Geographically speaking earth is the planet habituated by mankind. What then can earthing mean? In layman’s language, is it connecting non-current carrying conductive parts of equipment or an installation to the earth using a conductor. It also refers to connecting the neutral conductor of an electrical system to the earth. Earthing is widely used in Europe as Americans prefer to call it grounding.
Earthing is a critical need for every electrical system with some conductive parts that need not carry current through them. Take for example an equipment with metallic housing that is frequently being touched by users. When the metal casing is not earthed and a fault occurs such as a live conductor comes into contact with it, it will develop an electrical potential (same as the conductor). This potential or voltage can drive a current through a conductive object that is linked to a point of lower potential. The earth is a conductor with zero potential. Every object with conductive media such as water or metal will complete a circuit from high potential to low potential, the restriction to current flow is called impedance. Whenever a person touches a live conductor while touching the ground, his body provided a path for current flow to the ground. Since the body has resistance, the result is electrical shock, electrocution, and at times death.
Earthing is provided to provide an alternative low resistance path for current flow when the non-current carrying conductor is energized. This occurs usually as a result of the fault. When the live conductor touches the metal casing, a very high current flows to the ground, and protective circuit breaker trips. The user is protected from carrying a current that is lethal and equipment is protected from damage. Before resetting the breaker, an electrician is supposed to check the fault and restore the equipment or system.
To carry out successful earthing of equipment or installation, the following steps are followed;
- Get appropriate electrodes such as copperplate, copper rod, or copper earthing tape.
- Excavate the ground to bury the electrode, dig about 1.5m whole. One may add charcoal. Salt and water enhance the earthing.
- Using the appropriate crimp connect the electrode to the earth lead cable and fix it to run to the meter box.
- Depending on the electrical utility of your power provide terminate the lead wire appropriately. Install a termination block that electrically connects earth lead wire, meter box, and earth cables for sub-circuits of the installation.
- Test the earthing by measuring the earth’s resistance, and ensure it is within acceptable limits.
- For an electrical supply with a neutral, connect it with the earth termination box
- Run an earthing wire or continuous protective conductor from the main earthing terminal that connects all exposed conductive parts of your installations.
- Areas that require earthing
- Some key areas that must be properly earthed include;
- All-metal casing of electrical equipment
- Electric generators, motors, and transformers- needs at least two separate earthing points
- Stay wire of overhead cables installation.
- Earth pin of a plug.
Importance of earthing
Human safety- it protects humans in contact with equipment from carrying leakage current in case of a fault that makes the touched part energized.
- Protects the equipment or installation from lightning strikes by draining stray electric current to the ground.
- Protect equipment from damage caused by undesired parts being energized.
- Avoids risks of fire that could be caused by leakage current flowing through a high resistance path.
- Maintains constant voltage and avoids voltage surge by driving a leaking current to the earth
It is important to check the earthing of your installation after every 2 or 3 years as electrodes could rust or corrode rendering them ineffective. Always engage a registered electrician to install and test the integrity of your earthing. Having established that indeed this is a critical component of an electrical system, it is prudent that earthing cable is as important as the live cable. In case of a fault, it is the earthing and protective fuse or circuit breaker that saves both the user and the equipment. Ever touched a metal casing of equipment and felt an electric shock sensation? Have the earthing checked? Safety fast is not just a slogan, observe it.