Basic grounding systems

A person unfamiliar with electrical engineering may think that in all residential buildings the same schemes of energy distribution are used: the same two wires, switches and sockets.
However, everything is much more complicated, and what is in sight is just the "tip of the iceberg". The existing electric distribution schemes differ from each other, first of all, by the way of grounding the generating unit and equipment on the consumer side. In other words, their earthing systems are different. Although this is not obvious, this moment is very important.

Currently, three main grounding systems are widely used: IT, TN, TT, and their derivatives. This symbol is quite informative, but only if you know how to decipher it.

Existing earthing systems

This definition indicates a configuration of an existing power grid that takes into account the earthing option of the end-user equipment, how the ground wire and the zero line are turned on, and whether the neutral is grounded. That is, this concept is generalizing. Depending on the combination of these moments, three classes are distinguished.

One of the main is TN. It is an abbreviation for Terre Neutre that can be translated from French as grounded neutral.

Its logical development is TN-C. Here, "C" means "combined". The difference from the previous one is that the zero wire and the grounding wire are united in a single line. This feature allows you to reduce the number of lines to be laid, but when this wire breaks, an electrical potential appears on the enclosures of the devices included in the network, which is dangerous. However, sometimes this method is used by craftsmen in the absence of a third grounding wire in the apartment: in the sockets between zero, and a grounding jumper is placed. Such grounding systems are recommended to be used in two cases:

- there is no other way to earth the equipment;

- the line is additionally protected by a residual current circuit breaker.

The complete opposite of combined is TN-S (from "separate" - divided). In it, zero and earth are separate lines.

The next main system is TT. Structurally there are two independent grounding lines: one is located on the transformer side, and the other is on the consumer side.

Finally, one of the most reliable options is represented by the IT system, in which neutral lines are made isolated, and all cases of consumer devices are reliably grounded. As a result, the natural leakage current is extremely low and even when the person accidentally hits the electric potential, there is no danger, leaving in the ground. In this case it is important to control the resistance value.

With respect to any system, the rule that the grounding resistance can not exceed 4 ohms must be observed. Therefore, any system, starting from grounding pins and ending with conductors and connection points, is checked for compliance with this requirement.