Why is it dangerous to independently perform grounding in an apartment (converting TN-C to TN-C-S). The main types of grounding systems Tn c s pue grounding system

garden equipment 25.06.2019

garden equipment

Electrical networks up to 1000 volts, as a rule, have a deafly grounded neutral. This means that the neutral of the transformer, that is, the midpoint of the secondary phase windings connected in a star, is connected to the grounding device located in the transformer substation. The working neutral wire is also connected to the midpoint of the windings. Electrical installations with a solidly grounded neutral, in which open conductive parts are connected to a protective ground wire, are classified by the PUE as belonging to the TN system. This system has several varieties that differ in the way the protective ground is formed. This article discusses one of the options - the system grounding TN-C.

The figure shows the electrical connection diagram:

This system differs from others in the TN family in that a working neutral conductor is used as a protective earth conductor (PEN), moreover, along its entire length. The separation of the neutral conductor into a working and protective ground wire occurs only at the point of connection of the consumer to the electrical network.

By the way, the decoding of the TN-C abbreviation is as follows: “T” - (terre - earth) means grounded, N (neuter, neutral) - connected to the source neutral (zeroed), C (combined, combined) - zero working and protective wire combined into one conductor throughout the system.

The TN-C earthing system, having its own design features, has both advantages and disadvantages.The advantage of the system, however, not related to electrical safety issues, is:

The banal savings associated with the fact that the power supply of a three-phase consumer is carried out through four conductors instead of five, since there is no separate protective ground conductor.
The possibility of its application without the modernization of previously built cable and overhead power lines with four conductors.

The disadvantage of TN-C is one, but, unfortunately, it is related to safety - a higher probability, in comparison with other grounding systems, of losing the grounding circuit if a single grounded conductor is damaged.

You can often hear that the TN-C grounding system is a "heavy legacy of the past" and we got it from Soviet Union. One can agree with this statement only partially. Indeed, four-wire distribution networks with a dead-earthed neutral require the implementation of protective grounding in exactly this way. However, the following should be noted: the power supply scheme that took place in Soviet time, and which continues to exist to this day in many old buildings, is by no means a TN-C earthing system, and here's why.

The implementation of TN-C involves connecting to the PEN conductor "all open (that is, accessible to human contact) parts of electrical installations." This means that the metal parts of the case of any electrical appliance included in the electrical network of our home must be “zeroed”.

And what do we have in old houses today? The PEN conductor, also known as the working neutral wire, at best, is connected to the body of the input cabinet, at the input of the power cable to the building, and this is where the protective grounding ends. The wiring in the apartments is carried out in two wires, and the electrical sockets in the apartments are not equipped with grounding contacts. As a result, most of of the population uses household electrical appliances without protective grounding of their housings. And this is despite the fact that the operating instructions for each device emphasize the need to perform this measure, and all plugs for connecting equipment to the network are equipped with grounding contacts. Thus, scolding TN-C, while in most houses there is no one at all, is not entirely correct.

Each owner can implement a TN-C grounding system in an apartment or private house. To do this, it is necessary to separate the neutral wire coming with the power cable in the input cabinet or on the floor shield. We talked about how to do it in more detail in a separate article. After that, you need to make a three-wire wiring inside the apartment or house, connecting the third conductor, which will play the role of a protective one, to the ground contacts electrical sockets. If an electric stove is installed in the kitchen and it is powered by a separate cable, provide an additional core for connecting the housing electric stove with protective earth conductor.

We should not forget that a phase breakdown on the case in any electrical appliance causes a short circuit. Therefore, when performing the specified wiring, Special attention should be given to the protection of the wiring. It is best to mount an in-house shield by installing reliable, correctly rated circuit breakers in it. It is better to divide the power supply of the premises of a house or apartment into groups, each of which is powered from its own machine.

Every day people use different electrical appliances, ranging from a coffee maker and a hair dryer, ending with a refrigerator and washing machine. They live in high-rise buildings, go to work in the subway and do not even suspect how much effort has been made by the developers of these devices and devices so that they can use these gifts of civilization without fear for their lives. Now any device, building, structure is checked for electrical safety. When designing any electrical installations, regardless of their purpose, the main condition is their safe and normal operation, which is ensured by an impeccable design and an error-free grounding device. There are grounding systems tn, tt and others. The main document that determines the work of developers of grounding systems is the Electrical Installation Rules.

Types of artificial grounding

If we consider in terms of functionality, then there is a protective and working ground. The first ensures the safety of people when using electrical appliances, and the second ensures the normal operation of electrical installations. According to the type of grounding of the neutral wire, they are divided into systems with isolated (IT) and solidly grounded (TN) neutral. All are shown in the figure.

In an IT system, the neutral wire of the power generator is not galvanically connected to ground, and conductive parts are intentionally grounded. It is allowed to install an arcing device or devices with high internal resistance between the ground electrode and the neutral.

The TN grounding system is the most common. In it, the neutral wire of the electric power generator is deafly grounded, and the conductive parts are connected to it with the help of special tires.

It is subdivided into four subspecies:

grounding system TN-C, in which the working and protective neutral wires are one conductor from the source to the consumer of energy;
TN-S system, in which the working and protective neutral wires are two conductors from the source to the consumer of energy;
grounding system TN C S, in which the working and protective neutral conductors are one conductor, starting from the power generator, then in some area they are divided into two;
TT system, in which the neutral wire of the electric power generator is solidly grounded, and the open conductive parts of the electric power consumer are grounded through their own grounding, which is in no way connected with the neutral wire of the electric power generator.

The first symbol of the abbreviation tells what state the neutral wire of the electricity producer (generator, transformer) is in relative to the ground layer.

T - grounded neutral conductor.

I - isolated neutral conductor.

The second character informs about the state of the conductive parts in relation to grounding.

T - conductive parts are grounded, the state of the neutral wire of the power generator does not matter;

N - conductive parts are connected to the dead-earthed neutral conductor of the power supply.

The symbol after N shows how the working and protective neutral conductors are related.

S (separated) - working (N) and protective (PE) neutral conductors are separated.
C (combined) - combined in (PEN) wire N and PE conductors.

Systems with solidly grounded neutral wire

The TN C grounding system was first used by AEG at the beginning of the 20th century. Its classic look is conventional scheme power supply with three phase and one neutral wire. It is both functional (N) and protective (PE) "zero", tightly grounded. All cases and accessible conductive parts of devices are connected to it. The most a big problem the system occurs when the neutral wire breaks, on the current-carrying parts of the device cases, a linear voltage appears that is 1.73 times greater than the phase voltage. During normal operation, contact with the phase wire on the body will lead to a short circuit, but thanks to special devices, an instant shutdown will occur, which will protect people from electric shock. In the CIS countries, the TN C grounding scheme is used in outdoor lighting and in buildings built before the nineties of the twentieth century.

TN-S system

The most reliable and safe earthing system TN-S was created before World War II. Its main feature is the separate use of the working and protective neutral conductors, starting from the electricity generator. With a three-phase power supply, five wires are used, with a single-phase power supply, three. Electrical safety is ensured by the practical duplication of the protective conductor. Regardless of the location of the N conductor break, the system remained relatively safe. Later, thanks to this method of grounding, differential automata were developed.

GOST R50571 and the new edition of the PUE prescribe for the power supply of new facilities, with overhaul buildings use the TN-S grounding system. But its spread is hindered by the high cost and the fact that the entire Russian energy sector operates on a four-wire power supply system.

TN-C-S system

The TN-C-S grounding system became a compromise, which used the advantages of TN-S, but became much cheaper in cost. The thing is that electricity is supplied from the transformer using the combined zero “PEN”, tightly grounded. At the entrance to the PEN facility, the wire is divided into protective and working zero, but splitting is possible even before entering the structure. If the PEN wire breaks in the generating station - building section, dangerous voltage will appear on the electrical installations. Therefore, in the TN C S earthing system, the standards provide for special measures to protect the PEN conductor.

TT system

The most economical way to deliver electricity in the countryside via overhead lines. The use of the TN-S system, as the most secure, is expensive, it is difficult to provide grounding systems for TN-C and TN-C-S reliable protection neutral conductor PEN. Therefore, a TT system is often used, with a grounded neutral conductor at the power supply. With a three-phase power supply, the system operates in a four-wire circuit with one neutral conductor.

A local ground is made near the power receiver, to which the current-carrying parts and device cases are connected. In the event of a break in the neutral wire, and outside the city this is not uncommon, dangerous voltage does not arise on the device case due to local grounding. In urban areas, the TT grounding system is used for the power supply of temporary structures, while residual current devices must be installed and lightning protection must be carried out.

IT system

This is a system in which there is a neutral wire completely isolated from the ground or connected to it through a high-resistance resistance, as well as the consumer of electricity having its own protective ground. All conductive parts of the equipment are reliably grounded. The IT system is used in the electrical installations of buildings with increased safety requirements, such as in hospitals for medical equipment, in mines, quarries. Mobile power stations also use an isolated neutral, which allows the use of electrical appliances connected to them without grounding. In the past, the IT system was widely used in power supply as well. wooden houses. In the Soviet Union, 127/220 V voltage networks were used for a long time with an insulated neutral wire, this was due to the lack of grounding in houses. With the beginning of panel construction, it was abandoned.

The grounding devices themselves used to look like a set of three-meter steel rods dug into the ground at a distance of several meters, the tops of which were connected by a steel strip. The resulting huge contact element was tested for resistance, if it exceeded the normalized value, then additional rods were dug in until the required result was obtained. Its disadvantage was the large occupied area and insufficient resistance to corrosion. Modern grounding devices are devoid of these shortcomings. They are built on the basis of copper-plated steel rods, which can be interconnected using brass couplings and driven to a depth of 50 m. They are connected at the top with a copper strip. Due to this design, they can be installed on any soil, do not require earthworks and take up little space.

These grounding devices and grounding systems ensure the electrical safety of people.

Grounding is the removal of voltage that has arisen in a place threatening safety to a place where it will not harm anyone: this place is earth. Grounding connects all current-carrying parts, which in normal operation are not under U, to the ground.
Zeroing is the connection of all parts of an electrical appliance that should not be under U, with a working zero. V this case, if a phase break occurs on the current-carrying parts that are under the working zero, then a short circuit will occur and circuit breaker de-energize the electrical appliance. This is of course less safe than grounding, a short circuit can cause subsequent malfunctions in the device. Unfortunately, it is zeroing that is the main type of protection in most residential premises.

Grounding systems

Consider the systems used in domestic premises:

TN-C.
TN-S.
TN-C-S.

TN-C

The first letter T means that the neutral of the power supply is connected to the ground, which means that the conductor of the working zero at the substation goes into the ground. The second letter - N - means the connection of the open conductive parts of the electrical installation of the building with the grounding point of the power source. The third letter - C - means that the protective and working zero are on the same common PEN, that is, the working zero is protective. In fact, this system is the very “zeroing”. The most insecure of the systems. All current-carrying parts that should not be under U are under operating zero. Protection is built on the action of the machine after a short circuit. Protective and working zero are in the same conductor to the switchboard.

2.Power supply.

TN-S

The first two letters, as in the previous system, mean that the neutral of the power supply is connected to ground (which is located at the power source) and the exposed conductive parts of the electrical installation of the building are connected to the ground point of the power supply. The third letter - S - means that zero and protective PE and working N are on different conductors (grounding). This means that two separate wires go from the power plant to the working zero and to ground. This system is the safest for multi-storey buildings.

1. Exposed conductive parts.

2.Power supply.

The presented diagram shows that two separate wires go from the power source to the working zero and to ground, then the conductors do not meet.

TN-C-S

It is an upgraded TN-C system. The functions of the zero working and zero protective conductors are combined in one conductor in the part of the network that comes from the power source. Then, a grounded conductor is added in a certain area. For multi-storey buildings usually a grounded conductor is added to the ASU (introductory Switchgear on house). This system also provides sufficient security.

1. Exposed conductive parts.

2.Power supply.

3. Distribution board for the apartment.

The diagram shows the network before modernization - TN-C system and after modernization - TN-C-S system.

TT system

Usually used in the construction of private houses. The second letter T means that grounding and working zero are not connected anywhere. The first letter has already been mentioned above. Three wires enter the house in the same way as in the TN-S system: working zero, phase wire and ground wire. Only now the ground wire does not come from a power source (as in the TN-S system), but near a private house, its own ground loop is installed in accordance with all the rules of the PUE (electrical installation rules), it is from the ground loop that the ground wire comes.

1. Exposed conductive parts.

2.Power supply.

3. Ground loop near a private house and a conductor extending from it.

), the following systems are used in electrical networks up to 1 kV:

1. TN system - a system in which the neutral of the power source is deafly grounded, and the open conductive parts of the electrical installation are connected to the deafly grounded neutral of the source by means of zero protective conductors. It is divided into the following subsystems:

1.1. TN-C subsystem - a TN system in which the zero protective and zero working conductors are combined in one conductor throughout its entire length;

1.2. TN-S subsystem - a TN system in which the zero protective and zero working conductors are separated along its entire length;

1.3. TN-C-S subsystem - a TN system in which the functions of the zero protective and zero working conductors are combined in one conductor in some part of it, starting from the power source;

2. IT system - a system in which the neutral of the power source is isolated from earth or earthed through devices or devices with high resistance, and the exposed conductive parts of the electrical installation are earthed;

3. TT system - a system in which the neutral of the power source is solidly grounded, and the open conductive parts of the electrical installation are grounded using a grounding device, electrically independent of the solidly grounded neutral of the source.

Letter designation

In the designations of systems it is accepted:

The first letter is the state of the neutral of the power supply relative to earth:

T (terra - earth) - grounded neutral;

I (isolate - isolated) - isolated neutral.

The second letter is the state of open conductive parts relative to ground:

T - open conductive parts are grounded, regardless of the relation to the ground of the neutral of the power source or any point of the supply network;

N (neutral - neutral) - exposed conductive parts are connected to a solidly grounded neutral of the power source.

Subsequent (after N) letters - combination in one conductor or separation of the functions of the zero working and zero protective conductors:

S (selective - separated) - zero working (N) and zero protective (PE) conductors are separated;

C (complete - common) - the functions of the zero protective and zero working conductors are combined in one conductor (PEN-conductor);

Accepted the following letter designation zero conductors:

N - zero working (neutral) conductor;

PE (protecte eath - protective earth) - protective conductor (grounding conductor, zero protective conductor, protective conductor of the potential equalization system);

PEN - combined zero protective and zero working conductors.

Application area

The TN system should, as a rule, be used in electrical installations up to 1 kV residential, public and industrial buildings and outdoor installations.

The IT system should be implemented, as a rule, in electrical installations with a voltage of up to 1 kV with the inadmissibility of a power interruption during the first ground fault or on open conductive parts.

The TT system is allowed only in cases where the electrical safety conditions in the TN system cannot be ensured.

Check how well you have learned the question "Types of earthing systems for electrical installations" by answering a few control questions.

Grounding is one of the most important technological methods of protection against electric shock when working with electrical appliances. To properly upgrade or repair wiring, you need to accurately understand what kind of grounding system is used on the site. The safety of the person and the normal operation of the equipment depend on this. Information is also important when creating a reconstruction project. Accordingly, it is necessary to study all available grounding systems, the differences from each other, as well as the technologies for their installation.

The International Electrotechnical Commission (IEC) and the State Standard of the Russian Federation have established types of grounding systems. All of them are indicated in the PUE (rules for the installation of electrical installations). Distinguish:

TN system (with subsystems TN-C, also TN-S and finally TN-C-S);
TT system;
IT system.

They differ in the source of electricity and the method of grounding electrical equipment. The type of grounding system is indicated by the letters:

1. The first letter determines how the power source is grounded:

if it is T, then there is a direct connection of the zero working conductor (neutral) of the power source to the ground;
if it is I, then the neutral of the energy source is connected to the ground exclusively through resistance.

2. The second letter determines the grounding in the conductive open parts of the electrical installation of the building:

the letter T denotes local (separate) grounding of electrical equipment and power supply;
the letter N indicates that the power supply is grounded, but consumers are grounded only through the PEN conductor.

3. The next letters after N define functional way, along which the zero working and zero protective conductor is arranged:

if it is S, then the functions of the working (N) as well as the protective (PE) conductors are provided with separate conductors;
if it is C, then the functions of the zero working and protective conductors are provided with a common conductor (PEN).

TN system and its variants

The TN system is distinguished by the presence of a solidly grounded neutral: the open conductive parts of any electrical installation are connected to a specific solidly grounded neutral point of the power supply through special neutral protective conductors.

The term "hard-earthed neutral" means that the neutral (zero) at the transformer substation is connected directly to the ground loop (i.e., grounded).

The main condition for electrical safety TN is as follows: the value of the current between the open conductive part and the phase conductor at short circuit must exceed the value of the electric current of operation of the protection device for the normalized time.

Demanded subsystem TN-C

The TN-C subsystem is TN, in which the conductors (zero working, as well as protective) are combined throughout the system (into 1 PEN conductor), i.e. protective zeroing has been carried out. This is the most used variety of TN since the Soviet era. However, this system is now outdated. Of modern electrical installations, it is found only in street lighting(for the sake of economy, as well as reduced risk). It is not recommended for new housing. Now it has been replaced by more modern systems.

Grounding option TN-S

The TN-S subsystem is TN, in which the conductors (zero working, as well as protective) are separated throughout the system. This is the most modern, the safest, but the most expensive system. It has been used in telecommunications networks for a very long time (which is noteworthy, when using it, interference in a low-current network is excluded).

TN-C-S - device specific

Subsystem TN-C-S - can be attributed to an intermediate option. In it, the zero worker, as well as the protective conductors, are combined only in one part of it. Usually - in the main shield of the building (where protective earth supplemented by protective zeroing). Throughout the building further these conductors are separated. The system is optimal in terms of price-quality ratio. This scheme is currently the main one, which can be implemented in certain parts of electrical installations during reconstruction. Other grounding systems for electrical installations do not allow this. The cross sections of the conductors are selected based on the values of the currents (calculated) flowing through them. The cross-sectional area (minimum) of the PEN conductor is 4 mm2. It is necessary to provide that the switchboard has separate terminals on the PEN bus (for each conductor - N and PE). When using a stranded or single wire as a PEN conductor, its insulation color must be exclusively yellow-green.

What is a TT system

This system is different in that the zero of the source in it is grounded, while the open conductive parts of any electrical installation are connected to ground, which is electrically independent of the grounded zero (neutral) of the power source. In other words, the object uses its own ground loop, which is in no way connected with zero. To date, this system is used as the main one in mobile structures, such as change houses, caravans, etc. (where it is not always possible to mount the grounding conductor in accordance with the required standards). It is noteworthy that the harmonization of its application is more difficult than TN. The use of RCDs becomes mandatory, high-quality grounding is also necessary (namely, 4 ohms at 380 V), there are many features when selecting the necessary circuit breakers.

IT system: distinctive features

This system is distinguished by the fact that the source zero in it is isolated from the ground or grounded through devices that have high resistance, and the conductive open parts of electrical installations are grounded using grounding devices. IT is rarely used. Basically - in electrical installations of buildings for special purposes. For example, for emergency lighting and power supply in hospitals. In general, where there are increased requirements for safety and reliability.

Grounding system technologies

There are several technologies for installing a ground loop. The most used two: traditional and modular pin grounding system.

Traditional technology and materials

Grounding is carried out from black rolled metal: corners, pipe strips, etc. Installation begins with the creation of a project that reflects the place where the ground loop will be arranged, the location of technical communications in the ground. Then, focusing on the object, metal products (electrodes) of a certain section (not< 3-х). После этого эти электроды они свариваются в общий контур по периметру при помощи metal strip.

This technology has been the mainstream for many decades. However, it has a number of disadvantages (for example, metal corrosion, laborious installation, etc.), so now they are trying to replace it with another, more modern and advanced grounding technology.

Modular grounding system

What is included?

It consists of rods made of high quality steel and coated with copper. They are placed vertically in the ground. Each of these rods reaches a length of about one and a half meters, and a diameter of 14 mm, the mass of the 1st element is no more than 2 kg. On both sides of each rod, a copper-plated thread 30 mm in length is cut.
The steel elements of this system are interconnected using brass couplings.
The modular earthing system kit also includes a brass clamp used to connect horizontal (special steel strips or copper wire passing from the distribution board directly to the ground loop of this system) and vertical (copper-plated steel rods) grounding elements.
The kit also includes two steel tips that will be attached to the rod by screwing onto a copper-plated thread. Tips will have to be chosen depending on the soil (especially hard or ordinary). It will pass the entire device of this building grounding system.
For anti-corrosion protection of all grounding elements, a protective paste is usually attached, with which the elements of the entire future grounding system are processed.
For a safer and more reliable connection of horizontal and vertical components, a protective tape (for example, PREMTAPE) is used.

How is the installation?

Installation of a modular pin grounding system takes place in several stages:

The 1st vertical steel pin is installed.
Intermediate resistance is measured.
The remaining vertical pins are mounted.
The horizontal grounding is laid.
Then the elements are connected and processed with a protective tape.

Benefits of the modular pin earthing system

Allows you to save space (can be equipped on 1 m2 of area).
Simple, does not require laborious earthworks.
No welding required.
Such grounding can be used for any type of soil.
A great depth is achieved - up to 50 m.
Conductors are used of stainless steel.
There is no need for special equipment.
Long term operation.

Video: progressive protective circuit

From all of the above, we can conclude that today the most rational is the use of the TN-C-S system and the modular-pin technology of its installation. All the evidence suggests that the latest generation earthing device technologies are superior to traditional ones in many ways. Their use reduces the time of work, reduces financial expenses, increase the service life of grounding elements.