Low-voltage earthing systems and bonding

Earthing is the connection of a conductive part to the local earth. The connection to the local earth can be intentional, unintentional, or accidental, and permanent or temporary.

- Dr. Rajesh Kumar Arora

Significance of earthing (grounding)

• Safety from electric shock

• Protection against electrical fires

• Equipment protection

• Voltage stabilisation

• Legal and regulatory compliance

Concept of earthing (grounding)

When the neutral of any system is not connected to earth, it is known as an electrical system without earthing, as depicted in Figure 1.

Mostly, the galvanised iron is used for the earthing. Earthing provides a simple path for leakage and fault currents in the system. The short-circuit current of the equipment flows to ground, which is assumed to have zero potential. Thus, protects the system equipment and personnel working with it from damage and shock from current, as shown in Figure 2.

The system earth resistance should be such that, during any fault for which earthing is designed to ensure protection, the protective gear must operate to isolate the faulty section, for example, by a circuit breaker or fuses.

Types of electrical earthing (Figure 3)

The electrical equipment mainly consists of two non-current-carrying parts. These parts are neutral to the electrical equipment's system or frame/support structure. Earthing can be classified into two types:

• Neutral (system) earthing

• Equipment earthing

Equipment earthing: Such a type of earthing is provided to the electrical equipment. The non-current-carrying part of the equipment, such as its metallic frame, is connected to earth via a conducting wire, as shown in Figure 3. If any fault occurs in the apparatus, the short-circuit current passes to earth through the wire. Thus, protect the system from damage.

Classification of earthing system