Cable trays: types, sizes, installation and accessories

Cable Tray: Types, Sizes, Accessories and Installation

A cable tray is a supporting structure intended for laying cable lines inside buildings and on outdoor gantries. The safety, durability and ease of maintenance of the entire cable route depend on the correct choice of type, material and components. This material summarises basic information on the varieties of trays, their dimensions, the fittings used, as well as key requirements for installation and earthing. You can get to know a specific model of the wire‑mesh execution on the cable tray page.

1. Regulatory Framework, Certificates and Designation

The production and installation of trays are regulated by a number of documents. The main standard is GOST 52868‑2007 “Metal cable trays. General technical conditions”. Additionally, the technical specifications of manufacturers are applied. Each batch is accompanied by a passport and a certificate of conformity confirming the fire‑resistance class and mechanical strength. In design documentation, the series and type designation is used, for example, LK 20.5, KL, KM, OKL, as well as the article numbers of popular suppliers such as DKC, IEK, TMS opory. The OKPD 2 classifier assigns these constructions to group 27.33.14 “Other parts of electrical apparatus”.

2. Classification: Types, Kinds, Designs and Materials

Metal cable constructions are divided according to several criteria. By cross‑sectional shape and manufacturing method, ladder, wire‑mesh and sheet‑steel types are distinguished. Each of them has its own advantages and areas of application.

2.1. Sheet‑Steel Trays

A sheet‑steel tray is manufactured from cold‑rolled steel by a profiling method. It may be perforated or unperforated, as well as solid with a plain bottom. Perforation lightens the construction and ensures natural ventilation, which is important for power cables. The unperforated version is used when it is required to exclude the ingress of dust and moisture. The snap‑lock connection system allows sections to be joined without bolts: galvanized snap‑lock trays simply latch into each other, speeding up installation. Galvanized steel perforated snap‑lock sections are a sought‑after solution for office and industrial routes.

2.2. Ladder Trays

The ladder type consists of two longitudinal beams and transverse rungs, forming a rigid construction. Such systems are often called ladder systems. They withstand heavy loads and are suitable for trunk power lines. The rungs may be welded or bolted‑on. A ladder tray is convenient for branches: cables can be led out at any place without drilling.

2.3. Wire‑Mesh Trays

A wire‑mesh (grid) tray is welded from galvanized steel wire of 3.5–6 mm diameter. The mesh cell is usually 50×100 mm or 100×200 mm. Such constructions are light, quickly installed, and most importantly — provide excellent ventilation. They are suitable for low‑current and control cables. Wire‑mesh dimensions: width 50–600 mm, height 30–100 mm, section length — 3 metres. Examples of designations: KLP 200×50, 300×100.

2.4. Materials and Protective Coatings

By material, trays are divided into steel (galvanized, hot‑dip galvanized, stainless steel), plastic (PVC, polymer, composite) and reinforced concrete. Galvanized tray (electrolytic zinc coating) is intended for dry premises. Hot‑dip galvanized, treated by immersion in a melt, is resistant to atmospheric effects and is suitable for outdoor use. Stainless steel is used in aggressive environments of chemical productions. A plastic tray made of PVC or a composite one is light, not subject to corrosion, but less strong. Reinforced concrete (RC) is used for underground cable ducts and tunnels. For decorative purposes, trays painted black are produced.

2.5. Fire‑Resistant Versions

For fire protection systems, fire‑resistant trays and accessories are used. A fire‑resistant partition and special covers retain the load‑bearing capacity in a fire. Such constructions are certified according to GOST 30247.0‑94 and have a fire resistance rating of up to 90 minutes.

3. Dimensions, Series and Weight

The dimensions of trays are standardised. The width can be from 50 to 600 mm, the height — from 30 to 150 mm. The length of straight sections is most often 2000 mm or 3000 mm. Let us give typical dimensions in millimetres (width × height): 50×50, 80×80, 100×50, 100×100, 200×50, 200×100, 300×50, 300×100, 400×100. The metal thickness for sheet‑steel trays is 1.0–2.5 mm. Reinforced versions have an increased wall thickness. The weight of a section depends on the dimensions and material; for a galvanized steel tray 200×100 of 3 m length, the mass is about 4–6 kg.

For wire‑mesh trays the dimensions are similar, but the mass is lower. For example, a mesh tray 200×50 of 3 m length weighs about 2 kg. The wire thickness is usually 4 or 5 mm. The parameters of ladder constructions are set by the flange width and side height; typical spans are up to 6 metres with reinforced posts.

4. Components and Accessories

Various accessories are required for assembling routes. The nomenclature includes:

• Connection parts: connectors, sheet connector, plate, connecting plate, bolts. The snap‑lock connection allows joining sections without tools.
• A cover protects the contents from dust and mechanical impacts; it comes solid, perforated, with a lock.
• An end cap is installed on the tray ends.
• A partition, separator — separate power circuits from low‑current ones. A fire‑resistant partition prevents flame propagation along the route.
• Elements for fixing to structures: holders, holder for fixing to a profile, holder for fixing a cable, bracket, wall bracket, cantilever, galvanized cantilever, hanger, posts, profile, support, clamp, hold‑down clip.
• Rollers facilitate cable pulling on straight sections and bends.

All galvanized steel parts are supplied with an anti‑corrosion coating ensuring a service life of at least 25 years under normal conditions. Stainless steel accessories are used in chemically aggressive environments. The table below presents the most demanded items.

5. Installation, Laying and Distance Between Trays

Installation of cable trays is carried out according to the design layout. First, the route is marked out, the supporting structures are installed: posts, cantilevers, hangers. Fixing to a wall is performed with dowel‑nails or anchor bolts. Fixing to the ceiling — on threaded rods with clamps or a perforated profile. An installation instruction is attached to each kit.

Straight sections of trays are placed on the supports and fixed with bolts or snaps. When using the snap‑lock system, assembly takes place especially quickly. Connecting plates ensure the rigidity of the joint. At turns, angle elements are installed, at branches — T‑shaped sections. Height transitions are made using hinged connectors. To compensate for thermal expansion, gaps of 5–10 mm are left on long straight sections.

The distance between adjacent trays in parallel laying must be at least 100 mm clear for power lines. When laying power and control cables jointly without a dividing partition, the distance increases to 500 mm. With a partition, this space is reduced to 100 mm. More details on combining different types of conductors are described in the article cable laying.

When passing through a wall, a penetration is arranged — a length of tray in a steel sleeve, sealed with non‑combustible material. This ensures the required fire‑resistance rating. Crossing with heating pipes, water supply or air ducts is made with a clearance of at least 200 mm. At crossings with gas pipelines, the tray is laid below at a distance of at least 300 mm. Earthing of trays is mandatory: according to the PUE, all metal supporting constructions are connected to the earthing busbar at the beginning and at the end of the line. For this purpose, earthing bolts are provided on the body, to which a copper conductor of at least 4 mm² cross‑section is connected.

6. Fill Capacity and Calculation

Calculation of tray fill capacity is mandatory to ensure the thermal regime and the possibility of subsequent maintenance. According to the PUE, the total cross‑section of the laid power cables must not exceed 40 % of the tray cross‑sectional area. For low‑current lines, this norm is 30 %. For bundled laying, derating factors are introduced for the current load — 0.6–0.8 depending on the number of cables. The calculation formula: S_cables ≤ 0.4 × S_tray for power and 0.3 × S_tray for low‑current. The tray cross‑sectional area is calculated as the product of width and height. For example, a 300×100 mm tray has a cross‑section of 30 000 mm², which means the permissible area of power cables is not more than 12 000 mm². For VVG 3×2.5 cable with a diameter of 10 mm, the cross‑sectional area of the cable is about 79 mm², therefore up to 150 such cables can be placed in such a tray under single‑layer laying conditions. In practice, the quantity is limited for ease of maintenance.

7. Application and Installation Features in Various Environments

The choice of a specific tray type and material is determined by the laying environment.

7.1. Indoors

For offices, administrative and residential buildings, perforated sheet‑steel or wire‑mesh trays are used. They are light, aesthetic, and allow the laying of twisted pair and control cables. Often, black‑coloured trays are used for integration into the interior. Installation is carried out under a suspended ceiling, above a raised floor, or openly along walls.

7.2. Outdoor Laying

Outdoors, on gantries, open switchgears, hot‑dip galvanized or stainless steel trays are used. Hot‑dip zinc provides long‑term protection against corrosion. A stainless steel tray is preferred at chemical enterprises and in coastal zones. Outdoor installation provides for the mandatory installation of covers for protection from precipitation and solar radiation.

7.3. Underground Laying and Cable Ducts

In cable ducts, collectors and tunnels, reinforced concrete or reinforced metal trays are used. RC trays (OKL series) are placed on shelves, covered with floor slabs. Metal trays in ducts must have enhanced anti‑corrosion protection. Joints, connection parts and branching elements are also placed in the trays.

7.4. Floor Laying

In the floor of production workshops, data centres and warehouses, closed trays with covers are used, capable of withstanding the load from machinery and personnel. They are mounted in screed or in special niches. Covers are made of a checkered plate to prevent slipping.

7.5. On the Roof

For roofs, roof posts with an adjustable tilt angle and floor slabs of galvanized steel are produced. Trays on the roof are laid at a distance of at least 100 mm from the surface to avoid the accumulation of snow and ice.

8. Production, Brands and Russian Manufacturers

Russian plants produce products under the brands OKL, KL, KM, LK, L 20.5, S5, and also distribute the brands DKC, IEK. The manufacture of sheet‑steel trays is carried out by cold profiling and stamping. Wire‑mesh trays are welded into a grid on automatic lines. Hot‑dip galvanized products undergo additional treatment in baths with molten zinc. The nomenclature includes all types of sections, covers, brackets, hangers, partitions. When ordering, one refers to catalogues with drawings and specifications.

9. Drawings, Diagrams and Passports

Each manufacturer provides drawings and assembly diagrams for all series. The passport contains data on the material, the limit load, dimensions, and certificates. The installation diagrams show the fastening assemblies, turns, branches, and crossings. Compliance with the factory instructions guarantees mechanical integrity and electrical safety. When developing a cable route project, the category of the room, the presence of aggressive environments and fire‑safety requirements must be taken into account.

10. Conclusion

A cable tray is not simply a profile for laying conductors, but a full‑fledged supporting system. The correct choice of type, dimensions and components ensures ease of installation, fire safety and a long service life. When designing, it is important to take into account the standards, the fill calculation and the earthing requirements. All this makes it possible to create a durable and easy‑to‑maintain cable route for any conditions.