1. As a supporting component of cabling projects, cable tray systems lack specific standardized guidelines, and specifications vary across manufacturers. Therefore, the design and selection process must reasonably determine the appropriate tray type based on the specific cable types and quantities for each electrical system.
(1) Determine the route: Establish the optimal route for the cable tray based on architectural floor plans, the layout of HVAC and electrical piping, ease of maintenance, and cable density. Indoors, install the trays along building walls, columns, beams, and floor slabs whenever possible. If using a utility tunnel or integrated pipe gallery, install the trays parallel to the pipes (either to the side or above), ensuring that drop-down lines and branch lines minimize crossings; if no existing pipe racks are available, independent support columns must be installed.
(2) Load calculation: Calculate the weight of cables per unit length along the longitudinal section of the main cable tray run.
(3) Determine tray width: Select the cable tray model and specifications-including tray width, number of tiers, bracket arm length, and support column length and spacing-based on the number of cables, cable diameters, and required cable spacing.
(4) Determine installation method: Select the mounting method (suspended, upright, sidewall-mounted, or a hybrid approach) based on site conditions. Connection components and fasteners are typically supplied as a matching set; additionally, select appropriate cover plates based on the tray structure.
(5) Draft plan and section views of the cable tray system; create 3D spatial views for complex sections and compile a bill of materials.
2. When sharing a tray with power cables, place power cables and low-voltage (weak-current) cables on opposite sides, separated by a partition plate.
3. When low-voltage cables share a tray with other low-voltage cables, strictly select low-voltage system cables with external shielding to prevent mutual interference.
4. Other installation requirements
(1) When a cable tray enters a building from the outdoors, it must be installed with an outward slope of no less than 1:100. (2) When a cable tray crosses over or under electrical equipment, the clear distance between them shall be at least 0.5 m.
(3) When two sets of cable trays are installed parallel to each other at the same elevation, the clear distance between them shall be at least 0.6 m.
(4) Plot the cable tray route on the plan view, indicating the coordinates or positioning dimensions and elevations for the start point, end point, turning points, branching points, and elevation change points; creating an isometric view of the tray installation allows for more accurate material estimation.
Straight sections: Indicate total length, number of tray tiers, elevation, model, and specifications.
Turning and branching points: Indicate the model and specifications of the turning connectors used.
Elevation change sections: Indicate the change in elevation; this may also be represented by partial detail drawings or sectional views.
(5) Details regarding cable tray supports (such as uprights, cantilever arms, or non-standard support structures)-including spacing, installation method, model/specifications, and elevation-may be presented in a table on the plan view or indicated section-by-section using various sectional views, single-line diagrams, or detail drawings.
(6) Locations and methods for cable drop-downs: Generally, for a large number of cables, vertical elbow connectors and vertical riser racks may be used; for a small number of cables, guide plates or conduits may be used to facilitate the drop-down.
(7) Cable trays should be installed at least 2.2 m above the finished floor level; the clear distance from the top of the tray to the ceiling or other obstructions should be at least 0.3 m; the tray width should be at least 0.1 m; and the cross-sectional fill ratio within the tray should not exceed 50%.
(8) When cables are installed vertically within the tray, they must be secured to the tray supports at the top end and at intervals of 1.5 m; when installed horizontally, they must be secured at the start and end points, at turns, and at intervals of 3 to 5 m.
(9) When installed within a suspended ceiling, a vertical clearance of 80 mm must be maintained above the opening side of the trunking cover, and the cross-sectional utilization rate of the trunking should not exceed 50%. (10) Cables laid in cable trunking do not necessarily need to be bundled; however, they should be arranged straight and without crossing as much as possible, and must not overflow the trunking. Bundling and securing are required at entry/exit points and bends. For vertical trunking, cables must be secured to cable supports at intervals of 1.5 meters.
(11) Cables must be bundled when laid in horizontal or vertical cable trays and vertical trunking. 4-pair cables should be bundled in groups of 24; backbone cables (25 pairs or more), optical fiber cables, and other signal cables should be bundled according to type, diameter, and core count. The bundling interval should not exceed 1.5 meters, and the ties should be evenly spaced and moderately tight.
(12) For horizontal cable tray installations, the support spacing is generally 1.5–3 meters; for vertical installations, the spacing for fixing to the building structure should be less than 2 meters.
(13) When installing metal cable trunking, supports or hangers must be installed in the following locations: at trunking joints; at 3-meter intervals; 0.5 meters from the trunking ends; and at bends.
5. Material Estimation
(1) Cable Trays: Calculate the total length for each model and specification, divide by the standard unit length to determine the quantity, and then add a 1%–2% margin.
(2) Uprights: If using a uniform specification, divide the total cable tray length by the average upright spacing to determine the number of uprights, then add a 2%–4% margin. If specifications vary, calculate each type separately.
(3) Brackets: Divide the total cable tray length by the average bracket spacing and add a 1%–2% margin to obtain the total required quantity.
(4) Other Components: Calculate the total quantity by multiplying the number of main units by a specific ratio (determined by the overall project scale).
