6.5.7 Earthing systems in cable networks

The safe earthing of cable networks is a key element of protective measures in modern information and communication technology. The IEC 60728-11 standard stipulates specific safety requirements for fixed and, where applicable, mobile installations that transmit television signals, sound signals and interactive services. An essential part of these requirements concerns the earthing system, particularly with regard to the protection of people, connected terminal equipment and the specialist personnel carrying out the installation. 

The following earthing systems (Figure 6.5.7.1) meet the requirements of IEC 60728-11:

• Earthing system of the building (e.g. foundation earth electrodes).
• At least two horizontal earth electrodes (strip earth electrodes) with a minimum length of 2.5 m each, laid at an angle greater than 60° to each other.
• A horizontal earth electrode (strip earth electrode) at least 5 m long, laid at a depth of at least 0.5 m and at least 1 m away from the foundation.
• A vertical earth electrode at least 2.5 metres long. 
• Two vertical earth electrodes at least 1.5 m long, spaced 3 m from each other, laid at a depth of at least 0.5 m and at least 1 m away from the foundation.
• Intrinsic components, such as connected concrete reinforcement or other suitable underground metal structures.

The minimum cross-section of each earth electrode should be 50 mm² of copper or 90 mm² of stainless steel. Hot-dip galvanised steel with a cross-section of 90 mm² is also permitted as an earth electrode material, but its corrosion behaviour must be taken into account.