Grounding and neutralization of electrical installations: for what purpose it is produced, what is required for this, types of systems

Grounding of various electrical equipment and electrical installations that are connected to the mains supply is carried out in order to protect a person from electric shock. The effectiveness of this method depends on the potential difference at the contact of the circuit breaker. The larger it is, the higher the efficiency and speed of work.

Grounding device

Grounding is a special connection of a specific point in the network, electrical installation or other energy consumer with a grounding device. Reducing the voltage when touching a person to a safe level is what grounding of electrical equipment is for.

In a multi-storey building, it is performed using a narrow steel strip made of ferrous metal. In a private house, such measures are ineffective, because this steel is not alloyed, and not an alloy similar to rebar. The presence of different-phase power networks in a private house

are quite common, and for 220 V and 380 V, the grounding must be separate, but it does not exclude the inclusion of the entire system in one circuit. In this case, the entry point must perform the function of a fuse, and in the event of an emergency, it must be triggered first, and not after the failure of the conductive lines, including when the circuit breakers go out of building.

The protection level is based on the capacitance of the ground loop, the larger the capacitance, the higher its efficiency. The size of the loop means the potential difference and the speed at which the fault protection is activated in the event of a direct circuit.

Types and classification

On the territory of the Russian Federation, the rules for the installation and operation of grounding are regulated by the Rules for the Installation of Electrical Installations in the edition of the seventh edition.

There are several types of grounding in electrical engineering:

• Natural. It is customary to refer to this type of structures, the device of which provides for a constant presence in the ground, but their resistance is not regulated by anything, and no specific parameters have been established for the resistance parameters requirements. This type cannot be used for protection when working with electrical installations.
• Artificial. This is a specialized connection to connect any point in the power grid or equipment to a grounding device. It consists of a ground electrode system (it is a set of conductive parts connected to one another into one network) and a grounding conductor that connects the network point to the ground electrode system. The earthing switch can be either a simple metal rod or a complex factory element.

The quality of the grounding installation is determined by the current spreading parameter, the lower it is, the better.

Types of artificial grounding systems

Electrical installations according to the totality of electrical safety measures are divided into:

• Electrical equipment with an operating voltage above 1 kV in networks with a solidly grounded or effectively grounded neutral.
• Electrical installations operating at voltages above 1 kV, in networks with an installed isolated or grounded neutral (N) through an arc suppression reactor or resistor.
• Installations operating under voltage up to 1 kV, in networks with a solidly grounded neutral (N).
• Equipment operating under voltage up to 1 kV, in networks with isolated neutral (N).

Depending on the technical features of the electrical installation and power supply networks, its use may require the use of various grounding systems.

For electrical equipment with an operating voltage of up to 1 kV, the following designations are adopted:

• TN system - in which the conductor from the voltage source has a dead ground, and open elements, conductive, connected to a dead-grounded power supply line with a zero protective conductor.
• TN-C system - subsystem TN, in which the lines are combined into one conductor along its entire length. It was created by the German concern AEG in 1913. The working zero and the PE conductor in this system are combined into one conductor. The main disadvantage is the possibility of the appearance of line voltage on the open parts of the housing of electrical installations in the event of a zero break. At the moment, this system can be found in buildings built during the Soviet era. In modern installations, it is found only in some cases in street lighting.
• TN-S system - subsystem TN, in which the lines run separately along the entire length. Developed in 1930 to replace the above system. The protective and working zero were divided directly at the substation, and the ground electrode consisted of a complex metal structure based on fittings. In the event of a break in the working zero in the middle of the line, no line voltage was applied to the body of the electrical installation. Later, on the basis of this system, differential automata and leakage current metering machines were developed, which could record even minor current leakages and grounding of electrical installations. They were built on the basis of Kirchhoff's rules, according to which the current flowing through the working zero was numerically equal to the geometric sum of the current in the phase.
• TN-C-S system— subsystem TN, in which the function of the zero protective and working conductors is combined into one conductor in a certain gap, leaving the voltage source. Any transformer substation has a connection between conductive parts with ground and a tightly grounded neutral (N).

Among the advantages, it is worth noting a very simple lightning protection device, provided that a peak voltage between PE and N is impossible. As well as protection against short circuit of the phase and the body of the device when installing a conventional circuit breaker.

Of the shortcomings, there is a very weak protection against burnout of the zero contact, in which the PEN is destroyed on the way from the KTP to the dividing point of the conductors. There was an experience of application in post-Soviet buildings, provided that the dividing point was installed on the basis of an electrical panel, while PE was carried out only before the electric stove. In the modern construction industry, this system is relevant only with the division point in the basement, and independent N and PE pass on all floors.

• System I. T. The neutral (N) of the power supply is isolated from earth or grounded through a device that has a high resistance, and the exposed elements of the electrical installation are grounded. This system is used, as a rule, only in premises for special and special purposes, for which increased requirements for reliability and safety are imposed.
• TT system. In it, the conductor from the voltage source is deafly grounded, and the open elements that conduct current, grounded by means of a device electrically independent of a solidly grounded neutral source.

Among the advantages stands out high resistance to destruction N on the way from the point of supply to the consumer. In the event of the destruction of such a line, this will not affect the PE in any way.

Among the disadvantages is the high demand for the installation of protection against lightning strikes. In this case, there is a possibility of the appearance of a peak voltage between N and PE and the impossibility of determining normal short-circuit by the circuit breaker. This is due to the high resistance of local grounding, which can reach up to 40 ohms. This system is used very actively for installations in rural areas.

Definition of marking

In the listed classification, the first letter means the state of the neutral of the voltage source relative to earth:

• T - grounded neutral.
• I - insulated neutral.

The second letter is the state of open elements conducting current relative to earth:

• T - open conductors are closed regardless of the ratio of ground to neutral of the voltage source.
• N - open conductive parts are connected to a solid grounded neutral of the power supply.

Subsequent letters in the index - combination in one conductor or separation of the function of the zero working and protective conductors:

• S - working zero (N), and protective zero (PE), go separately.
• C - the tasks of the protective and working neutral conductor are combined into one conductor (PEN).
• N - working N conductor.
• PE - protective conductor.
• PEN - N and PE conductors are combined into one.

Errors when installing grounding

In practice, methods of installing grounding using pipes of the water supply system in a multi-storey building are fixed, which are strictly forbidden to be used for this purpose. Due to the fact that on the path of the pipe there may be plastic inserts that do not conduct current. Corrosion can also be an obstacle, and the most objective option is that part of the pipe can be dismantled. There may be danger for a person if an open part of the body touches a metal pipe.

Another misconception is that computer and telephone equipment requires an individual ground line from the entire building system. It can be considered erroneous for the reason that storage device has non-zero resistance, and in the event of a short circuit between the phase and PE, which will not be fixed automatic protection, the current will begin to flow, in parallel increasing the potential due to the presence resistance.

In case of incorrect separation of the PEN conductor, there is a high probability of electrical equipment failure. And this happens due to the installation of a jumper inside the socket between the neutral conductor and the PE contact of the socket. And what follows is that the PE conductor of the working current turns out to be connected to the working zero. And if this jumper of the zero line is broken or the phase and neutral conductor are swapped, a phase potential may arise.