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If not properly planned and installed, wiring within cable trays can lead to fire, electric shock and arc flash explosion events. As part of a planned cable management system, cable trays can be used to support, route, protect cable systems and provide pathways for cable systems. Cable trays can be used with power, low-voltage control, data or telecommunications wiring systems.
Proper use of cable trays makes it easier to mark, remove and locate cables. Cable trays are the choice for installations that may require future upgrades, reconfiguration or relocation.
During the maintenance, installation and inspection of cable trays, adequate safety precautions must be taken. Cable trays, the conductors and cables contained therein, and the wiring procedures employed must be listed or marked by a nationally recognized testing laboratory as acceptable installation environments.
Cable trays have a variety of layouts and must be adequately supported according to installation instructions. The design and installation of cable trays should meet current and future requirements. Several aspects must be considered, including but not limited to: the type and quantity of cable trays, and the support required to manage the load.
Environmental or meteorological factors
Weight of cable trays
Current and future cable requirements
Electric and magnetic forces
Any additional equipment placed
Securing cables within cable trays is crucial for maintaining proper cable spacing, keeping cables within the tray, and restricting cables to designated positions within the tray. Cable ties should be suitable for their use environment. When selecting cable ties, consider length, temperature, moisture resistance, UV resistance, chemical resistance, flammability, low smoke quality and strength.
Due to the existence of cable trays of various sizes, they can be constructed to support various load combinations. However, due to their versatility, cable trays are particularly prone to overloading.
Three factors determine the safe and acceptable load of cable trays:
Weight limits specified by the manufacturer
Cable fill limits due to cross-sectional area limitations
Conductor spacing specifications
Overloaded cable trays may cause failure of the tray, its connection points or supports, posing a danger to personnel below the tray, and even cause electric shock and arc flash/explosion events due to component failure when cables are suddenly no longer supported. When cable trays are overloaded, a large amount of heat buildup inside and around energized conductors can cause insulation failure, thereby creating electric shock or fire risks. When cable trays are too crowded, place another cable tray system above, below or next to them. Leave sufficient working space around the new cable tray. Cables left in cable trays should be removed. After the project is completed, temporary wiring inserted into cable trays should be removed.
Cable trays are common in hazardous situations with high concentrations of flammable or combustible gases, smoke and dust, but care must be taken during installation to avoid creating explosion hazards. Cable trays in hazardous areas must only contain wiring permitted in that area.
Cable trays can be rated for:
Corrosive and classified hazardous locations
Indoor or outdoor
Areas prone to electrical noise and vibration
Cable trays can be constructed to pass vertically through floors or platforms, or horizontally through walls and obstacles. Where cable trays pass through fire partitions, walls and floors, adequate fire protection devices should be installed to prevent the spread of fire or combustion byproducts. Cable trays should not be installed in areas where they may be damaged.
Cables and conductors permitted for use in cable trays must be insulated, but further safety measures may be required. If working on cable tray installations may expose employees to energized parts or damage insulation, the wiring must be de-energized. Grounding cable tray systems is essential for personal safety and to prevent arc discharges, which can occur anywhere in the wiring system.
Metal cable trays such as aluminum, steel and coated steel can all be used as equipment grounding conductors. Metal cable trays can only be used as equipment grounding conductors when regular maintenance and supervision ensure that the installed cable tray system is serviced by qualified personnel. Before wires can be energized, proper grounding must be performed and tested.
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