Installation of Cable Trays: Rules, Methods, Earthing and Standards
Cable trays serve as the basis for laying power, control and low‑current lines. The safety, durability of the route and the convenience of its maintenance depend on how competently their installation is performed. In this article we will examine the technology of assembling and fixing metal, galvanized, ladder and perforated constructions, the requirements of the PUE for earthing and fire protection, as well as the specifics of cable laying. Details on the characteristics and range of the trays themselves are described in the material details about cable trays.
1. Regulatory Framework and Design
The installation of cable trays is carried out on the basis of a project developed in accordance with the PUE, SP 76.13330.2016, GOST 52868‑2007 and the technical specifications of the manufacturers. The project contains a route layout, fastening assemblies, a material specification and requirements for fire protection. The drawings indicate the laying height, distances to engineering utilities, and places of wall penetrations. The manufacturer’s installation instruction supplements the design documentation with detailed directions for assembling specific series. Before starting work, the installation rules for the given facility are studied, as well as the requirements for fire protection and earthing. The route design takes into account not only current loads but also the prospect of expansion, therefore a reserve in width and fill is often provided. For facilities with special conditions, individual drawings are developed indicating the tray and accessory versions.
2. Route Preparation, Marking and Fasteners
The installation technology begins with marking the route. The laying axes and the locations for installing supporting structures are determined. For fastening to building bases, various elements are used: a cantilever for installation, a bracket for installation, a profile for fastening, a fastening post, a clamp for fastening. The fasteners are selected depending on the material of the wall or ceiling. To concrete and brick, trays are fixed with anchor bolts or dowel‑nails. To metal structures — with bolted connections. Fastening to a sandwich panel is performed with special self‑tapping screws with a sealing washer or through‑bolts. Fastening with a threaded rod is a convenient method for suspended ceilings: the rod is passed through the slab and secured with nuts. A profile for installation, such as a galvanized channel or a Z‑shaped profile, serves as the base for mounting cantilevers. How are trays fixed to a profile? Via special holders that snap on or are screwed on.
The laying height is standardised: in rooms with permanent human occupancy, the trays are located not lower than 2.5 m from the floor, on technical floors — at a height convenient for maintenance. Outdoor routes on gantries are raised at least 4.5 m above driveways. The PUE laying of cable lines also regulates the minimum clearances from pipelines: the distance from a pipeline with hot water or steam — not less than 0.5 m, from gas pipelines — 1.0 m. When crossing with pipelines, the tray is placed below. The standards for laying cable ducts prescribe maintaining the same distances. The installation layout includes all these parameters and the tie‑in to the building axes.
3. Assembly and Connection of Trays
Metal cable trays are assembled from straight sections, angle elements, and branches. The connection between them is made using connecting plates and bolts, or by a snap‑lock method. Galvanized snap‑lock sections latch together without tools, which speeds up assembly. An angle connector ensures a smooth turn of the route. When installing ladder trays, the rungs are fixed to the longitudinal beams with bolts or by welding, if provided for by the project. The assembly of ladder systems requires precise alignment, since misalignments can lead to cable slipping. It is important to observe the bolt tightening torque so as not to deform the tray and to ensure reliable contact for earthing. A hold‑down clip is used to fix the tray on the cantilever, and a fastening clamp embraces the side and is tightened with a screw. The connection of trays must ensure electrical continuity.
How to fix trays to supports? They are placed on cantilevers and fixed with bolts or hold‑down clips. For vertical sections, vertical elements are used with additional fastenings to posts every 1.5–2 m. The installation of suspended trays is performed on hangers secured to the ceiling with threaded rods. Height adjustment is carried out by nuts on the rod. During assembly, the alignment of the elements must be checked to avoid misalignments.
4. Installation of Various Types of Trays
The installation of metal trays is the most common. Galvanized steel sections are joined with plates, ensuring electrical continuity. The installation of galvanized trays outdoors provides for the use of hot‑dip galvanized or stainless steel parts to avoid corrosion. The installation of ladder systems requires a larger number of supports due to lower torsional rigidity. The support spacing for ladder trays is usually 1.5–2 m for a width of up to 400 mm. The installation of perforated trays is similar to sheet‑steel ones, but they are lighter and assemble faster. The installation of reinforced concrete trays is carried out on a prepared base: RC trays are laid on a mortar bed or on brick pads (laying on bricks). The joints are sealed with cement mortar. Reinforced concrete trays are massive; they are used in cable ducts and tunnels. For installation on a roof, special roof posts are used that do not impair the waterproofing.
The installation of covers is performed after cable laying. Covers can be solid or perforated, fixed by latches, screws or simply placed in slots. To ensure fire protection on critical sections, fire‑resistant partitions with a fire resistance rating specified in the project are installed. Such partitions prevent the spread of fire along the tray and must correspond to certified versions.
5. Laying Cables in Trays
The laying of cable lines in trays must comply with the PUE. Cables in trays are laid loosely, without tension. Power and control circuits are separated by partitions or placed in different trays. The distance from a pipeline with a hot medium — not less than 0.5 m, from a gas pipeline — 1.0 m. The standards for laying cable ducts prescribe maintaining clearances between trays during parallel installation: for power — 100 mm, for joint laying with control — 500 mm without a partition, 100 mm with a partition.
When laying cables, the fill requirements are observed: the total cross‑section of conductors must not exceed 40 % of the tray cross‑section. Cable lines are marked with identification tags. At places of turns, branches and crossings, angle and T‑shaped elements are mounted. Rollers are used to facilitate pulling. The laying of cable ducts inside trays also requires compliance with the cable bending radius, especially for power lines. For the installation of cable lines on horizontal sections, trays are often complemented with additional separators.
6. Earthing of Trays
The earthing of metal trays is a mandatory procedure regulated by the PUE. Clause 1.7.121 of the PUE requires that all metal structures on which cables are laid be earthed. Earthing PUE 1.7.121 prescribes connecting an earthing conductor to each tray at no fewer than two points — at the beginning and at the end of the line. The earthing of covers is performed with a separate flexible conductor if the cover does not have reliable electrical contact with the body. How to earth trays correctly? The tray body is provided with earthing bolts with marking. A copper conductor of at least 4 mm² cross‑section is connected to them, which is laid along the entire route and connected to the earthing loop. The connection between sections via connecting plates already ensures electrical continuity, but an additional earthing conductor duplicates this contact. All bolted connections are protected against corrosion by conductive grease. Measurement of the earthing circuit resistance after installation is mandatory.
7. Protection and Fire Protection
Fire protection of cable routes includes several levels. Fire protection is ensured by the installation of fire‑resistant partitions, the fire resistance rating of which must correspond to the fire‑protection requirements of the building. Fire protection also implies the use of non‑combustible materials and coatings. In places of passage through walls and floor slabs, the trays are protected by fire‑protective sleeves or seals. Protection against mechanical damage is provided by covers and reinforced sections. For outdoor routes, hot‑dip galvanized or stainless steel versions are used, ensuring protection against corrosion. In fire‑hazardous zones, trays may be made in a special fire‑resistant version with a certified fire resistance rating.
8. Testing After Installation
Upon completion of installation, tests are carried out. The reliability of fastenings and the integrity of the earthing circuit are checked. The resistance between any point of the tray and the earthing loop must not exceed 0.1 Ω. For fire‑resistant constructions, fire resistance tests are conducted in accordance with GOST 30247.0‑94. Only after successful tests is the route put into operation. The results are entered into a report.
9. Installation Features in Various Conditions
Installation to a wall is performed with a support spacing of 1.5–2 m. When installing on a ceiling, hangers with height adjustment are used. For installation on a roof, roof posts that do not impair the waterproofing are used. In cable ducts and boxes, trays are laid on shelves. In buildings with suspended ceilings, the route is mounted above the ceiling with access through hatches. Cable ducts and boxes are often combined with trays: the main tray receives cables from ducts and distributes them over the floors. For laying cable ducts in the ground, reinforced concrete trays are used, which are covered with slabs from above. In rooms with an aggressive environment, stainless steel or plastic trays are chosen.
10. Common Mistakes and Quality Control
During the installation of cable trays, the following mistakes occur: non‑observance of distances to pipelines, an insufficient number of fastening points, absence of earthing jumpers, incorrect choice of material for aggressive environments, exceeding the permissible fill, absence of fire‑resistant partitions at the joints of fire compartments. Quality control includes stage‑by‑stage acceptance: checking the base, the correctness of assembly, tightening of bolted connections, measurement of earthing resistance, visual inspection of the coating integrity. All deviations are recorded in a report and eliminated before the start of cable laying. Compliance with all requirements makes it possible to ensure reliable and safe operation of the tray route.
11. Conclusion
High‑quality installation of cable trays means compliance with the project, safety rules and the norms of the PUE. Reliable fastening, correct connection of sections, mandatory earthing and fire protection guarantee long‑term and safe operation of cable lines. For a detailed study of the range and characteristics of trays, we recommend that you view the catalogue cable tray and the guide on their selection.
