Below drawing shows how to install cable tray and its support system. This cable tray support system drawing has Isometric view and cross-sectional view. Following are the steps to be done for laying cables on wall mounted cable tray:
- Install cable tray support using a pre-fabricated flange or GI channel. The size, length and intervals of the support to be as per the specification, standards, number of cables, and size of the cable.
- Fix the cable tray as shown on the drawing.
- Lay the cable keeping the distance as per calculation.
- Tie the cable using cable tie and label the cables as required.
Below drawing shows the cross sectional view of wall mounted cable tray and its support system. This drawing has perforated cable tray screwed on cable tray support bracket.
Typical Specification Detail for Installing Cable Trays
Cables shall be laid in a single tier on the cable tray, unless otherwise accepted and neatly installed.
Cable tray shall only be cut along a line of plain metal (not through perforations). All cut edges shall be prepared and treated accordingly to original finish of metal. Where welding had been employed in fabrication and also on galvanised tray, a zinc rich paint shall be used for this treatment.
Holes cut in cable tray for the passage of PVC covered cables shall be provided with grommets or alternatively bushed and/or lined to Cable Tray 853/11 prevent damage to the PVC covering. Cable tray shall be manufactured from perforated mild steel and shall have hot-dipped galvanized finish.
Cable trays shall have the following dimensions:
|Width (mm)||Flange Height (mm)||Thickness (mm)|
|100 - 150||13||1.5|
|300 - 450||20||1.5|
|600 - 1200||20||2.0|
Bends and tees shall be made of the same material, finish and thickness as straight trays. At each end of the bends and tees, a minimum of 100mm straight run shall be provided.
Cable trays shall be supported by mild steel galvanized brackets at regular intervals of 1.2mm maximum and at 255mm from bends and tees. Mushroom-headed steel roofing bolts and nuts shall be used for the installation and coupling of trays. Cable tray brackets shall be sufficient depth to provide access to the rear of the tray for easy installation of PVC saddle type fixings.
All cables shall be secured to cable trays by means of PVC covered copper saddles of the two screw fixing type or PVC covered metal strip with non-corrodible cheese-headed screws and nuts. The shanks of the screws shall be protrude beyond the nut by more than three threads. Alternatively purpose made cable fixing devices may be proposed for consideration. Horizontal and vertical clearance between cables shall be such that no reduction in rating is necessary.
A continuous run of 25mm x 3mm tinned copper strip shall be installed to the full length of the trays to ensure earth continuity. Jumper links shall be provided for all breaks in cable tray and at connections. A complete run of tray shall be earthed using 25mm x 3mm tinned copper strip as necessary. Only 40% of cable tray space shall be occupied, a calculation shall be forwarded for acceptance and cable tray size shall be increased if required to meet the above without extra cost.
The above drawing shows how cable trays to be jointed when it cross the expansion joints of the building.