In a computer room project, compared with expensive, high-tech hardware and software, the cable tray is inconspicuous and rarely paid attention to, but it is also an indispensable part of the entire wiring project. The design and selection process should reasonably select the appropriate cable tray based on the type and quantity of cables in each system.
1. Selection of cable tray types and varieties
1) When shielding electrical interference cable networks or protecting against external influences (such as corrosive liquids, flammable dust, etc.), (FB) type trough composite anti-corrosion shielded cable tray (with cover) should be selected.
2) For highly corrosive environments, (F) type composite epoxy resin anti-corrosion flame retardant cable trays should be used. The same materials should also be used for the brackets and supports to increase the service life of the cable tray and accessories. In environments where dust is easily accumulated and other areas that need to be covered or outdoor places, a cover plate should be added.
3) In addition to the above situations, tray-type, trough-type, ladder-type, glass anti-corrosion flame retardant cable trays or steel ordinary cable trays can be selected according to the site environment and technical requirements. In environments where dust is easily accumulated and other areas that need to be covered or outdoor places, a cover plate should be added.
4) In public passages or outdoor crossing road sections, a pad should be added to the bottom of the bottom step or a tray should be used in this section. When crossing a public passage with a large span, the load capacity of the bridge can be increased according to user requirements or a row frame can be selected.
5) For large spans (>3m), composite bridges (FB) should be used.
6) Composite epoxy resin bridges (F)should be used outdoors.
2. Cable bridge specifications
1) The width and height of the composite epoxy resin cable tray shall be selected according to the table below, and the cable true charging rate shall not exceed the specified value of the relevant standards and specifications. The power cable can take 40-50%, and the control cable can take 50-70%. In addition, a 10-25% program development margin must be reserved.
2) The specifications of various bends and accessories should meet the project layout conditions and match the bridge.
3) The selection of support and hanger specifications should be configured according to the bridge specifications, number of layers, span and other conditions. And it should meet the load requirements.
3. egarding the configuration of the support and hanger of the cable tray:
1) The short span of the indoor support and hanger is generally 1.5-3m; the medium span of the outdoor column is generally 6m.
2) The configuration of the support and hanger of the non-straight section follows the following principles: When the width of the bridge is <300mm, a support and hanger should be set on the straight section side 300-600m away from the junction of the non-straight section and the straight section; when the width of the bridge is >300mm, in addition to meeting the following conditions, a support and hanger should be added in the middle of the non-straight section.
3) When the pultruded fiberglass cable tray is set in multiple layers, the center distance between the layers is 200, 250, 300, and 350mm.
4) A 20-30mm expansion joint should be left every 50m in the straight section of the bridge (metal bridge).
4. Some calculation formulas for cable trays Cable trays are stamped from thin steel plates.
Their load-bearing capacity has a certain limit. The load capacity of the cable tray is a quantity related to the specifications of the bridge and the support distance. For the same support distance and bending deformation, the bridge with a large side height has a large load-bearing capacity, while the bridge with a small height has a small load-bearing capacity. In addition, when the load capacity is the same, for the cable bridge of the same specification, the bending deformation of the cable bridge with a small support distance is smaller than that of the cable bridge with a large support distance. Generally, a set of support frames is installed every 1.5 to 2.0 m on the cable bridge.
1) Calculation of the actual load of the cable tray Gtotal = n1*q1+ n2*q2 + n3*q3…nn*qn In the formula: Gtotal is the total load, q1, q2, q3…qn is the unit weight of each cable (kg/m), and n1, n2, n3…nn is the number of identical cables. (Gtotal < gallow, gallow is the allowable load of the cable tray, because when the cable tray is installed outdoors with a shield, the influence of the maximum load of ice and snow on the cable tray should also be taken into account) < span>
2) Calculation of the width of the cable tray The determination of the width of the cable tray varies with the different working systems of the power cable and the control cable. Since power cables are generally laid out in a single layer horizontally in the bridge, the installation bridge width b is: b = n1*(d1+k1)+n2*(d2+k2)+n3*(d3+k3)+……nn*（dn+kn）In the formula: d1, d2, d3…dn are the outer diameters of various cables in the bridge, in mm; n1, n2, n3…nn are the number of cables of the same type and specification mentioned above; K1, k2, k3…are the spacing when the above cables are placed, and the minimum value should be greater than 1/4 of the cable diameter.
