What is Earth Fault? It’s Causes, Effects and Protection

Earth fault
In this article, we are going to discuss what is earth fault, the causes of an earth fault, the effects of an earth fault, and also what are protections used to prevent an earth fault. So let’s start but before that first of all we have to understand what is  earthing and grounding. Generally, people get confused and they consider them similar. But it’s not like that. Actually, earthing and grounding are two different concepts. Here we are discussing one by one.

What is Earthing and Grounding?

Earthing and grounding both are processes to connect electrical systems to the ground to protect people against electrical shock. The earthing process means connecting the dead part of the electrical system (parts that don’t carry current under normal conditions such as the motor body, Transformer body, electrical panels, etc.) to the earth. Whereas the Grounding process means connecting the live part of the electrical system (parts that carry current under normal conditions such as neutral of star connected Transformer and loads) to the earth. Now coming to our main topic of discussion:

What is Earth Fault?

Earth fault is an open circuit ground fault in which any live conductor or power-carrying cable is detached from its place or breaks and falls on the earth’s surface. In other words, We can say that ln earth-fault current-carrying conductor comes directly in contact with the earth’s surface. So because of the direct contact between a live conductor and the earth’s surface, a huge amount of current starts flowing to the earth due to the conducting nature of the earth.

Causes of Earth Fault

The main cause of earth fault in an overhead transmission and distribution line is the failure or puncture of the insulator. Insulators are used in overhead transmission lines to provide insulation between live conductors and metallic towers that are already connected with the earth’s surface. So if the insulation of insulator fails or in other words if the insulator is punctured then the fault current will flow through the live conductor and metallic tower to the earth creating an earth fault.

Another reason for earth fault is that sometimes overhead transmission lines break due to any unusual loads on line and hence fall to the ground. So in this case also live conductor gets in direct contact with the ground and creates a major earth fault in the electrical system. Whereas in the case of an underground PV cabling system, Earth fault may arise due to insulation damage during installation, abrasion damage to cable sheath, and damage to module back sheet during installation.

Effect of Earth Fault

Whenever an earth fault occurs in the electrical system than during earth fault, the System gets short, and hence huge amount of short-circuit current flows through the system. That huge current damages electrical equipment which comes in contact with a loop of earth fault circuits and also it interrupts the continuity of the power supply. Due to such a large amount of current flowing to the earth, a large voltage drop occurs that affects the other loads and it may cause the burning of phase or line.

How to check Earth Fault?

To identify the earth leakage fault in cables, megger is used. One terminal of the megger is connected to the live conductor and the other terminal is connected to the earth. If the merger indicates zero reading, it means the conductor is earthed. The same procedure is repeated for other conductors of the high-voltage cables.

Difference between Earth Fault and Ground Fault

Earth Fault vs Ground Fault:

Earth fault is an open-circuit fault where a power-carrying cable or conductor breaks and gets into contact with Earth or any conductor capability material in contact with Earth. In this fault, the system at the load side is disconnected from the source in case of radial power flow.

Whereas a ground fault is a short-circuit fault (such as L-G, L-L-G, L-L-L-G) where the power-carrying cable or conductor is not broken but gets into contact with the earth or any conductor capability material in contact with the earth. In this fault, the system at the fault point experiences the flow of a large amount of current into the ground.

Ground fault is more severe than earth fault due to flow of huge current to ground. That can dimage verious electrical equipments of power system, if fault is not cleared within specified time limits.

Earth Fault Protection

Well, after discussing the earth’s fault, its causes, and effects, one of the important questions that arises in our mind is.. ok, then what is the solution to minimize Earth-fault? Does it mean what protective equipment we can use to protect the earth fault? So let’s discuss the protection used to minimize earth faults in detail.

What are  Earth Fault Protection Devices?

The electrical equipment that  provides protection against earth fault is known as earth fault protection devices. These are normally Earth fault relay (EFR), Earth leakage circuit breaker (ELCB), and ground fault circuit interrupter, which are used to restrict the fault current. In these devices, the fault current is restricted and the fault is dispersed by the Restricted Earth Fault Protection (REFP) scheme. Now first let’s discuss both earth fault protection devices such as:

  • Earth fault relay (EFR)
  • Earth leakage circuit breaker (ELCB)

After that, we will see what is Restricted Earth Fault Protection (REFP) schemes.

Earth Fault Relay (EFR)

An earth fault relay (EFR) is a protection device used in electrical installation that can sense a fault between phase and earth.

The main function of an earth fault relay (EFR) is to operate the CB for leakage current to the earth. RCCB also does the same function but RCCB gives protection to the human body, Whereas EFR provides protection to electrical equipment from earth fault. EFR deals with high voltage and high current.

Hence we can conclude that an earth fault relay (EFR) is an earth fault monitoring device that works on the principle of Kirchhoff’s law.

Earth Leakage Circuit Breaker (ELCB)

Earth leakage circuit breaker (ELCB)

ELCB or earth leakage circuit breaker is a safety device used in electrical installation with high earth impedance to prevent electrical shock. In other words, we can say that ELCB is a special type of circuit breaker that is used for protection against earth leakage current. It is voltage voltage-sensing device that works on the concept of stray voltage. Whereas current sensing ELCB is also known as RCCB.

Whenever any earth leakage fault occurs in the system then a stray voltage appears across metal enclosures of electrical equipment ELCB interrupts the circuit if a dangerous voltage is detected. Then it disconnects the rest of the healthy system from the main supply. Once it tripped then it requires a manual reset process to work again normally.

Hence simply we can assume that ELCB is a safety device whose main function is to provide protection against electrical shock. It can’t assure protection against overloading and short-circuit faults.

What is the Restricted Earth Fault Protection (REFP) Scheme?

The restricted earth fault protection (REFP) scheme is very sensitive to internal earth faults for high-rating power transformers, alternators, etc. This scheme is comparatively cheaper than the differential protection scheme.

In this scheme, the common terminal of phase CTs is connected together with the secondary of neutral CT in such a manner that the secondary unbalanced current of phase CTs, and the secondary content of neutral CT will oppose each other.

Restricted earth fault protection (REFP) scheme


When an external fault F1 occurs in the system then the resultant of current I1 and I2 flowing through phase CTs and neutral CT respectively will be zero. But whenever an internal fault F1 occurs inside the protective zone then only I2 current will flow through the secondary of neutral CT and the resultant current will not be zero.

Hence earth fault relay will sense non-zero current and then it will operate the CB to protect the system with earth leakage fault. The fault current becomes 15% more than the rated current of each winding. To avoid magnetic inrush current, a stabilizing resistor is connected in series with an earth fault relay.

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Hey, I'm Satish Gupta an Engineer by profession and blogger by passion. I am writer and founder of this blog, Here I publish contents related to Electrical and Electronics Engineering..

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