An earthing system is a safety precaution in an electrical network that safeguards both electrical equipment and human life. Given that earthing systems vary from nation to nation and that the installed capacity of PV systems worldwide keeps growing, it is critical to have a solid understanding of the various kinds of earthing systems.
The vast majority of electrical supply installations throughout Australia will fall under the TN-C classification which within Australian Standards is also referred to the MEN configuration. TN-C meaning Terra (Earth) Neutral Combined, and MEN being Multiple Earth Neutral.
What is Australia’s Earthing System?
Australia and New Zealand use the Multiple Earthed Neutral (MEN) earthing system, which entails grounding the distribution system’s neutral conductor (PEN) at regular intervals beginning at the supply source and continuing all the way through the system, including all connected electrical installations.
Each electrical setup has an earthing system that connects to the exposed conductive parts of the equipment and is distinct from the neutral conductor. Every site ought to have a single MEN connection.
Why We Need the MEN System in Australia?
The MEN system is considered to be the most important safety component of any electrical system in Australia. Because there is no moisture or conductivity in the sandy soil of Australia, you have to make sure that all the installations you do have the MEN system with good earthing. It is also required by law and by science.
Purpose of Earthing
The main advantage of this system is that it achieves a lower earth fault loop impedance, allowing circuit breakers to operate quickly.
Earthing systems provide safety functions by supplying the electrical installation with a low impedance path for any faults in the electrical network. Earthing also acts as a reference point for the electrical source and safety devices to correctly work.
Earthing of electrical equipment is typically achieved by inserting an electrode into a solid mass of earth and connecting this electrode to the equipment using a conductor. There are two assumptions that can be made about any earthing system:
- Earth potentials act as a static reference (i.e. zero volts) for connected systems. As such, any conductor which is connected to the earthing electrode will also possess that reference potential.
- Earthing conductors and the earth stake provide a low-resistance path to ground.
Protective and Functional Earthing
Protective Earthing
The MEN system is aligned with protective earthing, where the purpose of the earthing system is to provide a safe environment for personnel, equipment, and animals.
Functional Earthing
In order to provide a reference point for proper operation, any of the equipment’s live components may be connected to the earthing system. When the earthing system has both functional and protective uses, the protective earthing requirements are applied.
Types of Earthing Configuration
The same overall result can be obtained by varying the earthing configurations at the supply and load sides. Using a two-letter identifier of the form “XY,” the international standard IEC 60364 (Electrical Installations for Buildings) distinguishes three families of earthing:
- T – Earth (from French ‘Terre’)
- N – Neutral
- I – Isolated
Subsets of these configurations can be defined using the values:
- S – Separate
- C – Combined
IEC 60364 defines three earthing families:
- TN Earthing System: Earth is directly connected to a single point on the source side, typically the neutral reference point in a three-phase system with a star connection. Earth electrodes must be installed at regular intervals.
- TT Earthing System: This type is used when a distribution network service provider (DNSP) cannot guarantee a low-voltage connection back to the power supply. It was common in Australia before 1980 and is still used in some parts.
- IT Earthing System: This arrangement involves either a high impedance connection or no earthing at the supply. It is common in substations and generator-supplied systems but not in distribution networks.
Implications for PV System Earthing
The earthing system used in a country determines the design for grid-connected PV systems. PV systems are treated as generators and need to be earthed accordingly. Countries with TT type earthing require separate pits for DC and AC sides, while TN-C-S type earthing allows for connection to the main earthing bar.
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