Equipment Earthing helps in limiting the voltage to ground on the electrical conductors or Equipment. It keeps equipment as well as people safe from shocks. This post will discuss about what is Equipment Earthing, its various types, architecture, qualities, how it works, applications, advantages & disadvantages.
What is Equipment Earthing
The basic objective of Equipment Earthing is human safety by preventing the surge of current to unsafe level. This might cause shock to any human being when he comes in contact with the metallic enclosure of a live conductor.
All the people living or working in residential, commercial or industrial areas work on electrical equipment. Therefore, electrical systems and equipment should essentially be protected against possible electrification. To achieve this protection, earthing system is defined, designed and installed according to standard specifications.
Fig. 1 – Introduction to Equipment Earthing
Earthing means to provide a safe path to the earth, in case of a fault current. It is a connection of electrical equipment to the nearest point having zero potential by means of a suitable size conductor which can sustain the fault current of the electric equipment.
A good earthing must have low Impedance to ensure that sufficient current can flow through the safety device so that it disconnects the supply. When the Fault current is more than the Load current of the circuit, the Circuit Breaker breaks the circuit. Hence, the Equipment is disconnected automatically from the supply mains.
Fig. 2 – Schematic Diagram of Equipment Earthing
Qualities of Good Equipment Earthing
Qualities of Good Earthing include:
- Electrical Resistance must be of low.
- Must be good corrosion resistant.
- Must be able to suppress high fault current repeatedly.
Types of Earthing
Most popular types of Equipment Earthing are:
- Pipe Earthing
- Plate Earthing
Fig. 3 – Types of Earthing (a) Plate Type Earthing (b) Pipe Earthing
A galvanized steel perforated Pipe in the ground connects the electrical conductors to the earth.
Plate Type Earthing
A copper or galvanized plate is buried in an earth pit below ground level. The Plate Electrode connects the conductors to the earth.
Architecture of Equipment Earthing System
The architecture of Equipment Earthing System consists of following components:
- Earth electrode
- Earth Electrically independent earth electrodes
- Earth Electrode Resistance
- Earthing Conductor
- Exposed Conductive Part
- Extraneous Conductive Part
- Bonding Conductor
- Main Earthing Terminal
- Equipotential Bonding
Fig. 4 – Architecture of Equipment Earthing
This is the conductor or group of conductors in close contact with and provides an electrical connection with Earth.
Earth is a conductive mass whose electric potential at any point is taken as zero.
Electrically Independent Earth Electrodes
These are Electrodes placed in such a way that the maximum current likely to flow through one of them does not significantly affect the potential of the others.
Earth Electrode Resistance
This is the Resistance of an Electrode with the Earth.
This is a Conductor connecting the main Earthing terminal of an installation to an Earth Electrode or to other means of earthing.
Exposed Conductive Part
This is the Conductive part of Equipment which can be touched (not a live part) but which may become live under fault conditions. Usually all open conductive parts are connected to the Earth Electrode as a part of Equipment Earthing by protective conductors with the object of providing a low resistance path for fault currents flowing to earth.
This is the conductor used for protection against electric shock and can be used for connecting together any of the following parts:
- Exposed Conductive Parts
- Extraneous Conductive Parts
- Earthing Terminal
- Earth Electrode
- Earth’s Point of Source
Extraneous Conductive Part
This is a conductive part liable to introduce a potential generally earth potential that is not part of the installation. Some examples of extraneous conductive parts are:
- Non insulated walls or floors.
- Metal work of buildings.
- Metal conduits and pipe work and metal materials associated with them.
This is the conductor that provides equipotential Bonding.
Main Earthing Terminal
The Terminal provided for the connection of protective conductors including Equipotential Bonding Conductors and conductors for functional earthing, if any, to the means of equipment earthing.
Equipotential Bonding means terminating all the conductive parts to the earthing system of the installation in a process known as Bonding.
Maximum Value of Earth Resistance to be Achieved During Earthing
|Equipment to be Earthed||Maximum Value of Earth Resistance to be achieved (in Ohms)|
|Large Power Stations||0.5|
|Lattice Steel Tower||3.0|
|Industrial Machine and Equipment||0.5|
* Earth Resistance also depends upon the moisture content in soil.
How does Equipment Earthing Work
The principle behind Equipment Earthing is to provide another path to earth to prevent a person from being electrocuted. The main principle of an Equipment Earth System is to provide a good resistance to earth. Any Electrical Equipment consists of two parts:
- Internal circuit/motor/engine
- External body/material/cover
The Equipment is basically designed to ensure proper insulation between these two parts. The Equipment is connected to the AC Mains through switches which drives the Equipment to work. The internal circuit of Equipment is provided with current-sink inputs and as the current flows from high potential to low potential , current flows into the Sink and completes the circuit to ground. This is connected to the Negative terminal of Power supply and the Source is reversed, which is positive. This principle is similar to connection in a battery.
Fig. 5 – Representation of Working of Equipment Earthing
Metallic frame work of all outdoor Equipment like Transformers, Circuit Breakers, Interrupters and Isolators are connected to the Earthing grid. This is achieved by means of two separate and distinct connections. One connection is generally made with the nearest longitudinal conductor, while the other connection is made to the nearest transverse conductor of the grid.
The Equipment is safe from shocks as there is an insulation between inner and outer covering. When there is any faulty current or malfunctioning of the Equipment then accidents of shock might occur. Equipment Earthing is done to prevent this. The conductor which is connected to the Equipment and the Earth has near zero resistance and hence there is a sudden current surge which exceeds the maximum rated value of circuit Breaker. Thus the risk or hazard is prevented as the circuit breaks. The issue gets fixed even before the user gets a chance to touch the Equipment.
Applications of Equipment Earthing
The applications of Equipment Earthing include (but not limited to):
- Heavy Industries
- Substations and Power Generations
- Transformer Neutral Earthing
- Lightner Arrester Earthing
- Equipment Body Earthing
- Water Treatment Plants
- Residential Building
- College, Hospitals, Banks
Advantages of Equipment Earthing
The advantages of Equipment Earthing include:
- To safeguard user of Equipment.
- To safeguard Equipment.
- To prevent or minimize damage to Equipment as a result of heavy currents.
- Prevents Equipment from over voltage damage.
- Improvement of the reliability to power system.
Disadvantages of Equipment Earthing
The only disadvantage of Equipment Earthing is it cost. The complete system of protective conductors, earth electrodes etc. are very expensive.