The Purpose of Earthing and Bonding in Electrical Systems

Purpose of Earthing

The primary purpose of earthing is to connect the source neutral (or another defined point of the electrical system) to the ground in order to provide a reference potential and a safe path for unwanted electrical energy to dissipate.

Earthing helps to safely discharge:

• Electrostatic charges

• Induced currents caused by atmospheric and environmental effects

• Transient overvoltages, such as those resulting from lightning activity or switching events

  
  

Atmospheric phenomena, including lightning, can induce voltages and currents in electrical system conductors through electromagnetic coupling. By connecting the system to earth, these induced currents are safely dissipated into the ground rather than remaining on exposed or conductive parts.

This reduces the risk that electrical energy will:

• Appear on equipment enclosures

• Flow through a person to ground when they touch conductive parts

  
  

In addition to safety, properly earthed systems are generally more reliable and longer-lasting. By controlling voltage levels and reducing electrical stress, earthing helps protect insulation and equipment from degradation over time.

Purpose of Bonding

Bonding is the intentional connection of exposed and extraneous conductive parts together, and to the earthing system, including the source neutral where required.

These conductive parts may include:

• Metal pipework

• Structural steel

• Cable containment systems

• Exposed metal parts of electrical equipment

The purpose of bonding is to:

• Ensure all conductive parts remain at the same electrical potential

• Provide a low-impedance path for earth fault currents

• Prevent dangerous touch voltages from occurring

In the event of an earth fault, bonding ensures that fault current flows back to the source via a defined path. This allows protective devices such as circuit breakers or fuses to operate correctly and rapidly, clearing the fault and isolating the affected circuit.

How Earthing and Bonding Work Together

While earthing and bonding serve different functions, they operate together as part of a single safety system:

• Earthing provides a reference to ground and a path for induced or transient currents

• Bonding provides an effective return path for earth fault currents to the source

Together, they:

• Minimise the risk of electric shock

• Ensure protective devices operate as intended

• Improve system stability and durability