According to the structural characteristics of the
building, calculate the load, tray size, deflection, etc. to determine an
appropriate span. It is necessary to meet the requirements of load and
deflection, and also consider the convenience of installation. Outdoors,
co-rack laying with process pipelines can be considered, but it should be noted
that the cable tray should be laid along the side with less flammable and
explosive hazards. When the explosive gas is lighter than air, the tray should
be installed below, and vice versa. And it should be avoided that the tray is
laid in parallel above or below the process pipeline.
The cable tray should have measures to prevent the
cables from being scratched. For example, various bends, tees, crosses, etc.
should preferably be arc-shaped, and a lead-down device should preferably be
used when leading down the cables. When the cable tray enters the room from the
outside (such as a substation), it should be sealed, and fireproof putty, sand
sealing, etc. can be used. At the same time, the cable tray should incline
towards the outside, generally with a slope of 1%, to prevent rainwater from
flowing back.
When the cable tray is laid horizontally, the
connection joints between the trays should preferably be set at about 1/4 of
the span. The horizontally running cables should be fixed every about 2 meters,
and the vertically running cables should be fixed every about 1.5 meters. The
cable tray should have a reliable grounding, and the entire tray should have
good electrical continuity. For the joint part of the tray, the connection
resistance should not be greater than 0.00033 ohms. Long-distance cable trays
should have temperature compensation measures (generally, for steel trays,
every 30 meters, and for aluminum alloy trays, every 15 meters). The cable tray
should be grounded every 30 to 50 meters.
