Electrical safety. Protective ground. Electrical safety What is protective grounding in electrical

Grounding is the electrical connection of the electrically conductive components of the equipment to the ground. It consists of a grounding conductor and a conductor connected to it. The figure below shows the classic connection diagram.

Ground connection diagram in a private house

Red indicates phase, blue indicates neutral. They go from the pole from the main power supply, respectively, to the L and N buses. The ground wire connected between the ground electrode and the PE bus of the shield is indicated in black. They go into the shield, from which wiring is made around the house.

Kinds

Depending on why grounding is needed, it is distinguished by types:

Working. In industry, points of current-carrying parts of electrical installations are grounded to create normal working conditions. Electrical safety is not the goal here. Working grounding is intended for the operation of electrical equipment in emergency mode, when a breakdown occurs on the case or damage to the insulation. This is how the neutral of the generator or transformer is grounded.

Working grounding is done directly with a grounding conductor or through additional devices (reactors, resistances, arresters).

Protective. Grounding is intended to protect a person so that he is not struck by an electric current. The body conducts electricity and has a lot of resistance. Electric shock occurs not only as a result of touching conductive elements. In this case, an electrical circuit must still be formed. It is created between the ground, on which a person rests with his feet, and a bare conductor, under voltage, with which contact occurs.

The higher the humidity of the earth's surface, the more current will pass through the body, which is a significant danger.

From lightning. At the place of the lightning strike, the temperature reaches 30 thousand degrees, which threatens the lives of people and the safety of buildings. Statistics show that 20% of fires in private homes are caused by lightning. Therefore, it is necessary to install lightning rods on buildings.

Protection system

The protection system includes 3 parts:

Lightning rod - catches the blow and transmits the current further. It is a round rod with a diameter of at least 10 mm and a length of 250 mm. It is located on the roof, at a high altitude, where there is a maximum probability of a discharge.

The radius of the protection zone at the base of the rod is determined by the formula:

r = 1.732∙h, where

h is the height difference between the upper points of the house and the lightning rod.

Consideration should also be given to the conical shape of the space to be protected.

Down conductor - serves to transfer current from the lightning rod to the ground electrode. For it, a wire rod with a diameter of 6 mm is used, which is welded to the lightning rod, after which it is lowered along the wall to the ground electrode with a maximum distance from windows and doors. The down conductor must not be bent so that a spark discharge does not occur in this place. It is made as short as possible.
Lightning protection grounding and household appliances are made common. The most common device is in the form of a circuit of three electrodes driven into the ground and interconnected by a steel strip, by welding. The earthing switch is located at a distance of more than 1 m from the walls and more than 5 m from the porch, walkways and walkways.

Lightning protection system for a private house

Natural ground

To create grounding, it is convenient to use metal parts of buildings and structures that are in contact with the ground. This can be foundation reinforcement, underground pipelines or cable sheaths, ground communications (railways). All this can be used only in cases where all the requirements for grounding conductors are met. The advantage of this method is significant cost savings and no need to operate the devices.

Foundations are often used as a ground electrode, but certain conditions must be met for this:

humidity of the surrounding soil is not lower than 3%;
the absence of an aggressive environment that contributes to the occurrence of corrosion;
the reinforcement is not under the influence of mechanical stress;
all details of metal structures constitute an inextricable electrical circuit, for which jumpers with a cross section of at least 100 mm 2 are welded into the gaps;
the presence in concrete of embedded metal parts with which a grounding conductor can be connected.

Protective earth

The main element is a ground loop, consisting of metal electrodes located in the ground. They are rods, angles, pipes or sheets with a length of at least 2.5 m. Their main task is to dissipate current in the ground, the effectiveness of which depends on the soil composition and climate.

When installing grounding, you need to know what the soil consists of. It can be clay, sand, earth, etc.

Each component has its own electrical conductivity, which determines how to properly design the ground. Clay has a resistance of 20 Ohm * M, sand - 10-60 Ohm * M (depending on humidity), garden soil - 40 Ohm * M, gravel - 300 Ohm * M.

A ground conductor is connected to the circuit.

Triangular ground loop

Electrodes are not allowed to be coated with dielectric anti-corrosion compounds. You can only apply varnish to the welding points.

The requirements for the conductor from the circuit to the electrical installation are strength and resistance to corrosion. The conductors can be steel tapes with a size of 5x30 mm and rods with a diameter of 10 mm or more. Due to the small load, a wire rod with a diameter of 6 mm is suitable for giving.

According to modern standards, electrical wiring in an apartment or in a private house is carried out with a three-wire wire, where one of them is a phase, the other is zero, and the third is grounding. Protection is connected between the circuit and the housings of electrical appliances. Sockets and plugs are supplied with grounding contacts connected to the device case, when turned on, in addition to electricity, grounding is connected.

When the phase hits the housing, due to the wear of the insulation, a leakage current occurs, which enters the circuit and dissipates in the ground. For small currents, the RCD is triggered, and for a short circuit - circuit breakers. In both cases, the current from the body of the electrical appliance passes through the protective conductor, designated PE, to the circuit and spreads in the ground.

The higher the electrical characteristics of the ground electrode, the more it protects a person from electric shock.

For private housing construction, the resistance of the protective ground loop under different conditions is:

protective - from mains voltage at 220V or 380V - 30 Ohm (TN-C-S system);
gas pipeline to the house - 10 ohms;
lightning protection - 10 Ohm;
telecommunications equipment - 2 or 4 ohms.

Earthing systems for electrical installations

Protective earthing systems depend on the characteristics of the power supply, such as an isolated or solidly earthed neutral. There are only three of them:

The TN system contains a dead-earthed neutral, with the connection of metal parts of the electrical installation to it.

What does a TN system look like?

Depending on the ways to use the zero worker (N) and protective (PE) conductors in the system, subgroups are formed:

TN-C - combination of PE and N conductors in one wire along the entire length of the network to the consumer (the old Soviet scheme, which is not currently used);
TN-C-S - combination of PE and N conductors in one wire from a transformer substation with their separation at the entrance to the switchboard. This system requires additional grounding.
TN-S - separation of neutral and protective wires throughout the network (the safest scheme).

IT system with isolated or resonantly connected neutral. Here, non-conductive metal parts of electrical equipment have a separate ground.

What does an IT system look like?

The IT system is used in institutions where particularly sensitive equipment operates.

A TT system with a solidly grounded neutral, and consumers have a separate protective ground (mainly modular-pin), not connected to the neutral wire N.

What does TT look like?

Video. Types of grounding

Grounding is necessary in all power supply networks, including in private houses and apartments. First of all, it is a security system when using electricity.

The presence of a grounding contact in modern electrical outlets has become commonplace. It corresponds to the contact on the plug of any electrical appliance. Let's try to figure out why grounding is needed.

What is grounding

Grounding is the connection of conductive elements that are not normally energized to a ground electrode - a metal structure buried in the ground with low electrical resistance. As the mentioned conductive elements, the metal case of the electrical installation, the working bodies of machines or household appliances, etc. can act.

The shielding braids of electrical cables are also grounded.

What is grounding for?

Depending on the purpose, there are several types of grounding:

functional;
for lightning protection.

Protective ensures the safe operation of electrical installations.

The functional is used to operate the device or circuit - it plays the same role as the neutral conductor in the mains.

In lightning protection systems, the ground electrode is connected to the lightning rod.

Principle of operation

The ground loop functions due to the ability of the soil to absorb an electrical charge. If the equipment case is energized as a result of insulation breakdown, then the charge will drain to the ground. When the user touches the case, the current will still follow the path of least resistance, i.e. through ground, and not through the human body. Without grounding, in such a situation, the user would receive an electrical injury.

The condition for the normal functioning of the grounding is a low resistance of the grounding conductor. This value depends on the soil parameters:

density;
humidity;
salinity;
ground contact area.

The ability of the soil to absorb the charge drops sharply when it freezes. Therefore, the grounding pins are driven in to a depth below the freezing mark, which depends on the latitude of the area. Data on the depth of soil freezing for different regions of the Russian Federation are given in SNiP "Construction Climatology".

Visual demonstration of grounding

On rocky, sandy and permafrost soils, which are difficult to penetrate, electrolytic ground electrodes from an L-shaped perforated pipe are used. Inside contains a reagent that forms a salty environment. The latter is characterized by high conductivity and low freezing point. The long part of the ground electrode is buried in a shallow trench, the short part is brought to the surface. It is used in three ways:

for backfilling a new reagent;
for pouring water (provokes a chemical reaction during the dry period).

Another modern version of the ground electrode is. It consists of many sections connected by threaded or otherwise. As they are driven into the ground, more and more sections are screwed on. So such a ground electrode, unlike the classic one of several pins, can be installed at any depth. The sections are connected according to special rules and using conductive paste. When clogging, a special nozzle is used that protects the thread from damage. The modules are made of steel and coated with copper or zinc, which reduces their resistance and increases their service life.

Electrolytic and modular grounding are expensive, because their traditional counterparts remain in demand. The pins in this design are arranged differently:

at the vertices of an equilateral triangle near the object;
at the corners of the object;
around the perimeter of the object.

The number of rods and the distance between them are determined by calculation.

The resistance of the earth electrode is checked periodically. The maximum allowable value is 30 ohms.

Combined protection of earthing devices and fuses

Grounding not only removes dangerous current, but in the presence of a protection device causes the emergency equipment to turn off. When a phase conductor contacts a grounded case, the network operates in a mode close to a short circuit (short circuit), accompanied by a sharp increase in the current strength in the circuit. An automatic switch (VA) reacts to this, which must be installed at the input of the electrical line to the object.

True, this is possible only with a very low resistance of the ground electrode, which is extremely rare. In most cases, the probability of a VA tripping is quite low. For example, with a grounding resistance of 10 ohms, the current in the circuit will be I \u003d 220 / 10 \u003d 22 A. Automatic machines, according to the requirements of GOST, can withstand a current that is 1.42 times the nominal value for an hour. That is, a 16 A machine with a current of 22 A will not turn off for almost 60 minutes (16 * 1.42 = 22.72 A).

Grounding scheme

More reliable automatic protection - or. This device compares the currents in the phase and neutral conductors and, if a difference is detected, indicating leakage, disconnects the circuit. By sensitivity, that is, the minimum amount of current leakage that causes operation, RCDs are divided into several categories:

Protecting against electric shock: 10 mA - installed in rooms with high humidity and 30 mA - in dry ones.
Fire-fighting - for 100, 300 and 500 mA.

Fire protection RCDs are used at facilities where a short circuit can cause a fire. They protect sections of the network where electric shock is practically excluded, for example, lighting circuits.

They are not interchangeable. VA protects against short circuits and overloads, RCD - against electric shock. Ideally, the input and each consumer group should be protected by both VA and RCD.

Grounded non-electrical equipment

Constructions that are not connected with electricity in any way are also connected to the ground electrode system:

Fences and other structures on overpasses and galleries, in which a dangerous potential difference is induced at a lightning discharge at close range. The same can happen with a pipeline or container containing a combustible substance. Due to the induced voltage, sparking is possible, followed by an explosion, therefore such structures are also grounded.
Products in which a static charge accumulates during operation. Basically, these are pipelines and containers: static electricity is formed due to the friction of the particles of the transported medium. For this reason, the rate of fuel supply to airliners is limited.
Pipelines of considerable length. In accordance with the law of electromagnetic induction, in such pipelines, when the Earth's magnetic field changes, and it is always unstable under the influence of the solar wind, so-called stray currents are formed. Therefore, they are connected with a certain step to the ground electrodes.

Difference from zeroing

Zeroing is the connection of the conductive parts of an electrical installation to a dead-earthed neutral of a current source (to a neutral conductor). Its resistance is much less than the resistance of the ground electrode. Therefore, when the phase is closed to the zeroed case of the device, a short-circuit current is guaranteed to occur, leading to the operation of the circuit breaker.

In the most common grounding system of the TN type, both grounding and grounding are carried out simultaneously.

Connection to the neutral core is carried out above the RCD. Otherwise, the currents in the phase and neutral conductors after the phase is closed to the case will remain equal and the protection device will not work.

About grounding systems

Several grounding systems are used, indicated by a combination of letters. The letters have the following meaning:

I: insulated conductor;
N: there is a connection to a solidly earthed neutral;
T: there is a connection to the ground wire.

There are three main types of grounding systems:

IT type- system with insulated neutral wire. In this system, it is isolated from or in contact with the neutral through a high value resistor or an air gap. Does not apply to residential buildings. Designed for connecting devices with special requirements for safety and stability. It is mainly used in laboratories and medical institutions.
Type TT- system with independent grounding. The best option. It provides for the use of two grounding conductors - for the source of electric current and metal elements of the system that do not have protection. The earth wire (PE) in this system is independent, and its performance in the area between the equipment and the transformer is improved. There may be difficulties in selecting the diameter for your own ground electrode. This disadvantage is compensated by the installation of a protective shutdown system.
TN type. The ground wire in such a system is combined with the neutral, therefore, when a phase breaks down on the case, a short circuit occurs and the machine disconnects the circuit. This ensures a high level of security.

Various grounding systems

TN systems are the most widely used. There are three subspecies:

TN-S: option with zero and divided working conductor. In order to increase safety, instead of one neutral wire, two are used: one is used as a protective one, the second one is used as a neutral one with a connection to a solidly grounded neutral. Such a system provides the best protection against electric shock.
TN and TN-C-S: option with PEN-wire and a pair of zeros. A neutral wire is connected to the equipment, split into PE and N conductors.
In TN-C-S after separation, a second grounding conductor is installed, which ensures uninterrupted operation of the system.

Advantages of the TN system:

the device is quite simple;
protection against lightning discharges;
to protect the wiring, it is enough to install circuit breakers.

Flaws:

there is a possibility of zero burnout from the outside with subsequent breakdown of the metal cases of the equipment;
potential equalization equipment is required.

The TN system is not well suited for rural areas.

The lives of people sometimes depend on the correct organization of grounding. Organization means not only the device, but also the timely control of the resistance of the ground electrode. Due to oxidation or changes in soil parameters, it may be overestimated, as a result of which the protective effect of grounding will be lost.

By creating an electrical connection of metal structures of industrial and domestic equipment with the ground, safety is increased during its operation. This method is used to prevent electric shock to a person in case of emergency.

The figure below shows the basic principles of the functioning of the protective system. Even when using high-quality automatic devices, the speed of their shutdown will be insufficient to completely eliminate the possibility of electric shock to a person. In the presence of grounding, a circuit with less resistance will be formed. This will reduce the harmful effects on the human body to a safe level.

Protective grounding is a necessary safety element to prevent electric shock

Principle of operation

It is usually installed for protection in the event of a short circuit. If the phase conductor is disconnected and touches the metal chassis of the unit, the housing will be energized.

A properly created protective earth forms an electrical circuit with low resistance. It is this path that is most favorable for electric current, so an accidental touch of a person to the body will not be dangerous (Fig. above).

It should be noted that such a device will simultaneously perform several important functions:

It will also provide protection in the event that a potentially dangerous voltage on the case is formed not by a short circuit, but by induction currents. Such situations are possible in installations with high voltage and where exposure to microwave radiation is acceptable.
When using a dead-earthed neutral and some other connection schemes in the power circuit, during a short circuit, long and large-amplitude pulses will appear, sufficient to trigger the automatons that turn off the voltage.
If grounded equipment is struck by lightning, such a conductor will provide some protection against damage.

According to this formula, the resistance of the conductor of the protective circuit between the main bus and the switchboard is calculated: 50 x STsFN / LV. STsFN - resistance in the zero-phase circuit; LV - nominal voltage in volts.

In order not to be mistaken with the terminology, one must understand the real meaning of the following names:

The worker is called grounding, which acts as a second conductor. It is used for electrical power supply of installations, solving other problems.
The lightning protection mentioned above is not intended. To ensure safety during thunderstorms, devices specially designed for this purpose are used. They are designed for relatively large currents and voltages.

Wiring diagrams

To choose the best option, you need to know for what purposes protective grounding is used in a particular case. Below are the different systems, their features, advantages and disadvantages.

Type TN, solidly earthed. According to this scheme, industrial and household equipment is connected, operating in networks with voltages up to and above 1000 V. The neutral of the generator (transformer) of the power source is connected to the ground electrode. Consumer devices, or rather cases, screens, chassis, are connected to a common conductor.

If the electrical circuit is created in accordance with international standards, then the following can be understood from the inscriptions. The Latin letter "N" denotes the "zero" conductor, which is used to operate the equipment. It's called functional. "PE" is a conductor used to create a protective circuit. The letters "PEN" denote a conductor designed to solve functional and protective tasks.

The following schemes are most often used. Their names are distinguished by a letter, which is added to "TN" through a hyphen.

Wiring diagrams

System	Principle of operation	Advantages, disadvantages, features
C	In the "C" system, the conductor performs working and protective functions at the same time. As an example, we can recall a typical three-phase power supply with a solidly grounded neutral, which is a neutral wire.	This scheme is relatively simple and economical. Housings of consumer devices are connected directly to the neutral. The disadvantage is the loss of protective properties if the electrical circuit is broken. Such damage cannot be excluded in case of an emergency increase in current, heating and destruction of the conductor. In such a situation, a dangerous voltage will appear on the case. When using such systems, automatic machines are especially carefully selected, which should quickly and reliably turn off the supply voltage.
S	This circuit uses two separate neutral conductors, working and protective.	Several conductors increase the cost of the system, but significantly increase the reliability of protection.
C-S	This is a combined system. The generating source is connected to a dead-earthed neutral. Only four conductors go to the consumer (three-phase power supply). A protective conductor "PE" is added to the property.	Low cost compared to the previous option is accompanied by lower reliability. If the conductor is damaged in the area to the object (or to "PE"), the protective functions will be lost. In accordance with current regulations, when using such systems, it is required to prevent mechanical damage to the relevant conductors.

The most commonly used connection schemes

Sufficiently high risks arise when using overhead power lines. They can be damaged by a hurricane, other negative external influences. To ensure a high level of security, the TT scheme is used.

A solidly grounded neutral is connected to the generator. Energy is transmitted through four wires. At the consumer, an autonomous grounding system is installed, to which the equipment cases are connected.

Kinds

In order to minimize the resistance, it is desirable to shorten the length of the protective conductor. This is ensured by creating a ground loop around the perimeter of the object.

Remote systems are used when equipping installations that operate with a supply voltage of up to 1,000 V.

Grounding conductors are also divided into artificial and natural. This distribution by groups is conditional, since in both cases metal parts of structures located in the ground are used:

In the first, they are created specifically for the grounding system. This approach allows you to accurately calculate the resistance, the dimensions of individual parts, and other important parameters.

Natural grounding - a metal part of a structure located in the ground

The second option provides for connection to the metal parts of the building structure, reinforcement of foundation blocks. It is more economical, since some finished parts are used for protection. However, it must be borne in mind that in order to connect the equipment, it will be necessary to lay the appropriate lines, which will have a resistance determined by the standards. The disadvantage is the relative accessibility of ordinary personnel.

For grounding use conductors made of copper, black and galvanized steel. Cross-sections and other characteristics of products are selected taking into account the electrical parameters of the installation and its operating conditions.

In particular, the level of humidity matters. When calculating, the resistivity and other features of the soils are checked.

In order to provide reliable protection when working under voltage, electrical installations are grounded. Protective earth is the intentional electrical connection of the machine housing to a grounding device. According to the principle of operation, all grounding is divided into two types. It can be performed in the form of protective grounding and grounding, which have exactly the same function, which consists in protecting people from the effects of electric current, in case of touching the case or other parts with broken insulation.

The essence of protective grounding

With a protective clamping device, a deliberate connection of parts of electrical installations and a grounding device is carried out. Thus, electrical safety is ensured in case of accidental contact with certain parts that are energized. This situation, as a rule, occurs during the breakdown of insulation, when there is a voltage between the case and the phase. In the presence of grounding, the current will not pose a danger, since the protective grounding, which has a very low resistance, will act as a conductor.

The main components of grounding are the grounding conductor itself and the grounding conductors. Grounding conductors can be natural and artificial. In the first case, these are metal structures that have a reliable connection to the ground. Earthing electrodes of artificial origin are steel rods, pipes or angles, the length of which must be at least 2.5 m. They are hammered into the ground and interconnected using welded wire or steel strips. To make grounding more efficient, it is necessary to reduce its resistance by increasing the number of artificial grounding conductors.

Protective earthing device

The essence of the protective is the deliberate electrical connection of certain parts of electrical installations with a neutral wire.

As a rule, such electrical installations are not under normal voltage. In these cases, any phase shorted to the case leads to its short circuit with the neutral wire. A very high current occurs, therefore, the equipment must be quickly and completely disconnected. This is precisely the main function of zeroing. The entire design of the protective grounding consists of a zero working and zero protective conductor.

13.07.2018

What is grounding in simple words and why is it needed

Some manufacturers write in the instruction manual for their equipment that grounding is necessary to work with the equipment.

Also, the installation of grounding is required when building a house. What is grounding, why is it needed, and whether it is possible to do without it, read below.

What is grounding

Grounding is a method of transferring an electrical or electrostatic charge to the ground or in a special charge-nulling device. In most houses and apartments, the electrical wiring is single-phase (alternating current), that is, it consists of a positive and negative charge.

This means that when there is a power surge, will change direction. As a result, the charge will transfer to the equipment, and will not leave the system. Electric shock will strike if you touch any electrical appliance connected to the network. At the same time, there is a high probability of failure of all equipment in the house connected to the mains.

In fact, grounding is a metal plate or wire that is used to divert "excess" electricity from the house to a place where it will not harm anyone. Grounding conductors also include lightning rods.

Unlike simple grounding, a lightning rod must be installed on high towers and poles, as such objects experience a very strong electrostatic effect, which makes them very attractive to lightning.

How to make grounding with your own hands

Grounding must be done at the construction stage. This is a mandatory rule in GOSTs and SNiP and PUE. Usually, the function of grounding is performed by the iron frame of reinforced concrete blocks. But if other materials are used in the construction of the foundation, then grounding will have to be done separately. To do this, dig a trench from the place where the shield is installed.

A wire or a metal plate with a thickness of not less than 6 mm. Then, thick reinforcing bars, 1-1.5 meters high, are driven into the trench at a distance of 80-70 cm from each other. They are interconnected by plates that are either screwed or welded to them.

The plates and the switchboard are fixed with a copper wire. The rods should protrude from the ground by 10-15 cm. The plate is connected on the switchboard to the bus using a copper cable and bolts.

A direct design can be used, but it has one drawback. In the event of a breakdown in the electrical system of the house, the pins will be under high voltage and if you touch them, there will be a strong electric shock. Therefore, a triangular type of grounding with a tap is most often used. It allows you to take the ground electrode to another place and protect it.

Triangle welded from plates welded to thick reinforcing bars and a discharge plate, which is placed in a trench dug in advance for this. The outlet plate is connected to the switchboard in the same way as with a direct earthing switch. There are other grounding schemes, but they are not much different from the previous two.

What will happen if you do not make grounding

Grounding work requires considerable physical effort and time. Naturally, the question arises why so much effort. What are the consequences if you do not carry out grounding work, how dangerous it is to strain like that.

Many do not make grounding in a house or apartment for one simple reason. Electrical breakdowns are rare. Even if it happened, so that the current hit strongly, the breakdown must be very large. And so, a slight pinching of an electric current has not yet killed anyone, especially if a person does not contact directly or through a conductor with the ground, then the electric current is also not felt.

Also, the risk of failure of household electrical appliances is not so great.

By and large, grounding is more technical standard requirement, not necessity. In many old houses, grounding is simply absent and no one has been electrocuted in such houses yet. The grounding requirement is most often a requirement of manufacturers of household electrical appliances, especially those made of metal rather than plastic.

How to determine if there is grounding in the house

If it is not possible to visually determine whether there is grounding in the house or apartment, that is, neither the connection to the grounding system nor the ground electrode pins are visible anywhere, then you can check it in several ways.

The first one is use special equipment. However, they must be able to use, besides, it costs a lot of money. But there is another way to check if there is a ground in the house, but it only works if there is a breakdown in the system, which is very important.

It is done like this: the phone is taken in one hand, make sure that it works. And put the other on the heating battery or any other metal object. The main thing is that while you are standing barefoot on the floor. If you feel light tingle from electricity- means there is no grounding in the house.