In electrical engineering, cable tray placement is a basic link. Whether this link is standardized or not will directly affect the safety and reliability of the entire wiring system. Properly doing this installation will not only allow the cable to run stably for a long time, but also prevent failures caused by vibration, overheating or mechanical damage. In actual projects, the bridge type, installation environment and load requirements must be considered comprehensively to ensure compliance with my country's electrical installation standards.
How to choose the appropriate type of cable tray
When selecting a cable tray, you must first evaluate the type and quantity of the cables. Power cables and control cables should be set up separately. Shielded bridges should be used for weak current cables to prevent signal interference. According to the installation conditions and environment, corrosive places should use hot-dip galvanized or stainless steel materials. Fire-fighting areas need to be equipped with fire-proof bridges. The width of the bridge should be reserved for 40% expansion space to prevent the entire system from being replaced when the capacity is expanded in the future.
The core indicator is the load-bearing capacity during selection. Communication cables are suitable for light-duty bridges, and large-section power cables are supported by heavy-duty bridges. The total weight of the cables and possible additional loads must be calculated. The additional loads include the weight of the maintenance personnel. The selection of bridge connectors is also critical. Ordinary plug-in types are suitable for indoors, and flexible connection systems must be used in earthquake-resistant areas. We provide global procurement services for weak current intelligent products!
What preparations are needed before installing the cable tray?
Before installation, it is necessary to complete the in-depth design of the comprehensive pipeline, coordinate the spatial layout with air ducts, water pipes and other professionals, use BIM technology to perform collision detection, and solve the problem of elevation conflicts in advance. The bearing capacity of the building structure must be verified on site, the concrete roof must be embedded with suspenders, and the steel structure must be fixed with special clamps. During the preparation stage, a construction permit must be obtained, and technical briefings and safety training must be completed.
When materials enter the site, there must be strict acceptance procedures to check whether the thickness of the bridge plates meets the standards and whether the surface treatment is uniform. Special installation tools should be prepared, such as laser positioners, torque wrenches, hydraulic lifting platforms, etc. According to the construction drawings, set out and position on site, mark the center line of the bridge with ink lines, and set positioning marks at turns and branches. At the same time, a temporary support system is prepared to ensure a stable state during the installation process.
How to determine the distance between cable tray brackets
The spacing between brackets must be comprehensively calculated based on the type of bridge and load conditions. When steel bridges are installed horizontally, the normal spacing is 1.5 to 3 meters. When aluminum alloy bridges are installed horizontally, the spacing can be extended to 2 to 4 meters. Large-span bridges can reach spans of 6 to 12 meters with the help of reinforced structures. When installed vertically, the spacing between brackets must be increased, usually no more than 2 meters, and each bracket must be able to bear load independently.
In special environments, the density of brackets must be adjusted. Two-way anti-sway brackets must be installed on each side of the seismic fortification area. The spacing must be halved. Additional reinforced brackets must be added at corners and on both sides of tee joints. When the width of the bridge exceeds 400mm, a double suspender bracket system must be used. The actual spacing should also take into account the deflection value of the bridge, which is generally controlled within 1/200 of the span.
What are the grounding requirements for cable trays?
The cable tray must form a continuous electrical path, and copper braid tape must be used to bridge each section of the bridge. The cross-sectional area of the bridged wire must not be less than 4mm², and the insulation layer must be removed from the contact surface. When the length of the bridge exceeds 30 meters, additional grounding connection points need to be set up, and the metal bracket must also be connected to the grounding system. The grounding resistance of the entire system should not be greater than 0.1 ohm.
Galvanized bridges are not required, and additional measures to prevent galvanic corrosion should be added to their connections. In an environment where there is an explosion risk, locking bolts must be used to ground the bridge, and they must be marked in red. It is best to use galvanized flat steel for the grounding trunk line, and the distance between it and the bridge connection point should not exceed 20 meters. A ground resistance tester should be used every year to check the connection quality to ensure that the safety protection is effective.
How does the cable tray pass through the fire protection zone?
When passing through firewalls and floors, a fireproof sealing system must be used. The gap between the reserved opening and the bridge should be wrapped with fireproof boards and filled with fireproof rock wool. The thickness of the fireproof sealing layer cannot be less than the thickness of the wall, and must meet the corresponding fire resistance limit requirements. Important areas are more suitable to use flexible fireproof tape systems to ensure that the sealing state can be maintained as the structure deforms when a fire occurs.
The bridge within the vertical hoistway should be equipped with fireproof partitions on each floor. When the bridge passes through different fire protection zones, fire dampers should be installed at the wall penetrations. When using a fireproof bridge, its fire resistance limit must match the building fire protection requirements. Daily maintenance requires regular inspection of the integrity of the fireproof sealing to prevent damage to the fireproof partition due to changes in pipelines.
How to accept the cable tray after installation
The acceptance must be carried out one by one according to the sub-projects. First, check the horizontality and verticality deviation of the bridge, which is stipulated not to exceed 2mm per meter. The direction of the connecting bolts must be consistent, and the nuts are on the outside of the bridge. The grounding system must use a torque wrench to check the tightness of the connection, and use a low-resistance tester to verify continuity. The surface of the bridge must not be scratched or deformed, and the coating must be complete.
The load test must simulate actual use conditions, apply 1.5 times the design load capacity to the middle part of the bridge for 24 hours, and then measure the change in deflection. The acceptance documents should include material certificates, installation records, grounding test reports, etc. Finally, a wiring test must be carried out to check whether there will be any friction with the edge of the bridge when the cables are laid.
In your engineering projects, what is the most complex cable tray installation scenario you have encountered? You are welcome to share actual cases in the comment area. If you think this article is helpful, please like it and forward it to colleagues who need it.
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