Caution in Using Cable Tray Covers Outdoors
Improperly secured covers on outdoor cable trays can cause a serious safety hazard in high winds. In the majority of cases, covers are not used on cable trays for technical or safety reasons, but due to the “raceway complex,” a feeling by specifiers that cables must be totally enclosed in metal. Quality tray cables have a life of 30 to 40 years without covers when exposed to the elements. For outdoor installations, the most desirable cable tray system is a ladder cable tray or a ventilated trough cable tray without covers. If covers are used they should be the ventilated type.
Cable tray wiring systems have a 30-year plus proven track record of safety and dependability. They are the best economic choice for commercial and industrial wiring systems.
Fig. 1. Wind Effect on Covered Cable Trays.
Strong winds moving across outdoor cable trays with solid covers create a negative pressure above the cable tray cover and a positive pressure inside the cable tray. This is the same aerodynamic phenomenon produced on aircraft wings to provide lift and maintenance of altitude. This pressure difference can lift covers off the cable tray if they are not properly clamped to the cable tray with heavy duty clamps.