6.5.6 Earthing systems for low-voltage installations

Earthing systems form the basis for the safe operation of low-voltage electrical installations. They represent the reference point for the protective conductor (PE) and the equipotential bonding and form the basis for the effectiveness of protective measures against electric shock. In addition, they perform important tasks for electromagnetic compatibility (EMC) and the functional safety of modern communication and control systems. The installation of an earthing system must be carried out in accordance with the specifications of IEC 60364-5-54 in conjunction with applicable grid codes of power utilities.

The earthing system must be designed in such a way that it ensures a permanent, low-resistance connection to earth. It must be able to withstand thermal, mechanical and corrosive stresses and its protective effect must not be impaired by changes in the earth resistance, as a result of drying out or frost, for example. Earthing is not only relevant for fault protection, but also for functional earthing (e.g. of communication systems) and lightning protection. However, protection requirements always take precedence over functional requirements such as EMC or signal reference planes for telecommunications systems.

The planning, execution and documentation of earthing systems for buildings should therefore be carried out by a qualified electrician. Where applicable, local regulations must be observed. (Chapter 6.5.9). The use of water and gas pipes as part of earthing systems is not permitted. When combining different materials, electrochemical corrosion must be taken into account.

The main earthing bar (MEB) is the central connecting point of the earthing system for the low-voltage installation.
It connects:

• the earthing system of the building.
• the protective conductor (PE).
• the equipotential bonding for extraneous conductive parts (e.g. pipelines).
• functional earthing for telecommunications and lightning protection systems.

The connection must be permanent, low-resistance and mechanically stable. The MEB should be located near the service entrance box to ensure short cable runs.