Electricity has long been an integral part Everyday life each of us. People are so accustomed to this benefit that they sometimes forget about the dangers that may arise during the operation of electrical installations (household electrical appliances). On initial stage When designing the power supply of any facility, special attention is paid to safety. Almost all users of electrical appliances know what a bare wire, insulation, and grounding are. But the term “potential equalization” is familiar only to professional electricians. If we don't see external signs problems, a false sense of absence of danger arises. And this despite the fact that alternating voltage above 42 volts can be fatal to humans.

When can voltage or electric current pose a threat to health or life?

The presence of voltage (or potential) in itself does not pose any problem. The danger is electrical current. It occurs when there is a potential difference between the ends of the conductor.

It is important to know! The human body is a good conductor for electric current due to the presence of fluid in the cells.

What is potential difference

For example, let's take the usual AA battery. On its positive contact there is a potential of approximately 1.5 volts, on the negative one - 0 volts. If you connect measuring device(multimeter) with the positive terminal (using both leads), the value will be zero. And if we measure between “plus” and “minus”, we will see a voltage of 1.5 volts on the device.

Why is this happening? There is a potential difference of 1.5 volts between the positive and negative contacts. Accordingly, if you connect these terminals with a conductor (electrical circuit, metal wire, etc.), electric current will flow between them.

How does this work using electrical appliances as an example?

Let's take a 220 volt household outlet. At the phase contact there is a potential of 220 V, at the zero contact - 0 V. Between them there is a potential difference of 220 volts. If you connect the contacts with a piece of wire with low resistance (conventionally 1 Ohm), then an electric current of 220 amperes will arise in the conductor (according to Ohm’s law). Of course, in practice this cannot be done; the wire will instantly melt and the insulation will catch fire.

If a person grabs two contacts, then despite the high resistance of the body, the current strength will be enough to cause a fatal outcome.

All devices that produce electricity have a zero contact connection to the “ground”: literally to the physical ground. This means that between any phase wire and the physical ground there is always a potential difference equal to the phase voltage.

The same thing happens in indoor conditions (residential, industrial, etc.). A phase can be supplied to the body of the electrical appliance. This can occur in an emergency: damage to the insulation, moisture entering the contact group, or a malfunction of the power supply. If you simultaneously touch a live enclosure and an element of the premises' infrastructure that is electrically connected to physical ground (for example, a pipeline), there is a risk of electric shock.

If the electrical appliance is properly grounded, the phase on the housing is connected to the ground: a short circuit occurs and the circuit breaker disconnects the circuit. Defeats electric shock not happening.

This is an ideal situation when the premises comply with the standards of the Electrical Installation Rules (PUE).

In practice the situation may be different

Let’s say your neighbor next door connected the neutral wire to the heating system (we won’t consider the reasons: from simple illiteracy to the desire to rewind the electricity meter). On metal pipes dangerous potential arises: from 50 to 220 volts. Theoretically, the voltage should “go into the ground”, since the steel pipes are laid in the ground. However, if a section of the pipeline is replaced with plastic between your apartment and the basement, the conductor opens. And your bathroom heated towel rail has a potential of, say: 170 volts.

You touch a metal pipe and a grounded washing machine. The same potential difference arises (with a life-threatening voltage), only the source of the problem is not your electrical appliance, but the energized heated towel rail pipe.

As can be seen from the illustration, protective grounding does not work in this case.

Let's consider another option:

There's a line in your wall power wire, next to which it passes water pipe. Under load (for example, the boiler is on or electric oven), EMF (electromotive force) can be induced in the pipe. The water will receive an unwanted potential, up to 50 volts. This may not be a fatal voltage, but when you touch the faucet in the kitchen, you will feel an unpleasant tingling sensation of electric current. Especially if the floor screed contains steel reinforcement, which according to damp walls premises has contact with physical soil.

In this case, the working ground also does not work.

Reasons for the appearance of electrical potential differences

In addition to obvious conditions, such as breakdown of insulation on the body of an electrical installation, or unauthorized connection to structural elements, there are hidden factors:

• Static voltage. Occurs due to friction (for example, the movement of water in a plastic pipe), dry air, dusty rooms.
• Electrochemical potential accumulation that occurs during the interaction of dissimilar metals.
• Atmospheric phenomena (thunderstorm, strong wind) contribute to the accumulation of electrical potential.
• Stray and induced currents, electromagnetic radiation (microwave ovens, switching power supplies, monitors, TVs).

How to protect yourself from similar situations? The electrical installation rules (PUE) provide for a potential equalization system.

Leveling and Leveling

Let's look at the basic concepts and terms:

• Potential equalization- leveling the difference in electrical potential values ​​between metal elements of an electrical installation in the room where the electrical installation is located, including conductive elements of the building. In this case, a situation is considered dangerous when it becomes possible for a person to simultaneously touch conductive parts. It is achieved by non-disconnecting connection of all current-carrying parts to each other using conductors.
• Potential equalization is a system for reducing the relative difference in electrical potential between grounding, accessible conductive parts of electrical installations, the surface of the earth and all metal structures of the building. To do this, the potential equalization system must have an unbreakable connection with the working (protective) grounding conductor.

In addition, potential equalization includes reducing the electrical potential difference on the ground surface (floor, ceilings) to prevent the effect of step voltage.

What does the term "unbreakable" mean? All conductive lines are permanently connected to each other (contact blocks, screw connections, soldering, welding, etc.). It is not allowed to install disconnecting devices: fuses, switches, circuit breakers. That is, the entire potential equalization system is a single conductive circuit combined with a similar circuit protective grounding.

Thanks to these systems, in all points that a person can simultaneously touch, the electrical potential is equalized to same value. The situation when, when touching at the same time, the voltage will be 220 volts at one point and 10 volts at another, is excluded.

Your home becomes absolutely safe.

Important! The system only works when all metal objects without exception are combined. If at least one element or electrical installation is excluded from the connection by conductors, consider that the entire circuit is inoperative.

What is the difference between a potential equalization system and a protective grounding system?

Grounding- this is an intentional non-detachable electrical connection of parts of an electrical installation or circuit with a ground electrode. Designed to reduce voltage (to a point where it should not exist under normal operating conditions) to a safe level.

As we can see, the definition does not contain the concept of potential (potential difference). In addition, grounding is carried out only at electrical installations or electrical circuits. Potential equalization also applies to infrastructure elements, as well as metal objects that are not electrical installations.

At the same time, protective grounding works effectively only in conjunction with residual current devices (fuse links, automatic switches). Without such devices, grounding does not reduce the safety of electrical installations, and can lead to a fire if a phase-to-ground fault occurs.

Unlike grounding, the potential equalization system is self-sufficient; no additional protective devices are required. The only condition is that there is an electrical connection to physical ground.

Requirements for organizing a potential equalization system in the PUE

There is no clear and universal definition of this system in the Electrical Installation Rules. The potential equalization device is specific depending on the location of application. IN different types premises, when working with various types electrical installations and laying current-carrying lines, there are their own methods.

For example, consider the application of portable protective grounding during repair work in electrical installations with three-phase power:

All current-carrying busbars within one electrical installation are connected to each other (potential equalization) and then connected to the ground electrode (potential equalization). If voltage appears on any of the parts, there will be no difference in electrical potential, the work is carried out in safe conditions.

The PUE has a list of protective measures, where this system is mentioned as one of the points required for use:

• organization of protective grounding;
• automatic power supply shutdown;
• equalization of potentials;
• potential equalization;
• double or reinforced insulation of conductors and electrical installation housing;
• organization of low voltage power supply (for alternating current - no higher than 50 volts);
• protective separation of electrical circuits;

Creation of potential equalization systems

The design of each system is individual and is developed in accordance with the configuration of the room. Exist general rules installations that need to be performed:

What objects are connected to the potential equalization system

• Metal enclosures of all electrical installations (unless they are properly grounded). The list also includes conductive housings of lamps (floor lamps).
• Of course, the entire protective grounding system. Actually, this is where the potential equalization system begins.
• Metal parts of the building frame, reinforcement of the foundation, walls, ceilings.
• Self-installed metal infrastructure elements. For example, steel mesh under a floor screed or metallic profile under sheets of drywall.
• Metal pipes and casings of the ventilation system.
• Copper pipes of the refrigerant supply system in air conditioners (if they are long).
• Metal sheaths of armored cables.
• Screen braiding of information cables (television, Internet).

Let's dwell on this point in more detail. The braided cable starts from a distribution or amplification device that is located far outside your premises. However, you have no way to control the correct power supply or grounding of these devices. A situation may arise when a phase comes across the screen to your house.

You, without suspecting anything, can simultaneously touch the live braid and the grounded metal object(for example, a heating radiator). The consequences are obvious - electric shock. When connecting the screen to the potential equalization system, external phase breakdown on the cable is not dangerous.

• All metal parts of the water supply and sewerage system: pipes, faucets, stainless steel sinks, trays and metal shower cabins, bathtubs.
• Components of water heating systems: boilers, internal pipes.
• Heating system: pipes, radiators, heated towel rails.
• Gas supply system.
• Lightning protection grounding (if you have a private home, in apartment buildings"option" is not available). In this case, the lightning rod is connected to the general system and its own grounding conductor at the same time.
• Metal-plastic window frames (if the conductive elements are not covered with plastic).
• Steel doors and door frames.

In the diagram it looks like this:

1. Potential equalization bus.
2. Lightning arrester from the power panel. Connected to phase. IN in good condition, there is no contact between the phase and grounding conductors - there is sufficient gap in the arrester. When struck by lightning in power cable, an arc current to ground occurs, and a potential difference of several thousand volts will not arise.
3. Data line surge suppressor.
4. Brackets for fastening grounding conductors to metal pipes.
5. Fundamental grounding conductor with busbar, part of the overall potential equalization system.

Installation of a potential equalization system for an apartment building (industrial premises)

Installation of system elements begins during the construction process. When creating the foundation, a metal bus is laid along the entire perimeter of the future structure. This is a closed conductor (steel strip or reinforcement) with welded branches for connection to grounding conductors, and for internal wiring of conductors. To ensure uniform spreading of potential into the physical ground, several groups of grounding conductors are installed along the contour of the building at an equal distance. If possible, equal distance is provided between them.

From common bus branches are made to each section (entrance), where the incoming power supply panel is installed. A grounding shield is formed, connected to a potential equalization system.

It is located in the panel room, or in basement. Access to the shield must be limited (unless it is a private house). Only representatives of the energy company, or state unitary enterprise, are allowed to perform maintenance.

Important! The entire contour (frame) system is connected to each other by welding. Only after checking the reliability and electrical conductivity of the connection is the final pouring of concrete carried out.

The ceiling reinforcement is welded to the vertical elements of the system. If necessary, bus transitions are made from room to room.

After the construction of the walls, external wall a conductive busbar is laid for lightning protection installed on the roof. All these conductors are part of the potential equalization system.

Bends in the form of reinforcement or steel strips must be made into the shafts through which vertical pipelines (risers) are laid. After installation of water supply and sewerage systems, steel pipes conductors are welded to connect to the potential equalization system.

Important! In old houses where they were held repeatedly renovation work(without major repairs), there may be plastic inserts in the risers.

This means that the integrity of the potential equalization system has been compromised. It is recommended to duplicate the connection by simply connecting the grounding conductor to the grounding bus. This can be done using a contact clamp.

Information for reference

To maintain aesthetics, in residential buildings A potential equalization bus is not created in each apartment. Its role is played by the grounding bus located in the input panel. According to modern electrical safety requirements, in all access shafts with risers, a steel strip is laid (for the potential equalization system), connected to protective grounding. It seems to loop the general circuit in a second circle, duplicating the grounding.

When creating your own system in an apartment, you can use this connection point. By creating your own panel, you can connect objects that are not electrical installations to it. For example, a bathtub (if it is not made of acrylic or plastic).

To do this, there must be a special contact on the case. If it is not there, use standard fasteners.

Creation of a potential equalization system in a private house

The principle is the same as in multi-apartment housing, only the amount of work is significantly less. After installing the grounding conductors (this is a topic for a separate article), you lay a potential equalization bus together with the grounding. Parallel wiring is made from it in accordance with the rules:

• Standard grounding points for sockets and electrical installations. Including conductive enclosures.
• Connection of the entire metal infrastructure of the building, including lightning protection on the roof.

To estimate the number of objects covered, take a look at the illustration.

Connection points are marked with circles.

When building a new house, you can optimize costs by providing several basic panels for grounding connections and a potential equalization system. This will save the grounding conductor when wiring to different rooms.

• In the bathroom it is necessary to create an additional potential equalization system, even if there is a main one in the house.
• When installing electric heating elements of a “warm floor” system, it is recommended to lay them on top steel mesh. The fittings are then connected to the potential equalization system and finishing fill screed or self-leveling mixture.
• If your water supply is normally grounded and connected to the mixer small area metal-plastic pipe(this scheme is widespread), the mixer body must be grounded with a separate conductor. This is especially true for the bathroom.
• Differential protection system (RCD) electric boiler does not conflict with potential equalization. Sharing is acceptable.

Non-residential premises

IN technical rooms, workshops, in production, a potential equalization bus (usually representing a working grounding) is laid open method By interior wall. The grounding conductors of electrical installations, as well as lines connecting all conductive elements of the room, are connected to it. This creates an ideal potential equalization system.

In office buildings, so as not to spoil interior decoration, you can hide the tire in a decorative plastic box for cable laying. Owners often ignore grounding conductors from heating radiators. This is unacceptable - most cases of electric shock occur when equipment and radiators touch simultaneously.

Important!
Office premises are more dangerous in terms of potential differences occurring in the most unexpected places. Uncontrolled tenant neighbors can throw up any “surprise” in the form of voltage in the water supply system or connection phase wire with braided internet cable. Therefore, before starting work in such a building, spend a little time and money checking the protective grounding and potential equalization systems. You will save both the health of your employees and your office equipment.

Bottom line

After studying the material, you have learned to distinguish between safety systems when working in rooms with electrical installations. Behind every requirement of the Electrical Installation Rules is someone’s life. Don't buy bad experience at the cost of your mistakes. The potential equalization system is installed once and provides confidence in safety forever.

Video on the topic

Modern apartment buildings equipped with various engineering systems and numerous household appliances, the metal elements of which serve as conductors of electric current and have their own potential. During normal operation, the potential is close to zero and does not differ from the potential of the surface and other surrounding objects. In the event of an accident, for example, insulation damage or potential drift through pipes, the potential of conductive parts can rise to several hundred volts. When a person simultaneously touches two objects with different potentials, there is a danger of electric shock. The cause of voltage on metal conductive parts can be not only damaged insulation, but also static electricity, as well as stray currents grounding systems. If electric current flows through the grounding device, it also becomes energized and does not guarantee a sufficient level of safety.
Reliable protection is provided by a potential equalization system (EPS), organized on the principle of electrical connection of all conductive parts of the building accessible to touch with a neutral protective conductor PE. In this case, potentially dangerous metal elements will have the same potential, which reduces the likelihood of electric shock when touching them at the same time.

Standardization of the potential equalization system

Additional potential equalization system

In areas of increased risk of electric shock to people, such as a bathroom, sauna, kitchen or shower, an additional potential equalization system (EPS) should be installed to ensure a sufficient level of electrical safety in the event of an emergency. The additional potential equalization system connects with each other all open and third-party conductive parts, neutral and grounding protective conductors of all equipment (depending on the type of system), including the protective conductors of plug sockets. see clause 1.7.83 PUE. The DSUP connection diagram is shown in the figure below.

As can be seen from the diagram, all potentially dangerous conductive structures are connected to the terminal box (bus) in the potential equalization box, which allows you to organize a DCPS without extending protective conductors from each element to the distribution panel of the apartment (house).
A DSUP bus is made of copper with a cross-section of at least 10 mm 2, connecting six or more connectors to it.
The PMC is connected to the input grounding bus distribution panel using a copper protective PE conductor with a cross-section of 6 mm2, thus grounding all metal parts of the room. Third-party conductive elements extending outside the premises are also subject to mandatory connection to the DSUP.
In new residential buildings, EPS conductors are installed during the construction phase, together with the installation of electrical wiring. If they are absent, for some reason, the conductors can be installed independently by cutting narrow grooves in the floor screed. Before starting work, you must make sure that there are no other communications in the floor. Conductors are connected to grounded objects by bolted connections, clamps or welded contact tabs, which ensures the presence of a strong metal connection between them.
DSUP is performed using specially designed conductors or using open and third-party conductive elements that meet the requirements of clause 1.7.122 of the PUE for protective conductors. see clause 1.7.83 PUE. Provided there is no mechanical impact, the required cross-section for conductors is 2.5 mm 2 or more. In case of possible mechanical impact, conductors with a cross section of 4 mm 2 or more are used. The connection of two open conductive elements is made with a conductor with a cross-section not less than the cross-section of the smaller of the protective conductors connected to them. The cross-section of the DSUP conductors connecting the open and external conductive parts must be at least half the cross-section of the protective conductor connected to the open conductive part. see clause 1.7.138 PUE.

Limitations when equalizing potentials

The installation of the control system is carried out during the construction stage of the building. However, there is a limitation on its use in existing buildings. In houses with a TN-C grounding system, with a combined PEN conductor, additional potential equalization is strictly prohibited. Otherwise, if there is a break neutral wire, there is a danger of electric shock to the remaining residents who did not make an emergency response. As a rule, this restriction applies to multi-storey buildings of old housing stock.
The problem can be solved if it is possible to switch to the TN-C-S grounding system: for this purpose, at the GZSh in the input distribution device of the building, the PEN conductor is divided into PE and N conductors, a ground loop is made and it is connected to the main ground bus copper wire. The current trend is to install utilities (water supply and sewerage) plastic pipes, does not require combining them into a potential equalization system. Replacing metal pipes in an existing DSUP with non-conducting plastic pipes leads to a disruption of the electrical connection with the grounding bus of all others metal elements premises (batteries, heated towel rails, etc.), making them potentially dangerous to humans in case of simultaneous contact.

Conclusion

Modern construction codes and regulations pay special attention to the correct installation of the potential equalization system. First of all, it is inspected and checked for compliance project documentation upon commissioning of the house. Electrical safety is ensured by organizing the electrical connection of all accessible conductive parts of the building with the main building using PE conductors. The OSUP is complemented by a potential equalization system in areas with an increased risk of electric shock.
It is important to remember that performing DSUP is only possible in houses with grounding systems with separate laying of PE and N conductors. These include modern system grounding TN-S, as well as an upgraded system to the TN-C-S circuit.
When installing the control system, it is necessary to ensure a strong metal connection between its elements connected in a radial pattern in compliance with the required cross-section of the protective conductors.

see also:

The potential equalization system (PES) is used to ensure the same electrical potential on all capable of accumulating charge and conducting electrical elements building. In other words, it is required to provide an equipotential surface. If this goal is achieved, then a temporary increase in the potential in the building is observed immediately on all objects, thereby eliminating the flow of currents dangerous to humans and equipment, or the occurrence of sparking between different elements.

The main protection system here is the basic potential equalization system (EPS). Equalization is achieved by connecting all conductors at the electrical input to the GZSh (main grounding bus).

The connection is usually made at the ASU (input switchgear) or in close proximity to it on a special clamp.

Elements that need to be connected to the GZSh:

— Main grounding conductor;

— Main protective conductors (PE, PEN);

— Metal pipes of internal and external communications in the building, as well as those passing between neighboring buildings (water supply, sewerage, gas pipeline);

— Metal parts of the frame of a building (structure);

— Any parts building structures made of metals (lightning protection system, air conditioning, ventilation, other centralized systems).

Typically, the main potential equalization system is equipped with only one output, which is connected to the main switch. The GZSh itself is most often installed in the same place where it is located Switchgear.

If several current leads are used in a building, then the GZSh must be implemented for each individual VU (ASU). Similarly for each built-in transformer substation a separate GZH is performed. The functions of the GZSh can be performed by the PE bus of the VU (VRU, RUNN). Each conductive element in the building must be connected to the circuit with a separate conductor. Series connection of several conductors is not allowed.

The conductor cross-section suitable for use in BPCS must be a minimum of 6 mm2 in the case of copper and a minimum of 16 mm2 for aluminum wire. A steel conductor is also used, which must have a cross-section of at least 50 mm2.

Protective measures in electrical installations. Protective measures for indirect contact. Potential equalization

Potential equalization

The electrical connection of conductive parts to achieve equal potential, performed for electrical safety purposes, is called protective potential equalization.

Protective potential equalization is used in electrical installations up to 1 kV.

According to the PUE, the main potential equalization system in electrical installations up to 1 kV must provide for the connection of the following conductive parts:

1. zero protective (PE) or combined zero protective and zero working conductor (PEN), in the TN system.
2. a grounding conductor connected to the grounding device of an electrical installation in IT and TT systems;
3. metal pipes of communications entering the building (hot and cold water supply, sewerage, heating, gas supply, etc.);
4. metal parts of the building frame, ventilation systems;
5. lightning protection grounding device;
6. working grounding conductor;
7. metal sheaths of telecommunication cables.

All specified parts must be connected to the main grounding bus using conductors of the potential equalization system.

Additionally, it is necessary to connect together all exposed conductive parts of stationary electrical equipment and metal parts of building structures that are simultaneously accessible to touch, as well as neutral protective conductors in the TN system and protective grounding conductors in IT and TT systems, including protective conductors of plug sockets.

Potential equalization

Potential equalization is a method of reducing touch and step voltage between points electrical circuit, which can be touched at the same time or on which a person can simultaneously stand.

Potential equalization is carried out electrical connection metal structures located near the electrical installation, with its body (potential equalization), as well as the formation of a spreading zone through the use of special grounding devices.

The grounding device, which is carried out in compliance with the requirements for its resistance in electrical installations with voltages above 1 kV, must have a resistance of at least 0.5 Ohm at any time of the year.

Electrical installations with voltages above 1 kV with a solidly grounded neutral are classified as electrical installations with high ground fault currents. These also include electrical installations of 110 kV and above, in which the neutrals of individual transformers are isolated or grounded through resistors or reactors. By reducing the resistance value of the grounding device, it is usually not possible to ensure the safety of personnel servicing these electrical installations due to large quantities touch voltage and step voltage obtained during ground faults (on housings and metal structures of electrical installations). Therefore, grounding in these electrical installations is used with potential equalization.

Potential equalization is carried out by constructing a contour grounding device on the territory of the electrical installation. This device is a system of electrodes 2.5-5 m long driven into the ground and interconnected by steel strips. This entire system is constructed in trenches 0.6 - 0.7 m deep and represents metal mesh

Fig. 4.15 Potential distribution in the current spreading zone (c) when using grounding with potential equalization (a) and (b).

When there is a short circuit to a grounded body, the current flowing into the ground forms a spreading zone. The distribution of potentials in the spreading zone is determined by the design of the grounding device. For a loop grounding device, the potentials of the individual electrodes are summed up, and as a result, the ground potential in the electrical installation area is leveled out and takes on a value close to the potential of the ground electrode. The current passing through the body of a person who has touched grounded electrical equipment will be determined by expression (2.10):

and will depend on the coefficient a.

By changing the coefficient a, it is possible to reduce the current in the human circuit to a safe value. The step voltage will also be reduced when using a loop grounding device. An example of the formation of a spreading zone of a contour device is shown in Fig. 4.15, c.

The placement of the grounding grid is determined by the requirements of limiting touch voltage to normal values ​​and the convenience of connecting the grounded equipment. The distance between the longitudinal and transverse horizontal grounding conductors should not exceed 30 m, and the depth of their placement in the ground should be at least 0.3 m. To reduce the touch voltage on the outdoor switchgear, a layer of crushed stone 0.1 - 0.2 m thick is also added.

Double or reinforced insulation

The PUE gives the following definitions of insulation:

1. basic insulation - insulation of live parts, including protection from direct contact;
2. additional insulation - independent insulation in electrical installations with voltages up to 1 kV, performed in addition to the main insulation for protection against indirect contact;
3. double insulation - insulation in electrical installations with voltage up to 1 kV, consisting of basic and additional insulation;
4. reinforced insulation - insulation in electrical installations with voltages up to 1 kV, providing a degree of protection against electric shock equivalent to double insulation.

Protection by double and reinforced insulation can be achieved by using class II electrical equipment (tools) or enclosing electrical equipment that has only basic insulation of live parts in an insulated enclosure.

Conductive parts of double insulated equipment must not be connected to the protective conductor or to the potential equalization system.

Ultra-low (low) voltage

It is used in electrical installations with voltages up to 1 kV as protection against electric shock due to direct and (or) indirect contact, in combination with protective electrical separation of circuits, or in combination with automatic power off.

Protective electrical separation of circuits

Used in electrical installations up to 1 kV, usually for one circuit.

Greatest operating voltage the separated circuit should not exceed 500V.

The power supply for the circuit to be separated must be supplied from an isolating transformer, or a safety isolating transformer, or from another source providing an equivalent degree of safety.

Current-carrying parts of the circuit powered by an isolation transformer must not have connections with grounded parts and protective conductors of other circuits.

If only one electrical receiver is powered from an isolation transformer, then its exposed conductive parts should not be connected either to the protective conductor or to the exposed conductive parts of other circuits.

In exceptional cases, it is allowed to power several electrical receivers from one isolation transformer if the following conditions are simultaneously met:

1. open conductive parts of the separated circuit must not have electrical connection with the metal body of the power source;
2. open conductive parts of the separated circuit must be connected to each other by insulated ungrounded conductors of a local potential equalization system that does not have connections with protective conductors and open conductive parts of other circuits;
3. all socket outlets must have a protective contact connected to a local ungrounded potential equalization system;
4. all flexible wires and cables, with the exception of those supplying class II equipment, must have a protective conductor for potential equalization;
5. the protection shutdown time for a 2-phase short circuit to open conductive parts should not exceed the normalized value in Table. 4.1 time (for IT system)

Insulating (non-conductive) rooms, zones and areas

In cases where in electrical installations up to 1 kV the requirements for automatic power off cannot be met, and the use of other protective measures is impossible or impractical, insulating rooms, zones and sites are used.

The insulation resistance of the floor and walls of such rooms, zones and areas at any point must be no less than:

50 kOhm for installations up to 500 V;

100 kOhm for installations above 500 V.

Protective conductors should not be provided in insulating rooms, zones and areas, and measures should be taken to prevent the transfer of potential to third-party conductive parts of the room from the outside.

The floors and walls of such premises should not be exposed to moisture.

When implementing measures to protect against direct and indirect contact in electrical installations with voltages up to 1 kV, the classes of electrical equipment (power tools) used according to the method of protecting people from electric shock should be taken in accordance with Table. 4.2.

Table 4.2. Use of electrical equipment (power tools) in electrical installations with voltage up to 1 kV

Over time, buildings acquire an increasingly wider and more complex electrical system. Thus, consumers with low voltage can receive greater damage from overvoltages caused by thunderstorms and arising due to the impact of electrical impulses and a decrease in the separating dangerous space between electrical objects and the lightning rod. A three-dimensional system of electrically conductive networks is organized by information supply, antenna structures, central heating communications, water supply, gas and power systems. The only lightning protection when exposed to an electromagnetic pulse is not able to prevent damage to fairly weak equipment. Therefore, a general lightning protection network must be formed, and first of all the main potential equalization system.

What is it used for?

Potential equalization is used to ensure equalization in all metal parts of a building that are connected to each other, that is, to form an equipotential surface. In this case, when increased potential enters the house on all metal structures, it increases synchronously, due to which a dangerous difference in voltage does not develop and sparking and the passage of dangerous currents do not form.

Connecting elements

An important protective measure is the creation of a main potential equalization system. It connects the grounding main bus, the main grounding line, the protective main line and conductive elements, which include:

• reinforcing parts of structures with reinforced concrete base;
• elements of metal buildings, climate systems, centralized heating;
• steel pipelines for system supply.

Most often, the potential equalization system has only one output method. The main busbar is mounted in the distribution element room at the closest possible distance from the insertion point.

Lightning protection system

Due to the rapidity of current rise and its great strength When a lightning strike occurs, a huge potential difference is created, much greater than that caused by current leakage. Therefore, potential equalization is required to protect against the influence of lightning currents.

To prevent an uncontrolled short circuit, a lightning protection structure, a grounding system, metal equipment, and electrical installations with protective mechanisms must be combined externally or directly.

Potential equalization bus with open access for verification work must have a connection to the equalization system. The bus also has a ground connection. IN large buildings There can be several of them if they are connected to each other.

Potential equalization in a lightning protection system is carried out at the point where conductors enter the room and where safe distances are violated, at ground level or in the basement.

A house built using steel frame or reinforced concrete base or with separate room for external lightning protection, it must have potential equalization at ground level. In houses with a height of more than 30 m, it is performed every 20 m.

Lightning conductive parts are installed at a safe distance to prevent the occurrence of impulse reactions. If it is impossible to maintain a safe distance, the potential equalization system, the lightning removal device and the receiver form complementary connections with each other. It is worth noting that they can lead to the introduction of increased potential into the structure.

Complementary device

An additional potential equalization system is being created, the PUE of which determines the form and application, at points where electrical equipment is located where the existing conditions may be dangerous, and in the event that the standards indicate the need for it. It forms a connection between all parts of existing equipment and third-party conductors that are located next to them.

Typical premises and facilities in which complementary safety measures should be used are antenna equipment, lightning protection facilities, remote communication facilities, areas with increased risk of explosion, hospitals, fountains, water parks, and bathrooms. A company that carries out installation work, must carry them out in accordance with the instructions of PUE-7.

Lightning protection potentials and equipment

A connection must be made between the lightning protection system and equipment parts, which include climate and air ducts. ventilation devices, crane frames, elevator guide elements, pipelines for systems such as fire extinguishing, heat supply, gas and water supply. If possible, each metal structure connects to equalization buses. Electrically conductive pipes can act as connecting lines(the exception is the gas pipeline).

If there is an isolated section on the water and gas pipeline, conductors of the potential equalization system are used for shunting. A special connection to a lightning protection device is not necessary for underground metal piping close to ground. The same goes for railroad tracks. If unification is unavoidable, it is first agreed upon with the operating company.

Grounding

The re-grounding device operates using two vertical electrodes with a length of at least 5 m, they are connected to each other by a horizontal ground electrode. The latter is played by a steel strip; it is also used to form a conductor connecting the main conductor and the additional ground electrode. The strip must be at least 4 mm thick with an area cross section 75 mm 2. There is no standardization of the resistance of the re-grounding electrode.

The cross-section of the supply cable influences the selection of the potential equalization conductor; it should not be less than half the cross-section of the cable. The most widely used wiring is PV1 and steel strip; single-core cable is also used. Special compressions are often used when branching a main line using a wire.

Technical equipment and lightning protection

In accordance with the theses of PUE-7 and subject to the cross-sectional boundaries of the conductors, all connections are made to equalize the potentials of lightning protection structures. Direct connections and those made through spark separation gaps must be separated.

The lightning protection system can be directly integrated with the following devices:

• grounding elements of the protection system against high voltage security structures;
• antenna devices;
• grounding lines located underground at a distance from communication and overvoltage protection systems;
• grounding of power structures whose power exceeds 1 kW, while there should be no possibility of introducing high potential into the ground electrodes;
• protective connections in TT-type networks for protection against electric shock during indirect contacts.

When conducting information or power lines in metal pipes or shielding, an additional potential equalization system is not needed.

Spark gaps

Routine tests must be carried out while gaining access to the spark isolation spaces. By properly designing and installing the internal lightning protection mechanism, damage caused by potential differences and surges is minimized.

Connection via spark intermediate separations is carried out for the following elements:

• grounding of measuring systems subject to separate design;
• installations protected from current leakage and having anti-corrosion cathodic protection;
• return wire of the traction element of direct current, as well as alternating current, in the absence of the possibility of direct integration for signal and technical reasons;
• auxiliary grounding parts of the protective shutdown, which is triggered by dangerous voltage.

Installation

During the construction of the building, the installation of the SUP must be carried out, since there are some difficulties when used in finished buildings. The additional potential equalization box is prohibited for use in buildings with TN-C grounding. If this rule is not followed during a break in the neutral wire, there is a possibility of electric shock to residents who did not install the DSUP. This restriction applies mainly to old multi-storey housing stock.

Another type of grounding system allows you to get rid of this problem: for this, a grounding loop is made and connected copper wiring to the pinching main busbar.

Plastic pipes

Today, communications using plastic pipes are quite widespread, which does not require integration with an equalization system. At the same time, if in the existing DSUP you replace metal pipes with plastic ones that differ in conductive properties, there will be a breakdown in the connection between metal parts indoors (towel rail, batteries) and a grounding bus, which makes them dangerous if touched at the same time.

When creating communications using plastic pipes, integration with an equalization system is carried out using metal combs, taps and check valves to secure the conductors. In the presence of dielectric inserts in metal pipes they are added to the main system after insertions inside the building.

What you need to know

According to building regulations and standards, today increased attention is paid to the competent installation of a potential equalization system. First of all, upon commissioning of the building, inspection and verification of compliance with the project are carried out. Creating an electrical connection of all conductive elements accessible to touch using special conductors ensures proper electrical safety. As an addition, there is a potential equalization box in places with high opportunity electric shock.

It is worth considering that DSUP can only be created in buildings that have a grounding system with separate laying of N- and PE-type conductors.

A strong metal connection must be established between the parts of the control system if they are connected in accordance with the radial diagram and required section protective conductor.