Guide to Cable Trays

Cable trays are available in six basic types, each with its own characteristics and intended applications.

Guide to Cable Trays
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Cable trays provide a support system for power, signal, communication and optical fiber cables. As defined by the National Electrical Code (NEC), a cable tray system is "a unit or assembly of units or sections and associated fittings forming a rigid structural system used to securely fasten or support cables and raceways." NEC Articles 318, 250 and 800 cover the various aspects of cable tray systems.
The types of cables permitted by the 2005 NEC for installation in cable tray systems are indicated in Section 392.3 uses permitted, (a) Wiring Methods. They include:
Power and Control Tray Cable (Type TC)—NEC Article 336Power Limited Tray Cable (Type PLTC)—NEC Sections 725-61(C) and 725.82(E) Instrument Tray Cable (Type ITC)—NEC Article 727Optical Fiber Cables—Article 770Fire Alarm Circuit Conductors—Article 760Communication Cables—Article 800Mineral Insulated (MI) Cable—Article 332Metal Clad (MC) Cable—Article 330Other cables, including those specially approved for installation in cable trays. Medium voltage (type MV) and single conductor cables in sizes 1/0 and larger are permitted with some restrictions in Industrial Establishments where qualified persons service the installation.
Cable trays are made of either steel, aluminum or fiber reinforced plastic (FRP) and are available in six basic types, each with its own characteristics and intended applications. These six types are:
Ladder Cable Tray
Generally used in applications with intermediate to long support spans—12 to 30 feet.
Characteristics
Solid side rail protection and system strength with smooth radius fittings and a wide selection of materials and finishesMaximum strength for long span applicationsStandard widths of 6, 12, 18, 24, 30 & 36 inchesStandard depths of 3, 4, 5 & 6 inchesStandard lengths of 10, 12, 20 & 24 feetRung spacing of 6, 9, 12 & 18 inches.Solid Bottom Cable Tray
Generally used for minimal heat generating electrical or telecommunication applications with short to intermediate support spans—5 to 12 feet.
Characteristics
Non-ventilated continuous support for delicate cables with added cable protection available in metallic and fiberglassSolid bottom metallic with solid metal covers for non-plenum rated cable in environmental areasStandard widths of 6, 12, 18, 24, 30 & 36 inchesStandard depths of 3, 4, 5 & 6 inchesStandard lengths of 10, 12, 20 & 24 feet.Trough Cable Tray
Generally used for moderate heat generating applications with short to intermediate support spans—5 to 12 feet.
Characteristics
Moderate ventilation with added cable support frequency—with the bottom configuration providing cable support every four inches.Available in metal and nonmetallic materialsStandard widths of 6, 12, 18, 24, 30 & 36 inchesStandard depths of 3, 4, 5 & 6 inchesStandard lengths of 10, 12, 20 & 24 feetFixed rung spacing of 4 inches on center.Channel Cable Tray
Used for installations with limited numbers of tray cable when conduit is undesirable. Support frequency with short to medium support spans—5 to 10 feet.
Characteristics
Economical support for cable drops and branch cable runs from the backbone cable tray systemStandard widths of 3, 4, & 6 inches in metal systems and up to 8 inches in nonmetallic systemsStandard depths of 1 1/4 to 1 3/4 inches in metal systems and 1, 1 1/8, 1 5/8 & 2 3/16 inches in nonmetallic systemsStandard length of 10, 12, 20 & 24 feet.Wire Mesh Cable Tray
Generally used for telecommunication and fiber optic applications, installed on short support spans—4 to 8 feet.
Characteristics
A job site, field adaptable support system primarily for low voltage, telecommunication and fiber optic cables. These systems are typically steel wire mesh, zinc platedStandard widths of 2, 4, 6, 8, 12, 16, 18, 20 & 24 inchesStandard depths of 1, 2 & 4 inchesStandard length of about 10 feet.Single Rail Cable Tray
Generally used for low voltage and power cable installations where maximum cable freedom, side fill and speed to install are factors.
Characteristics
These aluminum systems are the fastest systems to install and provide the maximum freedom for cable to enter and exit the systemSingle hung or wall mounted systems in single or multiple tiersStandard widths are 6, 9, 12, 18 & 24 inchesStandard depths are 3, 4 & 6 inchesStandard lengths are 10 & 12 feet.
Information provided by the CTI (Cable Tray Institute), a trade association comprised of the major cable tray manufacturers, formed to provide information to specifiers, designers and installers about using cable tray systems. www.cabletrays.com
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In Brief
Overview on available types of cable trays and their uses.
Related Products: Ladder Cable Tray; Solid Bottom Cable Tray; Trough Cable Tray; Channel Cable Tray; Wire Mesh Cable Tray; Single Rail Cable Tray.



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