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Introduction

Cable Tray as a structure of metal units forming a rigid assembly for carrying electrical cables. However they are types, classified according to their various functions. These trays use a variety of fittings, accessories and splices, to for it to be assembled.

 

Types of cable trays

Ladder Solid bottom Through bottom Chanel type Wire mesh Single rail

Ladder type

A ladder cable tray is a prefabricated metal structure with two side rails connected by crosswire members, uniformly spaced, generally referred to as rungs.

Ladder cable tray is generally used in applications with intermediate to long support spans, 12 feet to 30 feet.

Solid Bottom Cable Tray

A Solid Bottom Cable Tray is a non-ventilated continuous support for delicate cables with added cable protection available in metallic and fiberglass.

Solid Bottom cable tray is generally used for minimal heat generating electrical or telecommunication applications with short to intermediate support spans of 5 feet to 12 feet.

Trough bottom

A Trough- Type Cable Tray provides moderate ventilation bottom with added cable support frequency and with the bottom configuration providing cable support every 4 inches.

Trough- type cable tray is generally used for moderate heat generating applications with short to intermediate support spans of 5 feet to 12 feet.

Channel Cable TrayA Channel Cable Tray is a prefabricated metal structure consisting of one piece ventilated channel section not exceeding 4 inches in width.

Channel cable tray is used for installations with limited numbers of tray cable when conduit is undesirable. Support frequency with short to medium support spans of 5 to 10 feet.

Wire Mesh Cable Tray

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A Wire Mesh Cable Tray is a field adaptable support system primarily for low voltage, telecommunication and fiber optic cables. These systems are typically steel wire mesh, zinc plated.

Wire Mesh tray is generally used for telecommunication and fiber optic applications and are installed on short support spans, 4 to 8 feet.

Single Rail Type Cable TrayA Single Rail Type Cable Tray - These aluminum systems

are the fastest systems to install and provide the maximum freedom fort cable to enter and exit the system. Single hung or wall mounted systems in single or multiple tiers.

Single Rail Cable Tray is generally used for low voltage and power cables installations where maximum cable freedom, side fill, and speed to install are factors.

Fitting

Fitting are available to allow change in horizontal and vertical alignment, branch runs or transitions from one width to another. These include: 900

outside, 900 inside, 450 outside, 450 inside, cross, tee, 900 horizontal bend, 450 horizontal bend.

Types of fittings450 outside 450 inside

Cross Tee

900 horizontal bend 450 horizontal bend

Accessories

Accessories include: covers, cover lamps and clips, conduit adapters, expansion joint splices plates, drop outs, blind ends, tray to box connectors, divider strips, cable clamps and structural support.

Covers

Covers are available as solids, louvered or ventilated types. Solid covers provide protection from sunlight and accumulation of dirt. They also guard against unauthorized contact with the cables, mechanical damage, help isolate cables from fires and reduce radio frequency interference.

Solid type cover

Cover Clamps

Cover Clamps are generally a pair of flat bars on top of the cover and bottom of the tray and clamp by a pair of bolts on the exterior of both sides of the rails. Cover clips are economical device for holding horizontal or slowly rising run.

Cover Clamps

Blind end

Blind end provides cover for the “dead end” terminations of runs. Tray two box connectors are used to from neat connection of cable tray to junction box, switchgears, and any flat surface perpendicular to the trays.

Splices

Cable Tray splices are used for joining sections of the cable trays. Some of the common types are: standard splice plate, tray to box splice plate, expansion splice plate, vertical adjustable splice plates, and horizontal adjustable splice plate.

Types of cable splices

Standard splice plate - splice plates are shipped with each straight section. Fittings are provided with the appropriate number of splice require. Only 4 bolts per plate and slotted hold design make installation easy.

Types of cable splices contTray to box splice plate - A good

solution for attaching tray to distribution boxes, control centres or making a non- radius 900 bend or tee.

Types of cable splices contVertical adjustable splice plates- for

field installing vertical transition. Install on each end after rise angle is set. Then drill through centre pilot hold into back plate then bolt in plate.

Types of cable splices contHorizontal adjustable splice plate – an

inexpensive method to field install bends up to 450. Install hinged side, set desired angle then field drill holes in long hinge plate.

Construction of a typical cable tray system

Parts

Labeled parts

 Procedures for installing cable tray to a mainframe

Procedures

Conclusion

The research conducted on cable trays outline the many different types of cable trays and the different types of accessories such as splices, fixtures, reducers and wall brackets. Each types of cable tray has a unique construction to facilitate their various functions. Cable Trays are used in different applications and are not suitable for domestic wiring but is mainly used in telecommunication and high rise buildings.

References

Terrell,C. Wilford I. Summers, Frederic Hartwell American Electricians' Handbook

Ed Sarviel Construction estimating reference data

Joseph F. McPartland, Frederic Hartwell McGraw-Hill's National Electrical Code 2008 Handbook

Truman C. S, Jonathan R. A Interpreting the National Electrical Code: Based on the 2005 National.