Modern electrical installations are allowed to be operated only if there is a grounding system or SZ that fully complies with the provisions of the PUE (in terms of meeting the requirements of paragraphs 1.7.100-103.).
This measure reliably protects substation personnel and people consuming electricity from electric shock. According to the provisions of another regulatory document (PEEPT chapter 2.7), depending on the circuit design used, the protection systems can have several versions. TN, TT and IT systems are considered suitable for Russian realities (their general view is shown in the photo below).
SZ (IT) "isolated neutral" it is used at especially important facilities where a break in the neutral connecting the consumer with the substation ground electrode is unacceptable. These can be hospitals, defense and petrochemical industries, where reliable grounding is provided on the consumer's side.
TT variant "earthed neutral" it is realized by arranging not a repeated, but a separate local grounding. Protective systems of this class are in demand in rare cases when it is not possible to achieve the desired result by other means. This, as a rule, applies to regions remote from the center and suburban areas.
Next, we will consider the two most common varieties (TN-C and TN-S).
TN-C
In accordance with the designation given in the name, the feature of this system is the combination of 2 conductive buses. A typical TN-C circuit can be represented as a line with 3 phase and neutral conductors (as shown in the photo below).
The latter is designated as a combined PEN bus, earthed at the substation side at the terminal of the transformer winding. At the opposite end, the conductive parts of the electrical installations are connected to it (they are thus grounded). This circuit design has the following disadvantages:
- when the neutral PEN breaks, the system loses its protective properties;
- the impossibility of laying a special conductor to the sockets, which guarantees full grounding of the equipment;
- the complexity of arranging a local ground loop.
Today this system is used only in old houses built during the Soviet era. It is sometimes found in lighting networks where electric shock is unlikely.
TN-S
This option is characterized by separate wiring of the PE and N cores (figure below in the text).
Here, the safety of handling electrical equipment in the power network is significantly increased. The disadvantage of such a system is that at the same time, the cost of cable products doubles.
Installation and installation costs also increase significantly. Another distinguishing feature of this protection is an increase in the number of conductors at the entrance to a building or other object.
Additional Information: The 3-phase voltage is supplied here via five conductors.
Three wires are used for laying single-phase circuits (instead of 2). Recommendations for its arrangement, related to the facilities put into operation, can be found in the provisions GOST R50571-2011.