Types of electrical earthing system for electrical installation

What is the meaning electrical earthing system and electrical test equipment for electrical installation?

The electrical earthing system is a safety measure, which protects against the electric shock. The purpose of the electrical earthing system is to ground the potential difference between an energized conductor and earth.

Grounding of an energized conductor ensures that there is zero potential difference between earth and energized conductor. The grounding also protects against the electric shock in case of any fault, short circuit, leakage, etc.

There are two types of electrical earthing system such as:

1) Earth electrode system – In this type of grounding, a single earth electrode connects all conductors to ground at one point. This earth electrode may be correlated to earth by means of a deep well or buried pipe. It can also be connected by buried rods or pipe with separate connection to each conductor. It can also be connected by buried rods or pipe with separate connection to each conductor. In case there are several conductors (both hot and neutral), it will have more than one point of connection with ground at different levels as required for safety measures. The National Electrical Code (NEC) defines the minimum depth for this type of grounding at 3 meters below surface level i.e., 6 meters below finished grade level for residential buildings and 2 meters below surface level for industrial buildings (NEC Art 250-79). The purpose behind using deep well in this type of grounding is that it extends from surface level downwards, providing ample length of metal rod to dissipate the earth current from earth electrode system. The size of the pipe and metal rod used in this system will depend on the size of the electric motor, load and other factors.

2) Air electrode system – In this type of grounding, an air electrode is used as a ground connection for a conductor. Air electrodes may be vertical or horizontal depending on the arrangement required for safety measures. In this type of grounding, a single conductor is connected to ground using an air electrode at one point. In contrast, in the earth electrode system, all conductors are connected to ground using a single earth electrode at one point. This type of grounding has many applications such as:

(a) In case there is no available earth (or ground) connection then air electrodes can be used to connect each conductor with ground separately at different points depending upon the application.

(b) If there is only one conductor (for example, neutral wire in three phase systems or hot wire in single phase systems) then it can be grounded using an air electrode at one point instead of earth electrode system which uses three separate electrodes for each phase i.e., two hot wires and neutral wire or two hot wires and return wire (grounded conductor). The purpose behind using air electrodes instead of earth electrodes is that they have higher resistance than that of an earth electrode and thus do not allow much current to flow through them which makes them safer than an earth electrode under fault condition since they do not allow any damage to the equipment connected to them.

The most common applications of air electrodes are:

(a) Connecting neutral wire in three phase systems and grounding one hot wire of a single phase system.

(b) Connecting return wire (or grounded conductor) in three phase systems and grounding one hot wire of a single phase system.

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