Types and systems of grounding TN-S, TN-C, TN-C-S, IT in electrical installations, distribution of grounding conductors

Grounding is a key element of safe power supply for industrial, civil, and residential buildings. The principle of operation is based on conducting an electric current from the energized housing of the unit, electrical, plumbing fixture or other conductive element along the path of the smallest resistance.

The need and types of grounding systems

Its main function is to protect people and animals from electric shock. When calculating electrical circuits, a value of 1,000 is taken as a standard indicator of the resistance of the human body. Ohm (in reality, over 3 thousand. Ohm). The circuit resistance must be greater than 4 ohms. In this case, the action of an electric current minimizes unpleasant sensations for a person in the form of tingling, and completely eliminates serious negative consequences for the body, including severe traumatic or fatal outcome.

Protective grounding refers to complex electrical structures that need constant monitoring, testing and prevention. Particular attention is paid to checking the resistance level.

Protection of electrical installations from the appearance of voltage in unintended places as a result of insulation breakdown, violation of the electrical circuit connection diagram is carried out grounding or its subspecies - grounding.

1. Grounding uses the principle of reducing the potential difference between a conductive product and the ground itself to a safe level. Includes single or multiple conductor designs. Most often, a special circuit is created from the electrodes, which is installed in a safe place. Cables laid in the ground are brought to it from the building.
2. Zeroing. It is an electrical circuit in which the voltage from the body of the electrical installation is diverted to the switchboard or to the transformer device. In it, instead of a protective grounding conductor, a working zero core is used. Unlike grounding, grounding during sudden voltage drops (a person's touch to bare wires, the body of the device, which unexpectedly turned out to be under voltage) causes a short circuit in the electrical circuit with its immediate rupture through circuit breakers, called protective disconnecting devices (ZOU).

When developing an electrical circuit, it is not a person's resistance that is taken into account, but the maximum value of the current that he can safely pass through himself. When touching a device under a voltage of 220 V, a frequency of 50 Hz, the maximum current should not exceed 0.22 A. The indicator 0.5 A is fatal to humans. Zeroing is used in multi-storey buildings, since there are difficulties with the creation of ground loops. In low-rise buildings and small industrial facilities (workshops, workshops, service stations), preference is given to grounding.

Forms of structures

Protective grounding is a special electrical circuit that connects housings and other conductive elements of industrial and household units with a grounding structure. In addition to ensuring the safety of people and animals, grounding is necessary to protect the objects themselves. All lightning rods are closed to a common grounding circuit for the house. Incorrect installation of the structure leads to fires (20% of all fires). Grounding prevents emergency operation of generators and other units. The main elements of the circuit are ground electrodes. They are natural and artificial

Natural elements

The most commonly used, since their use is effective from an economic point of view. These include:

• metal or reinforced concrete products for industrial and civil buildings, farms, elevator equipment, conductive pipes for cables. The main condition is their contact with the ground;
• pipelines, product pipelines, sewerage systems, poles, cisterns dug into the ground, fittings, drainage systems. The main condition is the absence of flammable, explosive, combustible substances;
• railway tracks, lead cable sheaths, foundations of metal bridges, tunnels.

Artificial earthing

Steel pipes and rods are used. Copper products are more efficient because they have low resistance. However, the metal is rarely used due to its high cost. Steel is being replaced by special aluminum alloys. In fact, these are complex composite materials with increased strength, 5 times higher than those of steel products of similar size. They are inert to the effects of an aggressive environment, do not corrode, do not create conditions for the development of microorganisms (mold, fungi). They conduct electric current well.

Factors influencing the choice of the system

Grounding is a mandatory attribute of the operation of electrical consumers, regardless of their power and functional purpose. They can be represented by large industrial installations, machine tools, electric motors, lifting mechanisms, cranes or household appliances: refrigerators, washing machines, coffee makers, electric shavers. The principle of earthing for systems is identical. The safety of working with them is clearly regulated by the "Rules for the Installation of Electrical Installations" (PUE).

The document emphasized that the main indicator characterizing the correctness and quality of the design and installation of grounding is the resistance of the entire circuit. The formula for its definition is complex. It must take into account many factors, including the type of soil, the material of the structural elements of the structure, the area of ​​interaction of the device with the ground, the cross-section of the connecting cable, the conductive properties of the core.

General information and designation

In regulatory documents, basic design indicators are given for systems with artificial grounding. For natural electrodes, it is almost impossible to calculate dissipation currents, resistance and other indicators. They are individual for each specific case.

All artificial grounding systems are classified using letter designations. They are approved by the International Electrotechnical Commission and are used in the PUE. The letter T (from the French terre - ground) means ground, I (isole) - isolation, N (neute) - connection with neutral wire, C (combined) - combination of functional and neutral wires, S (separated) - separation of these wires.

The TN system is used for the blind connection of the zero of the transformer or the electrical panel to the ground. The neutral is essential for the fast response of the protection relay. Functional and protective conductors of cable connections are connected to it.

Conductive elements of electrical consumers: housings, screens, sockets, switches are connected to a single neutral wire in contact with the neutral. In addition to solidly grounded, grounding schemes with insulated neutral (IT systems) are used.

Types of grounding in electrical installations

In domestic and foreign electrical practice, the following grounding systems have become widespread.

TN-S system

Highly reliable electrical network safety circuit. Provides high-quality protection of a person from electric shock. It is not affected by high-frequency vibrations from electric shavers, drills, vacuum cleaners, washing machines, electric massage devices. The system does not need to frequently check the ground loops.

The main idea of ​​the method is that a complex combined neutral conductor PEN connected to the neutral is used for protection. At the entrance. PEN is divided into PE protective zero and N working zero. The system loses its protective properties if the PEN is damaged in the section from the substation to the entrance to the building. Therefore, regulatory documents require the use of additional measures to improve the operational safety of the conductor.

TN-C system

The most common, but gradually declining in popularity due to obsolescence. The grounding circuit is made at a transformer substation. The zero core from the circuit to the consumer is supplied via a single PEN wire. With a single-phase power supply of the structure, a two-wire electrical wiring (phase and zero) is used. With three-phase - four-core (3 phases and zero). Sockets are not grounded.

The only option is associated with the use of grounding Protection of humans and animals from electric shock exists, but is not reliable. The popularity of the system is due to its ease of installation. Installation of the TN-C system in buildings and houses under construction is prohibited.

TN-C-S system

Upgraded type TN-C. A distinctive feature is that the PEN conductor on its way to the consumer is divided into two components: a zero core N and a protective PE zero. Usually this operation is carried out in a switchgear (electrical panel), where the zero and protective busbars are mounted. They are connected by a jumper. The protective bus is connected to the ground loop.

With single-phase wiring, a cable with three cores (phase, zero and protection) is included in an apartment or a private house. For three-phase, a five-core cable (3 phases, N and PE). This allows the installation of sockets with grounding terminals. The protective conductor ensures the safety of electrical installations.

Working zero serves to transmit electricity to the consumer. TN-C-S has good prospects for use in the CIS countries, since many homeowners, for financial reasons, cannot install TN-S.

IT system

Outdated, but not outdated scheme. It is used in conditions requiring increased security of power supply: mines, mines, chemical, gas processing plants. Accumulation or sudden release of combustible gases is possible in these plants. Grounding with insulated neutral eliminates sparks.

They are usually used in networks with voltages up to 1 thousand. V. The main feature is the absence of a potential difference between conductive surfaces and local grounding. Low currents allow the installation to continue operating with single-phase grounding.

But the overall system is not very reliable. Standard current protective devices (OCD) are inapplicable in it. Safety schemes are complex and require constant operator involvement.

TN-C-S and especially TN-S earthing systems are highly efficient. PUE only they are allowed for installation in industrial facilities and in private households. The rest of the schemes with a solidly grounded neutral are used as residual phenomena. Their operational resources are small.

The risk of insulation breakdown or other malfunction is high. It increases as the current load on the part of consumers increases. Electric heating, pumps, electric machines and installations are becoming more and more widespread. In the private sector, electricity is used to run small and medium-sized businesses (farms, mini-factories for the production of building materials, service stations). Higher requirements are imposed on grounding. Preference should be given to artificial systems, since the norms are clearly regulated in them.