Pin grounding systems. Grounding the house. Grounding using homemade metal parts
One of the options for installing a grounding loop in a private house is to install a pin grounding. In this case, the operating time is significantly reduced, while the functionality of the ground electrode is not inferior to similar system options (linear, electrolytic, etc.). In this article we will tell you how to make modular-pin grounding with your own hands and what are the advantages of such a system.
Design features
What is such a system and what does it consist of? The device consists of one and a half meter steel pins, which are treated with copper and connected using couplings. The kit also includes a brass clamp with which to connect horizontal and vertical contours. Below is a diagram of the design.
The modular-pin grounding system is installed as follows: on top part A landing pad (nozzle) is mounted on the pin, which in turn is connected to the coupling. The attachment is necessary to transmit the force of the vibrating hammer. A steel tip is installed on the lower part of the structure. It makes it easier to drive the unit into the ground. There are several types of tips, the scope of which depends on the hardness of the soil.
In addition, the kit comes with a special electrically conductive liquid paste, the purpose of which is to protect against corrosion and constantly maintain electrical resistance during operation. Electrically conductive paste is applied to everything threaded connections designs. You can also use special moisture-proof adhesive tape to prevent corrosion. It is resistant to acids, salts and gases, and does not allow moisture to pass through.
Installation stages
Modular-pin grounding is installed according to a simple principle. First of all, the tip is put on the first pin. But before installation, it should be treated with electrically conductive paste against corrosion. We screw the coupling onto the other end and also treat it with anti-corrosion paste. The landing pad is then screwed onto the device to apply the vibratory hammer forces.
We place the assembled modular-pin grounding in a pre-prepared hole in the ground. You need to screw it into the ground as deeply as possible with your own hands. Then you need to connect the vibrating hammer to the network and place it on the rod site. Thus, the pin is immersed in the ground along its entire length. You only need to leave 20 cm in order to connect another rod.
This is followed by . To do this, you need to remove the landing nozzle and connect a special device, an ohmmeter, to the place where it was located:
When the first rod is located in the ground along its entire length, the landing attachment for the vibratory hammer is removed and another pin is mounted through the coupling. A special clamp that holds the pin in a vertical position rises along installed device up. And the connecting coupling and attachment for the vibrating hammer are again installed on the mounted structure, after which the process is repeated.
Spread resistance should be checked after installing each vertical rod. The pins are installed until the required resistance is established. The figure below shows a diagram of the change in resistance depending on the length:
Next, you need to connect the horizontal ground electrode and the vertical conductor. To do this, a brass clamp is attached to the end of the rod that protrudes from the ground and a horizontal ground electrode is connected to it. A special plate is placed between the pin and the horizontal cable, which protects against corrosion when dissimilar metals come into contact. After the system has been connected, the connection points are treated with special adhesive tape. It serves as additional protection against corrosion.
Advantages and disadvantages of the system
Modular-pin grounding, like any system, has its pros and cons. Compared to the classic and standard circuit, pin grounding has the following advantages:
- ease and simplicity of installation;
- occupies a small area;
- installation is carried out by a minimum number of workers (1–2 people);
- installation occurs without welding work, since all connections are made using couplings;
- thanks to the vibratory hammer, there is no heavy earthwork;
- modular-pin grounding is resistant to corrosion, as it is treated with special lubricants and coatings, thanks to which they last for several decades;
- regardless of the ground, the pin system is easily driven into the ground;
- structural elements are produced industrially, due to which they have high quality and are ready for immediate installation without additional preparatory work.
Modular-pin grounding has one significant disadvantage - its high cost. But, despite this drawback, the system is beneficial if you take into account all its advantages.
The industry produces many different kits that combine such elements that are necessary for reliable and high-quality installation. Modular-pin grounding has an important purpose - it protects the house from fire, and people in the room from electric shock.
This is a drawn steel rod with a diameter of 14 mm and a length of 1.5 meters, coated by electrolytic deposition (electrolysis) with copper of 99.9% purity, forming a coating with a molecular and inextricable bond with the steel.
Threads are applied along the edges using the knurling method for their mutual connection using a coupling.
In addition to electrical conductivity, high-quality steel in such a grounding device also plays a mechanical role necessary for burying the electrode in the soil. The pins have a high tensile strength (600 N/mm²) and can be driven into the ground with a jackhammer to a great depth - up to 40 meters.
The thickness of the copper coating is at least 0.25 mm along the entire length of the rod (including threads). This guarantees its (coating) resistance to bending, peeling, and scratching during installation. This is especially important on threads, where a thinner layer of copper will be completely destroyed from loads and friction with the coupling during penetration (installation) *.
These features guarantee the high corrosion resistance of the grounding pin and ensure such a long service life (up to 100 years).
* Features of creating threads
The “correct” thread is applied AFTER copper plating - by knurling, because Only this method makes it possible to achieve high overall quality of the pin.
An alternative “technology” for copper plating of pins: with already formed threads (before applying the coating) is cheaper, BUT it shows a worse (and dangerous during operation) result.
This is due to a feature of electrolysis: thickening of the coating in the recesses/cavities, due to which the base material (steel) on the thread can only be coated with a thin (0.03 - 0.05 mm) layer of copper.
Such a thin coating is easily damaged during installation by impacts and friction in the coupling. Subsequently, during operation of the grounding electrode with such violations, foci of electrochemical corrosion (“copper-iron”) arise, leading to its complete destruction within 2-3 years.
Copper plating technology
The key to making a quality ground pin is to create a steel billet strong, uniform copper coating of the required thickness with minimal impurities.
On a separate page "Copper-plated steel" are presented detailed description main characteristics, manufacturing processes and tests of the coating.
Comparison with galvanized pins
From 1910 to 1955, The National Institute of Standards and Technology (NIST) conducted an extensive study of underground corrosion, during which 36,500 samples representing 333 types of ferrous and non-ferrous metal coatings and protective materials were tested. in 128 locations throughout the United States*. This study is widely considered to be one of the most comprehensive corrosion studies ever conducted.
One of the results of this study was the fact that a ground pin coated with 254 microns of copper retains its specifications for over 40 years in most soil types. And rod electrodes coated with 99.06 microns of zinc in the same soils can retain their qualities only for 10-15 years.
In addition, the protection period zinc the coating decreases in proportion to the increase in the number of metal structures in the ground located next to the electrodes (the more structures, the less service the coating lasts / the faster it “disappears”). Examples of these structures can be: reinforcement of building foundations, pipes, etc.
Ground pin with copper plated 254 microns thick, extracted from soil (loam) after 10 years
Ground pin with zinc coating 99 microns thick, extracted from soil (loam) after 10 years
Another study of the corrosion properties of copper coating was carried out by the Polish company GALMAR. Artificial aging of samples under conditions simulating aggressive soil (an “acidic” swamp) showed that a grounding pin with a 250 micron copper coating retains the necessary technical characteristics for at least 30 years.
Under " grounding"is understood electrical connection equipment, devices to the grounding device, which in turn is connected to the ground (earth). The purpose of grounding is to equalize the potential of equipment, circuits and ground potential. Grounding is required for use at all power facilities to ensure the safety of workers and equipment from the action of currents short circuit. When a breakdown occurs, the short-circuit current flows through the grounding device circuit to the ground. The current passage time is limited by the action of relay protection and automation. This ensures the safety of the equipment, as well as the safety of workers in terms of electric shock.
To protect electronic equipment from electrostatic potentials and limit the voltage of the equipment case for the safety of operating personnel, the resistance of an ideal grounding circuit should tend to zero. However, in practice this is impossible to achieve. Considering this circumstance in modern standards security is set quite low valid values resistance of grounding circuits.
Grounding device resistance
The total resistance of the grounding device is composed of:
- The resistance of the metal of the electrode and the resistance at the point of contact between the grounding conductor and the grounding electrode.
- Resistance in the area of contact between the electrode and the ground.
- Ground resistance in relation to flowing currents.
In Fig. Figure 1 shows a diagram of the placement of a grounding electrode (pin) in the ground.
As a rule, the grounding pin is made of a metal that conducts electric current (steel or copper) and is marked with the appropriate terminal. Therefore, for practical calculations, we can neglect the resistance value of the grounding pin and the point of contact with the conductor. Based on the results of the studies, it was found that if the installation technology of the grounding device is observed (close contact of the electrode with the ground and the absence of foreign impurities in the form of paint, oil, etc. on the surface of the electrode), due to its small value, it is possible to ignore the resistance at the point of contact of the grounding electrode with earth.
Soil surface resistance is the only component of the grounding device impedance that is calculated during the design and installation of grounding devices. In practice, it is believed that the grounding electrode is located among identical layers of soil, arranged in the form of concentric surfaces. The closest layer has the smallest radius and therefore the minimum surface area and the greatest resistance.
As you move away from the ground electrode, each subsequent layer increases its surface area and decreases its resistance. At some distance from the electrode, the resistance of the soil layers becomes so small that its value is not taken into account for calculations. The area of soil beyond which the resistance is negligible is called the area of effective resistance. The size of this area is directly dependent on the depth of immersion of the grounding electrode into the soil.
The theoretical value of soil resistance is calculated using the general formula:
where ρ is the value of soil resistivity, Ohm*cm.
L – thickness of the soil layer, cm.
A – area of concentric soil surface, cm2.
This formula clearly explains why the resistance of each soil layer decreases with distance from the grounding electrode. When calculating soil resistance, its resistivity is taken as a constant value, but in practice the value of resistivity varies within certain limits and depends on specific conditions. Formulas for finding grounding resistance with a large number of grounding electrodes have complex look and allow you to find only an approximate value.
Most often, the grounding resistance of a pin is determined using the classic formula:
where ρ is the average value of soil resistivity, Ohm*cm.
R – electrode grounding resistance, Ohm.
L – depth of the grounding electrode, cm.
r – radius of the grounding electrode, cm.
Influence of the dimensions of the grounding electrode and the depth of its grounding on the value of grounding resistance
The transverse dimensions of the grounding electrode have little effect on the grounding resistance. As the diameter of the grounding pin increases, a slight decrease in grounding resistance is observed. For example, if the diameter of the electrode is doubled (Fig. 2), then the grounding resistance will decrease by less than ten percent.
Rice. 2. Dependence of the resistance of the grounding pin on the diameter of its cross-section, measured in inches
As the depth of placement of the grounding electrode increases, the grounding resistance decreases. It has been theoretically proven that doubling the depth can reduce drag by as much as 40%. In accordance with NEC (1987, 250-83-3), the pin should be immersed to a depth of at least 2.4 meters to ensure reliable contact with the ground (Figure 3). In many cases, a three meter grounded pin will fully satisfy current NEC standards.
NEC Standards (1987, 250-83-2) require a minimum diameter of 5/8" (1.58 cm) for a steel grounding electrode and 1/2" (1.27 cm) for a copper coated steel or copper electrode. cm).
In practice, the following transverse dimensions of the grounding pin are used with a total length of 3 meters:
- Regular primer – 1/2" (1.27 cm).
- Wet soil – 5/8" (1.58 cm).
- Hard ground – 3/4" (1.90 cm).
- For a pin length of more than 3 meters – 3/4 "" (1.91 cm).
Rice. 3. Dependence of the resistance of the grounding device on the grounding depth (vertically - the value of the electrode resistance (Ohm), horizontally - the grounding depth in feet)
Influence of soil resistivity on the value of electrode grounding resistance
The above formula shows that the value of grounding resistance depends on the depth and surface area of the grounding electrode, as well as on the value of soil resistivity. The latter value is the main factor determining the grounding resistance and the depth of electrode grounding required to ensure minimum resistance. Soil resistivity depends on the time of year and point globe. The presence of electrolytes in the soil in the form aqueous solutions salts and electrically conductive minerals in to a large extent affects soil resistance. In dry soil that does not contain soluble salts, the resistance will be quite high (Fig. 4).
Rice. 4. Dependence of soil resistivity (minimum, maximum and average) on the type of soil
Factors influencing soil resistivity
With extremely low moisture content (close to zero), sandy loam and ordinary land have a resistivity of over 109 Ohm*cm, which allows such soils to be classified as insulators. An increase in soil moisture to 20 ... 30% contributes to a sharp decrease in resistivity (Fig. 5).
Rice. 5. Dependence of soil resistivity on moisture content
The resistivity of the soil depends not only on the moisture content, but also on its temperature. In Fig. Figure 6 shows the change in the resistivity of sandy loam with a moisture content of 12.5% in the temperature range of +20 °C to –15 °C. The resistivity of the soil when the temperature drops to – 15 °C increases to 330,000 Ohm*cm.
Rice. 6. Dependence of soil resistivity on its temperature
In Fig. Figure 7 shows changes in soil resistivity depending on the time of year. At significant depths from the surface of the earth, the temperature and humidity of the soil are quite stable and less dependent on the time of year. Therefore, a grounding system in which the pin is located at a greater depth will be more effective at any time of the year. Excellent results are achieved when the ground electrode reaches the groundwater level.
Rice. 7. Change in grounding resistance during the year.
A water pipe (¾"") located in rocky soil was taken as a grounding device. Curve 1 (Curve 1) shows the change in soil resistance at a depth of 0.9 meters, curve 2 (Curve 2) - at a depth of 3 meters.
IN in some cases There is an extremely high value of soil resistivity, which requires the creation of complex and expensive protective grounding systems. In this case, you need to install a grounding pin small sizes, and to reduce the grounding resistance, periodically add soluble salts to the surrounding soil. In Fig. Figure 8 shows a significant decrease in soil resistance (sandy loam) with increasing concentration of salts contained.
Rice. 8. Relationship between soil resistance and salt content (sandy loam with humidity 15% and temperature +17 °C)
In Fig. Figure 9 shows the relationship between the resistivity of the soil, which is saturated with a salt solution, and its temperature. When using a grounding device in such soils, the grounding pin must be protected from the effects of chemical corrosion.
Rice. 9. The influence of the temperature of soil impregnated with salt on its resistivity (sandy loam - salt content 5%, water 20%)
Dependence of the resistance value of the grounding device on the depth of electrode grounding
To determine the required depth of the grounding electrode, a grounding nomogram will be useful (Fig. 10).
For example, to obtain a grounding value of 20 ohms in soil having a resistivity of 10,000 ohms*cm, it is necessary to use a metal pin with a diameter of 5/8 "" buried 6 meters.
Practical use of the nomogram:
- Set the required resistance of the grounded pin on the R scale.
- Mark the point of actual soil resistivity on the P scale.
- Draw a straight line to the K scale through the given points on the R and P scales.
- Mark a point at the intersection with the K scale.
- Select the required ground rod size using the DIA scale.
- Draw a straight line through the points on the K scale and on the DIA scale until it intersects the D scale.
- The intersection of this straight line with scale D will give the desired depth of the pin.
Rice. 10. Nomogram for calculating the grounding device
Measuring soil resistivity using the TERCA2 device
Available land plot large area.
The task is to find a place with minimal resistance and estimate the depth of the soil layer with the lowest resistivity. Among various types soil found in this area, the minimum resistance will be in wet loam.
After a detailed examination of the site, the search area is narrowed to 20 m2. Based on the requirements for the grounding system, it is necessary to determine the soil resistance at a depth of 3 m (300 cm). The distance between the outermost ground pins will be equal to the depth for which the average resistivity is measured (in this case 300 cm).
To use the simplified Wenner formula
the grounding electrode should be at a depth of about 1/20 of the distance between the electrodes (15 cm).
Installation of electrodes is carried out according to a special scheme shown in Fig. eleven.
An example of connecting a grounding tester (Mod. 4500) is shown in Fig. 12.
Rice. 11. Installation of grounding electrodes along the grid
- Remove the jumper that connects terminals X and X V (C1 and P1) of the measuring device.
- Connect the tester to each of the 4 pins (Fig. 11).
Example.
The tester showed a resistance of R = 10 Ohms.
Distance between electrodes A = 300 cm.
Resistivity is determined by the formula ρ = 2 π *R*A
Substituting the original data we get:
ρ = 2 π * 10 * 300 = 18,850 Ohm cm.
Rice. 12. Tester connection diagram
Touch voltage measurement
The most important reason for measuring touch voltage is to obtain a reliable assessment of the safety of substation personnel and the protection of equipment from exposure to high voltage currents. In some cases, the degree of electrical safety is assessed according to other criteria.
Grounding devices in the form of a separate pin or array of electrodes require periodic inspection and verification of resistance measurements, which are performed in the following cases:
- The grounding device is compact in size and can be temporarily disabled.
- When there is a threat of electrochemical corrosion of the grounding electrode caused by low soil resistivity and constant galvanic processes.
- If there is a low probability of a breakdown to ground close to the grounding device being tested.
As an alternative way to define security technological equipment substation uses touch voltage measurement. This method recommended in the following cases:
- If it is impossible to disconnect the grounding device to measure grounding resistance.
- In the event of a threat of ground faults near the grounding system being tested or in the vicinity of equipment connected to the grounding system being tested.
- When the circuit of the equipment in contact with the ground is comparable in area to the size of the grounding device to be tested.
It should be noted that measuring grounding resistance using the potential drop method or measuring touch voltage does not allow us to make a reliable conclusion about the ability of the grounding conductor to withstand significant currents when current leaks from the phase to the grounding conductor. For this purpose, a different method is required, in which a test current of significant magnitude is used. Touch voltage measurement is performed using a four-point ground tester.
In the process of measuring touch voltage, the device creates a small voltage in the ground, which simulates the voltage during a fault. electrical network close to the point being tested. The tester shows the voltage value in volts per 1 A of current flowing in the ground circuit. To determine the highest touch voltage that can occur in an extreme case, multiply the resulting value by the maximum possible current.
For example, when testing a grounding system with the highest possible fault current of 3000 A, the tester returned a value of 0.200.
Therefore, the touch voltage will be
U = 3000 A * 0.200 = 600 V.
Measuring touch voltage is in many ways similar to the potential drop method: in each case it is necessary to install auxiliary ground electrodes in the ground. However, the distance between the electrodes will be different (Fig. 22).
Rice. 13. Grounding conductor diagram (general case for an industrial power supply network)
Let's consider a typical case. Near the substation, an underground cable suffered insulation damage. Currents will flow through this place into the ground, which will go to the substation grounding system, where they will create a high potential difference. High leakage voltage can pose a significant threat to the health and life of substation personnel located in a dangerous area.
To measure the approximate value of the touch voltage that occurs in this case, you should perform a number of steps:
- Connect cable between metal fencing electrical substation and points P1 and C1 of a four-point grounding tester.
- Install a grounding electrode in the ground in the place where cable breakdown is most likely.
- Connect the electrode to input C2 of the tester.
- On the straight line between the first electrode and the point of connection to the fence, install an additional electrode in the ground. The recommended distance from the installation point of this electrode to the point of connection to the fence is one meter.
- Connect this electrode to point P2 of the tester.
- Turn on the tester, select the 10 mA range, record the device readings.
- To obtain the touch voltage value, multiply the tester readings by the maximum current value.
To obtain a voltage potential propagation map, it is necessary to install an electrode (of course, connected to the P2 terminal of the tester) in various places near the fence, located next to the faulty line.
Measuring grounding resistance with the "SA 6415" device using current clamps
Measuring ground resistance using current clamps is a new, very effective method, which allows measurements to be taken when the grounding system is turned on. This method also provides a unique opportunity to measure the total resistance of a grounding device, including determining the resistance of connections in an existing grounding system.
Operating principle of the device S.A. 6415
Rice. 14. Grounding conductor diagram (general case for an industrial power supply network)
Rice. 15. Operating principle of the grounding conductor
A classic grounding device for an industrial electrical network can be presented in the form of a circuit diagram (Fig. 23) or in the form of a simplified diagram of the operation of the grounding conductor (Fig. 24).
If voltage E is applied to one of the sections of the circuit with resistance RX using a transformer, then electric current I will flow through this circuit.
These quantities are related to each other by the relationship:
By measuring the current I at a known constant voltage E, we can determine the resistance RX.
In the diagrams shown (Fig. 23 and 24), a special transformer is used to generate current, connected to a voltage source through a power amplifier (frequency 1.6 kHz, constant amplitude). The resulting current is recorded by a synchronous detector in the resulting circuit, further amplified using a selective amplifier and, after conversion through an analog-to-digital device, displayed on the device display.
Typical examples of measuring ground resistance in real conditions
1. Measuring the grounding resistance of a transformer installed on a power line pole
Measurement procedure:
- Remove the protective cover from the grounding conductor.
- Provide the necessary space for the current clamp to freely reach the conductor or grounding pin.
- Clamps must be connected along the current path from the neutral or grounding wire to the grounding pin (pin system).
- Select current measurement “A” on the device.
- Grab the grounding conductor with a current clamp.
- Determine the current values in the conductor (the maximum permissible current is 30 A).
- If this value is exceeded, stop measuring the resistance.
- Disconnect the device from this point and take measurements at other points.
- If the current value does not exceed 30 A, you should select the “?” mode.
- The display of the device will show the measurement result in Ohms.
The resulting value includes the total resistance of the grounding system, which includes: the contact resistance of the neutral wire with the ground pin, as well as the local resistance of all connections between the pin and the neutral.
Rice. 16. Measuring ground resistance on a power line pole
Rice. 17. Measuring the grounding of a transformer installed on a power line support (grounding in the form of a group of pins)
Rice. 18. Measuring the grounding of a transformer installed on a power line support (a metal pipe is used for grounding)
According to the diagram shown in Fig. 25, the end of the pole and a pin located in the ground are used for grounding. To correctly measure the total grounding resistance, current clamps should be connected at a point located above the junction of the grounding conductors laid from the grounding pin and the end of the pole.
The reason for the increased ground resistance value may be:
- Poor grounding of the pin.
- Disconnected ground conductor
- High resistance values in the area of conductor contacts or at the splice point of the ground wire.
- You should carefully inspect the current clamps and the connections at the end of the pin to ensure that there are no significant cracks at the joints.
2. Measurement of ground resistance on distribution box or on the electricity meter
The technique for measuring grounding on a distribution box and on an electric meter is similar to that discussed when measuring the grounding of a transformer. The grounding circuit can consist of a group of pins (Fig. 26) or a metal water pipe in contact with the ground can be used as a grounding conductor (Fig. 27). When measuring resistance grounding, both types of grounding can be used simultaneously. To do this, it is necessary to select the optimal point on the neutral in order to obtain the correct value of the total resistance of the grounding system.
3. Measurement of grounding resistance on a transformer installed on site
When carrying out grounding measurements at a transformer substation, you must remember:
- At this power facility there is always high voltage, dangerous to human life
- The transformer enclosure must not be opened.
- All work may only be carried out by qualified specialists.
- When carrying out measurements, the requirements of safety and labor protection measures must be observed.
Rice. 19. Measuring the grounding value on a transformer located on a special site
Measurement procedure:
- Decide on the number of grounding pins.
- When the grounding pins are located inside the fence, measurements should be made according to the diagram shown in Fig. 28.
- When placing grounding pins outside the fence area, use the diagram shown in Fig. 29.
- If there is one grounding pin located inside the fence, you must connect to the grounding conductor at a point located after the contact of this conductor with the grounding pin.
- Using current clamps mod. 3730 and 3710 connected directly to the ground pin will provide better measurement results in most cases.
- In many cases, several conductors are connected to the terminal on the pin, going to the neutral or into the fence.
- The clamp meter should be connected at the point where the only path for current to flow into the neutral conductor is.
If low resistance values are obtained, the measurement point should be moved as close as possible to the ground pin. In Fig. Figure 29 shows a grounding pin outside the barrier area. To ensure correct measurements, it is necessary to select the connection point for the current clamps in accordance with the diagram shown in Fig. 29. If there are several grounding pins inside the fence, you should determine their connection in order to select the optimal point for measurements.
Rice. 20. Choosing the correct ground measurement point
4. Transfer stands
When conducting grounding measurements on transmission racks, it should be remembered that there are many different configurations of grounding devices, which introduces certain difficulties when assessing grounding conductors. In Fig. Figure 30 shows a grounding diagram for a single rack on a concrete foundation with an external grounding conductor.
The connection point for the current clamps is selected above the connection point of the grounding elements, which can be designed in the form of a group of plates, pins, or be structural elements rack foundation.
Figure 21. Measuring the ground resistance of the transmission rack
Operation of modern household and computer equipment without grounding is fraught with its failure. In a large part of our country, especially in rural areas, old-style power transmission systems. They do not provide for protective grounding or are in such a state that they simply do not meet electrical safety requirements. Therefore, owners have to do the grounding of a private house or cottage themselves.
What does it give
Protective grounding is necessary to ensure electrical safety in the home. If done correctly, when a leakage current appears, it leads to immediate tripping of the RCD (damage to the electrical insulation or when live parts are touched). This is the main and main task of this system.
The second function of grounding is to ensure the normal operation of electrical equipment. For some electrical appliances, having a protective wire in the socket (if any) is not enough. Direct connection to the ground bus is required. For this purpose there are usually special clamps on the case. If we talk about household appliances, these are a microwave oven, an oven and a washing machine.
The main task of grounding is to ensure the electrical safety of a private home.
Few people know, but a microwave without a direct connection to the “ground” can emit significant radiation during operation; the reception level of radiation can be life-threatening. In some models, you can see a special terminal on the back wall, although the instructions usually contain only one phrase: “grounding is required” without specifying exactly how it should be done.
When touched wet hands a tingling sensation is often felt towards the body of the washing machine. It is not dangerous, but unpleasant. You can get rid of it by connecting the ground directly to the case. In the case of an oven, the situation is similar. Even if it does not “pinch”, a direct connection is safer, since the wiring inside the installation operates under very harsh conditions.
With computers the situation is even more interesting. By directly connecting the ground wire to the case, you can significantly increase the speed of the Internet and minimize the number of freezes. It’s that simple because of the direct connection to the ground bus.
Do you need grounding in a country house or in a wooden house?
In holiday villages, grounding is mandatory. Especially if the house is built of flammable material - wood or frame. It's about thunderstorms. At dachas there are a lot of elements that attract lightning. These are wells, boreholes, pipelines lying on the surface or buried to a minimum depth. All of these objects attract lightning.
If there is no lightning rod and grounding, a lightning strike is almost equivalent to a fire. There is no fire station nearby, so the fire will spread very quickly. Therefore, in combination with grounding, also make a lightning rod - at least a couple of meter-long rods attached to the ridge and connected to the ground using steel wire.
Grounding systems for a private house
There are six systems in total, but in individual developments, mainly only two are used: TN-S-C and TT. IN last years TN-S-C system is recommended. In this scheme, the neutral at the substation is solidly grounded, and the equipment has direct contact with the ground. The earth (PE) and neutral/zero (N) are connected to the consumer by one conductor (PEN), and at the entrance to the house they are again divided into two separate ones.
With such a system, a sufficient degree of protection is provided by automatic devices (RCDs are not required). Disadvantage - if the PEN wire burns out or is damaged in the area between the house and the substation, phase voltage appears on the earth bus in the house, which cannot be turned off by anything. Therefore the PUE presents strict requirements to such a line: there must be mandatory mechanical protection of the PEN wire, as well as periodic backup grounding on poles every 200 m or 100 m.
However, many transmission lines in rural areas do not meet these conditions. In this case, the TT system is recommended for use. Also, this scheme should be used in free-standing open outbuildings with an earthen floor. There is a risk of touching the ground and ground at the same time, which can be dangerous with a TN-S-C system.
The difference is that the “ground” wire to the panel comes from an individual ground loop, and not from a transformer substation, as in the previous diagram. Such a system is resistant to damage to the protective wire, but requires the mandatory installation of an RCD. Without them, there is no protection against electric shock. Therefore, the PUE defines it only as a backup if the existing line does not meet the requirements of the TN-S-C system.
Grounding device for a private house
Some older power lines have no protective ground at all. They all must change, but when this will happen is an open question. If this is your case, you need to make a separate circuit. There are two options - do the grounding in a private house or country house yourself, with your own hands, or entrust the execution to a campaign. The company's services are expensive, but there is an important advantage: if problems arise during operation due to improper functioning of the grounding system, the company that carried out the installation will compensate for the damage (must be specified in the contract, read carefully). When independent execution everything is on you.
The grounding system of a private house consists of:
- grounding pins,
- metal strips combining them into one system;
- lines from the ground loop to .
What to make grounding conductors from
A metal rod with a diameter of 16 mm or more can be used as pins. Moreover, you cannot take the reinforcement: its surface is hardened, which changes the distribution of current. Also, the hardened layer in the ground collapses faster. Second option - metal corner with shelves 50 mm. These materials are good because they can be driven into soft soil with a sledgehammer. To make this easier to do, one end is sharpened, and a platform is welded onto the other, which is easier to hit.
Sometimes used metal pipes, one edge of which is flattened (welded) into a cone. Holes are drilled in their lower part (about half a meter from the edge). When the soil dries out, the distribution of the leakage current deteriorates significantly, and a saline solution can be poured into such rods, restoring the functioning of the grounding. The disadvantage of this method is that you have to dig/drill holes under each rod—it won’t be possible to hammer them in with a sledgehammer to the required depth.
Pin driving depth
The grounding pins should go into the ground below the freezing depth by at least 60-100 cm. In regions with dry summers, it is desirable that the pins be at least partially in moist soil. Therefore, corners or a rod 2-3 m long are mainly used. Such dimensions provide a sufficient area of contact with the ground, creating normal conditions for the dissipation of leakage currents.
What not to do
The job of protective grounding is to dissipate leakage currents over a large area. This happens due to the close contact of metal grounding conductors - pins and strips - with the ground. That's why Grounding elements are never painted. This greatly reduces the current conductivity between the metal and the ground, making the protection ineffective. Corrosion in welding areas can be prevented with anti-corrosion compounds, but not with paint.
Second important point: Grounding should have low resistance, and good contact is very important for this. It is provided by welding. All joints are welded, and the quality of the seam must be high, without cracks, cavities and other defects. Please note again: Grounding in a private house cannot be done on threaded connections. Over time, the metal oxidizes, breaks down, the resistance increases many times, the protection deteriorates or does not work at all.
It is very unwise to use pipelines or other metal constructions located in the ground. For some time, such grounding works in a private house. But over time, the pipe joints become oxidized and destroyed due to electrochemical corrosion, activated by leakage currents, and the grounding becomes inoperative, as does the pipeline. Therefore, it is better not to use these types of grounding conductors.
How to do it right
First, let's look at the shape of the ground electrode. The most popular is in the form of an equilateral triangle with pins hammered into the vertices. There is also a linear arrangement (the same three pieces, only in a line) and in the form of a contour - the pins are driven around the house in increments of about 1 meter (for houses with an area of more than 100 sq. m). The pins are connected to each other by metal strips - metal bonding.
Procedure
From the edge of the house to the installation site, the pin must be at least 1.5 meters. In the selected area, they dig a trench in the form of an equilateral triangle with a side of 3 m. The depth of the trench is 70 cm, the width is 50-60 cm - so that it is convenient to cook. One of the peaks, usually located closer to the house, is connected to the house by a trench with a depth of at least 50 cm.
At the vertices of the triangle, pins are hammered (a round rod or corner 3 m long). About 10 cm is left above the bottom of the pit. Please note that the ground electrode is not brought to the surface of the earth. It is located 50-60 cm below ground level.
A metal bond is welded to the protruding parts of the rods/corners - a strip of 40 * 4 mm. The created ground electrode is connected to the house with a metal strip (40*4 mm) or a round conductor (cross section 10-16 mm2). The strip with the created metal triangle is also welded. When everything is ready, the welding areas are cleaned of slag and coated with an anti-corrosion compound (not paint).
After checking the grounding resistance (in general, it should not exceed 4 Ohms), the trenches are covered with earth. There should be no large stones or construction waste, the earth is compacted layer by layer.
At the entrance to the house, a bolt is welded to the metal strip from the ground electrode, to which a copper conductor in insulation is attached (traditionally the color of the ground wires is yellow with a green stripe) with a core cross-section of at least 4 mm 2.
Grounding outlet near the wall of the house with a bolt welded at the end
In the electrical panel, the grounding is connected to a special bus. Moreover, only on a special platform, polished to a shine and lubricated with grease. From this bus, the “ground” is connected to each line that is distributed throughout the house. Moreover, wiring the “ground” with a separate conductor according to the PUE is unacceptable - only as part of a common cable. This means that if you have two-wire wiring, you will have to completely change it.
Why you can’t make separate groundings
Rewiring the entire house is, of course, time-consuming and expensive, but if you want to operate modern electrical appliances without problems and household appliances, it's necessary. Separately grounding certain outlets is ineffective and even dangerous. And that's why. The presence of two or more such devices sooner or later leads to the output of the equipment plugged into these sockets. The thing is that the resistance of the circuits depends on the condition of the soil in each specific place. In some situation, a potential difference occurs between two grounding devices, which leads to equipment failure or electrical injury.
Modular pin system
All the previously described devices - made from hammered corners, pipes and rods - are called traditional. Their disadvantage is the large volume of excavation work and the large area that is required when installing a ground electrode. All because it is necessary certain area contact of the pins with the ground is sufficient to ensure normal “spreading” of the current. The need for welding can also cause difficulty - there is no other way to connect the grounding elements. But the advantage of this system is relatively low costs. If you do traditional grounding in a private house with your own hands, it will cost a maximum of $100. This is if you buy all the metal and pay for welding, and do the rest of the work yourself
Modular pin (pin) systems emerged a few years ago. This is a set of pins that are driven to a depth of up to 40 m. That is, you get a very long grounding rod that goes to a depth. The pin fragments are connected to each other using special clamps, which not only fix them, but also provide a high-quality electrical connection.
The advantage of modular grounding is small area and less work required. A small pit with sides 60*60 cm and a depth of 70 cm, a trench connecting the ground electrode to the house is required. The pins are long and thin, drive them into suitable soil not difficult. This is where we come to the main disadvantage: the depth is great, and if you encounter, for example, a stone on the way, you will have to start over. But removing the rods is a problem. They are not welded, but whether the clamp will hold up or not is a question.
The second disadvantage is the high price. Together with installation, such grounding will cost you $300-500. Self-installation is problematic, since driving these rods with a sledgehammer will not work. We need a special pneumatic tool, which we have learned to replace with a hammer drill with impact mode. It is also necessary to check the resistance after each driven rod. But if you don't want to mess with welding and land works, modular pin grounding is a good option.
