Grounding of electrical installations and their protective effect. Grounding and grounding: let's figure out the difference. How to distinguish between working zero and protective grounding

Any electrical installation must be grounded. This requirement of the Electrical Installation Rules (PUE) equally applies to electrical appliances with metal and plastic casings, connection and switching devices: distribution and input panels, sockets, switches.

Why is grounding necessary?

If the energy supply in the room is organized in accordance with the PUE, circuit breakers are installed at the entrance, in the distribution panel.

These switches are triggered when the set current strength is exceeded: the bimetallic plate heats up, it deforms, and the contacts of the machine mechanically open.

Important! It is for this purpose that the machines are installed in the phase conductor gap. The zero bus can be connected directly.

When a live circuit breaks, the electrical installation (or the entire circuit) is de-energized, ensuring safety. How does this work in practice, and what is grounding in this chain?

Grounding is an electrical contact between a line specially allocated in the electrical network and the real (physical) ground. That is, the grounding bus has electrical contact with the ground. At the same time, any installation generating or distributing electricity, connected by a neutral wire to the same ground.

We are considering single-phase networks, in which two lines are used for power supply: zero and phase. Three-phase systems They are rarely used in everyday life, so knowledge of these systems is necessary only for professionals.

Even if three phases are installed in your house (this occurs in the private sector), for final consumption two wires are still used: zero and phase.

Let's say your electrical installation (refrigerator, boiler, washing machine), especially with metal body, a phase leak has occurred. That is, the live wire touches the housing (the contact is disconnected, the insulation is broken, water leaks). If you touch an electrical appliance, you will receive an electric shock. In addition, the resistance at the point of contact is negligible, as a result of which the wire will instantly heat up and the electrical appliance will ignite.

If your boiler is grounded, the electric current will flow along the path of least resistance, that is, along the circuit: phase - “ground” - zero bus. The current will spontaneously increase and an emergency shutdown will be triggered in the circuit breaker. No one will get hurt, no material damage will be caused.

If you have a superficial knowledge of electrical installations, the question arises: why do you need grounding if the same thing happens between the phase and neutral wires? And actually, what is the difference between grounding and grounding?

Let's analyze the situation with diagrams

From the point of view of the flow of electric current, there is no difference between grounding and grounding. The neutral wire in any case has electrical contact with physical ground.

Accordingly, when a phase is shorted to the housing, the same thing will happen short circuit, and the circuit breaker will turn off. Of course (provided correct connection: The socket must have a third ground contact, just like an electrical appliance. For this reason, electricians, violating the requirements of the Electrical Installation Rules, often disconnect the earth bus from the neutral contact of the input panel.

Let's imagine a situation where the neutral wire is broken for some reason:

• loss of contact due to corrosion (in old high-rise buildings this is a working situation);
• mechanical cable break due to repair work with violations of technology (unfortunately, also not uncommon);
• unauthorized intervention by a home-grown “electrician”;
• accident at the substation (only the zero bus may be disconnected).

In the diagram it looks like this:

When organizing protective zeroing, the electrical circuit between the physical ground and the grounding contact of the electrical appliance is broken. The installation becomes defenseless. In addition, a free phase without a load can create a potential equal to the input voltage at the nearest substation. Typically this is 600 volts. You can imagine the damage that will be caused to the electrical equipment that is turned on at this moment. In this case, there is no current leakage to the physical ground, and the circuit breaker will not trip.

Imagine that at this moment, you simultaneously touch a phase (breakdown on the electrical installation body), and metal object having a physical connection with the ground (water tap or radiator). You can get electrocuted at 600 volts.

Now let's see what the difference is between grounding and neutralizing (in our diagram). If the zero bus breaks, the power to all electrical installations in this circuit will simply disappear. There will be no electric shock under any circumstances: the electrical circuit between the physical ground and the grounding contact of electrical appliances is not broken. We have already preserved our health. Now let's see what happens to electrical installations. The maximum damage is a burnt-out incandescent lamp closest to the input panel. Moreover, trouble will only occur if the voltage on the phase wire increases. The current strength will increase (according to Ohm's law), the circuit breaker will work, and perhaps other electrical appliances will not be affected.

It is for this reason that the PUE strictly prescribes: protective grounding and grounding of electrical installations must be organized independently of each other, using different lines.

For reference: Commonly used color coding wires:

1. The phase is brown or white.
2. The working zero is blue.
3. Protective grounding - yellow-green shell.

If you have a house of modern construction, then grounding and grounding are carried out in accordance with the Electrical Installation Rules. This can be easily verified by looking at input cable in the shield. In addition, you can check the correct connection yourself.

How to distinguish between working zero and protective grounding

Of course, you should not check the resistance between the “neutral” and “ground” wires, especially if the power system is energized. No one will let you into the common control room either. Therefore, we will check the correctness of the separation of zero and ground using a multimeter (household tester).

Since the input points of grounding devices (zero at the substation and the grounding bus in the house) are located at a distance from each other, there is a certain resistance between them. The soil, even wet, is not an ideal conductor. If you organize electrical circuit without load, we will see the difference in potentials.

Connecting measuring device to the phase contact and working zero. In the diagram this will be circuit “A”. We fix the value.

We immediately connect the tester to the phase wire and the protective zero contact. In the diagram this is circuit “B”. There is no difference in potential: the device will record same value voltage. Why did it happen? When the working and protective zeros are combined, the current in both measurement options actually flows through the same wire. The resistance does not change, there are no losses, and there is no voltage drop.

If your measurement results show the same voltage, the wiring is connected in violation of the Electrical Installation Rules.

What happens when the working field and protective grounding are separated?

When the device is connected to phase and zero, there is practically no voltage drop (in the diagram this is circuit “A”). You will see the actual value of the operating voltage in the network. By connecting the tester to the phase wire and protective ground, you measure the potential in a long circuit. To complete the circle, an electric current (circuit “B” in the diagram) passes through the real ground between the physical contact points of the “ground”. Considering the soil resistance, a voltage drop of 5% to 10% will occur. The device will show a lower voltage.

This indicates that your electrical wiring is organized correctly, you have a true distributed protective ground. With properly selected machines, electrical equipment and users are reliably protected.

We figured out what the difference is between grounding and neutralizing. Benefit from proper organization power supply is obvious.

But what if your house does not have protective grounding at all?

It is clear that when carrying out major repairs, electricians will replace the wiring in accordance with the Electrical Installation Rules. At a minimum, three independent wires will appear in your input panel: phase, working zero and protective ground. All that remains is to replace the wiring in the outlet network.

But major renovation can be completed in a few years, but today you are already using a boiler and washing machine without grounding, or even worse - with a protective grounding. There is only one way out: organize grounding yourself. If you live in a private house, the technical side of the issue is significantly simplified. But for high-rise buildings, the cost and complexity of the work depends on the floor.

An alternative is to organize a grounding bus with your neighbors, with junction boxes on each stairwell.

The tire must be one-piece until it is inserted into the ground. Near the foundation, preferably not in the road surface, but in a flower bed, a grounding loop is organized in accordance with the Electrical Installation Rules. Each resident of the entrance can connect to the common bus and bring “ground” into the apartment. Then there are two options:

1. Organize a grounding contact group in the distribution panel, and replace all electrical wiring with three-wire wiring.
2. Inside the baseboard, stretch the earth cable under each socket and insert it into the mounting boxes.

Either way, you will protect both your electrical appliances and, most importantly, your health.

Important! How not to organize protective grounding

The fact that “land” cannot be taken from the working field is clear from our material. There are people who like to ground themselves on water supply or heating pipes. In theory - steel pipe has a connection with the ground. In practice, there may be inserts along the riser from polypropylene pipes, and there is no contact with the “real earth”.

In addition to the fact that you do not receive reliable grounding, your neighbors are at risk, who can receive an electric shock simply by holding the radiator.

Video on the topic

What is the difference between grounding and grounding? Experts have sorted out this issue. All these are protective measures against peak currents. They provide for work to prevent electrical damage to people and household appliances. The names are different, but all of these are protection systems.

To understand the difference between grounding and zeroing, you need to know the purpose and operating principle of electrical devices.

Operating principle

The grounding circuit of an electrical circuit is a system of wires that connects each consumer in the serviced circuit with a special grounding circuit of the building. In the event of a breakdown on the device body or current leakage from damaged wiring, the current flows through the wires to the ground electrode.

The grounding resistance is usually less than the resistance of the entire circuit. Therefore, the current flows along the “easy” path and is removed from the equipment housings.

Grounding is the electrical connection of conductive housings of devices with a solidly grounded neutral. When peak current values ​​occur, its potential is diverted, using a grounding bus, to a special switchboard or transformer booth. Its main purpose is in cases of breakdowns and voltage leaks on the equipment body, causing a short circuit, blowing fuses or tripping automatic circuit breakers.

This is the main difference between grounding and grounding. The grounding circuit absorbs short-circuit currents; grounding causes the safety devices to operate.

Let us examine in more detail the operation of protection systems against the effects of electric current.

Features of the grounding device

The main purpose of the grounding loop is to reduce the potential during a breakdown to the housing and a short circuit to a safe value. At the same time, the voltage and current on the equipment body are reduced to a safe level. In production, the enclosures of electrical equipment, buildings and premises are grounded from the effects of atmospheric currents.

When installing a circuit, in a network of three phase current no more than 1000 V, an insulated neutral is used. At high network voltage levels, a system with different modes neutral.

is a whole system that includes:

• ground electrode;
• grounding horizontal conductors;
• supply wires.

The ground electrode is divided into artificial and natural.

If possible, a natural grounding conductor should be used:

• underground water supply pipelines. But in this case, it is necessary to equip the pipeline with protection against stray currents;
• connected to metal structures of workshops and premises;
• steel or copper braided cable;
• pipelines in the well.

According to the PUE standards, it is prohibited to connect the grounding loop to heating pipes and with flammable materials.

With artificial equipment, the grounded equipment is protected by making a circuit in the form of an equilateral triangle from metal pins or corners. For alkaline and acidic soil, it is recommended to use a copper, galvanized ground electrode. To make a contour in the form of a triangle, you need to go 70 cm deep into the ground.

Group grounding conductors must not be installed in drilled holes. They must be driven in at the marking site to a depth of at least 2 meters. Then, the grounding conductors are connected into a single structure using sections of steel strip.

The housing of each device must be connected to the protection system. At the same time, several consumers cannot be connected in series; each device must be equipped with a connection line.

Now about the main thing - the value of the circuit resistance level. It sums up the resistance of each device in the circuit and its wires. When calculating the circuit resistance, you should take into account the level of the soil value, the size and depth of the grounding conductors. It is necessary to take into account the temperature characteristics of the region where the circuit is installed.

Remember - in hot weather, the installation site should be filled with water; the soil changes its resistance level as it dries.

When servicing networks up to 1000 V and equipment power over 100 kVA, the circuit resistance is no more than 10 Ohms. IN household networks optimal value will be 4 ohms. The touch voltage should be less than 40 V. Networks over 1000 V are protected by a device with a resistance of no more than 1 Ohm.

These are some of the features and operating principle of grounding. For more details, you can read the articles on this topic on the website.

Features and operating principle of zeroing

Purpose of grounding - the protective device method allows you to connect equipment housings and other metal parts with a neutral (neutral protective conductor). In conditions with a grounded protective conductor and a network voltage of no more than 1000 V, a grounding circuit is used.

When a phase current breaks down on the housing of electrical appliances and equipment, a phase short circuit occurs. At the same time, the circuit breakers are activated and the circuit is opened. This is the difference between the two protective systems.

Zeroing devices include:

• fuse;
• automatic circuit breaker;
• built into starters, thermal relays;
• contactor with thermal protection.

A phase voltage breakdown situation has arisen. In this case, from the electrical installation housing, the current passes through the neutral to the transformer winding. Then, from it in phase - to the fuse. Fuses burn out from peak current values, and the voltage supply to the electrical circuit stops.

At the same time, the zero conducts current freely, allowing the protection to operate. It is laid in a safe place; it is prohibited to equip it with additional switches and other devices. The conductivity level of the phase wire must be half the value of the neutral conductor. As a rule, in this case, steel plates, cable sheaths and other materials are used.

Grounding conductors are checked for serviceability when completing work on connecting and wiring electricity in a building, as well as, after a certain amount of time, when using the electrical circuit. At least once every 5-year period, the resistance values ​​of the entire phase and neutral conductor circuit are measured on the housings of the furthest equipment from the electrical wiring panel, as well as the most powerful equipment in the room.

Protective grounding, in some cases, can perform the work of protective shutdown. At the same time, these 2 protective systems differ in that in the event of a protective shutdown of the circuit, it can be used in any conditions, with different modes of the grounding conductor and circuit voltage indicators. In such networks you can do without a zero connection wire.

Zeroing calculations must be made taking into account all operating conditions and the principle of its operation.

Protective shutdown is performed using a protective system that turns off electrical equipment automatically. In the event of emergency situations and threats of damage and electrical injury to a person, such situations include:

• short circuit of the phase wire to the housing;
• damage to electrical wiring insulation;
• faults on the grounding circuit;
• violation of the integrity of the grounding conductors.

This protective system is often used when it is impossible to install protective grounding and grounding systems. But in critical areas, it is possible to install a protective shutdown as an additional circuit to protect people and equipment from damage by leakage currents and short circuits.

At the same time, they are divided, depending on the magnitude of the input current and changes in the response of protective devices, into several circuits:

• presence of voltage on the equipment casing;
• current strength when shorted to the ground wire;
• voltage or current in the neutral conductor;
• voltage level in the phase relative to the value on the ground wire;
• devices for direct or alternating current;
• combined devices.

All protection systems and shutdown of current supply to the network are equipped with automatic circuit breakers. Their design provides for the installation of special protective shutdown equipment. In this case, the period of time for disconnecting the network should not exceed 2 tenths of a second.

In conclusion, let’s look at a question that a novice electrician might ask.

Interchangeability of protective systems

Is it possible to install grounding instead of grounding? Any specialist will answer “yes” to this question, but only in an industrial building.

In a residential area, such a protection scheme should be used in very rare cases, and only in non-residential premises. This is due, first of all, to the uneven load on the phase and neutral wires. During operation, the wires of each phase receive the same load, but a fairly small current passes through the neutral of the common circuit. Everyone knows that you cannot touch a phase, but you can do work with a zero under load.

At the same time, the section neutral wire less phase wire. With prolonged use, it oxidizes on the twists, the insulation layer is damaged when heated, in the worst case, it will simply burn off. At the same time, the phase voltage approaches the panel board, then, through the zero wire, it goes to the consumer. The housings of the devices are energized, increasing the possibility of electric shock to a person.

As some craftsmen on the Internet advise, you can connect grounding system wires to each household appliance, but this will entail significant costs for wiring and subsequent repairs. Therefore, it is impossible to nullify sources in residential premises.

It is better to install a residual current device in the electrical panel and use it calmly household appliances. Each protective device fulfills its purpose, with proper calculation, installation and use.

Protective grounding is intentional electrical connection with earth or its equivalent of metal non-current-carrying parts that may become live. It consists (Fig. 24.6) of a ground electrode 3 (metal conductors located in the ground with good contact with it) and a grounding conductor 2, connecting the metal casing of the electrical installation 1 with ground electrode.

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

The protective effect of the grounding device is based on reducing to a safe value the current passing through a person at the moment he touches a damaged electrical installation. When voltage comes into contact with the body of an electrical installation, a person touches it and has good contact with ground, completes an electrical circuit: phase WITH – electrical installation housing 1 – man – earth – capacitive X A , X B ) and active R A , R B connection resistance of wires to ground, phases A And IN. A current will flow through the person. Although electric wires The networks are installed on insulated supports and there is an electrical connection between them and the ground. It occurs due to imperfect insulation of wires, supports, etc. and the presence of capacitance between the wires and the ground. With a long distance of wires, this connection becomes significant, and its active R and capacitive X resistance decreases and becomes commensurate with the resistance of the human body. That is why, despite the absence of a visible connection, a person who is energized and in contact with the ground completes an electrical circuit between the different phases of the network.

Rice. 24.6. Protective grounding circuit (systemIT):

1 – electrical installation; 2 – grounding conductor; 3 – grounding conductor

In the presence of a grounding device, an additional circuit is formed: phase WITH – electrical installation housing – grounding device – ground – resistance X A , R A , X B , R B – phases A and B. As a result, the fault current is distributed between the grounding device and the person. Since the resistance of the ground electrode (it should not exceed 10 Ohms) is many times less than the human resistance (1000 Ohms), a small current will pass through the human body without causing damage. The main part of the current will flow through the circuit through the ground electrode.

Grounding electrodes can be natural and artificial. As natural grounding agents use metal constructions and fittings of buildings and structures having good connection with the ground, water supply, sewer and other pipelines laid in the ground (except for pipelines of flammable liquids, flammable and explosive gases and pipelines coated with insulation to protect against corrosion).

As artificial grounding conductors use single or grouped metal electrodes 2.5-3.0 m long, driven vertically into the ground at a distance of 2.5-3.0 m from each other or laid horizontally in the ground. Electrodes are made from sections of metal pipes, angle steel, channels with a wall thickness of at least 4 mm. Thinner profiles quickly fail due to corrosion.

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

To carry out grounding functions, the resistance of the grounding device in electrical installations with voltages up to 1000 V in a network with an isolated neutral must be no more than 4 Ohms. When the power of generators and transformers supplying the network is 100 kVA or less, the resistance of the grounding conductors is allowed to be no more than 10 Ohms. The required resistance is achieved by installing the appropriate number of electrodes in the ground electrode, determined by calculation. For clayey wet soils Usually two or three electrodes are enough; in dry sandy or rocky areas this may not be enough.

The resistance of a grounding device is the ratio of the voltage across the grounding device to the current flowing from the grounding device into the ground.

There are remote and loop grounding devices. The remote device is located outside the site with the grounded equipment. Its advantage is the ability to select soil with the lowest resistivity. Loop grounding is performed by driving electrodes along the contour of the grounded equipment and between it. This installation of electrodes creates an additional protective effect by increasing and leveling (more uniform distribution) of the earth potentials in the area where a person is located.

Zeroing- this is an intentional electrical connection of metal non-current-carrying parts of electrical installations that may be energized with a solidly grounded neutral of a current source (generator or transformer).

In four-wire or five-wire networks with a neutral wire and a solidly grounded neutral of a current source with a voltage of up to 1000 V (the so-called system TN) grounding is the main means of protection. Grounding in such networks is ineffective.

Connection of electrical installation housings to the neutral of the current source is carried out using a neutral protective conductor ( RE- conductor). It should not be confused with the neutral working wire (N-conductor), which is also connected to the source neutral, but serves to power single-phase electrical installations. Neutral protective conductor RE laid along the route phase wires, in close proximity to them. A system where there is a neutral working wire N and neutral protective conductor RE, and they are separated along the entire route, they call TN-S system. Letter S means the separation of the specified conductors along their entire length.

As a neutral protective conductor in networks up to 1000 V, it is first of all recommended to use a neutral working conductor (except for specially specified cases), to which the housings of electrical installations are connected. In this case, it is called a combined neutral protective and neutral working conductor (PEN conductor), and the system itself is called TN-C system. This is the system TN , in which the neutral protective and neutral working conductors are combined in one conductor along its entire length (Fig. 24.7).

If the functions of the neutral protective and neutral working conductors are combined in one conductor only in some part of it, starting from the power source, and then they go separately (the first of them serves to protect electrical installations, and the second - to power single-phase electrical installations), then such a system is called TN-C-S system.

According to PUE requirements it is no longer possible to combine these separated conductors again.

Rice. 24.7. Zeroing circuit (systemTN-C ):

1 – transformer neutral grounding conductor; 2 – current source (transformer); 3 – neutral of the current source; 4 – grounding of the transformer housing; 5 – zero working (also zero protective) wire of the network; 6" – neutral protective conductor of the electrical installation; 7 – fuse; 8 – electrical installation; 9 – re-grounding of the neutral protective wire of the network; L 2, L 3 – phase wires; PEN – neutral working conductor and neutral protective conductor, combined in one

According to the PUE, it is not allowed to be used as RE conductors:

• metal shells insulating tubes and tubular wires, supporting cables for cable wiring, metal hoses, as well as lead sheaths of wires and cables;
• gas supply pipelines and other pipelines of flammable and explosive substances and mixtures, sewerage pipes and central heating;
• water pipes with insulating inserts.

The protective effect of grounding is based on reducing to a safe value the current passing through a person at the moment he touches a damaged electrical installation, and the subsequent disconnection of this installation from the network. Zeroing works as follows. When voltage comes into contact with the body of a neutralized electrical installation 8 (Fig. 24.7) most of the current from it will go into the network through the neutral protective wire 6. Through the human body along a circuit: electrical installation housing 8 – man - earth - grounding device 9 – the neutral working wire 5 will carry a small current that will not damage it (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 of the network, as a result of which, after 0.2–7 s, the current protection is triggered (fuse 7 blows, the circuit breaker turns off, etc.) .p.) and the electrical installation, and with it the person, are completely de-energized. Thus, at the initial moment, grounding 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, since the resistance of the neutral conductor usually does not exceed 0.3 Ohms, and the permissible resistance of the grounding conductor is 4 Ohms.

In electrical installations up to 1 kV with a solidly grounded neutral for the purpose of reliable provision automatic shutdown emergency section conductivity of phase and neutral protective conductors and their connections must provide a short circuit current of at least three times the rated current of the fuse element of the nearest fuse or circuit breaker having a release with an inverse current characteristic (thermal release), 1.4 times – for circuit breakers with electromagnetic releases with a rated current of up to 100 A and 1.25 times - with a current of more than 100 A.

The neutral protective conductor 5 of the network must ensure a reliable connection of electrical installation housings with the source neutral. Therefore, all connections are welded. It is prohibited to install fuses and switches in it (except for the case of simultaneous disconnection of phase wires).

The neutral protective wire 5 of the network is grounded: at the current source using a ground electrode 1; at the ends of overhead lines (or branches from them) longer than 200 m; at the inputs overhead line to electrical installations. Repeated groundings 9 necessary to reduce the risk of electric shock when the neutral wire breaks and a phase is shorted to the electrical installation body beyond the break point, as well as to reduce the voltage on the body at the moment of operation current protection. According to the PUE, the resistance of the grounding device to which the neutral of the current source is connected, taking into account the natural and repeated grounding of the neutral wire, should be no more than 2, 4 and 8 Ohms, respectively, at line voltages of the source three-phase current 660, 380 and 220 V. The resistance of each repeated grounding switch separately should be no more than 15, 30 and 60 Ohms, respectively, at the same voltages.

In a network where grounding is used, the housings of electrical installations cannot be grounded without grounding them, since in the event of a phase short circuit to the body of a grounded but not neutralized electrical installation, the iodine voltage will be on all the housings of other neutralized electrical installations. At the same time, additional grounding of neutralized electrical installations is very useful. It increases the reliability of grounding the neutral wire.

If there are several electrical installations in the room, then each of them is grounded or grounded by connecting to a grounding (grounding) line, which is a metal conductor with a cross-section of at least 100 mm2 (for example, a steel strip 40 x 4 mm), reinforced along the perimeter of the room. The main line is connected to a grounding conductor, or to a neutral protective conductor (depending on the adopted protection system), or to both at the same time.

Sequential grounding or grounding of electrical installations (one from the other) is not permitted (Fig. 24.8).

Grounding electrodes are connected to the grounding main line by at least two conductors, connecting them to the grounding electrode in different places.

The connection of grounding conductors to the grounding conductor and grounding structures is carried out by welding, and to the main grounding clamp, housings of devices, machines and power line supports - bolted connection(to ensure the possibility of making measurements) with measures taken against weakening of the contact and its corrosion.

Rice. 24.8.

1, 4, 5 And 6 – correct zeroing of the electrical installation; 2 And 3 – incorrect zeroing of the electrical installation; 7 – grounding line (grounding)

To provide reliable protection The cross-sections of all protective conductors (PE conductors) must be no less than those given in table. 24.3, provided they are made from the same materials as the phase conductors.

Table 24.3

Smallest cross-sectional areas of protective conductors RE

The cross-section of the PEN conductor must be at least 10 mm2 for copper or 16 mm2 for aluminum.

The dimensions of grounding conductors and grounding conductors laid in the ground are given in table. 24.4.

Grounding or grounding of electrical installations should be carried out when rated voltage:

• above 50 V AC or above 120 V DC - in all electrical installations, regardless of where they are operated;
• above 25 V AC or above 60 V DC – in hazardous areas;
• above 12 V AC or above 30 V DC - in particularly hazardous areas and in outdoor installations;
• at any AC and DC voltage - in explosive areas of any class.

Parts subject to grounding or grounding include: housings electric machines(including technological equipment with power supply), housings of transformers, lamps, frames of distribution boards, switches, control panels, metal shells and armor electrical cables; metal pipes in which electrical wiring is laid; metal cases of mobile and portable electrical receivers, etc. (in accordance with the requirements of the PUE).

Grounding (grounding ) metal casings of portable electrical installations carry out an additional core cable (conductor PEN in system TN-C in a system where the zero working and zero protective conductors are combined in one PEN- conductor): the third conductor for single-phase and the fourth – for three-phase electrical receivers.

If a system with separated zero workers is used ( N ) and a protective zero (RE) conductors (system TN-S), then the power cable should already have two additional cores: (N) And (RE). The same should be in the connecting plug and in the socket. The cores of these wires must be flexible, copper, their cross-section must be equal to the cross-section of the phase conductors and be at least 1.5 mm2.

Plug-in connectors (plugs and sockets) must be made in such a way that the connection of the 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. (RE or PEN), than for phase wires (Fig. 24.9 and 24.10).

If the housing of the socket or plug is made of metal, then protective conductors are also connected to them (PEN or RE, depending on what protection system is used). In all cases, the plug is connected to the electrical receiver, the socket to the network.

Table 24.4

The smallest dimensions of grounding conductors and grounding conductors laid in the ground

To determine the technical condition of the grounding device, visual inspections of its visible part are carried out (at least once every 6 months by those responsible for electrical equipment), inspections with selective opening of the soil, and measurement of the parameters of the grounding device in accordance with the testing standards for electrical equipment.

Rice. 24.9. TN-C :

A - socket; b - fork

Rice. 24.10. Plug-in connector (connector) for connecting a portable electrical installation to electrical network grounding systems TN-S:

A - socket; b - fork

Inspections with selective opening of the soil are carried out in places most susceptible to corrosion, as well as near the grounding points of power transformer neutrals, connections of arresters and surge arresters at least once every 12 years. During the inspection, the condition of the contact connections, the presence of anti-corrosion coating, and the absence of breaks are assessed. The results of the inspections are entered into the passport of the grounding device in the established form.

When opening the soil, an instrumental assessment is made of the condition of the grounding conductors and the degree of corrosion of the contact connections. The grounding element is replaced if more than 50% of its cross-section is destroyed. The results of inspections are documented in reports.

When determining the technical condition of the grounding device, the following is carried out:

• measuring the resistance of the grounding device;
• measurement of touch voltage (in electrical installations, the grounding device of which is made in accordance with touch voltage standards);
• checking the presence of a circuit between the grounding device and the grounded elements, as well as the connections of natural grounding conductors with the grounding device;
• measurement of short circuit currents in electrical installations;
• checking the condition of blow-out fuses;
• measurement resistivity soil in the area of ​​the grounding device.

Even people are confused about the purpose and installation of these methods of protection against electric shock. professional electricians. This is not the case for everyone, but there are precedents. But a basic understanding of terms sometimes saves dozens of lives. Even if we are not talking about electric shock, but about the commissioning of a new private house. If the protection is performed incorrectly, the controlling organization will not allow voltage to be supplied to the input panel. And rightly so, no one wants to take responsibility for people’s lives. Today we will figure out what the terms and nullification mean, what is the difference between them, and when it is possible to use one or another method of protection.

In accordance with GOST 12.1.009–76:

• protective grounding- this is the intentional electrical connection to the ground or its equivalent of metallic non-current-carrying parts that may be energized;
• zeroing- this is an intentional electrical connection with a neutral protective conductor of metal non-current-carrying parts that may be energized.

GOST R 50571.2–94 “Electrical installations of buildings. Part 3. Main characteristics" provides a classification of grounding systems for electrical networks: IT, TT, TN-C, TN-C-S, TN-S.

According to the PUE, grounding is mandatory (if there is a circuit or the possibility of installing it). All metal enclosures that could hypothetically become energized must be grounded. If there is no possibility of grounding, protective grounding is carried out with the mandatory installation of residual current devices (RCDs) and automatic ones in the electrical input.

Of course, the language in which PUE and GOST are written can be difficult for a person without electrical engineering education, which means it is worth examining in detail what grounding and grounding are in ordinary language that is understandable to the common man.

What is grounding: how it works, the principle of operation and the advantages of such protection

The principle of grounding is to prevent the passage of electric current through the human body if, due to any circumstances, the body becomes energized. This can happen if the cable insulation is damaged. Let's look at an example. A core with damaged insulation is in contact with a metal casing. The housewife, while preparing food in the kitchen, touches something that is not grounded. This causes current to rush to the ground, using the human body as a conductor. The result can be very disastrous, even death.

Now let's look at why grounding is needed and how it works. The same example, but using protection. The most stringent grounding requirements apply. When taking measurements, the circuit resistance should be practically absent, which allows the current to flow freely into the ground along the bus. The laws of physics do not allow voltage to flow through the human body, which has its own resistance. Some have more, others have less, but its presence is not disputed. It turns out that the current flows along the path of least resistance, through the ground electrode. If an RCD is included in the circuit, it will detect a leak and turn off the power supply to the device.

What is grounding of electrical appliances: application possibilities

Protective grounding of electrical appliances is used if it is impossible to install grounding. This situation may arise if an apartment building was built in Soviet times. Such houses do not have their own outline, and it will not be possible to arrange one on your own.

Protective grounding is a system that performs a different job from grounding. If the second is designed to divert the voltage to the ground, eliminating the possibility of electric shock, then the first is carried out with the aim of creating (if the insulation breaks down and hits the housing) a short circuit. In this case, the automation is triggered and the electricity is turned off.

Important information! In modern apartment buildings and private sectors, installation of grounding is prohibited these days. This is dictated by the safety of residents. Automation can fail, which will lead to irreparable consequences.

Protective grounding requires correct installation. You should not think that it is enough to throw a jumper from the neutral contact inside to the ground one. This is strictly prohibited. Let's consider a situation when an already “burnt” zero is subjected to a short circuit load, and the machine has not yet had time to operate. The zero burns out, eliminating the short circuit, but the device remains energized. A person, hoping for the absence of electricity (after all, there is no light, the zero has burned out), moves towards the exit by touch and leans on the body, which is under voltage. The outcome is clear, isn't it?

Grounding and grounding: what is the difference

The difference between these systems is in the method of implementing protection. When installing protective grounding, the role of a voltage cut-off device in the event of emergency situation The RCD takes over, and if the RCD is installed to zero, the RCD becomes powerless; only the automatic device can operate. Why is this happening? The residual current device reacts only to current leaks, completely ignoring any overloads, including short circuits. If a grounding is installed and an RCD is included in the circuit without a circuit breaker, in the event of a short circuit the RCD does not operate, but simply burns out without disconnecting the voltage from the line.

What is the difference between grounding and grounding: generalization

Grounding differs from grounding in the method of protection and installation. Such systems contradict each other, which means installing a circuit that includes both options is unacceptable. Zeroing is installed only in apartment buildings that are not equipped with their own circuit. In other cases, such installation is prohibited. Now let's talk in more detail about the methods of its construction.

What is zeroing and how to arrange it correctly

The installation diagram looks like this: The neutral arriving at the input machine is bifurcated, each of the cores goes to a separate bus. One of the buses becomes zero, and the second becomes grounding. From the neutral bus, the conductors go through the automation and further to all zero contacts of the apartment's consumers. The grounding wire is connected to the body of the input panel, a yellow-green wire from it goes to the corresponding contacts of the sockets and that require it. Contact of the ground wire with the neutral wire after protective automation forbidden.

Important information! Improper installation of protective grounding leads to burnout of cable cores and a fire. Electric shock and even death are also possible.

The best protection option is a grounding device?

The only correct answer to this question is yes. This is true. , mounted according to all the rules, will protect a person much better than the previous version. You can improve your protection by using additional devices– circuit breakers, RCDs or automatic circuit breakers. After all, what is protective grounding? At its core, it is a system for discharging electric current in the event of an accident to a place where it cannot harm a person.

Regarding the grounding device, we can say that it can be different - a grounding loop around the perimeter of the building, a “triangle” in the yard, or a natural grounding device. We will definitely consider all the rules and methods of its installation in one of the upcoming topics. But for general information It makes sense to understand the definition of what is a natural grounding agent.

Good to know! As natural grounding You can use any metal structures located underground, with the exception of fuel and lubricants pipelines, sewage systems and objects coated with anti-corrosion compounds. Water pipes can be used for this purpose.

Any electrical installation consists of more than just electrical conductors. They are placed in housings and shells, covered with casings. Between the current-carrying parts, the housings in which they are located or on which they are located are placed insulating materials.

All insulators are susceptible to damage. At the same time, they lose their properties and begin to conduct electric current. The potential of the working parts of an electrical installation that are energized penetrates through the site of damage onto conductive housings and shells. When a person touches them, he receives a life-threatening electric shock.

Methods of protection against dangerous potentials

The situation with damage to the phase-to-phase insulation of electrical equipment is immediately stopped protective devices: circuit breakers or fuses. But it only indirectly poses a danger to humans.

More dangerous for people single-phase fault, as a result of which the housings of electric motors, electrical cabinets, cable structures are under tension.

To eliminate the risk of electric shock, it is necessary that when voltage comes into contact with the housing a guaranteed short circuit has occurred and the potential on the body was reduced as much as possible.

First protective effect is achieved by creating a circuit between the housing and the grounded neutral of the electrical installation. When a short circuit occurs, a current is generated that is large enough to trigger the same protective devices, operating under phase-to-phase faults. This is called protective shutdown.

To implement the second method, all potentially dangerous metal parts of electrical equipment are given ground potential. This is done by deliberately connecting them to a grounding device. The event is called protective grounding.

Grounding systems for electrical installations up to 1000 V received classification in the 7th edition of the PUE. Let's consider these systems in turn.

TN-C grounding system

There is nothing new in this design. She was like this for many years.

It uses 4 wires to power consumers. Three of them are phase, one is zero. The latter carries the operating load current. But it is also used for protective purposes, connecting to the neutral grounding circuit power transformer, powering electrical installations. Electrical equipment housings are also attached to it. It is called a PEN conductor. Due to the fact that it combines the functions of protection and transport of operating current to its destination, it is called a “combined conductor”.

As a result, both tasks are realized: the ground fault current is high - the damaged section is disconnected quite quickly. In addition, if damaged, the low resistance of the PEN conductor shunts the body of the person touching the body, which has a resistance of the order of a kilo-ohm. Most of current flows into the ground.

But the operating load current flows through the PEN conductor. As a result, contact connections may be disrupted, the connection may become unreliable or be interrupted altogether.

This eliminates the much-needed connection to the grounding device.

Even if there is re-grounding of the PEN conductor at the entrance to the building.

Moreover, the presence of current in this conductor leads to the emergence of a potential that increases with distance from the point of connection with the ground loop.

And if the PEN conductor breaks, the picture is completely terrifying. The potential on the housings behind the break point can theoretically reach 220 V.

Let's add to all this the technologically difficult implementation of connecting the housings of some electrical receivers with PEN. How to ground the body of an electric stove connected to the network through an outlet?

The development of household electrical appliances requiring the use of protective measures for electrical safety has led to improvements TN-C systems. You can read more in a separate article.

Grounding system TN-S

The difference from the previous considered grounding system is that the functions of the working-zero and protective conductor are separated in different physical conductors. Zero operating (N) - conducts the load current, zero protective (PE) - connects to the ground loop.

As a result, there is a complete elimination of potential on buildings that appear in “particularly remote areas” of the electrical network, as well as in the event of conductor breaks. The maximum that threatens in the absence of the integrity of the PE conductor is lack of protection. But it has little chance of breaking - no current flows through it, why would it suddenly get lost with everything completed? electrical rules contact connections?

Since the cross section of PE conductors in the composition cable lines usually turns out to be equal to the cross-section of the phase ones, the task of connecting them to the housings of any electrical equipment has been simplified.

Even to the grounding contact of the socket. Which made it possible to extend protective security measures to all household electrical appliances: on the same electric stove, in particular.

All newly installed electrical installations are now, as a rule, carried out using this grounding system.

Grounding system TN-C-S.

A significant problem when implementing the TN-S system is that the reconstruction of electrical installations and the construction of new ones often occurs without reconstruction of the transformer substation itself. Usually some part of it is redone, starting from the switchboard at the input to the last consumer. Before this shield, the grounding system inevitably retains old design.

This problem was solved in advance by the same paragraph of the PUE, which describes the transitional version of the grounding system, designated as TN-C-S. In it, the part of the electrical installation that was untouched by reconstruction does not officially change its structure, remaining the same TN-C. But from a certain point, the distribution network follows the new rules.

The point is to divide the PEN conductor into two: working and protective.

This is done in the input distribution device. It contains two distribution busbars: N and PE. The PEN conductor must be connected to the PE, and a jumper is mounted between the busbars themselves.

Why to RE?

If the jumper between the buses breaks (this cannot be excluded in any case), then with this connection method the zero operating bus will lose contact with the neutral of the electrical installation. In this case, serious consequences for electrical equipment are possible - but the connection to the protective bus will not be affected, people will remain safe.

Moreover, it is impossible not to notice this fact of the break. They will immediately run to look for him.

With the reverse switching scheme, a broken jumper will only be noticed during routine measurements of the integrity of the protective circuit. And during this time, people will be left without protection - the buildings will “hang in the air.” It would be nice if so.

A network of interconnected protective conductors left to its own devices is no less dangerous than a TN-C system if a PEN conductor breaks.

Power supplies for household equipment (computers or washing machines, for example) and semiconductor ballasts fluorescent lamps in the absence of a connection between their housings and a grounding device, a potential of about 110 V is supplied to them through the capacitors of the input noise filter of the power supply. It spreads throughout the network, appearing on other metal parts, connected to a PE conductor.

Do not forget that this system inherited its main disadvantages from TN-C: the potential on the PEN conductor and dangerous voltages on it if it breaks. Main method to combat them - its own re-grounding circuit, the output from which is connected to the PE bus of the input panel.

But there are other grounding systems that are used in private cases to protect people.

CT grounding system

In previous systems, all grounding devices are connected into a single circuit using PEN and/or PE conductors. In a TT system, the consumer has its own ground loop, not connected to the PEN conductor of the supply line. All its electrical equipment is connected to this circuit by PE conductors.

Thus, problems with a possible break in the power supply disappear PEN conductor. It is used as a zero worker and is in no way connected to the buildings.

Protection using fuses and circuit breakers for consumers only works to eliminate faults between phases, as well as between a phase and the neutral conductor.

A measure for protective shutdown is the mandatory installation of an RCD at the consumer.

The introduction of this grounding method has indications for use in long distance supply lines, when the increased resistance of the phase-zero loop does not allow protective shutdown at the specified time.

IT grounding system

And here there is no neutral conductor at all, since this system has an isolated neutral. Connecting the load is only possible at linear network voltages.

Nothing dangerous for the consumer occurs when damage to one phase occurs on the housing. The ground fault current is negligible and will not cause much harm to the body.

And to eliminate dangerous currents, all lines are protected by RCDs without fail.

But to detect ground faults in such networks, special elements are installed - leakage relays. When it is triggered, damage must be actively searched for. And if a second short circuit occurs, the damaged section of the network must be immediately disconnected.