Cable Routing in Trays and Ducts

Cable Routing in Trays and Ducts

The installation of cable lines in trays and ducts is a widely adopted method within various industrial plants and electrical facilities. This approach is typically implemented openly on walls and ceilings across diverse environments, including dry, humid, high-temperature, and fire-hazardous areas, as well as spaces with chemically aggressive atmospheres. It finds primary application in industrial buildings, technical rooms, basements, warehouses, workshops, and outdoor installations.

Defining the Components: Trays vs. Ducts

This open cable management method utilizes trays and ducts to organize power and low-current systems, ensuring easy access and visual inspection of cable routes.

Cable Trays are open, non-combustible, trough-like structures made from various materials. They function as a supportive framework, fixing the position of cables but not providing protection from physical damage. Their main role is to facilitate safe, orderly, and manageable routing. In residential and administrative settings, they are typically used for concealed wiring (behind walls, above suspended ceilings, or under raised floors). Open cable laying using trays is generally permitted only for industrial mains.

Cable Ducts are enclosed hollow sections (rectangular, square, triangular, etc.) with a flat base and either removable or solid covers. Unlike trays, their key function is to protect the enclosed cables from mechanical damage. Ducts with removable covers are used for open wiring, while solid (blind) ducts are for concealed installation.

Both are mounted on supporting structures along walls and ceilings, creating “shelves” for cables.

Materials and Applications

Accordng to electrical installation codes, cable trays and ducts are manufactured from metal, non-metallic materials, or composites.

Metal Trays/Ducts: Commonly made from galvanized or stainless steel, or aluminum. Galvanized steel offers excellent corrosion resistance, making it suitable for both indoor and outdoor use on various surfaces. Steel ducts can be used openly in dry, humid, hot, and fire-hazardous rooms where steel conduit isn’t mandatory but are prohibited in damp, extremely wet, chemically aggressive, or explosive atmospheres.

Non-Metallic (Plastic) Ducts: Typically made from PVC, these are used for low-voltage cables indoors, especially in homes and offices. They are cost-effective, lightweight, moisture-resistant, and blend well with interiors. However, they lack strength, have lower heat resistance, a shorter lifespan, and can deform from cable heat, making them unsuitable for external use.

Composite Trays/Ducts: Made from synthetic polyester resins and fiberglass, these products offer high mechanical strength, rigidity, vibration resistance, moisture and frost resistance, corrosion/UV/chemical resistance, and low thermal conductivity. They are lightweight, easy to install, and have a long service life. Available in solid or perforated, open or closed types, they are ideal for demanding conditions, both indoors and outdoors, including aggressive environments.

Reinforced Concrete Trays: Used for underground or ground-level cable routes. They withstand heavy loads, are durable, waterproof, and resilient to temperature shifts and ground movement, making them suitable for seismic zones and wet soils. After installation and backfilling, they provide complete protection for the internal cables, while still allowing for easy inspection and repair by opening the cover.

Design Varieties

Perfrated: Feature holes in the base and sides, reducing weight, aiding direct mounting, and providing ventilation to prevent cable overheating and moisture buildup. However, they offer less protection against dust.

Solid: Have non-perforated, solid bases and surfaces, offering high protection from environmental factors, dust, and precipitation. This comes at the cost of restricted natural cable cooling due to lack of ventilation.

Ladder-Type: Consist of stamped side rails connected by cross-braces, resembling a ladder. They handle heavy loads well, are ideal for vertical runs and open routes, and provide excellent cable ventilation and access.

Wire-Type: Constructed from welded galvanized steel wire. They are very lightweight, provide maximum ventilation and access, and allow for easy branching. However, they are not for heavy loads and are best for lightweight horizontal runs and cable shafts.

Selection and Installation

The choice of type and material depends on the installation environment, room type, cable type, and size. The tray/duct dimensions must accommodate the cable diameter or bundle with sufficient spare capacity.

Instllation Sequence:

Route Marking: Mark the path, indicating locations for supports and attachment points.

Support Installation: Install racks, brackets, or hangers on walls/ceilings. A minimum height of 2 meters from the floor/service platform is required, except in areas accessible only to qualified personnel.

Tray/Duct Mounting: Secure the trays or ducts to the supporting structures.

Connecting Sections: Trays are connected via bolted splice plates or welding. Ducts are connected using connectors and bolts. Sealing of connections is mandatory in dusty, gaseous, oily, or wet environments and outdoors; dry, clean rooms may not require sealing.

Cable Pulling: Cables are pulled using a winch or manually (for shorter lengths) over rolling rollers.

Cable Laying & Fixing: Cables are transferred from rollers into the trays/ducts and secured.

Connection & Final Fixing: Cables are connected and finally fastened.

Cable Laying Methods in Trays:

In single rows with 5mm gaps.

In bundles (max 12 wires, diameter ≤ 0.1m) with 20mm between bundles.

In packages with 20mm gaps.

In multiple layers without gaps.

Fastening Requirements:

Trays: Bundles are secured with straps every ≤4.5m horizontally and ≤1m vertically. Individual cables on horizontal trays generally don’t require fixing but must be secured within 0.5m of turns/branches.

Ducts: The cable layer height should not exceed 0.15m. Fixing intervals depend on duct orientation: not required for lid-up horizontal; every 3m for side-lid; every 1.5m for lid-down horizontal; and every 1m for vertical runs. Cables are always fixed at endpoints, bends, and connection points.

Cables are laid to allow for length variation due to temperature changes. Trays and ducts should not be filled more than halfway to ensure access for maintenance, repair, and air cooling. Ducts must be designed to prevent moisture accumulation, using inspection hatches and removable covers. Marking tags are installed at ends, bends, and branches. The entire tray/duct system must be grounded.

Advantages and Disadvantages Summary

Advantages:

Ease of maintenance and repair due to open access.

Cost-effective installation compared to concealed methods or pipes.

Reduced labor for cable fastening.

Excellent cable cooling conditions (especially with trays).

Suitable for challenging environments (chemical, humid, hot).

Organized routing, safe distancing from hazards, and easy system expansion.

Disadvantages:

Trays: Offer minimal protection from external influences; open installation is restricted in damp rooms.

Ducts: Provide good mechanical protection but can impede cable cooling, potentially reducing current capacity.

Both methods require significant space and have limited aesthetic appeal.