 provides guidance for metal Cable Trays andassociated fittings designed for use in accordancewith the rules of the NEC. NEMA Standard VE 2-2006 addresses shipping, handling, storing, andinstalling Cable tray systems; it also providesinformation on Cable tray maintenance and systemmodification. Compliance with these standards helpsto ensure safe loading and the electrical continuity ofcable tray Trays may be designed to cross throughpartitions and walls, as well as go vertically throughplatforms and , where Cable Trays (and the conductorsand cables they contain) pass through fire-ratedpartitions, walls and floors, appropriate fire-stopsFigure 1. Ladder Cable tray, ventilated Cable tray,solid-trough Cable be provided in accordance with NEC to prevent the spread of a fire or the by-products of combustion.

7 Typically, specific buildingcodes should be consulted and the design andoversight should be done by a qualified of Cable Trays is popular in hazardous locationswhere concentrations of flammable or combustiblegases, vapors and dusts exist. However, the improperuse of Cable Trays in these environments could result inan explosion. 29 CFR (a)(3)(iv) requiresthat Cable Trays in hazardous (classified) locationscontain only the Cable types permitted in suchlocations (see for details on hazardous(classified) locations). In addition, the NEC alsocontains specific requirements for wiring in hazardousor classified environments. For example, NECS ection (D) states that Cable Trays in hazardouslocations should contain only the wiring permitted inspecific sections of Chapter 500 (Sections , , , and ).Proper Loading of Cable TraysSince Cable Trays come in a wide variety of sizes, theycan be designed to accommodate a wide range ofloading configurations.

8 Because of their flexibility, Cable Trays are especially subject to overloading. Safeand permissible loading of Cable Trays is governed bythree criteria: manufacturer-specified weightrestrictions; limitations of Cable fill because of cross-sectional area limitations; and conductor spacingFigure 2. Outdoor metal clad Cable in Cable 3. Electrical wires in multiple Cable The appropriate size and number ofcable Trays for an installation depends on the numberand size of conductors included and the allowable fillarea specified in the guidance provided by the Cable Trays offer flexibility for expansion andchanges, engineers and designers should design andsize Cable tray systems to anticipate both current andfuture and Support Requirements29 CFR (b)(8) requires the appropriatemounting and cooling of electrical , guidance provided in NEC (C) states, in part, that Cable Trays shoul besupported at intervals in accordance with theinstallation instructions.

9 This straightforward approachis corroborated in 29 CFR (b)(2), whichstates that listed or labeled equipment shall be usedor installed in accordance with any instructionsincluded in the listing or labeling, and guidanceprovided by NEC Section (B). The type andnumber of Cable Trays , and the support required tohandle loads must take into account several factors,including, but not limited to, environmental or weatherfactors; the weight of the Cable tray; current and futurecable needs; electromagnetic forces; and anyaccessories installed. Manufacturers of Cable traysystems provide a wide range of parts and typicalsupport methods, as well as detailed installation guidesand tables for appropriate supports and support4spacing for Cable Trays . However, engineeringcalculations are often required to determine where toplace supports so that the designed Cable tray systemprovides the proper , NEC (J) permits Cable traysystems to externally support raceways, cables andboxes, and conduit bodies as covered by , provided that the Cable tray is listed anddesigned for the application.

10 Support for theequipment also must be in accord with the appropriateNEC article. This permission does not extend toother non-electrical equipment, such as water pipes,sprinklers, and gas pipes. In addition, Cable traysupports should also take into account dynamic loads( , loads caused by the motion of the Cable traysystem and its contents) and lateral stressors. Cabletray systems need not be absolutely rigid; mostsystems are designed with about a 1/200 span-deflection ratio ( , inches in a 20-foot span)when fully Fill and Spacing RequirementsIn industrial establishments, where the conditions ofmaintenance and supervision assure that only qualifiedpersons will service the installation, (a)(3)(ii) defines the wiring methods thatmay be installed in Cable Trays . Cable tray fill isaddressed in NEC Sections , , ,and The type of Cable tray ( , solid,ventilated), ampacity (current-carrying limit)requirements, and the type and voltage rating of cableused determines the allowable fill for each Cable Cable Trays provide for the greatestallowable fill due to increased airflow.