Choosing the right earthing system for your power supply is crucial to protecting both people and property. And to make the right choice, you must understand how the different earthing systems affect electromagnetic compatibility.
An electrical installation’s earthing system determines how a power supply’s (usually a transformer) neutral is connected to earth. Earthing systems were developed decades ago to protect people and property and fix the potential reference for the electrical source. In terms of electromagnetic compatibility, the different earthing systems can cause disturbances or overvoltages. This is why it is important to choose the right earthing system when designing an electrical installation.
The four earthing systems:
- TT: The protective earth connection is independent from that of the installation.
- IT: Neutral is isolated to the protective earth or connected by impedance.
- TN-C: Neutral and protective earth are combined.
- TN-S: Neutral and protective earth are independent.
The main characteristics of the four earthing systems:
EU and international standards recommend the TN-S earthing system, which raises fewer electromagnetic compatibility issues for installations that include IT networks (and communications networks in particular).
The earthing system should be chosen at the beginning of the installation design process.
Neutral must be connected to earth at a single point as close to the transformer as possible.
IT, TT, and TN-C earthing systems are often the source of disturbances; a separation transformer should be used in these cases.
If the earthing system is not known, use a dedicated transformer to supply sensitive equipment (automation devices, electronics, interfaces, etc.).
Use separate transformers to supply sensitive systems or systems that create disturbances.
Use EMC filters (of the right size and correctly implemented).
Use overvoltage protectors (of the right size and correctly implemented).
Pay special attention to leakage current generated by EMC filter (phase and neutral to earth capacitors).