I would like to ask everyone how to design cable trays

I. Cable tray structure: Cable trays come in various structures such as trough type, tray type, and ladder type, and are composed of brackets, support arms, and installation accessories. (As shown in Figure 1), when selecting, it is necessary to ensure that all components of the cable tray meet the requirements for serialization, standardization, and integration into standardized sets. The cable trays inside buildings can be designed as independent units or mounted on various structural elements and pipe rack supports. They should feature a simple structure, an attractive appearance, flexible configuration, and ease of maintenance. All components must be galvanized. For cable trays installed outdoors in buildings, those located near the sea or in areas prone to corrosion require materials with properties such as corrosion resistance, moisture resistance, good adhesion, and high impact strength. To reduce weight, aluminum alloy cables and fiberglass cable trays can also be used. Their dimensions and load-bearing characteristics are roughly similar to those of steel cable trays. Due to the different specific gravities of aluminum and steel (Al=2.7, Fe=7.86), the weight ratio of aluminum to steel is approximately 1:3. Based on the market prices of these two materials, the cost of aluminum alloy cable trays is about 2.0 times higher than that of galvanized steel cable trays. Aluminum alloy cable trays offer advantages such as good appearance, light weight, and ease of installation. In recent years, they have been utilized in various projects. II. Load on cable trays and load characteristics 1. Loads on cable trays The loads on cable trays are divided into permanent loads, dynamic loads, and additional loads. Static load refers to the type of cables, the number of cables, and the outer diameter and weight per unit length of each cable installed in the cable tray; these values are listed separately according to the different routes along which the cables are laid. Dynamic load refers to the weight of construction and maintenance workers during the installation and maintenance of cable trays. For lightweight cable trays, dynamic loads are generally not taken into account; that is, standing (or walking) on the tray is not allowed. If it is necessary to account for people standing on it, the span should be reduced accordingly. Additional loads applied outdoors refer only to those caused by ice and snow, wind, and electromagnetic forces; they are related to the natural meteorological conditions of the location where installation takes place as well as the properties of the charged bodies. In design, these loads must be calculated taking various conditions into account. III. Expansion and contraction issues of cable trays: Due to changes in ambient temperature, steel cable trays experience thermal expansion and contraction. Outdoor cable trays are greatly affected by temperature. For example, if the maximum ambient temperature is 40°C and the minimum temperature is -20°C, the maximum contraction amount of the cable tray can be calculated using the following formula: Δt=11.2 ×10-6×60°×1000mm. From this, it can be concluded that when the temperature difference is 60°C, Δι = 0.672mm/m; when the temperature difference is 50°C, Δι = 0.560mm/m; and when the temperature difference is 40°C, Δι = 0.448mm/m. In engineering design, expansion joints should be considered for cable trays in straight sections, and the spacing between these expansion joints is recommended to be as follows: 50 meters when the temperature difference is 40°C; 40 meters when the temperature difference is 50°C; and 40 meters when the temperature difference is 60°C. IV. Grounding: In accordance with relevant regulations, galvanized cable trays must be properly grounded. (1) The contact resistance of each fixing bolt on a galvanized cable tray should be less than 0.005Ω; under such conditions, the cable tray can be used as a grounding main line (powder-coated cable trays are not suitable for use as grounding main lines). The resistance value of each cable tray can be calculated using the formula: r = P·L/S, where P = 15×10⁻⁶/cm (at 20°C) ； L=Length is calculated in 100mm units ； S = cross-sectional area in cm2. (2) The unit resistance value of the ladder frame per tray is shown in Table 2. Table 2: Unit resistance value of the ladder frame on the tray. (3) The unit resistance value of the cable tray is shown in Table 3. (4) Once the cable tray installation is complete, the resistance of each ladder side (or each cable tray) is given by: R = L(r + 1/3r’), where R represents the total resistance of the entire length of the ladder side (or cable tray), in mΩ ； r--Resistance per unit length of the ladder edge (mΩ/m); r’--Contact resistance of the bolts used to fix the board directly. V. Requirements for the design and installation of cable trays 1. As a component of wiring projects, cable trays currently lack specific regulatory guidelines; the specifications provided by various manufacturers are not universal. Therefore, during the design and selection process, it is necessary to choose the appropriate cable tray based on the type and quantity of cables used in different low-voltage systems. (1) Determine the direction: Based on the building layout plan, taking into account the arrangement of air conditioning and electrical pipelines, the convenience of maintenance, as well as the density of cable routes, the optimal route for the cable tray is determined. Indoors, it should be installed as much as possible along the walls, columns, beams, and floor slabs of the building. When using a utility tunnel for installation, it should be placed parallel to the pipes on one side of them or above them, and care should be taken to ensure that the drop wires and branch wires avoid crossing each other. If no other pipe racks are available, it will be necessary to install (support) columns separately. (2) Load calculation: Calculate the weight per unit length of the cables on the longitudinal section of the main cable tray. (3) Determine the width of the cable tray: Based on the number of cables to be installed, the diameter of the cables, and the spacing between them, determine the model and specifications of the cable tray, as well as the length of the support arms, the length and spacing of the supports, the width of the tray, and the number of layers. (4) Determine the installation method: Decide on the way in which the cable tray will be fixed based on the conditions of the installation site; choose between a suspended, upright, sidewall, or mixed installation style. Connectors and fasteners are usually supplied as a set. In addition, select the appropriate cover plates according to the structure of the cable tray. (5) Draw the plan and sectional views of the cable tray; space views should also be drawn for specific areas, and a material list should be provided. 2. When used in conjunction with power cable trays, the power cables and low-voltage cables should be placed on separate sides, with a partition used to separate them. 3. When low-voltage cables are used together with other low-voltage cables in the same tray, it is necessary to strictly use low-voltage cables for low-voltage systems that have an outer shielding layer, in order to avoid interference between them.

Thank you. In the text, it is mentioned that \"in engineering design, expansion joints should be considered for cable trays that consist of straight sections, and the spacing between these expansion joints is recommended to be as follows: 50 meters when the temperature difference is 40°C; ...\" What exactly are expansion joints?

This post was last edited by zhaohh3211 on 2010-9-15 at 15:35. It’s great; although we also use cable trays, we borrow those used for instruments, which saves us trouble: lol

We don’t need cable trays anymore; just welding some brackets will do

I am also thinking about the layout of the cable trays. The company classifies cable trays into 5 categories: high-voltage cable trays, low-voltage cable trays, variable-frequency drive cable trays, control cable trays, and instrument cable trays. Except for trough-type trunking used for instrument trays, ladder-type is used for others. Below are some materials I found; I hope they will be useful to the original poster. 1. Selection of cable tray types and varieties: 1) In cable networks where electrical interference needs to be suppressed, or when protection against external factors such as corrosive substances or flammable dust is required, (FB) type trough-type composite anti-corrosion shielded cable trays (with covers) should be used. 2) In highly corrosive environments, (F) type composite epoxy resin anti-corrosion and flame-retardant cable trays should be employed. The armrests and brackets should also be made of the same material to increase the service life of the cable tray and its accessories. Cable tray. In environments prone to dust accumulation and other areas that require covering, as well as outdoor sites, it is advisable to install covers. 3. Except for the situations mentioned above, tray-type, trough-type, stepped-type, glass anti-corrosion flame-retardant cable trays, or ordinary steel cable trays can be selected based on the on-site environment and technical requirements. In environments prone to dust accumulation and other areas that require covering, as well as outdoor sites, it is advisable to install covers. 4. In public passages or outdoor road crossings, pads should be placed under the bottom steps, or trays should be used in such sections. When spanning public passages over long distances, the load capacity of the bridge frame can be increased as required by the user, or a truss structure can be used. 5. For large spans (>3m), composite cable trays (FB) should be used. 6. For outdoor use, composite epoxy tree-type cable trays (F) should be selected. II. Specification Selection 1. The width and height of the cable tray should be selected as per the table below, and it must ensure that the cable filling rate does not exceed the values specified in relevant standards and specifications. For power cables, a filling rate of 40-50% is acceptable, while for control cables, it can range from 50-70%. In addition, a margin of 10-25% should be reserved for future expansion needs. 2. The specifications of various elbows and accessories shall meet the requirements of the project layout and be compatible with the cable trays. 3. The selection of support and hanger specifications should be determined based on factors such as the tray specifications, number of layers, and span length. It shall also meet the load requirements. 4. The selection of the cross-sectional area of the cable tray is shown in the table below: Maximum rated current value or setting value (A) for automatic overcurrent protection of any circuit in the cable network on the tray; Minimum allowable cross-sectional area of the tray (mm2): 0–60: 129; 61–100: 258; 101–200: 452; 201–400: 645; 401–600: 968. III. Configuration of supports and hangers: 1. For indoor applications, the short span between supports and hangers is generally set at 1.5–3 meters. The span between outdoor columns is generally set at 6m. 2. The layout of supports and hangers for non-linear sections follows the principles below. When the tray width is 300 mm, in addition to meeting the following conditions, an additional support or hanger should also be installed in the middle of the non-linear section. 3. When the cable tray is installed in multiple layers, the center distance between layers should be 200, 250, 300, or 350 mm. 4. Expansion joints of 20–30 mm should be provided every 50 m in the straight sections of the cable tray (for metal cable trays). IV. Fire protection: In sections of the cable tray where fire protection is required, steel or non-combustible, flame-retardant materials must be used. All the BJⅢ series cable trays produced by our company are fire-resistant tray systems. V. Grounding 1. The tray system shall have a reliable electrical connection and be grounded (applicable only to metal trays). 2. When it is permitted to use a tray system to form a grounding main circuit, the following requirements shall be met. The connection resistance between the ends of the cable tray should not exceed 0.00033 ohms, and the insulation coating on the grounding holes should be removed. In 1KV and lower systems with directly grounded neutral points, the grounding of the powered equipment is connected to the grounding of the system’s neutral wire. When equipped with a power cut-off device for emergency shutdown, the metal cross-sectional area in the length direction of the tray shall be no less than the specified value. 3. When a separate grounding main is laid along the entire length of the cable tray, each section of the cable tray (including non-linear sections) shall have at least one point that is in reliable connection with the grounding main. 4. In vibrating areas, spring coils should be installed at the connections of the grounding points. VI. Design aspects of the cable tray system The design of the cable tray system should be carried out in close coordination with civil engineering, process engineering, and other relevant fields in order to determine the optimal layout. The design may include: 1. Relevant cross-sectional views of the cable tray system. 2. Plan layout diagram of the cable tray system. 3. A detailed list of the specifications and quantities of straight sections, elbows, supports, and hangers required for the cable tray system, along with necessary explanations. 4. Technical specifications or schematic diagrams for non-standard components with special requirements. VII. Installation: For the installation of cable trays, please refer to the JSJT-121 National Standard Design for Building Electrical Installations – Cable Tray Installation, issued by the China Academy of Building Standard Design. VIII. Design Requirements 1. Plan layout diagram of the tray system route ； 2. Relevant sectional views of the cable tray system. 3. A detailed list of the anti-corrosion materials used in the cable tray system, as well as the specifications and quantities of straight sections, elbows, supports (hangers), etc., along with necessary instructions; the connection plates, screws, and protective caps shall be provided by the manufacturer in accordance with the above requirements. 4. Non-standard technical specifications or drawings with special requirements

Thanks for sharing. . . . . .