If it is deemed, in view of the installation, to be necessary to have an independent earth conductor, its section must be at least 16 mm2, and must be mounted on the outside throughout the rack system, connected using the right accessories to each length of the installation. A cable-carrying tray system comprises straight lengths and accessories (bends, crossovers, Tee-joints) joined together using suitable fasteners.

The electrical continuity in the system ifself (in the case of metal trays), which is necessary to achieve proper earthing and to ensure personal safety, can be adversely affected by a wide range of causes (oxidisation, nuts coming loose, insulating coatings, etc.). To avoid this, it is advisable to install an independent earth circuit by connecting up every single element in the system (trays and accessories) to a suitable sized conductor - with a section of at least 16 mm2.

In the case of trays that are painted or coated with epoxy resin, the electrical continuity needed in the system is broken. In such cases, arranging an earth connection is absolutely essential.
That is a difficult operation, since it can only be done by removing the protective layer by mechanical means at the earth-connection point. This inevitably creates an oxidisation zone which further hinders the earthing.

That is why electrically safe tray systems must be made of metal with metal coating or made soley of insulating material.
The earth connection is to be made using the right parts - see Rejiband.