Earthing and grounding
- Earth’s ground considered for electrical installations as a reference of 0V - Variable electrical conductivity – naturally electrical currents are flowing.
- Lightning current flowing - Leakage current flowing - Protection of persons (IEC 364 – Electrical Installations of Buildings & IEC 50164 – Lightning protection components)
A properly grounded electrical system serves mainly two purposes:
- It prevents from the risk of electrical shocks to any human being coming in contact with the system.
- It protects the connected equipment from any possible damage occurring due to leakage currents or lightening or voltage surges, by providing a safe passage to these currents to ground. Earthing of an electrical system is achieved by inserting an electrode (plate type / rod type) in to the solid mass of earth and then connecting this electrode to the earth wire coming from the electrical equipment.
Different types of earthing systems are available. Popular methods are:
- Plate Earthing: A copper plate or galvanized plate is buried in an earth pit below ground level. The plate electrode connects the electrical conductors to the earth.
- Pipe Earthing: A galvanized steel perforated pipe inside the ground connects the electrical conductors to the earth.
- Rod Earthing: Similar to the Pipe earthing. A copper rod replaces the pipe electrode.
- Chemical earthing: Similar to the pipe earthing. A chemical compound material replaces the charcoal and salt layers.
The choice of earthing method primarily depends on:
- Service continuity requirement at different voltages
- Safety requirements for humans and equipment
- Possibility of overvoltage
- Maintenance requirements
- Cost consideration
Factors affecting Earth Resistivity:
- Soil Resistivity
- Soil Condition
- Dissolved Salt
- Climate Condition
- Physical Composition
- Location of Pits
- Effect of grain size and distribution
- Effect of current Magnitude