The deliberate electrical connection of any point in the network, electrical installation or radio electronic equipment with a grounding device (ZU) is a working ground. With regard to electrical installations, there are two main types of grounding: functional (working) and protective. Sometimes there are such types as measuring, control and instrumental.
Content
- Service or functional ground
- Main parts of the structure
- Goals and principles of work
-
Grounding systems
- Subsystem TN-C
- Subsystem TN-C-S
- TT system
Service or functional ground
What is the definition of grounding can be found in paragraph 1.7.30 of the PUE (rules for electrical installations. Working grounding is the connection of one or more points of current-carrying parts of an electrical installation, which serve to ensure uninterrupted operation of equipment and partial protection of personnel.
It is designed to eliminate the risk of electric shock or to minimize damage caused by such exposure. This protective mechanism is intended for use in three-phase current distribution systems.
Main parts of the structure
The system is a device with a simple design, consisting of the following elements:
- two iron pins;
- busbars or wires with a cross section exceeding 4 mm2, which are color-coded in the form of longitudinal yellow and green stripes.
The pins are a frame used to connect the equipment grounding terminals to the corresponding bus and act as conductors of electrical energy. As a rule, they are driven into the ground to a depth of 2 to 3 meters. Together with the bus, the pins form a so-called metal bond.
Metal connection is an indispensable element located in any residential building, which is an iron welded structure that connects the upper ends of the ground electrodes to each other. It is brought to the house's introductory panel for further wiring to apartments.
In accordance with Appendix 3, clause 26 of the PTEEP rules for the technical operation of electrical installations of consumers, the resistance of a metal bond is measured at the following frequency:
- more than 1 time in 12 years for supporting structures of overhead lines (OHL) with voltage over 1 kV and more than 1 time in 6 years for overhead lines up to 1 kV;
- more than 1 time in 12 years in accordance with the scheduled preventive maintenance (PM) schedule.
To carry out the measurement, the grounding terminals of the electrical installation and the most distant ground loop are used.. The resistance is checked at each section of the line and the value of this parameter in each section should not be more than 0.1 Ohm.
Goals and principles of work
A working ground is used to reduce the level of voltage that passes between the chassis equipment under the influence of current due to an accident, and earth to safe for humans magnitudes.
In the case of correct operation, the current that passes through a person will be safe, since the voltage during contact is minimal. Under these circumstances, due to the grounding conductor, the overwhelming part of the electrical energy will be diverted to the ground.
Grounding systems
In practice, three types of systems are implemented:
- TN;
- TT;
- IT.
In accordance with the international classification, grounding systems are designated by capital letters. The first letter determines the nature of the power source, and the second character of the grounding of open parts of electrical installations. The letters in the system abbreviations are deciphered as follows:
- T - connected to ground, that is, grounding has been made;
- N - connected to the neutral of the power supply, that is, zeroing has been performed;
- I - insulated.
In any system, there are zero conductors whose values are displayed in GOST R 50462−92. Such conductors include:
- N - zero working (neutral);
- PE - zero protective;
- PEN is a combined version of neutral and protective conductors.
In a TN system, the neutral of the power supply is grounded firmly, and protective neutral conductors are used to connect exposed conductive parts of the wiring to it.
Such a neutral is called deafly substituted because a non-arcing neutral is used to connect it. reactor, and the ground loop, mounted in the immediate vicinity of the transformer substation (TP).
Within the TN system, three subsystems have been developed:
- TN-C;
- TN-S;
- TN-C-S.
Subsystem TN-C
This is a circuit where, within one conductor, there is a combination of zero working and zero protective conductors throughout the system. This is evidenced by the designation C: combined / combined. In such a system, the PE conductor is not separately implemented, therefore, in houses with such a system, there is no individual grounding in the apartment sockets.
Advantages:
- ease of implementation;
- profitability.
disadvantages:
- lack of independent protective grounding;
- inability to equalize potentials in the bathroom;
- outdated standard.
Subsystem TN-C-S
It is a scheme where, within the framework of one conductor, a zero working and protective conductor are combined, but within a certain area, as a rule, from the power source to the entrance to the building. At this stage, it is possible to split the conductors into two independent buses N and PE, but then re-grounding is required.
Advantages:
- wide range of uses;
- simplicity of technical implementation;
- simple upgrade when switching from the TN-C subsystem.
Disadvantages:
- modernization of access cable risers;
- danger to electrical appliances due to breakage of the PEN conductor.
TT system
In a TT system, the neutral is earthed in the same way as in a TN-C system, and exposed conductive parts electrical wiring is connected to a ground electrode, which has electrical independence from neutral.
A similar system is implemented in mobile residential and retail facilities: trailers, stalls, and so on. The key is to provide high quality re-grounding in the form of a modular pin design.
