Basic Grounding System

Why we use a grounding system for our electricity ? The answer is may as simple as : it for safety; but the explanation is quite long.
In from philosophy , there is 2 grounding that we know :
1. Protective grounding or system grounding.
2. Equipment grounding.
Protective ground or P.E (Protective Earthing) in short, it grounding that include neutral conductor as a part of ground loop. Its intended to make our electricity system become more stabil.

In another side, Equipment grounding, its to make that open body of electrical equipment such of electrical pump , etc. its guaranted that there are no voltage in it. So this grounding is intended to protect human from electrical shock.

How p.e grounding is build?
There are several methode to make p.e grounding :
1. Solid grounding
2 . Resistance grounding
3. Reactance Grounding
4. Impedance grounding

Solid grounding is grounding methode that neutral conductor is connected to ground rod directly, is usualy met in system with low voltage (under 1000 v).
Resistance grounding is grounding methode that neutral conductor is connected to ground rod dvia a grounding resistance, is usually met in system with high voltage (above 1000 v).
We us a resistance as current limiter, so the ground cable willnot overheating due harmonis current or abnormal condition.

Classification Grounding System According IEEE :
IEC terminology

International standard IEC 60364 distinguishes three families of earthing arrangements, using the two-letter codes TN, TT, and IT.

The first letter indicates the connection between earth and the power-supply equipment (generator or transformer):
T: Direct connection of a point with earth (Latin: terra);
I: No point is connected with earth (isolation), except perhaps via a high impedance.

The second letter indicates the connection between earth and the electrical device being supplied:
T:direct connection of a point with earth
N:direct connection to neutral at the origin of installation, which is connected to the earth


TN networks
In a TN earthing system, one of the points in the generator or transformer is connected with earth, usually the star point in a three-phase system. The body of the electrical device is connected with earth via this earth connection at the transformer.

The conductor that connects the exposed metallic parts of the consumer is called protective earth (PE). The conductor that connects to the star point in a three-phase system, or that carries the return current in a single-phase system, is called neutral (N).
Three variants of TN systems are distinguished:
TN−S :PE and N are separate conductors that are connected together only
near the power source.
TN−C :A combined PEN conductor fulfills the functions of both a PE and an N
conductor.
The combined PEN conductor typically occurs between the substation and the entry point into the building, whereas within the building separate PE and N conductors are used. In the UK, this system is also known as protective multiple earthing (PME), because of the practice of connecting the combined neutral-and-earth conductor to real earth at many locations, to reduce the risk of broken neutrals - with a similar system in Australia being designated as multiple earthed neutral (MEN).


TN−C−S :Part of the system uses a combined PEN conductor, which is at some
point split up into separate PE and N lines.

TN-S: separate protective earth (PE) and neutral (N) conductors from transformer
to consuming device, which are not connected together at any point after
the building distribution point.
TN-C: combined PE and N conductor all the way from the transformer to the
consuming device.
TN-C-S earthing system: combined PEN conductor from transformer to building
distribution point, but separate PE and N conductors in fixed indoor
wiring and flexible power cords.

It is possible to have both TN-S and TN-C-S supplies from the same transformer. For example, the sheaths on some underground cables corrode and stop providing good earth connections, and so homes where "bad earths" are found get converted to TN-C-S.


TT network

In a TT earthing system, the protective earth connection of the consumer is provided by a local connection to earth, independent of any earth connection at the generator.

The big advantage of the TT earthing system is the fact that its clear of high and low frequency noises that come through the neutral wire from various electrical equipment connected to it. This is why TT has always been preferable for special applications like telecommunication sites that benefit from the interference-free earthing. Also, TT does not have the risk of a broken neutral.

In pre-RCD era, the TT earthing system was unattractive for general use because of its worse capability of accepting high currents in case of a live-to-PE short circuit (in comparison with TN systems). But as residual current devices mitigate this disadvantage, the TT earthing system becomes attractive for premises where all AC power circuits are RCD-protected.



IT network
In an IT network, the distribution system has no connection to earth at all, or it has only a high impedance connection. In such systems, an insulation monitoring device is used to monitor the impedance.



You can learn abaout P.E grounding with this file , i hope its will helpfull.