What Is Earth Fault? Definition & Meaning

Earth fault (UK and IEC) or ground fault (US): occurrence of an accidental conductive path between a live part and the Earth [defined in the IEC 60050-195-2021].

Note 1 to entry: The conductive path can pass through a faulty insulation, through structures (e.g. poles, scaffoldings, cranes, ladders), or through vegetation (e.g. trees, bushes) and can have a significant impedance.
Note 2 to entry: Earth faults with negligible fault impedance in a solidly earthed neutral system or in a low-impedance earthed neutral system are also named line-to-earth short-circuits.

Types of Earth Faults

IEC 60050-604-2016 defined the following terms describing specific types of earth faults [2]:

  • line-to-line insulation fault: insulation fault between two or more line conductors, combined or not with an earth fault. Note 1 to entry: Line-to-line insulation faults with negligible fault impedance are also named line-to-line short-circuits.
  • double insulation earth fault: two earth faults, occurring simultaneously at two different locations in one or several electric circuits originating from a common source;
  • multiple insulation earth faults: earth faults, occurring simultaneously at more than two different locations in one or several electric circuits originating from a common source;
  • symmetrical insulation fault or three-phase insulation fault: insulation fault at one point of a three-phase electric circuit, affecting the insulation of all three line conductors between one another and usually to the earth;
  • developing insulation fault: earth fault which affects one line conductor and develops into a line-to-line fault or insulation fault which begins as a line-to-line fault and develops into a three-phase fault.

Meaning

In international documentation, a earth fault is defined as the occurrence of an accidental conductive path between some live part and earth. This occurs, for example, when a phase wire of an overhead line falls to the ground because it is broken. However, in the event of a single fault condition in the insulation of a live part of the electrical installation of building, an electrical connection is most likely to occur between this live part and an exposed conductive part of Class I equipment, a protective conductor or an extraneous-conductive-part of the building.

It is practically impossible to connect this live part directly to earth.

For this reason, in the international standards applying to the electrical installations of buildings, it is reasonable to define a earth fault as an electrical connection between a live part and an exposed conductive part (the most probable event), a protective conductor, an extraneous-conductive-part and the earth (the least probable event).

Indeed, in electrical installations of buildings corresponding to the TT and IT types of system earthing, when a live part is shorted to an exposed conductive part of Class I equipment, the earth-fault current flows to local earth via the protective conductor and the earthing arrangement of the electrical installation of building. That is, in such electrical installations of buildings, the live part to earth is short-circuited via intermediate conductive parts.

In electrical installations of buildings corresponding to the TN-C, TN-S and TN-C-S types of system earthing, a “classic” earth fault does not occur when a live part is shorted to an exposed conductive part of Class I electrical equipment. In such electrical installations of buildings, the earth-fault current flows from the live part through the protective conductors to the earthed live part of the power source. Only a small fraction of this current flows through the earthing arrangement of the electrical installation of building to the local earth.

However, in order to unify the concepts for the same faults, it is logical to call the considered faults of live parts to the exposed conductive parts both in the TT and IT systems and in the TN-C, TN-S and TN-C-S systems as earth faults.

What Is the Danger of a Earth Fault?

As a result of a earth fault, an earth fault current flows from the live part to the earth, as well as to the conductive parts connected by protective conductors to the earthing arrangement of the electrical installation of building or to the earthed live part of the power source. Such fault conditions in the electrical installation of building are dangerous for humans and animals, as they can be electrocuted.

Therefore, protective devices are installed in electrical installations of buildings that detect the earth fault current and disconnect the emergency parts of the electrical installation of building or the entire electrical installation of building when an earth fault occurs.

Earth-fault current path in the TT system
Figure 1. Earth-fault current (Iefc) path in the TT system

FAQ

What Can Cause a Earth Fault?

There are a few things that can cause an earth fault. The most common is when something goes wrong with the electrical wiring in your home. This can be caused by a number of things, including loose connections, damaged insulation, or even rodents chewing on the wires. Other causes of earth faults include lightning strikes and power surges.

How Do You Fix Earth Fault?

If there is an earth fault on your electrical system, it is important to have it fixed as soon as possible. An earth fault can cause serious problems and even damage to your equipment.

There are two main ways to fix an earth fault. The first way is to install an earth electrode. This will provide a path for the current to flow back into the ground, preventing it from damaging your equipment.

The second way to fix an earth fault is to install a circuit breaker. This will break the circuit if there is too much current flowing through it, preventing damage to your equipment.

Either way, it is important to have a qualified electrician fix any earth faults on your system. They will be able to assess the situation and determine the best course of action.

What Is an Earth Fault Indicator?

An earth fault indicator is a device that monitors the electrical current flowing through a circuit and indicates when there is an imbalance. This can be due to a variety of factors, including faults in the equipment or wiring, or simply because the load on the circuit has changed.

The indicator usually takes the form of a light or sound, but some more sophisticated models may also provide a digital readout. It is important to note that an earth fault indicator does not necessarily indicate a dangerous situation, but simply that there is an imbalance in the current flow which should be investigated.

How Earth Fault Is Detected in a Relay?

When an earth fault occurs, it sets off a relay which trips the circuit breaker and cuts off the power supply. This prevents further damage to the system and protects people from electrocution. There are two main types of relays used for this purpose – phase comparison relays and residual current relays.

Phase comparison relays compare the currents flowing through each phase of the system. If there is a significant difference, it indicates an earth fault and the relay trips the circuit breaker. Residual current relays measure the overall current flowing through the system. If there is a significant difference between the expected current and the actual current, it indicates an earth fault and the relay trips the circuit breaker.

Which type of relay is used depends on the particular installation, but both are effective at detecting and preventing damage from earth faults.

References

  1. IEC 60050-195-2021
  2. IEC 60050-604-2016