Electric shock protective grounding zeroing. The most scandalous issue is grounding (zeroing). Specifics of the TN-S system

Which is called electric shock provides a comfortable life modern man. Without it, production and construction capacities, medical devices in hospitals do not work, there is no comfort in the home, urban and intercity transport is idle. But electricity is the servant of man only if complete control, if the charged electrons can find another way, then the consequences will be dire. To prevent unpredictable situations, special measures are used, the main thing is to understand what the difference is. Grounding and zeroing protect a person from electric shock.

The directed movement of electrons is carried out along the path of least resistance. To avoid the passage of current through the human body, it is offered another direction with the least loss, which provides grounding or zeroing. What is the difference between them remains to be seen.

grounding

Grounding is a single conductor or a group made up of them, which is in contact with the ground. With its help, the voltage supplied to the metal case of the units is reset along the path of zero resistance, i.e. to the ground.

Such electrical grounding and zeroing of electrical equipment in industry is also relevant for household appliances with steel outer parts. A person touching the refrigerator body or washing machine energized will not cause electric shock. For this purpose, special sockets with a grounding contact are used.

The principle of operation of the RCD

For the safe operation of industrial and household equipment, they use devices of automatic differential switches. Their work is based on a comparison of the electric current entering through the phase wire and leaving the apartment through the neutral conductor.

Normal operation electrical circuit shows the same current values ​​in the named sections, the flows are directed in opposite directions. In order for them to continue to balance their actions, ensure the balanced operation of devices, they perform the installation and installation of grounding and grounding.

A breakdown in any section of the insulation leads to the flow of current directed to the ground through the damaged area, bypassing the working neutral conductor. The RCD shows an imbalance in the current strength, the device automatically turns off the contacts and the voltage disappears in the entire working circuit.

For each individual operating condition, there are different settings for tripping the RCD, usually the setting range is from 10 to 300 milliamps. The device works quickly, the shutdown time is seconds.

Operation of the grounding device

To attach to the housing of a household or industrial equipment a PE conductor is used, which is output from the shield along a separate line with a special output. The design provides connection of the body to the ground, which is the purpose of grounding. The difference between grounding and zeroing is that at the initial moment when the plug is connected to the outlet, the working zero and phase are not switched in the equipment. The interaction disappears last minute when the contact opens. Thus, the chassis grounding has a reliable and permanent effect.

Two way grounding device

Protection and voltage tap systems are divided into:

• artificial:
• natural.

Artificial grounds are designed directly to protect equipment and people. Their device requires horizontal and vertical steel metal longitudinal elements (often pipes with a diameter of up to 5 cm or corners No. 40 or No. 60 with a length of 2.5 to 5 m are used). Thus, grounding and grounding are different. The difference is that a specialist is required to perform high-quality grounding.

Natural grounding conductors are used in the case of their closest location next to the object or residential building. Pipelines made of metal in the ground serve as protection. It is impossible to use for the protective purpose lines with combustible gases, liquids and those pipelines, the outer walls of which are treated with an anti-corrosion coating.

Natural objects serve not only to protect electrical appliances, but also fulfill their main purpose. The disadvantages of such a connection include access to pipelines by a sufficiently wide range of people from neighboring services and departments, which creates a danger of violating the integrity of the connection.

Zeroing

In addition to grounding, in some cases zeroing is used, you need to distinguish what the difference is. Grounding and grounding divert voltage, just do it different ways. The second method is electrical connection corps, in normal condition not energized, and the output of a single-phase source of electricity, the neutral wire of a generator or transformer, a source direct current at its midpoint. When zeroing, the voltage from the case is reset to a special switchboard or transformer box.

Zeroing is used in cases of unforeseen power surges or breakdown of the insulation of the case of industrial or household appliances. A short circuit occurs, leading to blown fuses and instantaneous automatic shutdown, this is the difference between grounding and neutralizing.

Zeroing principle

Variables three-phase circuits use a neutral conductor for various purposes. To provide electrical safety with its help get the effect short circuit and the voltage that has arisen on the case with phase potential in critical situations. In this case, a current appears that exceeds the nominal value. circuit breaker and contact is terminated.

Zeroing device

The difference between grounding and grounding can be seen from the connection example. Frame separate wire connects to zero on To do this, the third core is connected in the outlet electric cable with the terminal provided for this in the socket. This method has a disadvantage, which is that for automatic shutdown a current is needed that is larger than the specified settings. If in normal mode the disconnecting device ensures the operation of the device with a current of 16 amperes, then small breakdowns of the current continue to leak without tripping.

After that, it becomes clear what is the difference between grounding and grounding. The human body, when exposed to a current of 50 milliamps, may not withstand and cardiac arrest will occur. Zeroing from such current indicators may not protect, since its function is to create loads sufficient to turn off the contacts.

Grounding and zeroing, what's the difference?

There are differences between these two methods:

• when grounding, the excess current and the voltage that has arisen on the case are discharged directly to the ground, and when zeroed, they are reset to zero in the shield;
• grounding is more effective ways in the issue of protecting a person from electric shock;
• when using grounding, safety is obtained due to a sharp decrease in voltage, and the use of zeroing ensures that the section of the line in which the breakdown to the case has occurred is turned off;
• when performing zeroing, in order to correctly determine the zero points and choose the protection method, you will need the help of a specialist electrician, and any home craftsman can make grounding, assemble the circuit and deepen it into the ground.

Grounding is a system for diverting voltage through a triangle located in the ground from metal profile welded at the joints. A properly arranged circuit gives reliable protection but all the rules must be followed. Depending on the desired effect, grounding and zeroing of electrical installations are selected. The difference between zeroing is that all elements of the device that are not under current in normal mode are connected to the neutral wire. Accidental contact of the phase with zeroed parts of the device leads to a sharp jump in current and shutdown of the equipment.

The resistance of the neutral neutral wire is in any case less than the same indicator of the circuit in the ground, therefore, when zeroing, a short circuit occurs, which is basically impossible when using an earth triangle. After comparing the operation of the two systems, it becomes clear what the difference is. Grounding and zeroing differ in the method of protection, since there is a high probability of burnout over time neutral wire which must be constantly monitored. Zeroing is used very often in high-rise buildings, since it is not always possible to arrange a reliable and complete grounding.

Grounding does not depend on the phase of the devices, while the grounding device requires certain connection conditions. In most cases, the first method prevails in enterprises where, according to safety requirements, increased safety is provided. But also in everyday life Lately often a circuit is arranged to discharge the resulting excess voltage directly to the ground, this is a safer method.

Grounding protection refers directly to the electrical circuit, after a breakdown of the insulation, due to the flow of current into the ground, the voltage is significantly reduced, but the network continues to operate. When zeroing, a section of the line is completely turned off.

Grounding is in most cases used in lines with an isolated neutral in IT and TT systems in three-phase networks with voltages up to 1 thousand volts or more for systems with a neutral in any mode. The use of grounding is recommended for lines with a grounded dead neutral wire in TN-C-S, TN-C, TN-S networks with available N, PE, PEN conductors, this shows the difference. Grounding and zeroing, despite the differences, are human and instrument protection systems.

Useful terms of electrical engineering

To understand some of the principles by which protective earthing, grounding and disconnection are performed, you should know the definitions:

A solidly grounded neutral is a neutral wire from a generator or transformer that is directly connected to a ground loop.

It can serve as an output from the source alternating current V single-phase network or the pole point of a DC source in two-phase lines, as is the average output in three-phase DC networks.

An insulated neutral is a neutral wire of a generator or transformer that is not connected to the ground circuit or is in contact with it through a strong resistance field from signaling devices, protective devices, measuring relays and other devices.

Accepted designations in the network

All electrical installations with grounding conductors and neutral wires present in them must be marked without fail. Designations are applied to tires in the form letter designation PE with alternating transverse or longitudinal identical stripes of green or yellow color. Neutral neutral conductors are marked with the blue letter N, which is how grounding and grounding are indicated. The description for the protective and working zero is to affix the letter designation PEN and color it in a blue tone throughout with green-yellow tips.

Letter designations

The first letters in the explanation to the system indicate the selected nature of the grounding device:

• T - connection of the power source directly to the ground;
• I - all current-carrying parts are isolated from the ground.

The second letter is used to describe the conductive parts in relation to the connection to earth:

• T speaks of the mandatory grounding of all open live parts, regardless of the type of connection with the ground;
• N - indicates that the protection of open parts under current is carried out through solidly grounded neutral from the power source directly.

The letters through the dash from N indicate the nature of this connection, determine the method of arranging the zero protective and working conductors:

• S - PE protection of the zero and N-working conductors is made with separate wires;
• C - one wire is used for protective and working zero.

Types of protective systems

The classification of systems is the main characteristic according to which protective grounding and grounding are arranged. Are common technical details are described in the third part of GOST R 50571.2-94. In accordance with it, grounding is carried out according to the schemes IT, TN-C-S, TN-C, TN-S.

The TN-C system was developed in Germany at the beginning of the 20th century. It provides for combining a working neutral wire and a PE conductor in one cable. The disadvantage is that when zero burns out or another connection failure occurs, voltage appears on the equipment cases. Despite this, the system is used in some electrical installations up to our time.

The TN-C-S and TN-S systems are designed to replace the failed TN-C grounding scheme. In the second protection scheme, two types of neutral wires were separated directly from the shield, and the circuit was a complex metal structure. This scheme turned out to be successful, since when the neutral wire was disconnected, line voltage did not appear on the casing of the electrical installation.

The TN-C-S system is different in that the division zero wires is performed not immediately from the transformer, but approximately in the middle of the line. This was not a good decision, since if a zero break occurs before the separation point, then the electric current on the case will be life threatening.

The TT connection scheme provides a direct connection of live parts to earth, while all open parts of the electrical installation with the presence of current are connected to the earth circuit through an earthing conductor, which is independent of the neutral wire of the generator or transformer.

According to the IT system, the unit is protected, grounding and grounding are arranged. What is the difference between this connection and the previous scheme? In this case, the transfer of excess voltage from the housing and open parts occurs to the ground, and the neutral of the source, isolated from the ground, is grounded by means of devices with high resistance. This circuit is arranged in special electrical equipment, which must have increased safety and stability, for example, in medical institutions.

Types of grounding systems

The PNG grounding system is simple in design, in which the neutral and protective conductors are combined along the entire length. It is for the combined wire that the indicated abbreviation is used. The disadvantages include increased requirements for the well-coordinated interaction of potentials and the conductor cross section. The system is successfully used for zeroing asynchronous units.

It is not allowed to perform protection according to this scheme in group single-phase and distribution networks. It is forbidden to combine and replace the functions of zero and protective cables in a single-phase DC circuit. They use an additional one marked PUE-7.

There is a more advanced zeroing system for electrical installations powered by a single-phase network. In it, the combined common conductor PEN is connected to the current source. The division into N and PE conductors occurs at the point of branching of the main into single-phase consumers, for example, in the access shield of an apartment building.

In conclusion, it should be noted that protecting consumers from electric shock and damage to electrical household appliances during power surges is the main task of energy supply. The difference between grounding and grounding is simply explained, the concept does not require special knowledge. But in any case, security measures household electrical appliances or industrial equipment must be carried out constantly and up to standard.

For safe operation on various electrical installations and conductors, open metal taps are connected to the ground and the network is connected to the neutral cable. But few novice masters know exactly how grounding and grounding of electrical installations and electrical equipment differ.

Grounding Definition

Grounding is the intentional connection of exposed parts. electrical equipment, which are energized, to a special grounding tap, busbar or other protective equipment. This may be fittings in the ground, part of an electrical installation and other devices. Such an approach, according to the PUE, is a mandatory measure for the deliberate protection of both residential and non-residential stock. This is also stated by the rules and requirements of GOST 12.1.030-81 SSBT (electrical safety and the system of labor safety standards).

In almost every modern house a TN-C-S or TN-S earthing scheme is installed. But in buildings of an old building, grounding is often absent at all, so the owners of an apartment in such buildings have to organize the land on their own. Such a system is called TN-C. It is carried out by connecting the tap to the ground loop, which can be located directly in the ground near the building or near the transformer box.

Figure TN-C

Theoretically, a special installation company can organize such a wiring upgrade, but this is rarely practiced. More often to the shield on the floor (in apartment building) the ground is brought in, and the rest of the wires are already connected to it.

1. If a phase hits an open metal outlet of any electrical device, then voltage appears in it. The same happens if, for example, the cable insulation is broken. The human body is an excellent conductor of current, if you touch such a tap, you will get swipe current. Grounding will help avoid this;
2. Stray currents go to the grounding conductor, this guarantees the protection of life;
3. Especially dangerous is the voltage that falls on heating radiators. In this case, all the batteries in the house become current conductors. But if the ground is installed, then all the voltage will go through the conductor.

If it is not possible to conduct a full-fledged ground loop, then other methods are used. For example, it is now very common to connect portable grounding pins (portable tires). Their action does not differ in any way from a standard stationary outlet, but at the same time they are much more practical in terms of their functionality.

Purpose of zeroing

Sometimes zeroing and grounding are confused with each other, so what is the difference between them? Zeroing is applied according to the PUE only for industrial installations and is not a guarantee of security. If the phase falls on the open part of the device, then the current does not go away. After that, the pairing of two phases occurs, and, as a result, a short circuit. A neutral conductor is required for rapid response differential circuit breaker for short circuit, but not to protect a person from electric shock. Therefore, it is customary to use it only in production, where a quick power off is required in the event of an emergency.

Do I need to do zeroing in a private house or apartment? No, this is not necessary, and is even fraught with various negative consequences. Let's say if the neutral wire burns out, then more of the electrical devices to which it was connected will break due to an extremely high voltage surge. It is worth remembering that your safety will not be affected if, along with grounding, you also equip grounding, install an RCD and a protective switch.

How to set zeroing so that the device connected to it does not burn out:

1. A three-core insulated wire must be used. One core is reserved for phase, the second for zero, the third for grounding;
2. Earth connects at the very end electrical work on the body of a safe conductor to the ground loop, etc. The most practical is a special ground tap near the shield;
3. For safety reasons, various power switches and other protective installations must be installed.

Video: what is the difference between zeroing and grounding

Main difference

The most important thing to remember: grounding and grounding circuits have different protective action. Zero guarantees a fast response to potential changes or current leakage for protection installations. Accordingly, at high voltage, all energy consumers are disconnected: lighting fixtures, computer and other machines (including machine tools, transformers).

Grounding provides equalization of potentials and protection against electric shock. Earth is more often used at home, its installation can be easily done by hand. But there is no guarantee that the fuses will respond quickly to a leak. The best option to increase the guarantee of safety is the joint use of grounding and grounding of networks and open parts of machines.

Before installing any of these protection options, it is imperative to obtain a work permit. In addition, a protective conductor is calculated, the land is connected to each consumer in the dwelling, and protective equipment is installed.

Our whole life is inseparable from all kinds of electrical appliances. The failure of any electrical equipment is a frequent and quite normal phenomenon; not a single device can work forever and without a single failure. Our task is to protect these electrical assistants from short circuits or overloads that occur in the circuit, and ourselves from damage to the body by high voltage. In the first case, all kinds of help come protective apparatus, but for human protection, grounding and zeroing of electrical installations are used. This is one of the most difficult parts electricians, but we will try to figure out what is the difference between these works, and in what cases it is necessary to apply certain protective measures.

If automata, plugs and other protective devices do not respond to a malfunction, and as a result a breakdown of the internal insulation is formed, an increased voltage appears on the metal case of the installation. A person touching such a device can lead to muscle paralysis (at a current strength of 20-25 mA), preventing independent separation from contact, arrhythmias, blood flow disorders (at 50-100 mA) and even death.

If parts of the electrical installation are in effect technical features must be energized, they must be protected in accordance with generally accepted safety precautions, for example, special casings, barriers or mesh barriers. In order to prevent accidental electric shock when the insulating layers are damaged, protective grounding and zeroing are used. To understand the difference between grounding and zeroing, you need to know what they are.

What is grounding

Often, novice electricians do not quite understand what is the difference between zeroing and grounding. Grounding is the connection of an electrical installation to the ground in order to reduce the contact voltage to a minimum. It is used only in networks with isolated neutral. As a result of the installation of grounding equipment most of the current supplied to the case must go through the grounding part, the resistance of which must be less than the rest of the circuit.

But this is not the only function of grounding. Protective grounding of electrical installations also contributes to an increase in the emergency circuit current, no matter how contrary to its purpose. When using a high-resistance earthing switch, the fault current may be too low for the protective devices to operate, and the installation will remain energized in an emergency, presenting a huge danger to humans and animals.

A grounding conductor with conductors forms a grounding device, where, in fact, it is a conductor (a group of conductors) connecting the conductive parts of installations to the ground. By purpose, these devices are divided into the following groups:

• lightning protection, for the removal of pulsed lightning current. They are used for grounding lightning rods and arresters;
• workers, to maintain the required mode of operation of electrical installations, both in normal and in emergency situations;
• protective, to prevent damage to living organisms by electric current that occurs during a breakdown phase wire on the metal case of the device.

All ground electrodes are divided into natural and artificial.

1. Natural - these are pipelines, metal structures reinforced concrete structures, casing pipes and others.
2. Artificial ground electrodes are structures constructed specifically for this purpose, that is, steel rods and strips, angle steel, substandard pipes, and more.

Important: for use as natural grounding pipelines of flammable liquids and gases, pipes covered with anti-corrosion insulation are not suitable, aluminum conductors and cable sheaths. It is strictly forbidden to use water and heating pipes as grounding conductors in residential premises.

Classification of grounding systems

Depending on the connection scheme and the number of zero protective and working conductors, it is possible to distinguish the following systems grounding of electrical installations:

• TN-C;
• TN-C-S;

The first letter in the name of the system indicates the type of grounding of the power supply:

• I - current-carrying parts are completely isolated from the ground;
• T - the neutral of the power supply is connected to the ground.

By the second letter, you can determine how the open conductive parts of the electrical installation are grounded:

• N - direct connection with the grounding point of the power supply;
• T - direct connection to the ground.

The letters immediately following N, through a hyphen, speak of the method of constructing a protective PE and a working N zero conductors:

• C - the functions of the conductors are provided by one conductor PEN;
• S - the functions of the conductors are provided by different conductors.

Legacy TN-C system

Such grounding of electrical installations is used in three-phase four-wire and single-phase two-wire networks, which prevail in old-style buildings. Unfortunately, this system, despite its simplicity and availability, does not allow achieving a high level of electrical safety and is not used in newly constructed buildings.

For retrofitting old houses TN-C-S

Protective grounding of electrical installations of this type is used mainly in reconstructed networks, where the working and protective conductors are combined into input device scheme. In other words, this system is used if in an old building where grounding is used type TN-C, it is planned to locate computer equipment or other telecommunications, that is, to carry out the transition to the TN-S system. This relatively inexpensive scheme differs high level security.

The TN-C-S system allows you to migrate from legacy TN-C to TN-S

Specifics of the TN-S system

Such a system differs in the location of the neutral and working conductors. Here they are laid separately, and the zero protective conductor PE connects all the conductive parts of the electrical installation at once. To avoid re-grounding, it is enough to arrange transformer substation having the main ground. In addition, such a substation allows you to achieve the minimum length of the conductor from the cable entry into the electrical installation to the grounding device.

1. Ground electrode;
2. Conductive parts of the installation.

TT system features

The system, where all current-carrying open parts are directly connected to the ground, and the earthing conductors of the electrical installation are not electrically dependent on the earthing conductor of the neutral of the substation, was called TT.

The TT earthing system is distinguished by the presence of earthing conductors for each conductive part of the installation

Characteristic differences of the IT system

The difference in this system is the isolation of the neutral of the power supply from the ground or its grounding through devices with high resistance. This method allows you to minimize the leakage current to the case or to the ground, so it is better to use it in buildings where stringent electrical safety requirements are established.

What is nulling

Zeroing is the connection of metal parts that are not energized, or with grounded neutral step-down source of three-phase current, or with a grounded output of the generator single-phase current. It is used to ensure that when an insulation breakdown occurs and current enters any non-current-carrying part of the device, a short circuit occurs, leading to the rapid operation of the circuit breaker, blown fuses or the reaction of other protection systems. It is mainly used in electrical installations with a solidly grounded neutral.

circuit diagram neutralization of electrical installations

Additional installation RCD in the line will lead to its operation as a result of the difference in current strength in the phase and neutral working wire. If both an RCD and a circuit breaker are installed, then a breakdown will either trip both devices, or turn on a faster element.

Important: When setting the zeroing, it must be taken into account that the short-circuit current must necessarily reach the value of melting the fuse insert or tripping the circuit breaker, otherwise the free flow of the fault current through the circuit will lead to voltage on all zeroed cases, and not just on the damaged area. Moreover, the value of this voltage will be equal to the product of the resistance of the neutral conductor and the fault current, which means it is extremely dangerous for human life.

The serviceability of the neutral wire must be monitored most carefully. Its break leads to the appearance of voltage on all zeroed cases, since they are automatically connected to the phase. That is why it is strictly forbidden to install any means of protection (switches or fuses) in the neutral wire that form its gap when triggered.

In order to reduce the likelihood of electric shock when the neutral wire breaks, re-groundings are performed every 200 m of the line. The same measures are taken on the end and input supports. The resistance of each repeated ground electrode must not exceed 30 ohms, and the total resistance of all such grounding devices must not exceed 10 ohms.

Zeroing and grounding: what's the difference?

The main difference between grounding and grounding is that when grounding, safety is ensured by a rapid decrease in voltage, and when grounding, by disconnecting the section of the circuit in which the current breakdown occurred on the case or any other part of the electrical installation, while in the time interval between the short circuit and termination power supply, the potential of the electrical installation case decreases, otherwise a discharge of electric current will pass through the human body.

Wiring diagram grounding and grounding

Requirements for grounding (zeroing)

In all electrical installations where the neutral is isolated, protective earthing is mandatory, and it must also be possible to quickly search for ground faults.

If the device has a solidly grounded neutral, and its voltage is less than 1000 V, then only zeroing can be used. When equipping such an electrical installation with a separating transformer, the secondary voltage should be no more than 380 V, step-down - no more than 42 V. At the same time, only one electrical receiver with rated current protective device not more than 15 A. In this case, grounding or zeroing of the secondary winding is prohibited.

If the neutral of a three-phase network up to 1000 V is isolated, then such electrical installations must be protected against breakdown as a result of damage to the insulation between the windings of the transformer and a breakdown fuse, which is mounted in the neutral or phase on the low voltage side.

What and when to ground

Protective grounding and zeroing of electrical installations must be carried out in the following cases:

1. With a variable rated voltage over 42 V and constant rated over 110 V in especially hazardous and outdoor installations.
2. At AC voltage over 380 V and constant over 440 V in any electrical installations.

Housings of electrical installations, apparatus drives, frames and metal constructions distribution cabinets and shields, secondary windings transformers, metal sheaths of cables and wires, cable structures, busbars, boxes, cables, steel pipes electrical wiring and electrical equipment located on moving parts of mechanisms.

in residential and public buildings electrical appliances with a power of more than 1300 watts must be grounded (grounded). If dropped ceilings made of metal, it is necessary to ground all metal cases lighting fixtures. Bathtubs and shower trays made of metal must be connected to water pipes with metal conductors. This is done to equalize electrical potentials. To ground the housings of air conditioners, electric stoves and other electrical appliances, the power of which exceeds 1300 W, a separate conductor is used, which is connected to the neutral conductor of the power supply network. Its cross section and the cross section of the phase wire laid from the switchboard must be equal.

To equalize the electrical potentials, the bath must be closed to water pipes

WITH complete list equipment requiring grounding or grounding, as well as devices where, on the contrary, it is allowed to neglect these protective measures, can be found in the PUE (Electrical Installation Rules). Here you can find all the basic rules for grounding electrical installations.

The grounding and grounding device is a very responsible job. The slightest mistake in the calculations or neglect, it would seem, one insignificant requirement can lead to a great tragedy. Only people with the necessary knowledge and experience are required to carry out grounding.

Grounding of an electrical installation is the provision of electrical safety by purposeful electrical connection of the device case with the "ground". Protection is divided into two options: grounding and grounding. Their common goal is to neutralize the impact of electric current harmful to humans when touched, if the equipment on the case or at any other accessible point has broken through to a dangerous voltage.

grounding

The essence of protective grounding is to ensure safe operation electrical equipment by connecting its protected part to the appropriate device - "ground". If the outer casing of the unit or any other part of it suddenly becomes electric potential harm to humans will be minimized. The main characteristic of a grounding device is its resistance, the quality of protection improves with its decrease. Grounding can be divided into two main parts - a ground electrode and conductive connectors that provide contact with the grounded part. The area of ​​​​use of protective earthing are three-phase networks, the neutral in which is isolated.

Protective grounding operates on the basis of a serious reduction in the potential difference between the part on which the voltage has broken through (case, etc.) and the ground, up to a level that is safe for humans. If grounding is not available, the contact with a dangerous place in the electrical installation is a direct contact with the phase. The resulting electric current has no other way than the human body. With a low electrical resistance of the shoes worn, the floor itself and the presence of isolation of the wires from the "ground", the current value will be unacceptable for the victim. If organization of work on labor protection was performed correctly and the problematic part has a protective ground, then even in the case large values applied voltage, it will not cause serious consequences for the body. According to Ohm's law, the current will be inversely proportional to the resistance. In the presence of two parallel circuits - the human body and the ground loop, with an equal value of the initial voltage (phase), the strength of the passing current will be the higher, the lower the resistance of the circuit. Designed to provide a minimum resistance, the protective earth will take over the main electric current, securing a person with a much higher resistance.

Two types of grounding

Grounding conductors are divided into two types - natural and artificial. If metal structures (pipes, fittings, etc.) that already existed during the construction of the building are used for grounding, the ground electrode is called natural. When steel rods, angles or pipes are deliberately hammered or buried in the ground, the structure is artificial. In order to increase safety, the length of the artificial earth electrode cannot be less than 2.5 m, and to improve protection, metal fragments are combined by welding with steel plates or wire. To ensure electrical contact between the grounded device and the grounding conductor, it is customary to use tires made of copper or steel. Grounding conductors are attached to the body of the equipment by welding or using a reliable threaded connection. Mandatory protection using earthing technology is required for transformers, electrical cabinets and shields, as well as most industrial and some household appliances and mechanisms.

Although protective earthing reduces the risk to humans to a large extent, it does not completely eliminate it. A potential problem is that the earth electrode, connecting wires and even earth have their own resistance. If the insulation is broken, the closing current will make its way from the earthed part to earth, and at each stage the existing resistance will create an additional potential difference. The resulting total voltage will be significantly lower than the 220 V generally accepted in Russia, but it may still be values ​​that are unsafe for humans. To reduce the total voltage, it is necessary to reduce the resistance of the grounding conductor relative to the final point - the earth. A common practice is to increase the number of artificial ground electrodes.

Zeroing

The second type of protection against electric shock during a breakdown on the case is protective zeroing. It consists in a purposeful connection of parts electrical appliance, potentially in phase, with an earthed terminal of an AC source or with a similar midpoint in DC networks. Thus, the breakdown of any phase on the equipment case is translated into a short circuit with a grounded zero. The current flowing with protective grounding is many times greater than in the case of grounding. Therefore, the main purpose of creating protective zeroing is a quick cessation of work and a complete de-energization of a broken device in principle.

The neutral conductor is working and protective. The working conductor is designed to fully power the electrical installation, therefore it does not differ from other carriers in terms of thickness and quality of insulation, material and wire cross section. The purpose of the protective conductor is only to create a short circuit of a very high current in a short period of time, which will allow the protection to work and quickly de-energize the faulty device. As a neutral protective conductor, steel pipes often used when laying wiring or neutral wires without additional parts (switches and fuses). As well as grounding, grounding cannot fully protect a person from the effects of electricity in direct contact with a structural element under phase. If ensuring electrical safety in the room requires increased attention, it is strictly necessary to combine zeroing with other protective measures - potential equalization and protective shutdown.