Is It Necessary to Ground Cable Trays?

Within a cable tray system, one may use an Equipment Grounding Conductor (EGC), or use the body of the cable tray itself to ground the system—provided the cable tray is made of metal. There are no restrictions as to where one installs a cable tray system. Since the function of the EGC is to provide electrical safety, the EGC is the most important conductor in the electrical system. Therefore, one has three options for grounding in a cable tray wiring system:

  • Use an EGC conductor within or on the cable tray
  • Use individual EGC conductors on each multi-conductor cable
  • Use the metal cable tray itself as the EGC

Irrespective of the option used, one must follow proper bonding practices to ensure the cable tray system is effectively grounded.

If an EGC cable is installed within or on the cable tray, use grounding clamps to bond it with each or alternate cable tray section. The grounding clamps ensure an electrical connection exists between all the sections of the cable tray system. In addition, the grounding clamps also serve to anchor the EGC to the cable tray, so that the EGC is not thrown out of the cable tray due to magnetic forces generated during fault current conditions.

For cable trays made of Aluminum, a bare copper EGC should preferably not be used, as a moist environment has the potential to start electrolytic corrosion of the tray. In such cases, an insulated conductor is a better choice, with tin or zinc plated connectors for bonding to the cable tray, raceways, or equipment enclosures, after removing the insulation of the conductor at such places.

According to industrial standards, when cable trays are used as equipment grounding conductors, there is a minimum requirement for both steel and aluminum cable trays. For circuits with ground-fault protection above 600 amperes, steel cable trays are not recommended for use as EGC. However, one can use aluminum cable trays as EGC for circuits that have ground-fault protection above 2000 amperes.

The standards further clarify that if the cable tray cannot be used as a protective device because of its maximum ampere rating limitations, a separate EGC may be included along with the cable assembly. Alternatively, each cable assembly may include an EGC. Where the cable tray system is in the form of discontinuous segments, it is recommended to use vertical adjustable splice plates to link the various segments. As non-metallic cable trays cannot work as a conductor, they should preferably have a separate EGC along with the cables. In addition, wire mesh cable trays are not to be used as an equipment grounding conductor, as the wire mesh is not a reliable continuous conductor.

For wire-mesh cable trays supporting cables with a built-in equipment grounding conductor along with control or signal cables, one must provide a low impedance path on the tray to a non-system ground for reducing noise and removing induced or stray currents. It is usually not necessary to provide a separate grounding cable attached to the wire mesh of the cable tray.