Grounding (Earthing) is a system of electrical circuits that are connected to the ground that functions when a leakage current can discharge electricity to the earth.
According to Institute of Electrical and Electronics Engineers (IEEE) Standard 142 ™ 2007, the purpose of the grounding system is to:
- Limit the amount of voltage to the earth to be within the allowed limits
- Provide a path for current flow that can provide detection of the occurrence of an undesired relationship between the system conductor and the earth. This detection will result in the operation of automatic equipment that decides the supply of voltage from the conductor.
Characteristics of an Effective Grounding System
Based on the IEEE standards, the grounding system is divided into:
- TN-S (Terre Neutral – Separate)
- TN-C-S (Terre Neutral – Combined – Separate)
- TT (Double Terre)
- TN-C (Neutral Terre – Combined)
- IT (Isolated Terre)
Terre originates from the French language and means earth.
The first letter is the connection between ground and the power supply, while the second letter shows the connection between ground and electronic equipment supplied with electricity. The meaning of each letter is as follows:
- T (Terra) = Direct connection to ground.
- I (Isolation) = There is no connection to ground (even if there is a high impedance)
- N (Neutral) = Connection directly to neutral power supply cable (where this cable is also grounded in the power supply)
TN-S (Terre Neutral – Separate)
In a TN-S system, the neutral part of the electrical energy source is connected to the earth at one point, so that the neutral part of a consumer installation is directly connected to the neutral source of electricity. This type is suitable for installations that are close to electrical energy sources, such as for large consumers who have one or more HV / LV transformers for their own needs and if the installation / equipment is adjacent to the energy source (transformers).
TN-C-S (Terre Neutral – Combined – Separate)
A TN-C-S system, has a neutral channel from the main distribution equipment (power source) connected to the earth and earthing at a certain distance along neutral channels leading to consumers, usually referred to as Protective Multiple Earthing (PME). With this system, a neutral conductor can function to restore the earth fault current that might arise on the consumer’s side (instation) back to the power source. In this system, the installation of equipment in the consumer only connects the ground to the terminal (channel) provided by the power source.
TT (Double Terre)
In the TT system, the neutral part of the electricity source is not directly connected with neutral earthing on the consumer side (equipment installation). In TT systems, consumers must provide their own connection to the earth, namely by installing an earth electrode that is suitable for the installation.
TN-C (Neutral Terre – Combined)
In the TN-C system, the neutral channel of the main distribution equipment (power source) is connected directly to the consumer’s neutral channel and the frame of the installed equipment.
With this system, a neutral conductor is used as a protective conductor and a combination of neutral and earthing side frames of the equipment is known as a conductor of PEN (Protective Earthing and Neutral).
This system is not permitted for conductors less than 10 mm2 or for portable equipment. This is because if a fault occurs, then at the same time the PEN conductor carries the phase unbalance current and the third level harmonic current and its multiples.
To reduce the impact on equipment and living things around the equipment, then in the application of the TN-C system, the PEN conductor must be connected to a number of electrode rods for earthing on the installation.
IT (Isolated Terre)
From the first letter (I) it is clear that, in this type of IT system, neutral is isolated (not connected) to the earth. The PE point is not connected to the neutral channel but directly connected to the earthing.
In its application, the neutral point of the IT system is not really isolated from the earth, but is still linked to the Zs impdedance which has a very high value of around 1000 ohms to 3000 ohms. This serves the purpose of limiting the level of voltage overload when there is interference in the system.
|Earth fault loop impedance||High||Highest||Low||Low||Low|
|Need earth electrode at site||Yes||Yes||No||No||Optional|
|PE conductor cost||Low||Low||Highest||Least||High|
|Risk of broken neutral||No||No||High||Highest||High|
|Safety||Safe||Less Safe||Safest||Least Safe||Safe|
|Safety risks||High loop impedance (step voltage)||Double fault, overvoltage||Broken neutral||Broken neutral||Broken neutral|
|Advantages||Safe and reliable||Continuity of operation, cost||Safest||Cost||Safety and cost|