EMC - Earthing principles and structures
This section deals with the earthing and equipotential bonding of information-technology devices and other similar devices requiring interconnections for signalling purposes.
Earthing networks are designed to fulfil a number of functions. They can be independent or operate together to provide one or more of the following:
- Safety of persons with respect to electrical hazards
- Protection of equipment with respect to electrical hazards
- A reference value for reliable, high-quality signals
- Satisfactory EMC performance
The system earthing arrangement is generally designed and installed in view of obtaining a low impedance capable of diverting fault currents and HF currents away from electronic devices and systems. There are different types of system earthing arrangements and some require that specific conditions be met. These conditions are not always met in typical installations. The recommendations presented in this section are intended for such installations.
For professional and industrial installations, a common bonding network (CBN) may be useful to ensure better EMC performance with respect to the following points:
- Digital systems and new technologies
- Compliance with the EMC requirements of EEC 89/336 (emission and immunity)
- The wide number of electrical applications
- A high level of system safety and security, as well as reliability and/or availability
For residential premises, however, where the use of electrical devices is limited, an isolated bonding network (IBN) or, even better, a mesh IBN may be a solution.
It is now recognised that independent, dedicated earth electrodes, each serving a separate earthing network, are a solution that is not acceptable in terms of EMC, but also represent a serious safety hazard. In certain countries, the national building codes forbid such systems.
Use of a separate “clean” earthing network for electronics and a “dirty” earthing network for energy is not recommended in view of obtaining correct EMC, even when a single electrode is used (see Fig. R3 and Fig. R4). In the event of a lightning strike, a fault current or HF disturbances as well as transient currents will flow in the installation. Consequently, transient voltages will be created and result in failures or damage to the installation. If installation and maintenance are carried out properly, this approach may be dependable (at power frequencies), but it is generally not suitable for EMC purposes and is not recommended for general use.
