Cable trays are used for mechanical protection and giving a perfect routing path for running large quantities of power or control cables overhead or under-floor.
According to the National Electrical Code (NEC), a cable tray 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.
Common cable trays are made of galvanized steel, stainless steel, aluminium, or glass-fiber reinforced plastic. The material we are choosing based on where it will be used means installation environment (corrosion and electrical considerations) and its cost. .
Cable tray materials used
Aluminium type: – Cable trays fabricated by aluminium are known as aluminium type trays .Commonly this types are using in all area because of their high strength-to-weight ratio, superior resistance to certain corrosive environments, and ease of installation. They also offer the advantages of being light weight (near to 50% that of a steel tray) and maintenance free, and aluminium trays are non-magnetic, It will reduce electrical loss.
Steel type: – The main benefits of steel cable tray are its high strength and low cost. Disadvantages include high weight, low electrical conductivity and relatively poor corrosion resistance.
Stainless steel: – Stainless Steel is resistant to dyestuffs, organic chemicals, and inorganic chemicals at elevated temperatures.
Types of Cable trays
Ladder type: – 80 % trays used in the industries are ladder type. Its shaped like ladder that’s why its name. A ladder cable tray without covers permits the maximum free flow of air across the cables. This allows the heat produced in the cable’s conductors to effectively dissipate.
Advantage: – Moisture can’t accumulate in ladder cable trays
Solid bottom cable trays: – The main reason for selecting solid bottom cable tray with covers is the concern of EMI/ RFI shielding protection for very sensitive circuits. As name shows it has a solid bottom part with solid cover contains in this system.
Disadvantage: – Chance for accumulating moisture in the cable trays. It will cause corrosion and affect electrical safety. It avoided by drilling 1/4 inch drain holes in the bottom of the cable tray at three foot intervals at the middle and very near the sides.
Trough cable tray: – It’s a type of solid bottom tray but it contains more ventilation for avoiding heats produced in the cable due to electricity passing through conductor or short circuit.
Channel cable tray: – It is used for installations with limited numbers of tray cable when conduit is undesirable.
Wire mesh cable tray:- Normally its used for telecommunication or fiber optic cable routing.Its shaped like a wire mesh.
Single rail cable tray:- used for low voltage and power cable installations where maximum cable freedom, side fill and speed to install are factors.A single hanger rod is used at each support point. This reduces support requirements and eliminates pulling cable through the supports, as cables can be layed in on both sides. Very few fittings and variations, as well as single bolt connections. It a very simple and lower the cost of installation on this system.
Pic credits : Husky