Choosing the right earthing system

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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).

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  • It’s a great article i’ve come so far on earthing arrangement.

    One more help please!!

    Which on is applicable for Solar PV Power Plant ranging from 500KW to 5MW?

  • José Soares

    10 years ago

    This topic is very important and there should be mandatory training for people working in the electrical infrastructure

  • Lucas sitoe

    10 years ago

    I have been in Electrical Power supply the problem is electricity quality , under voltage, over voltage, differential circuit beaker strip all time. After all investigation we found neutral not earthing to ground, neutral earthing with high resistance.
    The earthing system in the infra structure, represent the less cost compare with the damage cause the people and infra- structure without that system.
    Installation and maintanence program is needed to have a good power quality.

  • Bernard Jover

    10 years ago

    Dear Amrit. Thank you for your interesting question!

    3 main points:
    1-DC part (PV arrays):
    Earthing system arrangements are described inside IEC/TS 62548
    Depend also on:
    • PV modules specifications and the PV array architectures
    • Countries local safety rules or code of practice

    2-AC power production part:
    The earthing system arrangements depend on:
    • Electricity provider’s requirements for the grid,
    • DC to AC Inverters specifications/requirements
    • Inverter’s upstream/downstream isolation (e.g. transformer).
    The following standards provide more information: IEC 60364 (all parts) and particularly IEC 60364-7-712

    3-AC utilities part (e.g. monitoring, communication, etc.):
    The recommended earthing system arrangement is TN-S.
    It is recommended to use local dedicated transformers to provide isolation and/or change the existing earthing system if it is different from TN-S.

    Anyway, lightning effects is a high cause of trouble in PV plants:
    • Minimize all the cabling loops (+, – and PE; phase(s) neutral and PE together)
    • Use of a well meshed earthing and bonding network
    • Use of Surge Protective Devices (DC, AC and communication)

    I hope this information will be useful for you!
    Best regards,

  • i have a m340 plc in our site. we have a power system earthing but i think it’s not reliable. what i must do for protection of the plc???
    should i connect my analog output wire shields to the earthing or no???

  • how many pole for TNC system are using??
    because when i pull cable 4x35mm^2 and my mccb is 4P my consultants rejected.. please help mee

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