What is the difference between the concepts of "grounding", "grounding device" and "earthing switch"?
Grounding, grounding and earthing are three different terms that should not be confused.
Grounding refers to the deliberate connection of parts of an electrical installation to a grounding device. Thus, unlike a grounding device and a grounding device, grounding is a process, an action.
A grounding device is a set of earthing and grounding conductors, and a grounding conductor is a conductor or a group of conductors in direct contact with the earth and connecting certain parts of the electrical installations to it.
Earthing devices, depending on the purpose, can perform various functions.
These devices are divided into protective, working and lightning protection.
- Protective earthing devices are designed to protect people and animals from electrical shock by accidentally closing the phase wire to the non-conductive metal parts of the electrical installation.
- Working grounding devices are necessary to create a certain operating mode of the electrical installation under normal and emergency conditions.
- Lightning-protective earthing devices are used for grounding rod and cable lightning arresters and arresters and are designed to drive pulsed lightning current to the ground.
In many cases, the same grounding device can combine several functions (for example, be protective and operational). All grounding devices are divided into two main types. It is customary to distinguish between natural and artificial earthing switches.
Natural grounders include water pipes laid in the ground and other metal pipelines (with the exception of pipelines of flammable or explosive liquids and gases); casing; metal structures and reinforcement of reinforced concrete structures of buildings and structures; lead shells of cables laid in the ground, provided that at least two of them are laid and if there are no other earthing switches, etc.
Do not use pipelines covered with insulation to protect them from corrosion, pipelines for transferring flammable liquids and gases, aluminum cable sheaths and bare aluminum conductors as earth conductors.
To the artificial earthing devices include the designs made especially for grounding. They can be vertically immersed in the ground steel rods and sub-standard pipes, corner steel, horizontally laid steel strips, round steel rods, etc.
An earthing conductor is designed to connect the grounded parts of electrical installations to the earth electrode. As the grounding conductors, metal structures of buildings and structures, as well as metal structures for industrial purposes, such as steel pipes for wiring, aluminum cable sheaths, metal stationary openly laid pipelines of any purpose (other than those intended for transportation of flammable and explosive mixtures), metal trusses , crane runways, etc.
In residential buildings and structures, water pipes, heating pipes are not allowed as grounding conductors. The smallest permissible sizes of grounding conductors and earthing element elements are given in the table.
The smallest permissible sizes of earthing conductors
| The name of the grounding conductor or the earthing element | unit of measurement | Acceptable dimensions | ||
| In buildings | In outdoor installations | In the ground | ||
| Round steel | mm (diameter) | 5 | >6 | 6 |
| Rectangular steel | mm2 (cross section) | 24 | 48 | 48 |
| Corner steel | mm (thickness of shelves) | 3 | 4 | 4 |
| Steel gas pipe | mm (wall thickness) | 2,5 | 2,5 | 2,5 |
| Steel thin-walled pipe | mm (wall thickness) | 1,5 | Not allowed | Not allowed |
The main electrical characteristic of a grounding device is its resistance. It is equal to the sum of the resistance of the earthing switch and grounding conductors. The resistance of the earth electrode is called the resistance to the flow of electric current.
The electric current, flowing from the earth electrode to the ground, is distributed unevenly in the volume, meeting on its way in the ground a certain resistance. Therefore, they talk about the resistance to the flow of current from the earthing switch to the ground. For brevity, it is simply called spreading resistance.
Resistance to spreading of the earthing switch is equal to the ratio of its potential (voltage) at the point of injection to the current that goes from the earth electrode to the ground: R = U / I
In electrical installations with a voltage of up to 1 kV with a grounded neutral, the resistance of the grounding device to which the generator or transformer neutral terminals or the single-phase current source terminals are connected should not exceed 2, 4 and 8 ohms at any time of the year at line voltages of 660, 380 and 220 V, respectively three-phase or 380, 220 and 127 V single-phase current.
This resistance must be ensured taking into account the use of natural earthing switches, as well as grounding earths of the zero wire of the overhead line (VL) up to 1 kV with the number of outgoing lines of at least two. But even if this requirement is fulfilled, the generators or transformers should still have their own artificial earthing switches, the resistance of which must be no more than 15, 30 and 60 Ohms at line voltages of 660, 380 and 220 V, respectively, of a three-phase source or 380, 220 and 127 V single-phase current.
If the specific electrical resistance ρ of the earth exceeds 100 Ω m, it is allowed to increase these values in ρ / 100, but not more than 10 times. At the ends of overhead lines (or branches) with a length of more than 200 m, as well as on the entrances to buildings, the electrical installations of which are subject to zeroing, they perform repeated earthing using primarily natural as well as lightning-proof earthing switches.
The total resistance of all these earthing switches, artificial and natural, for each overhead line should not exceed 5, 10 and 20 ohms at any time of the year at linear voltages of 660, 380 and 220 V, respectively, of a three-phase source or 380, 220 and 127 V single-phase current. In this case, the resistance of the grounding device of each of the repeated groundings must be no more than 15, 30 and 60 ohms, respectively, at the same voltages. As for grounding devices of generators and transformers, the values of these resistances can be increased by ρ / 100 times, but not more than 10 times.
The resistance of the grounding device used to ground the electrical equipment of the electrical installation with a voltage of up to 1 kV with an isolated neutral must be no more than 4 ohms. This resistance can be increased to 10 ohms with the power of generators and transformers 100 kVA or less, for parallel-running generators and transformers, the resistance of 10 ohms is allowed with their total power not exceeding 100 kVA.
The following requirements are imposed on grounding devices in electrical installations with voltages above 1 kV.
Earthing devices of electrical installations with voltages above 1 kV in networks with effectively earthed neutral intended for grounding electrical equipment, except for overhead transmission lines, are performed in compliance with the requirements for the resistance of the grounding device or to the touch voltage, as well as to the structural performance and to limiting the voltage on the grounding device.
If the grounding device is executed, observing the requirements for its resistance, then the value of the latter at any time of the year should not be more than 0.5 Ohm, including the resistance of natural earthing switches. In order to equalize the electrical potentials between the electrical equipment and the ground and to connect this equipment to the earth electrode at a depth of 0,5 ... 0,7 m from the ground surface, longitudinal and transverse conductors, called horizontal earthing conductors, are laid on the territory occupied by the equipment. Conductors connect with each other. As a result, a grounding grid is formed. Longitudinal horizontal earthing conductors are laid along the axes of the electrical equipment on the maintenance side at a distance of 0.8 ... 1.0 m from the foundations or equipment bases. In the event that the service sides are facing one another and the distance between the foundations or the bases of the rows of equipment does not exceed 3 m, it is allowed to lay one earthing switch for two rows of equipment. In this case, the distance from the longitudinal earthing device to the foundations or equipment bases can be increased to 1.5 m. The transverse earthing switches are laid at the same depth in convenient locations between the foundations of the equipment. To save metal and more evenly equalize electrical potentials, the distances between transverse earthing switches are assumed to increase from the periphery to the center of the grounding grid. In this case, the first and subsequent distances, starting from the periphery, should not exceed 4, respectively; 5; 6; 7.5; 9; eleven; 13.5; 16 and 20 m. The size of the meshes of the grounding grid adjacent to the places of connection to the earthing switch of short-circuiting switches and neutral transformers of power transformers should not be more than 6X6 m2. On the edge of the territory occupied by the grounding device, horizontal earthing switches are laid so that together they form a closed loop. If this circuit is located within the outer fence of the electrical installation, the potentials are equalized at the entrances and entrances to its territory by installing two vertical earthing switches with a length of 3 ... 5 m. The distance between them is chosen equal to the width of the entrance or entrance. With the help of welding, these earthing switches are connected to an external horizontal earthing switch.
The implementation of grounding devices to acceptable resistance often leads to an unjustified overexpenditure of metal and money.
More economical, sometimes several times, grounding devices performed in compliance with the requirements imposed on the touch voltage.
Such grounding devices must ensure, at any time of the year (when ground-fault currents flow down from them) the values of contact stresses not exceeding normalized. In determining them, the sum of the time of operation of the primary or backup protection and the total time for switching off the circuit breaker is taken as the estimated time of action.
If the permissible touch voltage values are determined at workplaces where, in the case of operational switching, there may be closures on the structures accessible to the personnel who perform the switching operations, then the specified amount of times should include the duration of the backup protection, and for the rest of the territory, the main one.
For grounding devices made with touch voltage, longitudinal and transverse horizontal earthing switches are placed, observing only the requirements of limiting contact stress to normalized values and the convenience of connecting grounding equipment, however in all cases the distance between two adjacent longitudinal or transverse horizontal artificial earthing switches should not exceed 30 m , and the depth of their laying in the ground should be at least 0.3 m. At workplaces, earthing switches can be laid on a smaller depth, provided that the need for this is confirmed by calculation, and the convenience of maintenance and the lifespan of the earthing switch are not reduced.
To reduce the touch voltage, gravel padding with a thickness of 0,1 ... 0,2 m or asphalt pavement can be made at workplaces in justified cases. The resistance of grounding devices made at permissible contact voltages can be any, but should not exceed the values determined by permissible voltages on grounding devices and ground fault currents.
Voltages on grounding devices made both by resistance and touch voltage must not exceed 5 kV when the earth fault current flows from them.
Voltages higher than 5 kV but not more than 10 kV are allowed for earthing devices of those electrical installations for which special measures are provided to protect the insulation of outgoing communication cables and telemechanics and to prevent the removal of hazardous potentials beyond the limits of electrical installations.
For earthing devices, with which the removal of potentials outside the buildings and external fences of the electrical installation is excluded, voltages above 10 kV are allowed. Earthing devices of electrical installations with voltages above 1 kV with insulated neutral are made in such a way that their resistances, taking into account the resistance of natural earth conductors, at any time of the year do not exceed the quotient of the K coefficient from the calculated earth fault current expressed in amperes.
When the grounding device is simultaneously used for electrical installations with voltage up to 1 kV, K = 125. At the same time, the requirements for grounding electrical installations with a voltage of up to 1 kV must also be met.
If the grounding device is used only for electrical installations with voltages above 1 kV, then K = 250. In both cases, the resistance of the grounding device must not exceed 10 ohms.
In soils with a high electrical resistivity, the resistance values of grounding devices may be increased in ρ / 500 times, where ρ is the specific earth electrical resistance in ohms. However, this increase should not be more than tenfold.
As the rated ground fault current, the earth fault current is assumed, provided that there are no capacitive current compensation devices in the network. In networks with compensation of capacitive currents, the rated current for earthing devices to which compensating devices are connected is chosen equal to 125% of the rated current of these devices, and for grounding devices to which no compensating devices are connected, equal to the residual earth fault current that can be in the given network at switching-off of the most powerful of compensating devices or the most branched out site of a network.
Often the rated current is taken as the melting current of the fuse links of the fuses or the tripping current of the relay protection against single-phase earth faults.
As a design, the tripping current of the phase-to-phase fault protection is also assumed, provided that this protection ensures that earth faults are disconnected. In all cases, the earth fault current must be not less than one and a half times the tripping current of the relay protection or three times the rated current of the fuses.
The rated earth fault current is determined for that of the network circuits possible in operation, at which it has the greatest value. The earthing device of open electrical installations must contain a closed horizontal earthing switch (circuit). The depth of its laying in the ground should be at least 0.5 m. Grounding equipment is connected to this circuit. In those cases where the grounding device is in the ground with a specific electrical resistance of more than 500 Ohm m and its resistance exceeds 10 Ohm, along the rows of equipment from the maintenance side at a distance of 0.8 ... 1.0 m from the foundations or equipment bases, horizontal earthing switches at a depth of at least 0.5 m.
Zeroing.
Zanjeniem refers to the connection of metal housings of electric receivers with the neutral of the feeding transformer or generator via a neutral wire.
Zeroing should ensure reliable automatic shutdown of the network section where the fault occurred. Due to zeroing, any shorting to the case turns into a short circuit and, therefore, the emergency area is immediately switched off by an automatic device or fuses.
Zeroing is carried out by connecting the electrical equipment enclosures to the neutral wire of the network. In this case, each housing must be connected to the neutral wire of the network by a separate conductor (see "Zeroing the group of electrical receivers", "a").
In the zeroing conductor it is forbidden to consistently include several parts of the electrical installation (figure "Zeroing of the group of electric receivers", "b").
What is the difference between a zeroing conductor and a neutral conductor?
The zeroing conductor is intended only for zeroing. In normal operation mode, the current does not pass through it (Fig. "Electrical wiring diagram", "a", "c").
Fig. Zeroing of the group of electric receivers: a - correct; b - wrong.
Fig. The scheme of zeroing of electric receivers:
Zero conductor is used to connect single-phase consumers. It can not be used as a zeroing device (see Figure "Electrical Wiring Diagram", "6").
- a, c - correct zeroing;
- b - incorrect
1 - the neutral wire of the network; 2 - zero working wire; 3 - zeroing wire.
In networks with a dull neutral neutral, the neutral wire must be grounded, and in several places.
The main grounding of the neutral wire is at the power substation, the second one on the power line and at the entrances to the premises.
Zeroed consumer equipment is usually not necessary to ground. The ground wire of the network is reliably grounded and therefore the equipment connected to it does not need additional grounding.
The need for grounding of the zoned equipment, as a rule, is separately specified in the operation manual or the technical description of the equipment.
Especially it should be emphasized that there is no separate grounding bus in residential houses. Therefore, the requirement of manufacturers of household appliances for mandatory earthing of housings of household appliances are, as a rule, technically unworkable and the housing is being nullified, which subsequently allows you to remove legal liability from household appliances manufacturers.Resistance to spreading of the earth electrode is measured as follows.
This resistance is usually measured by the method of an ammeter and a voltmeter, using portable devices according to the scheme shown in the figure "Schemes for measuring the resistance to spreading of the earth electrode", "a".
Two auxiliary electrodes are required for the measurement. The current T is used to pass an electric current through the measured earth electrode, and potential P is used to measure the potential of the earthing switch.
The resistance of the earth electrode, measured in the above diagram, is calculated from the known formula R = U / I As a source of measuring current, a welding or any other transformer can be used, in which the secondary winding does not have an electrical connection with the primary.
The potential and current electrodes are positioned as shown in the figure "Schemes for measuring resistance to spreading of the earth electrode", "b". In the above scheme, distances are given for measuring the resistance to spreading of the earthing terminal of a consumer substation, made in the form of a closed loop. When measuring the resistance of the spreading of single earthing switches intended for repeated earthing of the neutral conductor of the power transmission line, these distances can be reduced by a factor of 2.
When measuring the resistance to spreading of the earthing switch by the device MC-08, it is located in the immediate vicinity of the place of connection to the tested earthing switch and one of the circuits shown in figure "c" "Schemes of resistance to spreading of the earth electrode" or "g", which differ from each other only in that in the diagram "d" from the reading of the device it is necessary to subtract the resistance value of the connecting conductor going from the earth electrode to the terminals I1 and E1. After the assembly of the circuit, the resistance of the potential circuit is regulated. 
Drawing. Schemes of measuring resistance to spreading of the earthing switch:
- a is a schematic diagram;
- b - arrangement of electrodes;
- c - measurement of the resistance of the earthing switch;
- d - measurement of the total resistance of the earthing switch and the connecting conductor.
For this purpose, the range switch is placed in the "Adjust" position and by rotating the generator knob at a frequency of about two revolutions per second, the device adjusts the device's arrow to the red line using the adjusting rheostat.
If you can not set the arrow on the red line, then the sum of the resistance of the grounding electrode and the potential electrode is greater than 1000 ohms and the resistance of the potential electrode needs to be reduced. To do this, resort to local moistening of the land with salted water, a deeper laying of the potential electrode or the use of several parallel-connected rods slammed into the ground at a distance of 3 ... 4 m from each other.
After adjusting the potential circuit, proceed directly to the measurement. To do this, the range switch is moved to the "XI" position, which corresponds to a measurement range of 10 ... 1000 Ohm, and by rotating the generator knob, measure the resistance to spreading of the earth electrode. If the arrow falls on the non-working part of the scale (0 ... 10 Ohm), then go to a smaller measuring range, shift the range switch to "X0.1" or "X0.01".
If the equipment is reliably grounded (eg submersible pump motor for water supply), but not reset, then such equipment is a source of increased danger of electric shock. Therefore, it must be reset to zero, following the above requirements for the zeroing device.
Additional electrical protective measures in addition to grounding and zeroing are widely used devices for equalizing electrical potentials and high-speed highly sensitive residual current devices (RCDs).
Under traditional grounding means a grounding conductor made of black steel without a protective coating.
We classify the artificial earthing switches used for traditional grounding in various parameters.
To begin with, we recall that the earthing switches can be horizontal and vertical.
As a vertical earthing rod, a steel equal-angle corner and a circle are used most often, and a horizontal bar or bar (circle, armature).
Regulations
The minimum dimensions of the earthing switches are normalized by the rules for the installation of electrical installations (Table 1.7.4.), And technical circular No. 11/2006 (Table 1).
Despite the fact that this circular is recommendatory for most organizations, in recent years, the supervision structures refer to it more often. We advise you to use it, since the requirements of the circular are more suitable for modern electrical installations.
Corners
Corners for earthing usually have the sizes 45х45х5, 50х50х5, 63х63х5 and 63х63х6. In order to speed up the installation procedure, the corners are sharpened at the end on one side at an angle of 30 °.
Earthing Corner
Circle and fittings
The steel circle most often it has a diameter of? 18 or? 20. You can also use the construction armature.
Earthing ring and fittings
Earthing strip
For a horizontal earthing switch, lane with a length and width of 40x5 mm and 50x5 mm, as well as a circle ? 10 mm.
Earthing strips and circle
Earthing installation
Recall that the earth electrode should not be painted. Only welding places can be painted. When installing in a ground with an aggressive environment, it is necessary to increase the area of the earthing conductors, for example, not a 45x45x5 corner, but a circle with a diameter of O20.
The process of mounting such a grounding device is easy to understand, but tedious in performance, especially when it is necessary to achieve a sufficiently low resistance of 2-4 ohms.
Digging out a trench
First, you need to mark out and dig a trench depth of 70-80 cm under the horizontal earthing switch. If the access of technology is possible, then you can save on physical labor. For excavating a trench, it is best to use a backhoe loader.
Clogging corners in the ground
After the trench has been excavated, you can start mounting the corners. There are many ways and devices for dipping corners in the ground, but most often use two of them. First - clogging the corners with a sledgehammer. This method is suitable if there are not many corners.
The second method is quicker and more simple, the corners are pressed into the excavator bucket. This method is the most optimal, but the rental of equipment is not cheap.
If a corner of a long length is used, it is recommended to make a pit in advance in the trench, otherwise the corner will be difficult to score.
The distance between the vertical earthing switches must be no less than their length.
Grounding
We lay the horizontal earthing switch on the bottom of the trench and weld it with vertical earthing switches.
Do not forget to coat the welds with bituminous varnish or paint to prevent corrosion.
Drawing up the act of work
Before backfilling the trench, it is necessary to draw up a passport (act) for hidden work on the installation of a storage device, in which the representative of the customer and the installation organization are signed.
Years, because it will be possible to measure the resistance value of the grounding device immediately or more or less accurately. And digging the ground will be much easier on dry ground.
It is easier to make ground from a black steel corner 50х50х5 mm and a steel strip 50х5 mm, connection by a method, and using a grounding bar. Steel corners should not be painted.
There is an opinion that earthing electrodes must be located in the place of the infield where it is most humid, that is, where the soil is shaded, and where the rainwater merges. But this is not entirely true, as rainwater moistens the soil to a depth of 1-1.5 m. Deeper soil layers remain unchanged throughout the year, and it is in this layer that the grounding rods should be located.
It is most optimal to arrange grounding from the most electrified premises of the house. This will reduce the cost of the material of the grounding conductor.
Earthing installation consists of the following main stages:
1. excavation work;
2. clogging corners;
3. Connecting the corners and connecting the ground bus;
4. connection of the protective conductor to the grounding bus;
5. Measuring the resistance of the grounding device.
1. Earthwork
The following tools are required for excavation:
- Bayonet shovel;
- The lobster shovel;
- Scrap.
Pit for mounting the ground electrode. The trench is 3 m long for two rods 2, 5 meters in height.
To make it easier to drive a grounding rod 50x50x5 mm, you need to remove the top layer of the soil.
For those who do not like to do extra work, I advise first to dig a pit 50x50 cm to the depth of freezing. Usually, this is about 1 m for the middle band. This will allow one electrode to be clogged. Next, measure its resistance, then you can calculate the number of electrodes needed for the ground loop. Usually, in clay soils there are three angles of 2.5 m each.
2. Clogging of the earthing corners
To hammer a steel corner 50х50х5 mm to a depth of 2.5 m with a sledge hammer by hand, is not so easy. But you can go for a little trick, and to facilitate your work you need to sharpen the end of the corners at an acute angle, for example, with the help of "Bulgarians". The optimal angle is about 20-30 degrees, less is not advisable, otherwise the end of the corner can begin to strongly curl if it hits a pebble.
If you use the advice of this article, and have dug a trench for corners with a depth of at least 1 m, then it is possible to clog a corner with a height of 2.5 m simply standing on the ground, in the worst case, standing on a low chair. One strong blow with a sledge hammer the angle by about 1 cm.
The device with their own hands earthing trikutnikomOblashtuvannya with their own hands grounding triangle BudinkaZazemlennya home
3. Connecting the corners and attaching the ground bus
When the corner is killed, then their ends are very splashy. This is normal, everyone has. It will be necessary to simply cut off the splashes of the end of the corners, and connect the corners of the steel strip 50x5 mm by welding.
When welding, you will need to make three welds - two side verticals and one horizontal top of the steel strip, which provides the maximum quality of welding. For welding, any electrodes for low-carbon steel are suitable.
Connecting the steel strip to the corner with the help of welding: 1. steel strip, 2. corner, 3. welding seam. Connecting the steel strip to the corner by welding: 1. steel strip, 2. corner, 3. welding seam Grounding from galvanized profile to the line
4. Connecting the protective conductor to the ground bus
This is a very important step, if you do a trash, then sooner or later the contact place will start to rust, the resistance will deteriorate sharply and from grounding will not be of use. The copper conductor must be insulated and have a cross-sectional area of 10 mm 2. The conductor itself must be laid in a plastic corrugation and the junction box must be closed with a conduit.
Fastening of a grounding conductor to a steel strip 50х5 mm by means of the zinced washers. Connection of the grounding loop to the grounding conductor of copper with a diameter of 4 mm2. The connection of the grounding loop to the grounding conductor of copper with a diameter of 4 mm2
Use zinc-plated fasteners! Unprotected black steel forms a galvanic couple with copper and quickly rusts, i.e. The copper wire should only touch the galvanized washers and do not touch the steel strip directly. The steel staff itself, before connecting the conductor, must be stripped of the rust at the fixing point.
Measuring the resistance of the ground loopVimiryuyuvannya resistance of the ground loop 5. Measuring the resistance of the received ground loop
Measurement of the ground resistance is best entrusted to specialists, especially if you have never held an ohmmeter. The resulting resistance of the ground loop of the building should not exceed 47 ohms. This is the permissible resistance of the ground loop with the mandatory use of a RCD with a minimum leakage current of 30 mA.
If it was possible to meet the 47 ohm impedance immediately after the grounding, it will be necessary to repeat the measurements twice during the unfavorable season for the conductivity of the soil: during the dry warm season and during the cold season. The resistance value must remain within the permissible limits. In the article "Protective Grounding at Home", the necessity of using a ground loop for a private house is justified.