Grounding and grounding of electrical installations and their parts. Protective ground. Zeroing. TT earthing system

To ensure the protection of people when touching metal non-current-carrying parts that may for some reason be energized, protective grounding and grounding are used along with other means.

According to GOST 12.1.009-76 “System of labor safety standards. Electrical safety. Terms and definitions "protective grounding - intentional electrical connection with earth or its equivalent, metal non-current-carrying parts that may be energized. The purpose of protective grounding is to eliminate the danger of hitting people electric shock when voltage appears on the structural parts of electrical equipment, i.e. when a short circuit occurs on the case.

Metal non-current-carrying parts of electrical equipment are subject to protective grounding, which, due to a faulty insulation, may become energized and which can be touched by people and animals.

The principle of operation of protective grounding is to reduce the voltage between the housing that is energized and the ground to a safe value.

It should be noted that in the technical code of established practice “Electrical installations for voltage up to 750 kV. Overhead power lines and current conductors, distribution devices and transformer substations, electric power and battery installations, electrical installations of residential and public buildings. Rules for the device and protective measures for electrical safety. Accounting for electricity. Norms of acceptance tests”, approved by the Decree of the Ministry of Energy of the Republic of Belarus dated August 23, 2011 No. 44, defines not only the term “grounding”, but also terms derived from it:

grounding - intentional electrical connection of any point of the network, electrical installation or equipment with a grounding device;

protective grounding - grounding made for the purpose of electrical safety;

functional grounding (working, technological) - grounding of a point or points of a system, or installation, or electrical equipment for purposes other than electrical safety purposes.

According to GOST 12.1.009-76 “System of labor safety standards. Electrical safety. Terms and definitions "zeroing - a deliberate electrical connection with zero protective conductor metal non-current-carrying parts that may be energized.

The purpose of zeroing is to eliminate the danger of electric shock to people during a breakdown on the body.

The principle of zeroing operation is the transformation of a short circuit to the case into a single-phase short circuit (i.e., a short circuit between phase and zero wires) in order to induce a high current capable of providing protection operation and thereby automatically disconnecting the damaged installation from the supply network. Such protection can be fuses, magnetic starters with built-in thermal protection, contactors in combination with thermal relays, automatic machines that simultaneously protect against currents short circuit and from overload.

Grounding is subject to metal structural non-current-carrying parts of electrical equipment that must be grounded: cases of machines, apparatus, etc. In a network with grounding, the receiver housing cannot be grounded without connecting it to a neutral protective wire.

This question baffles novice home masters. And it is not surprising, not even every certified electrician will answer how these types of protection differ. Let's take a look at these definitions today. After all misapplication species will lead to irreparable consequences. Electricity does not forgive mistakes. Today we will understand what the terms grounding and zeroing mean, what is the difference between them and in what cases this or that protection is applied. It is important to know how to arrange a grounding device, and when to do without it. We ask the reader to carefully study today's article. Information is extremely important for everyone.

Read in the article:

Basic requirements of the PUE: excerpts from articles

Let's start with the fact that the definitions of grounding and zeroing are clearly spelled out in the electrical installation rules (PUE) and GOST. Let's try to identify some.

• PUE 7. Clause 1.7.28- intentional electrical connection of any point of the network, electrical installation or equipment with a grounding device;
• PUE 7. Clause 1.7.31 – protective zeroing in electrical installations with voltage up to 1 kV - intentional connection open conductive parts with solidly grounded neutral of a generator or transformer in networks three-phase current, with solidly grounded source output single-phase current, with a grounded source point in networks direct current performed for electrical safety purposes;
• GOST 12.1.009-76. Grounding (protective grounding) - a deliberate electrical connection with a zero protective conductor of metal non-current-carrying parts that may be energized.

It is not difficult for an electrician to understand this, but for a novice master everything written will seem like a set of words. Today we will “translate” everything into a simple language and everything will immediately fall into place.

What is grounding and how does it work

In ordinary language, grounding is mounted so that when voltage occurs, where it should not be (the body of the washing machine, microwave oven or refrigerator), electricity went into the ground. This can happen if the insulation is broken in the device and the current-carrying wire is in contact with the case. Let's see how grounding works.

Imagine that a pipe is leaking at home. Water rushes down, but not through the plate, through which it cannot pass, but where there are cracks. The same is true here. The resistance of a properly performed grounding is negligible (many times less than that of the human body). And if a person touches a grounded case, electricity continues to "flow" along the path of least resistance, like water, without causing harm. But it is worth breaking the ground, as the current will go in the other direction, rushing to the ground through the human body.

Expert opinion

“Grounding is installed to protect a person from electric shock, while maintaining the operability of the equipment.”

Having answered the question why grounding is needed, we turn to protective grounding.

What is zeroing: principle of operation and device

Zeroing is mounted according to a different principle. But in order to understand this, let's analyze what a dead-earthed neutral is. 3 phases come to the transformer substation (transformer substation) via power lines. Own grounding, mounted around, and is deaf earthed neutral, which goes to residential buildings from the substation, along with phase wires.

Zeroing is done like this. In the switchboard, wiring is done, the dead-earthed neutral (PEN) coming from the TP is broken in front of the introductory machine to zero (N), which goes to the apartment, and what can be considered ground (PE). In fact, in fact, this will remain a dead-earthed neutral, which will be used for zeroing. It is forbidden to zero the equipment from working N - it is life-threatening. If everything is done correctly, then when the case of the switched on device comes into contact with a live bare wire, a short circuit occurs, after which the machine is triggered.

Expert opinion

Design engineer of ES, EM, EO (power supply, electrical equipment, interior lighting) LLC "ASP North-West"

“Protective zeroing is a system that is mounted for instantaneous operation of automation when voltage appears on the device case and a complete power outage.”

Only a complete understanding of what grounding and zeroing are, what are their features, will make it possible to perform in an apartment or house that type of protection that will be effective and safe.

What is the difference between grounding and grounding?

This question may arise in the reader against the background of the previous information. Indeed, in fact, the same grounding comes from the TP. Let's explain. The fourth wire that came into the house can no longer be grounding, because it is used by other residents as a zero one. For example, let's take a situation in which we decided that zero and ground are one and the same. We make the wiring directly in the outlet, throwing a jumper between zero and ground contact and calm down - we are protected.

No matter how! The bare wire is close to the body of the device, but has not yet touched it, but the magnetic field has already arisen and the current-carrying conductor begins to heat up. But at the same time, the neutral wire heats up even more in the place of a weak connection. The insulation of the current-carrying conductor burns out, it touches the case, annealing the zero. Everything, there is no light in the apartment, but the machine did not work. The body of the instrument is now under phase voltage. What happens if you touch him? The voltage will pass through the person into the ground along the path of least resistance, causing maximum damage to the conductor (it is clear who we are talking about).

Zeroing and grounding: what is the difference in scope

The main rule is that both types of protection cannot be applied at the same time. If there is a possibility of grounding, then grounding is not considered as possible variant. In what cases is this or that type mounted? Now we'll find out.

When equipment is grounded

IN apartment buildings the ground loop is arranged around or on two sides of the building. The only exceptions are the houses of the old building - they may not have a contour. In private homes, the circuit device falls on the shoulders of the homeowner. How it looks, how the grounding device is mounted, we will consider below.

Related article:

And what is it for? What to choose RCD or differential machine? How do we connect the device to single-phase network with or without grounding? How to choose the right device for home protection? You will learn the answers to these questions from our review.

Good to know! Grounding is considered a more reliable method of protection, but when turning off the input electrical panel and wiring indoors, you need to be extremely careful. Nowhere should the ground be in contact with the neutral. If this happens, installed devices protective shutdown(RCD) will trip for no reason.

What is protective grounding, where it is used, figured out. What about the second kind?

When protective grounding is applied in the apartment

This type of protection is applicable, provided there is no grounding. Usually this apartment buildings old building. Using this type of protection, it is necessary to install automatic machines and RCDs. It is performed as follows.

The neutral wire before connecting to the RCD is output to a separate bus, from which the yellow-green wire of the dead-earthed neutral will go. The main zero is divorced by RCD and follows the apartment. The simplest option is a three-core cable for wiring the apartment, two wires of which (phase and zero) pass through protective automation, and one (grounded neutral) directly. It is connected to the grounding contacts of sockets and lighting fixtures.

Requirements for grounding and grounding

Having understood what grounding and grounding are, it is easy to understand the requirements for them. The main thing is to ensure safety and protect a person from electric shock. The rest has already been said, but it is worth repeating in general.

Zeroing requirements - shutdown protective automation when current-carrying parts (see "bare wires") come into contact with the surfaces of the housings household appliances, parts where tension should not be.

The requirement for grounding is the removal of voltage to the ground, which excludes electric shock to a person.

What is a grounding device: everyone should know this

A grounding device is a structure in the form of a triangle or square of metal tires or corners welded together, as well as pins driven into the ground by 1.5-2 m (sometimes more), which has minimal resistance. The charger is connected to the ground bus in the switchboard.

Grounding device methods

Grounding is carried out in the form of a circuit that has a minimum resistance. Ideally, the phase-to-ground voltage should be equal to line-to-line (line-to-neutral). You can familiarize yourself with the device of the protective grounding loop with your own hands on our website.

Instead of a circuit, you can use natural ground electrodes. However, this is rarely used due to misunderstanding of the term. What is the definition of the concept of "natural grounding"? So to speak. Pipes or others metal constructions passing underground, not having anti-corrosion coating fall under this term. The exception is sewer pipes, as well as those through which fuels and lubricants or gas pass.

Let's just say that if the zeroing is done according to the rules (in the absence of grounding), there are no shortcomings. However, it loses to high-quality grounding. One of the reasons is a complete disruption of the power supply during a phase breakdown to the case. Although on the other hand, this can be called an advantage. Indeed, when grounding (if there is no RCD), you may not know about the malfunction, which will lead to increased electricity bills.

Article

Generally speaking, it can be noted that the great and terrible power of electricity has long been described, calculated, listed in thick tables. Normative base, defining the paths of sinusoidal electrical signals frequency of 50 Hz is able to plunge any neophyte into horror with its volume. And, despite this, any frequenter of technical forums has long known - there is no more controversial issue than grounding.

The mass of contradictory opinions in fact does little to establish the truth. Moreover, this issue is actually serious, and requires closer consideration.

Basic concepts

If you omit the introduction of the "electrician's bible" (), then to understand the grounding technology, you need to refer (to begin with) to Chapter 1.7, which is called "Grounding and Electrical Safety Protective Measures".

In clause 1.7.2. PUE says:

Electrical installations in relation to electrical safety measures are divided into:

• electrical installations above 1 kV (with high currents ground fault), ;
• electrical installations above 1 kV in networks with isolated neutral(with low earth fault currents);
• electrical installations up to 1 kV with dead-earthed neutral;
• electrical installations up to 1 kV with isolated neutral.

The vast majority of residential and office buildings in Russia use solidly grounded neutral. Clause 1.7.4. reads:

A dead-earthed neutral is a transformer or generator neutral connected to a grounding device directly or through low resistance (for example, through current transformers).

The term is not entirely clear at first glance - a neutral and a grounding device are not found at every step in the popular science press. Therefore, below all incomprehensible places will be gradually explained.

Let's introduce a few terms - so it will be possible to speak at least one language. Perhaps the points will seem "taken out of context". But not fiction, and such separate use should be quite justified - as the application of individual articles of the Criminal Code. However, the original PUE is quite available both in bookstores and online - you can always turn to the original source.

• 1.7.6. The grounding of any part of an electrical installation or other installation is the intentional electrical connection of this part with a grounding device.
• 1.7.7. Protective grounding is the grounding of parts of an electrical installation in order to ensure.
• 1.7.8. Working grounding is the grounding of any point of the current-carrying parts of the electrical installation, which is necessary to ensure the operation of the electrical installation.
• 1.7.9. Zeroing in electrical installations with voltages up to 1 kV is the deliberate connection of parts of an electrical installation that are not normally energized with a dead-earthed neutral of a generator or transformer in three-phase current networks, with a dead-earthed output of a single-phase current source, with a dead-earthed midpoint source in DC networks.
• 1.7.12. A grounding conductor is a conductor (electrode) or a set of metal-connected conductors (electrodes) that are in contact with the ground.
• 1.7.16. A grounding conductor is a conductor connecting the grounded parts to the ground electrode.
• 1.7.17. A protective conductor (PE) in electrical installations is a conductor used to protect against electric shock to people and animals. In electrical installations up to 1 kV, a protective conductor connected to a dead-earthed neutral of a generator or transformer is called a neutral protective conductor.
• 1.7.18. Zero working conductor (N) in electrical installations up to 1 kV is a conductor used to power electrical receivers, connected to a solidly grounded neutral of a generator or transformer in three-phase current networks, with a solidly grounded output of a single-phase current source, with a solidly grounded source point in three-wire DC networks. A combined zero protective and zero working conductor (PEN) in electrical installations up to 1 kV is a conductor that combines the functions of a zero protective and zero working conductor. In electrical installations up to 1 kV with a solidly grounded neutral, the zero working conductor can perform the functions of a zero protective conductor.

Rice. 1. The difference between protective grounding and protective "zero"

So, a simple conclusion follows directly from the terms of the PUE. The differences between "ground" and "zero" are very small... At first glance (how many copies are broken at this point). At the very least, they must be combined (or even can be performed "in one bottle"). The only question is where and how it was done.

In passing, we note paragraph 1.7.33.

Grounding or grounding of electrical installations should be carried out:

• at a voltage of 380 V and above alternating current and 440 V and above direct current - in all electrical installations (see also 1.7.44 and 1.7.48);
• at rated voltages above 42 V, but below 380 V AC and above 110 V, but below 440 V DC - only in rooms with increased danger, especially dangerous and in outdoor installations.

In other words, it is not necessary to ground or neutralize a device connected to 220 volts AC. And there is nothing particularly surprising in this - there is really no third wire in ordinary Soviet sockets. We can say that the Eurostandard (or a new edition of the PUE close to it) that comes into practice in practice is better, more reliable, and safer. But according to the old PUE, we lived in our country for decades ... And what is especially important, houses were built by entire cities.

However, when it comes to grounding, it's not just about supply voltage. A good illustration of this is VSN 59-88 (Goskomarchitectura) "Electrical equipment of residential and public buildings. Design standards" Excerpt from chapter 15. Grounding (zeroing) and protective safety measures:

15.4. For grounding (grounding) of metal cases of household air conditioners, stationary and portable household appliances class I (without double or reinforced insulation), household electrical appliances powerSt. 1.3 kW, cases of three-phase and single-phase electric stoves, digesters and other thermal equipment, as well as metal non-current-carrying parts technological equipment premises with wet processes, a separate conductor with a cross section equal to the phase should be used, laid from the shield or shield to which this electrical receiver is connected, and in the lines supplying medical equipment - from the ASU or main switchboard of the building. This conductor is connected to the neutral conductor of the mains. The use of a working neutral conductor for this purpose is prohibited.

This creates a normative paradox. One of the results visible at the household level was the acquisition of washing machines"Vyatka-automatic" skein of single-core aluminum wire with the requirement to perform grounding (by the hands of a certified specialist).

And one more interesting point:. 1.7.39. In electrical installations up to 1 kV with a solidly grounded neutral or a solidly grounded output of a single-phase current source, as well as with a solidly grounded midpoint in three-wire DC networksnulling must be performed. The use in such electrical installations of grounding the housings of electrical receivers without their grounding is not allowed.

In practice, this means - if you want to "ground" - first "zanuli". By the way, this is directly related to the famous issue of "batteries" - which, for a completely incomprehensible reason, is mistakenly considered better than zeroing (grounding).

Grounding parameters

The next aspect to consider is numerical parameters grounding. Since physically it is nothing more than a conductor (or a set of conductors), its main characteristic will be resistance.

1.7.62. Grounding device resistance, k toto which the neutrals of generators or transformers or the outputs of a single-phase current source are connected, at any time of the year there should be no more than 2, 4 and 8 ohms, respectively, at line voltages of 660, 380 and 220 V of a three-phase current source or 380, 220 and 127 V of a single-phase current source. This resistance must be provided taking into account the use of natural grounding conductors, as well as grounding conductors for repeated grounding of the zero wire of overhead lines up to 1 kV with the number of outgoing lines of at least two. In this case, the resistance of the ground electrode located in the immediate vicinity of the neutral of the generator or transformer or the output of a single-phase current source should be no more than: 15, 30 and 60 Ohms, respectively, at line voltages of 660, 380 and 220 V of a three-phase current source or 380, 220 and 127 In a single-phase current source.

For lower voltage, more resistance is acceptable. This is quite understandable - the first purpose of grounding is to ensure human safety in the classic case of a "phase" hitting the electrical installation case. The lower the resistance, the smaller part of the potential may be "on the case" in the event of an accident. Therefore, the risk for higher voltages must be reduced first.

In addition, it must be borne in mind that grounding also serves to normal operation fuses. To do this, it is necessary that the line during the breakdown"on the body" significantly changed the properties (primarily resistance), otherwise the operation will not occur. The greater the power of the electrical installation (and the voltage consumed), the lower its operating resistance, and, accordingly, the ground resistance must be lower (otherwise, in case of an accident, the fuses will not work from little change total circuit resistance).

The next normalized parameter is the cross section of the conductors.

1.7.76. Grounding and zero protective conductors in electrical installations up to 1 kV must have dimensions not less than those given in Table. 1.7.1 (see also 1.7.96 and 1.7.104) .

It is not advisable to give the entire table, an excerpt is enough:

For bare copper, the minimum cross section is 4 square meters. mm, for aluminum - 6 sq. mm. For isolated, respectively, 1.5 square meters. mm and 2.5 sq. mm. If the ground conductors are in the same cable as the power wiring, their sectionlenie can be 1 square. mm for copper, and 2.5 sq. mm for aluminium.

Grounding in a residential building

In a normal "domestic" situation, users of the power grid (i.e. residents) deal only with the Group network ( 7.1.12 PUE. Group network - a network from shields and distribution points to lamps, socket outlets and other electrical receivers). Although in old houses where shields are installed directly in apartments, they have to deal with part of the distribution network ( 7.1.11 PUE. Distribution network - a network from VU, ASU, MSB to distribution points and shields). It is desirable to understand this well, because often "zero" and "ground" differ only in the place of connection with the main communications.

From this, the first grounding rule is formulated in the PUE:

7.1.36. In all buildings, group network lines laid from group, floor and apartment shields to lamps of a commonbroadcasting, socket outlets and stationary electrical receivers must be three-wire (phase - L, zero working - N and zero protective - PE conductors). It is not allowed to combine zero working and zero protective conductors of various group lines. Zero working and zero protective conductors are not allowed to be connected on shields under a common terminal.

Those. 3 (three) wires must be laid from the floor, apartment or group shield, one of which is a protective zero (not earth at all). Which, however, does not prevent at all from using it for grounding a computer, a cable screen, or a "tail" of lightning protection. Everything seems to be simple, and it is not entirely clear why go into such complexity.

You can look at your home outlet ... And with a probability of about 80% you will not see a third contact there. What is the difference between zero working and zero protective conductors? In the shield, they are connected on the same bus (albeit not at one point). What will happen if we use a working zero as a protective one in this situation?

Assume that a negligent electrician is a perpetratormelts in the shield phase and zero, difficult. Although this constantly scares users, it is impossible to make a mistake in any state (although there are unique cases). However, the "working zero" goes through numerous strobes, probably passes through several junction boxes (usually small, round, mounted in the wall near the ceiling).

It is already much easier to confuse the phase with zero there (I did it myself more than once). And as a result, 220 volts will appear on the case of an incorrectly "grounded" device. Or even simpler - a contact will burn out somewhere in the circuit - and almost the same 220 will pass to the case through the load of the electrical consumer (if this is an electric stove for 2-3 kW, then it will not seem enough).

For the function of protecting a person, frankly, this is an unsuitable situation. But for grounding connection, lightning protection of the APC type is not fatal, since a high-voltage decoupling is installed there. However, it would be unequivocally wrong to recommend such a method from a security point of view. Although it must be admitted that this rule is violated very often (and usually without any adverse consequences).

It should be noted that the lightning protection capabilities of the working and protective zero approximately equal. Resistance (up to connecting bar) fromdiffers insignificantly, and this is, perhaps, the main factor influencing the runoff of atmospheric pickups.

From the further text of the PUE, you can see that literally everything that is in the house must be connected to the zero protective conductor:

7.1.68. In all rooms it is necessary to connect exposed conductive parts of luminaires general lighting and stationary electrical receivers ( electric stoves, boilers, domestic air conditioners, electric towels, etc.) to the neutral protective conductor.

In general, it is easier to represent the following illustration:

Rice. 2. Grounding scheme

The picture is quite unusual (for everyday perceptionand I). Literally everything that is in the house must be grounded on a special bus. Therefore, the question may arise - after all, they lived without it for decades, and everyone is alive and well (and thank God)? Why change everything so seriously? The answer is simple - there are more consumers of electricity, and they are more and more powerful. Accordingly, the risk of injury increases.

But the dependence of safety and cost is a statistical value, and no one has canceled the savings. Therefore, it is not worth blindly laying a copper strip of a decent section around the perimeter of the apartment (instead of a plinth), leading everything to it, up to the metal legs of the chair, is not worth it. How not to walk in a fur coat in the summer, and constantly wear a motorcycle helmet. This is a question of adequacy.

Also, independent digging of trenches under a protective contour should be attributed to the area of ​​\u200b\u200ba non-scientific approach (in a city house, apart from problems, this will certainly bring nothing). And for those who still want to experience all the delights of life - in the first chapter of the EMP there are standards for the manufacture of this fundamental structure (in the truest sense of the word).

Summarizing the above, we can draw the following practical conclusions:

• If the Group network is made with three wires, you can use protective zero. It is, in fact, designed for that.
• If the Group network is made with two wires, it is advisable to start a protective neutral wire from the nearest shield. The cross section of the wire must be more than the phase one (more precisely, you can consult the PUE).

One of effective means protection against electric shock are protective grounding and zeroing of electrical installations. In accordance with GOST 12.1.009–76:

protective earth – it is an intentional electrical connection to or from groundvivalent metal non-current-carrying parts that may be energized;

nulling – it is an intentional electrical connection withzero protective conductor of metal non-current-carryingparts that may become energized.

In matters of application and practical implementation of protective grounding and grounding, one should be guided by the requirements of not only the PUE, but also GOST R 50571. In GOST R 50571.2-94 “Electrical installations of buildings. Part 3. Main characteristics ”is a classification of grounding systems for electrical networks: IT, TT, TN-C, TN-C-S, TN-S (Fig. 2).

With regard to AC networks with voltage up to 1 kV, the designations have the following meaning.

First letter - the nature of the grounding of the power source (neutral mode of the secondary winding of the transformer):

I– isolated neutral;

T- dead-earthed neutral.

Second letter - the nature of the grounding of open conductive parts (metal cases) of the electrical installation:

T– direct connection of open conductive parts (HFC) with the ground (protective grounding);

N- direct connection of the HRC with the grounded neutral of the power source (zeroing).

Subsequent letters (if any) - the device of the zero working and zero protective conductors:

WITH- zero working (N) and zero protective (PE) conductors are combined throughout the network;

C– S- conductors N and PE are combined in part of the network;

S– N and PE conductors operate separately throughout the network

Rice. 2. Varieties of grounding systems

Conductors used in various types networks should have certain designations and colors (Table 1).

Table 1

Conductor designation

The scope of these protection methods is determined by the neutral mode and the voltage class of the electrical installation.

Protective grounding consists (Fig. 3) of the ground electrode 3 (metal conductors in the ground with good contact with it) and a grounding conductor 2, connecting the metal case of the electrical installation 1 with earth conductor.

Rice. 3. Protective earth circuit:

1 - electrical installation; 2 - ground conductor; 3 - grounding

The combination of a grounding conductor and grounding wires is called grounding device. Protective grounding is used in three-phase three-wire and single-phase two-wire AC networks with voltage up to 1000 V with an isolated neutral, as well as in networks with voltages above 1000 V AC and DC with any neutral mode.

Protective action of the grounding device based on reducing to a safe value the current passing through a person at the moment of contact them damaged electrical installations.

When voltage hits the body of the electrical installation, a person, touching it and having good contact with the ground, closes electrical circuit: phase L1 - electrical installation case 1 - man - earth - capacitive X L3 , X L2 and active R L 3 , R L 2 resistance of connection of wires with the ground, phase L3 andL2. Electricity will flow through the person. Despite the fact that the electrical wires of the network are installed on insulated supports, there is an electrical connection between them and the ground. It occurs due to the imperfection of the insulation of wires, supports, etc. and the presence of capacitance between the wires and the ground. With a large length of wires, this connection becomes significant, and its active R and capacitive X resistances decrease and become commensurate with the resistance of the human body. That is why, despite the absence of a visible connection, a person who is energized and has contact with the ground closes an electrical circuit between the various phases of the network.

In the presence of a grounding device, an additional circuit is formed: phase L1- electrical installation housing - grounding device - earth - resistances X L3 , R L3 , X L2 , R L2 - phases L3 And L2. As a result, the fault current is distributed between the grounding device and the person. Since the resistance of the grounding conductor (it should be no more than 10 ohms) is many times less human resistance (1000 ohm), then a small current will pass through the human body, which does not cause damage to it. The main part of the current will go through the circuit through the ground electrode.

Earthing switches may be natural or artificial. As natural earthing conductors use metal structures and fittings of buildings and structures that have a good connection to the ground, water, sewer and other pipelines laid in the ground (with the exception of pipelines of flammable liquids, flammable and explosive gases and pipelines covered with insulation to protect against corrosion).

As artificial ground electrodes use single or metal electrodes connected in groups, hammered vertically or laid horizontally into the ground. The electrodes are made from sections of metal pipes with a diameter of at least 32 mm and a wall thickness of at least 3.5 mm, angle steel with a shelf thickness of at least 4 mm, a strip with a cross section of at least 100 mm 2, as well as from segments of channels, bar steel with a diameter of at least 10 mm . Electrodes made of thinner profiles quickly fail due to corrosion. In addition, thin profiles have little contact with the ground, so their use is undesirable. The length of the electrodes and the distance between them is taken to be at least 2.5–3.0 m.

Between themselves, the vertical electrodes in the group grounding are connected by welding with a jumper made of similar materials and the same sections as the electrodes themselves. The grounding device must have an output to the outside (to the surface of the earth), made by welding from the same materials. It serves to connect the ground conductor.

For grounding functionsgrounding device resistance in electrical installations with voltage up to 1000 Vin a network with isolated neutral should be no more than 4 ohms.

The required resistance is achieved by installing the appropriate number of electrodes in the ground electrode, determined by calculation.

Grounding device resistance- this is the ratio of the voltage on the grounding device to the current flowing from the grounding electrode to the ground. Distinguish remote And contour grounding devices.

remote the device is located outside the site with grounded equipment. Its advantage lies in the possibility of choosing a soil with the lowest resistivity.

Contour grounding is performed by plugging electrodes along the contour of the equipment to be grounded and between it. Such an installation of electrodes creates an additional protective effect due to the increase and equalization (more uniform distribution) of the ground potentials in the area where a person is located.

Zeroing - this is a deliberate electrical connection of metal non-current-carrying parts of electrical installations that may be energized with a dead-earthed neutral of a current source (generator or transformer).

In four-wire networks with a neutral wire and a dead-earthed neutral of a current source with a voltage of up to 1000 V, zeroing is the main means of protection.

The connection of electrical installations to the neutral of the current source is carried out using zero protective conductor (RE- conductor). It must not be confused with zero worker by wire (N - conductor), which is also connected to the source neutral, but serves to power single-phase electrical installations. Zero protective conductor is laid along the route phase wires in close proximity to them.

Zeroing protective action based on a decrease to a safe value of the current passing through a person at the moment of contact them damaged electrical installations, and subsequent disconnection of this installation from the network.

Zeroing works as follows: when voltage is applied to the body of a zeroed electrical installation 8 (Fig. 4) most of the current from it will go to the network through the neutral protective wire 6. By circuit: electrical installation housing 8 - man - earth - grounding device 9 - zero working wire 5 - a small current will flow that does not cause damage (due to the higher resistance of this circuit compared to the resistance of the circuit through the neutral protective wire 6). At the same time, a short circuit to the body of the phase wire with such a protection scheme automatically turns into a single-phase short circuit between the phase and neutral working wire 5 networks, resulting in after 0.2-7 s current protection trips(fuse blown 7, the circuit breaker trips, etc.), and the electrical installation, and with it the person, is completely de-energized.

Thus, at the initial moment, zeroing works similarly to protective grounding, and subsequently it completely stops the effect of current on a person. Only in this case, the current passing through the human body before the protection is triggered will be several times less, because. the resistance of the grounding conductor usually does not exceed 0.3 ohms, and the resistance of the ground electrode is allowed up to 4 ohms.

Rice. 4. Grounding scheme:

1 - transformer neutral grounding; 2 - current source (transformer); 3 - neutral current source; 4 - grounding of the transformer case; 5 - zero working (it is also zero protective) wire of the network; 6 - zero protective wire of the electrical installation; 7 - fuse; 8 - electrical installation; 9 - re-grounding of the neutral protective wire of the network

In grounded electrical installations up to 1 kV with a solidly grounded neutral, in order to reliably ensure automatic shutdown of the emergency section, the conductivity of the phase and neutral protective conductors and their connections must provide a short-circuit current that is at least 3 times higher than the rated current of the fuse element of the nearest fuse or circuit breaker having release with a characteristic inversely dependent on current (thermal release), 1.4 times - for circuit breakers with electromagnetic releases with force rated current up to 100 A and 1.25 times - with a current value of more than 100 A.

IN zeroed in electrical installations up to 1 kV with a dead-earthed neutral (in order to reliably ensure automatic shutdown of the emergency section), the conductivity of the phase and neutral protective conductors and their connections must provide a short circuit current.

Zero protective wire 5 network (Fig. 4) must ensure a reliable connection of electrical installations with the neutral source, therefore, all connections are welded. It is prohibited to install fuses and switches in it (except for the case of simultaneous disconnection and phase wires).

Zero protective the wire 5 networks ground: at the current source with the help of a ground electrode 1; at the ends of overhead lines (or branches from them) longer than 200 m; as well as on the inputs overhead line to electrical installations. Re-grounding 9 necessary to reduce the risk of electric shock in the event of a break in the neutral wire and a phase short circuit on the body of the electrical installation behind the break, as well as to reduce the voltage on the body at the time the current protection is triggered.

According to the PUEgrounding device resistance, to which the neutral of the current source is connected, taking into account natural and repeated grounding conductors of the neutral wire should be no more 2, 4 and 8 ohm respectively, at linear voltages of a three-phase current source 660, 380 and 220 V.

Total resistance spreading of ground electrodes (including natural ones) of all repeated grounding PEN conductor of each overhead line at any time of the year should be no more than 5, 10 and 20 Ohm respectively at line voltages 660, 380 and 220 V three-phase current supply or380, 220 and 127 V single-phase current source. Wherein ground electrode spreading resistance each of the repeated groundings should be no more than 15, 30 and 60 ohms, respectively, at the same voltages.

With earth resistivity ρ O > 100 Ohm∙m it is allowed to increase the indicated norms by 0.01 ρ O times, but not more than ten times.

Zeroing (grounding) of metal cases of portable electrical installations is carried out by the third core for single-phase or the fourth core for three-phase electrical receivers, located in the same sheath with phase wires.

The conductors of these wires must be flexible, copper, their section must be equal to the cross section of the phase conductors and be at least 1.5mm 2 .

Plug-in connectors (plugs and sockets) must be designed so that the connection of the grounding and zero protective conductors occurs before the connection of the phase conductors, and the disconnection occurs in the reverse order. This is usually achieved by using a longer prong on the plug for the protective conductor than for the phase conductors. In all cases, the plug is connected to the electrical receiver, the socket - to the network.

Individual protection meansfrom electric shock

Individual protection means from electric shock - electrical protective environmentsstva (EZS), which are divided into basic and additional.

Basic EZS- these are means of protection, the insulation of which can withstand the operating voltage of electrical installations for a long time, which allows them to touch live parts that are energized with their help.

For work on electrical installations up to 1000 V These include: insulating rods, insulating and electrical pliers, dielectric gloves,fitting and assembly tool with insulated handles, voltage indicators.

At the voltage of the electrical installation over 1000 V fixed assets include insulating pantsgi, insulating and electrical clamps, pointers toyarn.

Additional EZS- these are means of protection, the insulation of which cannot withstand the operating voltage of electrical installations for a long time. They are used to protect against touch and step voltage, and when working under voltage, only with the main EZS.

These include: voltage before 1000 V - dielectric galoshes, mats, insulating underrates; over 1000 V - dielectric gloves, boots, kovricks, insulating pads.EZS must be marked with the voltage for which they are designed, their insulating properties are subject to periodic verification within the time limits established by the standards.

The test dates for protective equipment against electric shock are presented in Table 2.

table 2

Terms of testing protective equipment against electric shock (fragment)

Grounding the electrical installation- intentional electrical connection of its body with a grounding device.

Grounding electrical installations is of two types: protective earth And nulling, which have the same purpose - to protect a person
from electric shock if he touched the body of the electrical installation or its other parts that were energized.

Protective earth- intentional electrical connection of a part of an electrical installation with a grounding device in order to ensure electrical safety. Designed to protect a person from touching the body of the electrical installation or its other parts that are energized. The lower the resistance of the grounding device, the better. To take advantage of grounding, you need to buy sockets with a grounding contact.

In the event of an insulation breakdown between the phase and the body of the electrical installation, its body may be energized. If a person touched the case at that time, the current passing through the person is not dangerous, because its main part will flow through the protective ground, which has a very low resistance. Protective grounding consists of a grounding conductor and grounding conductors.

Eat two types of grounding – natural And artificial.

Natural grounding conductors include metal structures of buildings that are securely connected to the ground.

Used as artificial grounding steel pipes, rods or angle, not less than 2.5 m long, hammered into the ground and connected to each other with steel strips or welded wire. As grounding conductors connecting the ground electrode with grounding devices, steel or copper tires are usually used, which are either welded to the machine bodies or connected to them with bolts. Protective grounding is subject to metal cases electrical machines, transformers, shields, cabinets.

Protective grounding significantly reduces the voltage that a person can get under. This is due to the fact that the ground conductors, the ground electrode itself and the ground have some resistance. If the insulation is damaged, the fault current flows through the body of the electrical installation, the ground electrode and further along the ground to the neutral of the transformer, causing a voltage drop across their resistance, which, although less than 220 V, can be felt by a person. To reduce this voltage, it is necessary to take measures to reduce the resistance of the grounding conductor relative to the ground, for example, to increase the number of artificial grounding conductors.

Zeroing- deliberate electrical connection of parts of an electrical installation that are not normally energized with a deadly grounded neutral with a neutral wire. This leads to the fact that the short circuit of any of the phases on the body of the electrical installation turns into a short circuit of this phase with a neutral wire. The current in this case is much greater than when using a protective earth. Quick and complete shutdown of damaged equipment is the main purpose of zeroing.

Distinguish zero working conductor And zero protective conductor.

The zero working conductor is used to power electrical installations and has the same insulation as other wires and a sufficient cross section for the passage of the working current.

Zero protective conductor is used to create a short-term short-circuit current for protection operation and quick disconnection
damaged electrical installation from the mains. As a neutral protective wire, steel pipes of electrical wiring and neutral wires without fuses and switches.

Grounding system symbols

Grounding systems differ in connection schemes and the number of zero working and protective conductors.

The first letter in the designation of the grounding system determines the nature of the grounding of the power source:

T - direct connection of the neutral of the power supply to the ground.

I - all current-carrying parts are isolated from the ground.

The second letter in the designation of the grounding system determines the nature of the grounding of the open conductive parts of the electrical installation of the building:

T - direct connection of the open conductive parts of the electrical installation of the building with the ground, regardless of the nature of the connection between the power source and the ground.

N - direct connection of the open conductive parts of the electrical installation of the building with the grounding point of the power source.

The letters following through the dash behind N determine the method of constructing the zero protective and zero working conductors:
C - the functions of the zero protective and zero working conductors are provided by one common PEN conductor.
S - functions of zero protective PE and zero working N conductors are provided by separate conductors.

Basic grounding systems

The TN-C system includes three-phase four-wire (three phase conductors and a PEN-conductor that combines the functions of zero working and zero protective conductors) and single-phase two-wire (phase and zero working conductors) networks of old buildings. This system is simple and cheap, but it does not provide the necessary level of electrical safety.

Currently application TN-C systems on newly built and reconstructed facilities is not allowed. When operating the TN-C system in
an old building intended to house computer equipment and telecommunications, it is necessary to ensure the transition from the TN-C system to the TN-S (TN-C-S) system.

The TN-C-S system is typical for reconstructed networks in which the zero working and protective conductors are combined only in part of the circuit, during input device electrical installations (for example, an introductory apartment shield). In the input device of the electrical installation, the combined zero protective and working conductor PEN is divided into a zero protective conductor PE and a zero working conductor N. At the same time, the zero protective conductor PE is connected to all open conductive parts of the electrical installation. The TN-C-S system is promising for our country, it allows to provide high level electrical safety at a relatively low cost.

In the TN-S system, the zero working and zero protective conductors are laid separately. A five-wire cable comes from the substation. All open conductive parts of the electrical installation are connected by a separate neutral protective conductor PE. Such a circuit eliminates reverse currents in the PE conductor, which reduces the risk of electromagnetic interference. good option to minimize interference is an attached transformer substation(TP), which allows to ensure the minimum length of the conductor from the input of power supply cables to the main grounding clamp. The TN-S system, in the presence of an attached substation, does not require re-grounding, since this substation has a main grounding conductor. This system is widespread in Europe.

4. TT grounding system

In the TT system, the transformer substation has a direct connection of current-carrying parts to the ground. All open conductive parts of the electrical installation of the building have a direct connection to the ground through a grounding conductor, electrically independent of the neutral grounding conductor of the transformer substation.

5. IT grounding system

In an IT system, the neutral of the power supply is isolated from earth, or earthed through high impedance appliances or devices, and exposed conductive parts are earthed. Leakage current to chassis or ground will be low and will not affect the operating conditions of the connected equipment. Such a system is used, as a rule, in electrical installations of buildings, which are subject to increased safety requirements.

Loop grounding scheme

1. Grounding
2. Ground conductors
3. Grounded equipment
4. Industrial building.

An example of a house grounding scheme

1. Water heater
2. Lightning protection grounding
3. Metal pipes
plumbing, sewerage, gas
4. Main ground bus

5. Natural grounding(building foundation reinforcement)

Measures to protect against electric shock

Used to protect people from electric shock protective equipment- rubber gloves, tools with insulated handles,
rubber boots, rubber mats, warning posters.

Wire insulation monitoring

To prevent accidents from electric shock, it is necessary to control the condition of the insulation of the wires of electrical installations. The condition of the wire insulation is checked in new installations, after reconstruction, modernization, a long break in work.
Preventive control of wire insulation is carried out at least 1 time in 3 years. The insulation resistance of wires is measured with megohmmeters on Rated voltage 1000 V in the areas with the fuse-links removed and with the current collectors switched off between each phase wire and neutral working wire and between every two wires. The insulation resistance must be at least 0.5 Mohm.