Define earthing related to electrical wiring system.
1 Answer
Definition of Earthing
Earthing (also known as grounding in North American terminology) is a fundamental safety measure in electrical wiring systems. It is the process of connecting the non-current-carrying metallic parts of electrical equipment and appliances to the Earth itself, via a low-resistance wire.
In simple terms, it provides a safe, alternative path for electricity to flow away in the event of an electrical fault, thereby protecting people from electric shock and preventing electrical fires.
The Primary Purpose of Earthing
The main purpose of earthing is safety. It achieves this by:
- Protecting from Electric Shock: It prevents the outer metal casing of an appliance from becoming dangerously "live" (energized).
- Protecting Equipment: It safeguards electrical equipment and devices from damage due to lightning strikes or voltage surges.
- Preventing Fire: By quickly clearing a fault, it prevents excessive current from overheating wires and starting a fire.
How Earthing Works: A Step-by-Step Example
To understand how it works, consider a common household appliance like a metal-cased washing machine, which has three wires: Live, Neutral, and Earth.
1. Normal Operation:
Electricity flows from the Live wire, through the appliance's motor, and back through the Neutral wire to complete the circuit.
The Earth wire is connected to the metal casing of the washing machine but carries no current during normal operation.
2. Fault Condition (The Danger):
Imagine an internal wire becomes frayed, and the Live wire accidentally touches the metal casing of the washing machine.
Without an earth connection, the entire metal casing would become live at the full mains voltage (e.g., 120V or 230V). The appliance might still appear to work, but it is now an invisible and lethal hazard. If you were to touch it, your body would become the path for the electricity to flow to the ground, resulting in a severe or fatal electric shock.
3. How Earthing Provides Safety:
With a proper earth connection, the moment the live wire touches the earthed metal casing, a safe path is created.
Because the earth wire has very low resistance, this fault creates a short circuit.
This short circuit causes a massive surge of current to flow instantly down the earth wire.
This huge current is detected by the circuit breaker or fuse in your consumer unit (fuse box).
* The circuit breaker trips (or the fuse blows) in a fraction of a second, disconnecting the power supply to the appliance and making it safe.
Key Components of an Earthing System
An earthing system consists of several parts working together:
- Earth Conductor (Earth Wire): The wire inside the electrical cable that connects the metal casing of the appliance to the building's main earth point. It is typically color-coded green-and-yellow (in IEC countries like the UK) or green (in North America).
- Main Earthing Terminal (MET): A central connection point, usually near the main electrical panel, where all the individual earth wires from different circuits are connected together.
- Earthing Electrode: A metal rod, plate, or pipe buried deep in the ground outside the building. This electrode makes the physical connection to the Earth.
- Earthing Lead: A heavy-duty conductor that connects the Main Earthing Terminal inside the building to the Earthing Electrode outside.
Summary
In essence, earthing is like an emergency exit for electricity. It provides a dedicated, low-resistance escape route for fault current, ensuring that this dangerous current flows harmlessly to the ground instead of through a person, and forces the circuit's safety device (breaker or fuse) to operate immediately. It is a non-negotiable, critical component of any safe electrical installation.