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Permissible resistance of the protective earth loop. Ground resistance
Page 1
The resistance value of the grounding device on the 0-4 kV side should be 4 ohms. This resistance must also be accepted for the 6 kV side with a common ground.
The value of the resistance of the grounding device r3 in comparison with the resistance of the human body Kchsya is very small: according to the norms, it should not exceed 4 ohms.
The resistance value of the grounding device of a mobile electrical installation must be checked during its construction, as well as during the next technical services. If natural grounding conductors are also used to reduce the resistance of artificial grounding conductors in an electrical installation, then the measurement of their resistances must be carried out separately. Only if it is not possible to separate artificial ground electrodes from natural ones, is it possible to measure the total resistance.
The resistance value of the grounding device normalized by the PUE depends on the ground fault current, the installation voltage and the method of grounding the neutrals of transformers or generators of the network in question.
At the same time, the value of the resistance of the grounding device (R) should be no more than 4 ohms. As an exception for transformer substations with one transformer with a power of 100 kVA or less, the grounding device can have a resistance of not more than 10 ohms.
It is equivalent to limiting the value of the resistance of the grounding device and, consequently, the voltage in relation to the earth to some valid value. As such a resistance value of the grounding device in the Rules, 4 ohms are accepted.
To obtain the resistance value of the grounding device required by the norms, in addition to the circuits, beam ground electrodes are laid.
As you can see, with this method, the value of the resistance of the grounding device is not limited, and safety must be achieved by equalizing the potentials.
The first condition is to a certain extent satisfied by the requirement of the Rules on the value of the resistance of the grounding device is not more than 4 ohms. This is also facilitated by the presence of repeated grounding of the neutral wire.
Artificial grounding conductors are used in cases where there are no natural grounding conductors near the electrical installations to be grounded, or when, after using natural grounding conductors, the resistance value of the grounding device does not meet the standards or design requirements.
In soils with higher resistivity, the natural conductivity of reinforced concrete foundations, supports and stepchildren should not be taken into account, and the required table. P-5-14, the resistance value of the grounding device should be ensured only by the use of artificial grounding conductors.
The design resistance of the grounding device is determined. The value of the resistance of the grounding device is determined depending on the purpose and in all cases is regulated by the Electrical Installation Rules. The resistance of the grounding device in networks up to 1,000 V should not exceed 4 ohms, and with a power of generators or transformers of 100 kVA or less - 10 ohms.
The design resistance of the grounding device is determined. The value of the resistance of the grounding device is determined depending on the purpose and in all cases is regulated by the Electrical Installation Rules. The resistance of the grounding device in networks up to 1000 V should not exceed 4 ohms, and with a power of generators or transformers of 100 kVA or less - 10 ohms.
Ground resistance- this is the resistance of the soil (earth) to the spreading of electric current through it, which comes through the ground electrodes.
As we know from the physics course, resistance is measured in ohms and the smaller it is, the better. The ideal option is a zero value, which means there is no resistance at all.
Such an ideal does not exist in nature, therefore, all electrical equipment and electronics are standardized with resistance values of 60, 30, 15, 10, 8, 4, 2, 1 and 0.5 ohms.
When connecting local grounding to the neutral of the transformer / generator in the TN system, the total grounding resistance (local + all repeat + grounding of the transformer / generator) must be no more than 4 ohms (PUE 1.7.101). This condition is met without any additional measures if the current source (transformer or generator) is properly grounded.
As for private houses with a 220/380 Volt electrical network, the value of ground resistance should not exceed 30 ohms.
If a gas pipeline is connected to a private house, then the grounding resistance should be no more than 10 ohms, since dangerous equipment is used.
Grounding used to connect lightning rods must have a resistance of no more than 10 ohms.
For a current source (generator or transformer), the ground resistance should be no more than 2, 4 and 8 ohms, respectively, at line voltages of 660, 380 and 220 V of a three-phase current source or 380, 220 and 127 V of a single-phase current source (PUE 1.7.101)
For reliable operation of gas dischargers in protection devices for overhead communication lines (for example, a local area network based on a copper cable or a radio frequency cable), the ground resistance to which they (arresters) are connected must be no more than 2 ohms. There are instances with a requirement of 4 ohms.
When connecting telecommunications equipment, grounding should usually have a resistance of no more than 2 or 4 ohms.
For a 110 kV substation, the current spreading resistance should be no more than 0.5 Ohm (PUE 1.7.90).
The ground resistance standards given above are valid for normal soils with a specific electrical resistance of not more than 100 Ohm * m (for example, clay / loam).
If the soil has a higher electrical resistivity - then often (but not always) minimum values ground resistance is increased by 0.01 of the soil resistivity.
For example, with sandy soils with a resistivity of 500 ohm * m, the minimum local grounding resistance of a house with a TN-C-S system increases 5 times - up to 150 ohms (instead of 30 ohms).
Grounding quality
Grounding resistance is the main quality indicator of the ground electrode system and directly depends on:
Soil resistivity;
- configuration of the ground electrode, in particular: the area of electrical contact of the electrodes of the ground conductor with the ground.
Soil resistivity
The parameter determines the level of "electrical conductivity" of the earth as a conductor - how well the electric current coming from the ground electrode will spread in such an environment. The smaller this value will be, the lower the grounding resistance will be.
The electrical resistivity of the soil (Ohm * m) is a measured value that depends on the composition of the soil, the size and density of its particles, its humidity and temperature, the concentration of soluble chemical substances(salts, acidic and alkaline residues).
Usually, a table of indicative values \u200b\u200b"soil resistivity" is used, since. its exact measurement is possible only in the course of special geological survey work.
Grounding configuration
The ground resistance directly depends on the area of electrical contact of the ground electrodes with the ground, which should be as large as possible. The larger the surface area of the ground electrode, the lower the ground resistance.
Most often, due to the least complexity of installation, a vertical electrode in the form of a rod / pipe / angle is used as a ground electrode.
To increase the contact area of the ground electrode with the ground:
The length (depth) of the electrode increases;
. several short electrodes connected together are used, placed at some distance from each other (
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NORMS OF RESISTANCE GOST 464-79
Moscow
STATE STANDARD OF THE UNION OF THE SSR
Introduction date 01.01.80
This standard applies to (SKPT), for which stationary grounding devices are equipped, and establishes the resistance standards for grounding devices that ensure the normal operation of the structures and installations listed above, as well as the safety of maintenance personnel.
The standard does not apply to grounding devices that are provided in special-purpose equipment.
The terms used in this International Standard and their definitions are given in the annex.
1. GENERAL PROVISIONS
1.1. To the working protective or protective earthing device by means of grounding wires, the shortest way must be connected:
one of the poles of the power supply installation;
the neutral of transformers, the output of a single-phase current source of a transformer substation or its own power plant supplying equipment of communication enterprises, a radio relay station or a PV station;
metal parts of power, static and switching equipment;
metal reference equipotential surface of electronic telephone exchanges;
metal pipelines for water supply and central heating and other metal structures inside the building;
screens of equipment and cables;
metal sheaths of cables, elements of protection circuits, lightning rods;
SKPT antennas subject to lightning protection in accordance with regulatory and technical documentation (hereinafter RTD).
The number of ground wires and the procedure for connecting equipment and equipment to them are established in the NTD for equipment of a particular type.
(Revised edition, Rev. No. 2).
1.2. Communication facilities should be equipped with protective earthing device, if there are no connecting lines and remote power supply circuits for equipment using earth as a wire electrical circuit.
Requirements to protective grounding and zeroing- according to GOST 12.1.030.
(Revised edition, Rev. No. 1).
1.3. Communication facilities should be equipped with one working and protective grounding device, if the "minus" of the remote power supply is grounded (in this case, the remote power supply circuits can be switched on according to the "wire-to-ground" scheme) or the "plus" of the current source is grounded, but there are no remote power supply circuits according to the "wire-to-ground" scheme. In this case, the connecting lines can use the "ground" as the wire of the electrical circuit. The circuit of the working-protective grounding device, in the presence of remote power supply circuits, must have two independent inputs to the building (up to the ground shield).
Enterprises should equip separate working and protective grounding devices if there are remote power supply circuits according to the "wire-ground" scheme with grounding "plus" of the current source.
1.4. The neutral of the transformers, the output of the single-phase current source of the transformer substation or its own power plant that supplies the equipment of communication enterprises, a radio relay station or a PV station, must be connected to a protective or working and protective grounding device. In this case, the grounding device for the above enterprise and for the transformer substation must be common if the distance between the enterprise and the transformer substation is less than 100 m.
Common ground resistance must comply with the grounding device resistance standards for each connected installation.
Resistance grounding device, to which the neutrals of generators or transformers or the output of a single-phase current source are connected, with a soil resistivity of up to 100 Ohm m, there should not be more than, Ohm:
2 - installations with a voltage of 660/380 V;
4 - installations with a voltage of 380/220 V;
8 - installations with voltage 220/127 V.
When the specific soil resistance r is more than 100 Ohm m, it is allowed to increase the resistance value of the grounding device by r / 100 times, but not more than ten times, and also not more than the values \u200b\u200bspecified in Table. Table 1-Table 3, Table 5 and in paragraphs. Clause 2.1.5, Clause 2.4.5, Clause 2.7.2.
1.3, 1.4. (Revised edition, Rev. No. 2).
1.4a. The resistance of a protective or working-protective grounding device must be ensured taking into account the use of natural grounding conductors (metal pipes laid underground, metal structures, reinforcement of buildings and their concrete foundations, etc., with the exception of pipelines of combustible and explosive mixtures, sewerage, central heating and domestic water supply located outside the building in which the equipment of the communication enterprise or the PV station is located).
1.5. The design of artificial ground electrodes or various circuits of the grounding device, the brand and cross section of the connecting conductors from the grounding device to the ground shield, the list of equipment, equipment and protection elements connected to the grounding device, the methods of connecting wires and their number, the method for measuring the resistance of grounding devices and soil resistivity set in the NTD for equipment of a particular type.
(Revised edition, Rev. No. 2).
1.6. The distance between individual non-insulated parts of different grounding devices (between working, protective, measuring, etc.) in the area before entering the building should not be less than 20 m.
1.7. The resistance of the measuring grounding device should not be more than 100 Ohm in soils with a resistivity of up to 100 Ohm m and 200 Ohm in soils with a resistivity of more than 100 Ohm m.
1.8. Resistance of linear-protective grounding devices for communication lines and wire hanging in areas of dangerous influence of power lines, electrified railways, as well as under the influence of radio stations and impulse effects (excluding lightning discharges), determined by calculation in accordance with the requirements of the NTD, should not exceed the values established by this standard.
(Revised edition, Rev. No. 2).
1.9. During the operation of grounding devices, their resistances should be checked at intervals:
twice a year - in summer (during the period of the greatest drying of the soil) and in winter (during the period of the greatest freezing of the soil) - at intercity, urban and rural telephone stations, telegraph stations, telegraph broadcasting, terminal and subscriber points;
once a year - in the summer (during the period of the greatest drying of the soil) - at radio relay stations, at stations and substations of radio broadcasting nodes;
once a year - before the beginning of the thunderstorm period (April - May) - in unattended amplification points (NUP) and regeneration points (RP) of long-distance, urban and rural communications; for containers of equipment of transmission systems (IKM-30, etc.);
once a year - before the start of the thunderstorm period - on cable and overhead communication lines and radio broadcasting networks, at cable poles and poles on which protective equipment is installed, at subscriber stations of telephone and radio broadcast networks, at step-down transformers of payphone booths;
at least once a year (before the beginning of the thunderstorm period) - for antennas of collective television reception systems.
2. STANDARDS OF RESISTANCE
2.1. Resistance standards of grounding devices for intercity telephone exchanges and terminal points of selective railway communication
2.1.1. Intercity telephone exchanges (MTS), end points of selective railway communication, linear equipment shops (LATS) and intermediate amplifying points with power supply installations must be equipped with a protective or working-protective grounding device and two measuring grounding devices. When equipping a working and protective grounding device in accordance with clause 1.3, one measuring grounding device is arranged, which must be connected in parallel with the protective grounding device.
In working condition, the measuring grounding devices must be connected on the grounding shield in parallel with the protective or working-protective grounding devices.
2.1.2. The resistance of protective grounding devices of MTS, linear equipment shops and intermediate amplifying points, as well as terminal points of selective railway communication with power supply installations that do not use earth as a current conductor in the circuits of connecting lines or remote power supply of unattended amplifying and regeneration points according to the “wire- earth”, should be no more than the values specified in clause Clause 1.4.
2.1.3. The resistance of protective grounding devices of intermediate points that do not have power supply installations should be no more than 10 Ohm for soils with a resistivity of up to 100 Ohm m and no more than 30 Ohm for soils with a resistivity of more than 100 Ohm m.
2.1.4. The resistance of working or working-protective grounding devices of MTS using earth as one of the wires of connecting lines of any type (custom, service from MTS and ATS, transit service lines, etc.), or in remote power supply circuits (DP) should not exceed the values indicated in the table. Table 1, and working and protective grounding devices must also comply with the requirements of clause 1.4.
Table 1
(Revised edition, Rev. No. 2).
2.1.5. Resistance of working or working-protective grounding devices of linear hardware shops, strong points; serviced amplifying points supplying remotely unserved or regeneration points according to the “wire-to-ground” scheme should be determined based on the voltage drop on the grounding device from the remote supply current of not more than 12 V. However, the resistance of working or working-protective grounding devices should not be more than the values specified in clause Clause 1.4.
2.1.6. Serviced amplification points of submarine cable lines that remotely feed underwater amplifiers according to the “wire-to-ground” scheme must be equipped with two separate working grounding devices (main and backup), which must be connected at the ground shield when in operation. The resistance of the main working grounding device should be no more than 5 ohms and the reserve - no more than 10 ohms.
(Introduced additionally, Amendment No. 2).
2.2. Resistance standards of grounding devices for unattended amplifying points of long-distance communication and intermediate points of selective railway communication
2.2.1. Unattended amplifying points (NUP), powered remotely according to the "wire-ground" scheme, in which the remote power supply circuit ends, must be equipped with three separate grounding devices - working, protective and linear-protective.
As a protective grounding device, it is allowed to use magnesium protectors used to protect metal tanks of LLP from soil corrosion.
In cases where it is not required to protect LLP metal tanks from soil corrosion, as well as when using non-metallic hulls, LLP must be equipped with a working and combined protective grounding device.
2.2.2. Unattended amplifying points (NUP) and regeneration points (RP) powered remotely according to the “wire-wire” scheme, as well as NUP fed according to the “wire-to-ground” scheme, in which the remote power circuit does not end, must be equipped with two separate grounding devices - protective and linear-protective.
As grounding conductors for a protective grounding device, it is allowed to use magnesium protectors used to protect metal tanks of LNP or RP from soil corrosion.
In cases where it is not required to protect metal LLP or RP tanks from corrosion, as well as when non-metallic LNP or RP tanks are used, a combined protective grounding device must be equipped.
2.2.3. The resistance of the working grounding device for NUP fed according to the "wire-ground" scheme should be no more than 10 Ohm for soils with a resistivity of up to 100 Ohm m and no more than 30 Ohm for soils with a resistivity of more than 100 Ohm m. In this case, the voltage drop from remote supply currents on the resistance of the grounding device should be no more than 12 V for soils with a resistivity of up to 100 Ohm m and no more than 36 V for soils with a resistivity of more than 100 Ohm m.
2.2.4. The resistance of protective grounding devices for NUP or RP fed according to the "wire-ground" and "wire-wire" schemes should be no more than 10 Ohm for soils with a resistivity of up to 100 Ohm m and no more than 30 Ohm - for soils with a specific with a resistance of more than 100 ohm m.
2.2.5. The resistance of line-protective grounding devices for cable sheaths, equipped at NUP or RP, when protecting cables from lightning strikes, should not exceed, Ohm:
10 - for soils with resistivity up to 100 Ohm m inclusive;
20 - for soils with specific resistance of St. 100 to 500 Ohm m incl.;
30 - for soils with specific resistance of St. 500 to 1000 Ohm m incl.;
50 - for soils with specific resistance of St. 1000 ohm.m.
(Revised edition, Rev. No. 2).
2.2.6. Intermediate points of selective railway communication must be equipped with one protective grounding device, the resistance of which must not exceed the values \u200b\u200bspecified in Table. Table 2.
table 2
2.3. Norms of resistance of grounding devices for telegraph stations and telegraph broadcasting terminals and subscriber points.
2.3.1. Telegraph stations, broadcasting, terminal and subscriber points operating on two-wire circuits, located in a separate building (not combined with MTS, ATS and other enterprises) and not using the "ground" as a wire of an electrical circuit, must be equipped with a protective and two measuring grounding devices. In working condition, all grounding devices must be connected in parallel on the grounding plate. Telegraph stations, broadcasting terminals and subscriber points combined with other enterprises (MTS, ATS) must include ground wires to a common protective grounding device.
For telegraph stations, where up to five telegraph sets are installed, it is allowed to use temporary measuring grounding devices.
2.3.2. The resistance of the protective grounding device of telegraph stations with power supply installations should not exceed the values \u200b\u200bspecified in clause Clause 1.4.
Broadcasting, terminal and subscriber points that do not have power supply installations must be equipped with a protective grounding device with a resistance of not more than 10 ohms with a specific soil resistance of up to 100 ohm m and 20 ohm for soils with a specific resistance of more than 100 ohm m.
2.3.3. Telegraph stations and telegraph broadcasting points operating on single-wire circuits must be equipped with a working-protective and two measuring grounding devices. For telegraph stations, where up to five telegraph sets are installed, it is allowed to use temporary measuring grounding devices.
The resistance of the working-protective grounding device, depending on the number of single-wire telegraph circuits introduced into the station (see GOST 5238, drawings 26-31), should not exceed the values \u200b\u200bspecified in Table. Table 3
Table 3
2.4. Resistance standards for grounding devices for city telephone exchanges and local railway stations
2.4.1. Telephone exchanges with a central battery (automatic exchanges and manual - PTS) must be equipped with three separate grounding devices - protective or working-protective and two measuring.
In working condition, all three grounding devices must be connected in parallel on the grounding shield and are disconnected only to measure the resistance of the protective or working-protective grounding device.
2.4.2. Telephone exchanges that have connecting lines and do not use earth as a current conductor (for example, connecting lines equipped with inductive sets of the RSL type) should be equipped with protective grounding devices (clause 1.2), the resistance of which should not exceed the values \u200b\u200bspecified in clause 1.2. 1.4.
Telephone exchanges that do not have supply transformer substations powered by electrical networks voltage 380/220/127 V, must be equipped with a protective grounding device with a resistance not exceeding the values \u200b\u200bspecified in Table. four.
Table 4
(Revised edition, Rev. No. 2).
2.4.3. Telephone exchanges with connecting lines using earth as current conductors (according to clause 1.3) must be equipped with working and protective grounding devices, the resistance of which must not exceed the values \u200b\u200bspecified in Table. 5.
Table 5
Note. In cases where at the station the connecting lines are equipped with inductive and battery (using earth as a current conductor) sets of the RSL type, the value of the resistance of the working and protective grounding is selected depending on the number of battery (polar) sets of the RSL type.
2.4.4. Unattended amplifying and regenerating points, fed remotely according to the "wire-wire" and "wire-ground" schemes, must be equipped with one protective grounding device, the resistance value of which must correspond to that given in clause 2.2.4.
2.4.5. The resistance of the protective or working-protective grounding device of electronic telephone exchanges must be no more than 4 ohms, and also comply with the requirements of paragraphs. 2.4.2 and 2.4.3.
(Introduced additionally, Amendment No. 2).
2.5. Resistance standards for grounding devices of rural telephone exchanges (STS)
2.5.1. Rural telephone exchanges with a central battery (RTS and ATS) must be equipped with three separate grounding devices in accordance with paragraphs. 2.4.1-2.4.3.
2.5.2. It is allowed to equip telephone exchanges with a capacity of up to 3000 numbers with one protective or working-protective grounding device, and temporary grounding devices can be used as measuring grounding devices.
(Revised edition, Rev. No. 2).
2.5.3. For compaction equipment of rural exchanges and RTSs, in the case of using the power supply system of the NUP "wire-wire", one combined protective grounding device should be used. At the same time, unattended amplifying points must be equipped with protective grounding devices with a resistance not exceeding the values \u200b\u200bspecified in paragraphs. 2.1.2 and 2.1.3.
2.5.4. Unattended amplifying points fed remotely according to the "wire-ground" scheme should be equipped with two separate grounding devices: working and linear-protective. The resistance of working and linear protective grounding devices should be no more than the values \u200b\u200bspecified in paragraphs. 2.2.3 and 2.2.5.
2.6. Ground resistance standards for telephone exchanges with a local battery (MB)
2.6.1. Telephone exchanges of the MB system operating on two-wire circuits must be equipped with three separate grounding devices - protective and two measuring. In working order, these three earthing devices must be connected in parallel at the earthing board. With a station capacity of up to 200 numbers, it is allowed not to equip stationary measuring grounding devices, and when measuring a protective grounding device, use temporary grounding devices.
2.6.2. The resistance of the protective grounding device of MB stations operating in two-wire circuits should not exceed the values \u200b\u200bspecified in Table. 2.
2.7. Resistance standards for grounding devices for stations and PV
2.7.1. Stations and PV should be equipped with one protective or working-protective grounding device. For control measurements of the resistance of the protective and working-protective grounding device, it is allowed to equip two stationary measuring grounds or use temporary grounding devices.
2.7.2. The resistance of a protective or working-protective grounding device for PV stations should be no more than 10 ohms.
2.7-2.7.2. (Revised edition, Rev. No. 2).
2.7.3. PV stations and transformer substations feeding them, geographically close to one another (clause 1.4), should be equipped with a common protective or working-protective grounding device with a resistance of not more than the values \u200b\u200bspecified in clause 1.4.
(Introduced additionally, Amendment No. 2).
2.8. Resistance standards of grounding devices for combined installations of wire communication and PV
(Revised edition, Rev. No. 2).
2.8.1. Stationary installations of wire communication for various purposes, located in one or nearby buildings and powered by one transformer substation: long-distance, urban, railway selective communications and others, as well as stations and substations of radio broadcasting nodes, should be equipped with one common protective or working protective grounding device . In this case, the resistance of the connecting wires from the grounding device should be taken into account.
2.8.2. The resistance value of the common earthing device must comply with the regulations for each connected installation.
2.8.3. Not allowed in unattended amplification points powered remotely direct current, combine a common protective grounding device with a working one.
2.9. Resistance standards for protective grounding devices for long-distance communication lines
2.9.1. Grounding device resistance values for:
spark gaps of cascade protection types IR-7, IR-10, IR-15 and IR-20;
spark gaps IR-0.2 or IR-0.3 - when they are installed on supports adjacent to the cable support or station;
spark gaps installed on the wires of overhead lines to protect underground communication cables from lightning strikes;
lightning rods installed on the supports of overhead lines;
rope and metal sheaths of cables suspended on overhead line supports should be no more than the values \u200b\u200bspecified in Table. 6.
Table 6
(Revised edition, Rev. No. 2).
2.9.2. The resistance of protective grounding devices for input, cable and other supports of long-distance communication lines and selective railway communication, on which, in accordance with the requirements of GOST 5238, it is required to include spark gaps of types IR-0.2 and IR-0.3 or gas-filled arresters, must not be more than the values indicated in the table. 7.
Table 7
2.9.3. The resistance of protective grounding devices for arresters of the IR-0.3 type, included to protect locking coils in the third circuits (see GOST 5238, drawing 9), should not exceed the values \u200b\u200bspecified in Table. 6.
2.9.4. The resistance of linear protective grounding devices for metal cable sheaths, protective wires (cables) or tires laid in the ground when protecting the cable from lightning strikes should not exceed the values \u200b\u200bspecified in Table. eight.
Table 8
Note. The number of linear protective grounding devices, their placement on cable lines and the method of connecting metal sheaths, cables and cable screens is established in the regulatory and technical documentation.
2.10. Resistance standards for protective grounding devices for urban and rural telephone networks and local railway networks
2.10.1. Resistance of grounding devices for spark gaps of types IR-0.2; IR-0.3; IR-7; IR-10 and IR-15, attached according to the schemes of features. 19, 22-24 GOST 5238, should be no more than the values \u200b\u200bspecified in table. 6.
2.10.2. Resistance of grounding devices for gas-filled arresters of R-84 and R-35 types installed in cable boxes at the junctions of wires of overhead lines of GTS, STS and railway communication networks with cable lines (see GOST 5238, drawings 15-17; 21a), a also for installation points of blockers (see GOST 5238, drawing 24), should be no more than the values \u200b\u200bspecified in Table. 9.
Table 9
Soil resistivity, Ohm m Up to 100 incl. St. 100 to 300 incl. St. 300 to 500 incl. St. 500
Resistance of grounding devices, Ohm, no more than 10 15 20 25
(Revised edition, Rev. No. 2).
2.10.3. The resistance of grounding devices for subscriber stations (see GOST 5238, drawings 16, 17, 21), for step-down transformers of payphone booths and lightning rods installed on overhead line supports, should not exceed the values \u200b\u200bspecified in Table. ten.
Table 10
Soil resistivity, Ohm m Up to 100 incl. St. 100 to 300 incl. St. 300 to 500 incl. St. 500 to 1000 inclusive St. 1000
Grounding device resistance, Ohm, no more than 30 45 55 65 75
2.10.4. Resistance of grounding devices for the metal sheath of the cable, the screen of the cable with non-metallic sheaths when suspended on the supports of pole and rack lines, the rope used for hanging cables, as well as for the housing of telephone distribution cabinets type ShR or ShRP, which include cables, should be no more than the values \u200b\u200bspecified in Table. 6.
2.10.5. The resistance of linear protective grounding devices for protection against lightning strikes of GTS and STS cables laid in the ground, as well as for the case of telephone switchboards of the ShR and ShRP types, which include cables, should not exceed the values \u200b\u200bspecified in Table. eight.
2.11. Resistance standards of protective grounding devices on PV lines
2.10.4, 2.10.5, 2.11. (Revised edition, Rev. No. 2).
2.11.1. Resistance of linear protective grounding devices for spark gaps of types IR-0.5 and IR-7.0 (see GOST 14857, drawings 1, 2), as well as for arresters of types IR-0.3 and IR-7.0 (see GOST 14857, drawings 3, 5, 6) should be no more than the values \u200b\u200bspecified in table. 6.
2.11.2. Resistance of linear protective grounding devices for grounding the metal sheath and screen of cables laid in channels cable duct and collectors (at the beginning and at the end of the cable) should be no more than the values \u200b\u200bspecified in Table. eight.
2.11.3. The resistance of linear protective grounding devices for lightning rods installed on the poles of overhead power lines should not exceed the values \u200b\u200bspecified in Table. ten.
(Revised edition, Rev. No. 2).
2.12. Resistance standards for grounding devices for radio relay stations
2.12.1. Radio relay stations, including those with compaction equipment, must be equipped with one protective grounding device. To control the resistance of the protective grounding device, it is allowed to equip two stationary measuring grounding devices or use temporary grounding devices. In working condition, protective and measuring stationary grounding devices must be connected in parallel on the grounding board.
2.12.2. The resistance of the protective grounding device must not exceed the values specified in clause 1.4.
2.13. Resistance standards of grounding devices for antennas of the collective television reception system
2.13.1. To protect the SKIT antennas from dangerous voltages and currents arising from lightning discharges, a protective grounding device must be equipped. To control the resistance of the protective grounding device, it is allowed to use temporary measuring grounding devices.
2.13.2. It is allowed to connect lightning rods from two or more SKPT antennas located on the same building to one grounding device.
2.13.3. The design of the grounding device, as well as the lightning rod connecting the SKPT antenna to the grounding device, and the method of their connection are established in the regulatory and technical documentation.
2.13.4. The resistance of the grounding device for SKPT antennas should be no more than the values \u200b\u200bspecified in Table. 6.
2.13.5. If there is a grounding device for the building on which the SKPT antennas are located (when protecting buildings from lightning strikes or for protecting telephone communication and broadcasting equipment), it is allowed to connect lightning rods from the SKPT antennas to the existing grounding device. The resistance of the grounding device should be no more than the values \u200b\u200bspecified in Table. 6.
APPENDIX
Reference
TERMS USED IN THIS STANDARD AND THEIR DEFINITIONS
Term Definition
Grounding for wired communication installations, radio relay stations, PV radio broadcasting nodes, etc. Intentional electrical connection of equipment or apparatus of an enterprise with a grounding device
Grounding conductor A metal conductor or a group of conductors of any shape (pipe, angle, wire, etc.) in direct contact with the ground (soil)
Grounding conductor A metal conductor that connects equipment or equipment to be grounded to the grounding conductor.
Grounding device A combination of ground electrode and ground conductors
Grounding device resistance or current spreading resistance The total electrical resistance of the grounding conductors and the grounding conductor relative to the ground, expressed in ohms. The resistance of the earth electrode relative to the earth is defined as the ratio of the voltage of the earth electrode relative to the earth to the current passing through the earth electrode to the ground
Soil resistivity The electrical resistance exerted by soil with a volume of 1 m3 when current flows from one face of the soil to the opposite. Soil resistivity, denoted by r and expressed in ohms per meter, should be measured seasonally, taking the most unfavorable value as the design
Working grounding device A device designed to connect wired communication equipment and radio engineering devices (PV substations, radio relay stations) to the ground in order to use the earth as one of the wires of the electrical circuit
Protective grounding device A device designed to connect neutral wires of the windings of power transformer substations, lightning rods, arresters, screens of equipment and wires for in-station installation, metal sheaths and armored covers of cables, metal tanks, maintenance-free amplifying points (NUP), metal parts of power equipment of wired installations communication and PV stations, installations for keeping cables under pressure and other equipment that is not normally energized, but may become energized if the insulation of current-carrying wires is damaged. Protective grounding devices provide equalization of the potential of the metal parts of the equipment with the ground potential and thus protect the operating personnel and equipment from the occurrence of a dangerous potential difference with respect to the ground.
Linear protective grounding device A device that provides grounding of cable metal sheaths and armored covers along the cable route and at stations (NUP) where cable lines are suitable, as well as on overhead lines for grounding lightning rods, cables and metal sheaths of the cable, etc. In some cases, it is allowed to combine protective and linear protective grounding devices. Such a grounding device is called a combined protective
Measuring grounding device Auxiliary device designed for control measurements of the resistance of working, protective and working-protective grounding devices. The resistance of the working and protective grounding devices should be measured, as a rule, from the grounding shield at the station, including the grounding conductor towards the grounding conductor. The resistance of grounding devices on overhead and cable lines is measured directly on the line
Working and protective grounding device A device that simultaneously serves as both a working and protective grounding device. The resistance of the working and protective grounding device must be no more than the smallest value provided for the working and protective grounding devices.
(Revised edition, Rev. No. 2).
INFORMATION DATA
1. DEVELOPED AND INTRODUCED by the Ministry of Communications of the USSR
DEVELOPERS:
A.K. Slanov (topic leader); V.V. Zakharov
2. APPROVED AND INTRODUCED BY Decree State Committee USSR according to the standards of 29.01.79 No. 304
3. The standard is unified with BDS 4722-70
4. Periodicity of inspection - 5 years
5. REPLACE GOST 464-68
6. REFERENCE REGULATIONS AND TECHNICAL DOCUMENTS
7. The limitation of the validity period was removed according to protocol No. 4-93 of the Interstate Council for Standardization, Metrology and Certification (IUS 4-94)
8. REPUBLICATION (October 1997) with Amendments No. 1, 2, approved in December 1983, June 1989 (IUS 4-84, 10-89)
Registration: 09.02.09 Messages: 149 Acknowledgments: 4
Registration: 17.07.10 Messages: 884 Acknowledgments: 301
Also, the resistance of the circuit to pulsed currents is less than to currents with a frequency of 50 Hz, while for a deep modular memory it is the other way around!
You also need to know that the protective grounding of the house and the equalization, potential equalization systems in the house when using TN systems, one of which is the TN-C-S system, do not protect outdoors when using electrical appliances protection class 1, these are those with protective contacts on the plug or ground terminal on the case, in case of a power failure.
GOST R 50571.3-94 413.1.3.9 said:
When a residual current protective device is used to automatically disconnect a circuit outside the coverage of the main potential equalization system, exposed conductive parts should not be connected to the TN system network, but the protective conductors should be connected to an earthing conductor having a resistance to ensure operation of this device. A circuit protected in this way may be considered a TT system network (see 413.1.4).
Note - Outside the coverage of the main potential equalization system, other protective measures can be used:
- power supply through a separating transformer;
- application of additional insulation (see 413.2)
The maximum consumption will be up to 10 kW. What section to pull the wire from the metal plate, which will be on the foundation, to the shield?
Power has nothing to do with it at all. The cross section must be at least 10 mm2 for copper or 16 mm2 for aluminum.
Why dig so much, not to mention the fact that unnecessary soil will be loosened, which will affect the memory resistance for the worse. Everything is done much easier.
Instead of the notorious triangle driven into the heads of inexperienced, it is better to drive the same pins with the same distance in a straight line along the wall of the house, at least the resistance of such a memory will be less due to the better pin utilization. Also, such a design will be part of the ground loop of the house, which will provide at least a primitive equalization, alignment of the conductive parts of the house. In the future, in parts or all at once, it will be possible to make a full-fledged grounding loop at home.
Places of welding and exit to the surface from a depth of 30 centimeters to a height above the surface of 30 centimeters should be well cleaned and treated with an anti-corrosion coating. The backfilled soil should be homogeneous, without stones and debris. At least the first backfilled soil up to 20 centimeters above the grounding device must be tamped.
It is called a device for measuring ground resistance, there are many different models, it is expensive to buy for a one-time use.
It is easier to drive in a corner that the grinder needs to make sharp. The pipe is flattened on one side, so that it is easier to drive in; before flattening, it is also better to cut it obliquely with a grinder.
Registration: 23.05.10 Messages: 10.446 Acknowledgments: 3.313
Registration: 20.07.07 Messages: 1.377 Acknowledgments: 366
C. Electrical safety Resistance of grounding devices (PUE-76, GOST 12.1.030-81)
Protective grounding provides, in systems with an isolated zero of the transformer, the discharge of current to the ground along the line of least "Resistance (compared to the resistance of the human body) through a metal conductor, firmly and tightly bolted to the body of the equipment, fencing. This conductor is connected to a grounding line, deeply grounded in the ground with special grounding conductors (pipes, plates).It is necessary to check more often the serviceability of grounding at workplaces in order to detect breaks, violations at the junctions in time.Once a year, a mandatory check of grounding resistance by equipment is carried out.In networks with voltages up to 1000 V, the resistance of grounding devices -
Inspection of the above-ground part of grounding devices electrical installations should be carried out simultaneously with the inspection of electrical equipment, but at least once a year. It is necessary to measure the resistance of grounding devices and check the presence of a grounding circuit with selective opening of individual elements of the grounding device at least once every 3 years, and also after rearranging the equipment.
The resistance of grounding devices should be measured during periods of the lowest conductivity: in summer - with the greatest drying, in winter - with the greatest freezing of the soil.
In electrical installations with high ground fault currents, the resistance of grounding devices at any time of the year should be no more than 0.5 ohm.
The resistance of the grounding device used to ground equipment with voltages above 1000 V should not exceed 10 ohms, and with high ground fault currents (over 500 A), the resistance of grounding devices should not exceed 0.5 ohms. .
According to the rules for the installation of electrical installations, protective grounding is normalized by the value of its resistance. The greatest resistance of grounding devices in installations with voltage up to 1000 V depends on the power of the current source (generator or transformer). If the power of the current source is less than 100 kVA, then the grounding resistance is allowed to be 10 ohms; with a current source power of more than 100 kVA, the grounding resistance should be no more than 4 ohms. In electrical installations with voltages above 1000 V with high earth fault currents (more than 500 A), the resistance of the ground gel should not exceed 0.5 Ohm. In installations with voltages above 1000 V with low earth fault currents, the resistance of the earth electrode is determined by the ratio 250//3; if the grounding device is simultaneously used for electrical installations up to 1000 V, then the resistance of the ground electrode should not exceed 125//3, but should not exceed 10 ohms (or 4 ohms if required for installations up to 1000V). Here /z is the earth fault current.
The resistance of earthing devices in explosive rooms and outdoor installations should only be measured with explosion-proof instruments designed for the respective explosive atmospheres. As a rule, the resistance to current spreading is
With a loop (distributed) ground electrode, when the resistance of the ground conductors is usually small, the resistance of the grounding device K3.y can be considered equal to R3- , and D3,y In this case, the impedance of the grounding device, Ohm,
Re-grounding of the neutral wire must be carried out at the ends of branches of overhead lines with a length of more than 200 m and in the middle of a line and branch with a length of 500 m. 4 and 8 ohms, respectively, at line voltages of 66U, 380 and 220V of a three-phase current source or 380, 220 and 127 V of a single-phase current source.
Metallic and electrically conductive parts of process equipment must be grounded to prevent sparking of static electricity. The resistance of grounding devices should not exceed 100 ohms.
1 - transformer; 2 - network; 3 - body of the current collector; 4 - motor winding; 5 - ground electrode; 6 - neutral grounding resistance (conditionally)
/ - transformer; 2 - network; 3 - fuse; 4 - motor winding; 5 - motor housing; 6 - grounding conductor; 7 - zero protective conductor; 8 - neutral earthing resistance
In the presence of grounding, due to current draining to the ground, the contact voltage decreases and, therefore, the current passing through a person is less than in an ungrounded installation. In order to minimize the voltage on the grounded equipment case, the ground resistance is limited. In 380/220 V installations, it should be no more than 4 ohms, in 220/127 V installations, no more than 8 ohms. If the power supply capacity does not exceed 100 kVA, the ground resistance can be within 10 ohms.
resistance of grounding and isolation of phases. With good insulation, gf is equal to tens of kΩ, so the current / s will be small. So, with a phase voltage of 220 V g, \u003d 4 Ohm, /F \u003d 40,000 Ohm, L \u003d 220 / (4 + +40,000) \u003d 0.0055 A. The potential drop will be distributed as follows: on the ground - between the case and the base U3 \u003d / Eg3 \u003d \u003d 0.0055-4 \u003d 0.022 V, between the base and the phases (potential drop on the insulation
In a network with a grounded neutral (see Fig. 7.5, 6) 13 \u003d U $ / (r3 + /b) \u003d \u003d 220 / (4 + 10) \u003d 15.7 A (/b is the electrical resistance of neutral grounding, usually not exceeding 10 ohms), and the touch voltage? / pr \u003d U3 \u003d 15.7 4 \u003d 62.8 V, which is dangerous for humans. As can be seen, in this case, 13 increases significantly with decreasing r, and the grounding efficiency is low. The lower the electrical resistance of the grounding of the installation case in comparison with the neutral grounding resistance, the higher the protective properties of the grounding will be.
According to the PUE, the electrical resistance of protective grounding at any time of the year should not exceed: 4 ohms in installations with voltages up to 1000 V with isolated neutral (with a current source power - generator or transformer - less than 100 kW, no more than 10 ohms is allowed). In installations with a grounded neutral, the ground resistance is determined by calculation based on the requirements for the allowable contact voltage, but not more than 0.5 Ohm.
Installations for the application of powder polymer paints must be equipped with local exhaust ventilation interlocked with the powder supply system, as well as devices that prevent sparking when the sprayer approaches the product to be painted due to static electricity discharges. To eliminate spark discharges of static electricity, it is necessary to ground the suspension of the product. Ground resistance should not exceed 1C6 ohm; it is subject to control at least once a shift.
During a scheduled inspection of the compressor unit, the following should be checked: the compressor and its motor; serviceability of the lubrication system; safety valves, pressure gauges; tightening degree of bolted connections; electrical insulation resistance and grounding resistance; operation of automatic devices; condition of check valves. Scheduled inspections should be carried out according to a schedule drawn up taking into account the recommendations of the manufacturer.
neutral grounding resistance (for networks with grounded neutral) (Fig. 39, biv). If the value of the insulation resistance of the network is large, then in practice the current passing through the person is very small, and in this case the network with a line voltage of the network U up to 1000 V is relatively safe with a single-phase connection.
Grounding conductors connect the electrical equipment housings to the grounding conductor. Overhead cranes, except those operating in an explosive atmosphere, are grounded through the crane runway. Grounding resistance in networks with an operating voltage of up to 1000 V, which include electric taps, should not exceed 4 ohms along with the loop resistance.
When checking grounding, keep in mind that the grounding resistance should not exceed 4 ohms. The witness must familiarize himself with the results of the resistance measurement.
