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The cross-section of the grounding wire must satisfy the requirements for the corresponding conductors of this installation.
The cross-section of the grounding wire must meet the requirements for the corresponding earthing conductors of this installation.
| The scheme of the protective device. Frequency response of the input resistance of the protective device. |
The cross-section of the descents from the line wires to the protective device circuit, the ground wire section, as well as the parameters of the arresters and separating capacitors Cp, are selected such that they provide operator safety in case of possible emergency situations and lightning overvoltages.
When working in open switchgears and in the guard zone of an active overhead line, machines and lifting cranes must be grounded. The cross-section of the grounding wire must be no less than that adopted for the electrical installation in which the crane is located. Machines and cranes on caterpillar tracks when installing them directly on the ground are not required to ground.
All parts of stationary and mobile electric welding machines, which are under voltage, must be reliably grounded. The cross-section of the ground wire and the grounding device must comply with the guidelines for grounding and zoning. In addition, the welded object itself must be grounded. Wires that supply current from the machines to the switchboard and from it to the welding places are reliably isolated. These wires must be protected from high temperature and mechanical damage.
In networks with a deafely earthed neutral, the closure of the phase conductor to a grounded electrical housing or neutral wire is a single-phase ground fault that triggers protection and automatically trips the emergency area. The cross-section of the grounding wire is chosen so that when a short to ground or a neutral wire is shorted, a short-circuit current occurs that is at least 3 times the rated current, to which the fuse-link of the nearest fuse or the release of the circuit-breaker is designed. If the machine only has an electromagnetic release (cut-off), then the grounding conductor is selected such that a short-circuit current equal to 1 25 - 1 4 values of the instantaneous tripping current setting occurs in the phase-zero loop.
The body of the contact machine, regardless of the installation method, must be grounded by connecting the ground wire to the general workshop grounding. The cross-section of the copper ground wire must be at least 6 mm2, and the iron wire must be at least 12 mm. In addition, butt-end machines must be provided with shields to protect workers from splashing molten metal.
To avoid damage to workers with a voltage of 220 or 380 V in case of accidental breakdown of the primary winding of the transformer or the motor windings of the converter of the housing of these machines are grounded. On the body of each unit or transformer there is a bolt, which must be securely connected to the workshop ground network. The cross-section of the ground wire must be at least 6 mm2 for copper and at least 12 mm2 for steel wire.
In order to avoid damage to 220 or 380 V operating voltages with accidental breakdowns of the primary winding of the transformer or the motor windings of the converter, the housings of these machines are grounded. On the body of each unit of the transformer, there is a bolt, which must be reliably connected to the workshop ground network. The cross-section of the grounding wire must be at least 6 mm for copper and at least 12 mm2 for steel wire.
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For the full functioning of the protective system, which reduces the level of voltage to safe in case of accidents, a suitable ground wire is used. It is chosen according to the material, cross-sectional area and other parameters that are regulated by the current norms. This article will consider the selection of such products for household networks 220 V, their installation and operation.
Earthing wire with mounting kit
Criteria and limitations
In order not to be mistaken when completing an electrical design, the provisions of the "Rules for the installation of electrical installations" (hereinafter "PUE", or "Rules") are used. Currently, the seventh version of the edition of normative acts is in force. It was approved by the Ministry of Energy of Russia by order of 08. 07. 2002.
To exclude doubts at any time, you can refer to the source, check the latest changes in legislation. In practice, the following rules are used to determine which grounding system cable can be used to equip a house in a sectional area. To check, use the cross-section of the phase conductor of the existing power network (S) in mm 2:
- S - with a conductor area smaller than, or equal to 16 mm 2;
- 16 mm 2 - if the cross-section of the phase conductor is greater than 16 mm 2, but less than or equal to 35 mm 2;
- S / 2 - with an area exceeding 35 mm 2.
Thus, if the electrical wiring of a house with an area of 20 mm 2, a 16 mm 2 ground cable is suitable.
These standards apply in cases where the phase and protective conductors are made of the same materials.
To make a more accurate calculation, use a special formula. It is suitable for situations where the shutdown time of the circuit breaker is less than or equal to 5 s:
/
k, where the following notation is used:
- S - cross-section, which should have a grounding system cable in mm 2.
- I is the current that passes through the ground conductor in the event of a short circuit. Its value should be sufficient to trigger an automatic power-off device in a time not exceeding five seconds.
- t is the time in seconds that an automatic protection device needs to interrupt the electrical power circuit.
- k is the complex coefficient.
The exact value of the last parameter is taken from the tables 1.7.6., 1.7.7., 1.7.8. and 1.7.9. PUE. It is calculated taking into account what material is used to make the conductor, in which shell the cable of the grounding system is enclosed. It also matters what the initial and final temperatures are assumed to be.
For example, if a copper ground multi-core cable is used, then for the different shells, the following coefficients must be added to the formula.
Table of the complex coefficient versus temperature and cable material
If the result of the calculation is less than the typical size, select the cable of the grounding system with the nearest large section.
Features of installation operations
In PUE separately considered the situation where the grounding wire is not isolated, and it is laid so that nearby there will be metal products. This is possible when using mounting trays of metal, if the conductive parts of the frame of the house are located nearby. With sufficient proximity, even a relatively small 220 V voltage can create sparks. They, in turn, can destroy the polymer layer of phase conductor insulation.
To ensure a high level of safety, in such cases an isolated grounding protective cable is used. The dielectric parameters of its insulating layer should not be worse than in adjacent phase wires.
You also need to check the home line laying, taking into account the following negative factors:
- In the absence of a quality insulating sheath, the metallic conductor will be poorly protected from destructive oxidation processes. Corrosion occurs in the presence of oxygen and water, so we must exclude such effects.
- If the protective earthing conductor is installed near the pipeline, railways, in other places where the risk of mechanical damage increases, it must be protected additionally or another route selected.
- With a rigid installation, the compatibility of the gasket line and the placement of seams designed to compensate for dimensional changes with increasing / decreasing temperature are checked. If necessary, make a stock of the length of the conductor, apply other design solutions to ensure the integrity of the electrical circuit.
The laying of the ground wire is carried out taking into account the structural features of the structure (the figure shows that the entrance to the building is protected from mechanical damage)
Other grounding options
Above is described one of the options for connecting equipment to the system of grounding the house. As conductors, you can use not only a specialized copper cable. The rules allow the application of the following engineering solutions:
- wire, which is in a single insulating shell with a phase line;
- metal protective layers of busbars;
- parts of structures of buildings, reinforcement in reinforced concrete products;
- trays in which power lines are laid.
The latter option is permissible to apply, if such a designation is provided by the manufacturer. The corresponding entries must be present in the official instructions, in the accompanying technical documentation.
Connecting the ground conductor to the elements of the building structure
Conductors of other types can be used if they meet the requirements for chain integrity, and their electrical parameters are not worse than in the examples discussed above. The Rules specify the requirements. So, it is necessary that such parts are well protected from mechanical and other external influences. Measures should be provided to prevent disassembly work, which is capable of accidentally interrupting electrical contact in the grounding circuit.
- Metal pipes of water supply, if in the corresponding system there are gaskets made of dielectric materials.
- Pipelines of heating, sewerage, gas supply systems. Other elements used to transport explosive compounds and chemicals.
- Cable lead casing, metal corrugations, cables used for fixing wires.
If a copper conductor is used which is not a component of the power circuit cable or it is not in a common insulating protective jacket with phase conductors, then the minimum cross-section in mm 2 is limited by the following rules:
- the conductor is protected from mechanical influences - 2,5;
- there are no protective structures - 4.
When using an aluminum conductor made of a less strong metal than in the previous example, in the case of a separate gasket, the cross section must be equal to or greater than 16 mm 2.
Cable products and their selection
Above, we considered the criteria for choosing the right products, the nuances that must be taken into account when creating a home ground line laying. To accelerate the identification of inspections, facilitate the installation of switching cabinets and other stationary equipment, a special system of standards is used. The grounding cable corresponding to the introductory data of this article is indicated on the diagrams by PE letters. The yellow-green color (alternating strips) should have its insulation.
The presence of color marking simplifies installation
Certain correct conclusions can be made even with a visual study of the assortment of the store. If it is a yellow-green cable, then it is suitable for creating a protective earthing system at home.
Some sellers offer cheaper products like PPV, with three cores to reduce the cost of the project. The color designations there do not meet the requirements of the PUE, but there is a natural desire to save, because the electrical parameters can be quite sufficient.
With this choice, the probability of errors in the installation process increases. Damage to expensive equipment after power-up, negates such excessively "rational" use of funds.
The following list shows the parameters of suitable types of cable products:
- NYM - there is a yellow-green cable, so installation errors are excluded. An additional thick layer of external insulation allows the use of the product even in explosive areas. At home, these products can be used for laying lines in the basement, garage, in the sauna rest room, in other places where moisture and temperature changes are not excluded.
- The yellow-green cable is installed in the central vein in the BBG brand. The "flat" design facilitates the installation of the house. If necessary, they purchase a product with a reservation layer. It is resistant to mechanical influences.
- When the name has the letters "NG", it means that a non-combustible polymer is used. The "LS" shell emits a minimum of smoke during combustion. "FRLS" - remains stable even when exposed to open flames. Such products are more expensive, but its use increases the overall level of security at home.
- The yellow-green layer of insulation covers the conductor of twisted copper veins. This is the cable of the PV-3 series. It is used for a separate gasket.
Video
When choosing cable products to equip your own home, the brand is important. A responsible manufacturer with an impeccable reputation will offer not just a yellow-green cable that meets external standards. It will ensure the availability of the same product parameters in each product lot.
Grounding in an apartment and a private house is necessary to ensure the protection of a person from electric shock. Protective earthing is the deliberate connection of electrical wiring, electrical equipment and electrical receivers to the ground, since the soil is a medium capable of taking over the current. Electrical wiring, equipment and electrical receivers are connected to the ground by means of grounding conductors. In their quality can act as a strand of a multicore cable, and a single-wire cable. More details can be found in the articles: "and".
In this case, the grounding wire in any case should be copper, multiwire or single. The cross-section of the ground wire depends on the characteristics of the mains, i.e. from the power of electric receivers and electrical equipment, which it protects. The main thing is that the cross-section of the grounding wire must be at least the section of the wires of the electrical cable.
Consider suitable cable brands and wiresused for earthing, which are allowed by the norms of the PUE (Rules of the Electrical Equipment Device).
The cable brand with a grounding conductor is selected depending on the type of grounding: stationary or non-stationary (portable). For stationary (ie, stationary) grounding, the following examples can be assigned - grounding of buildings, electrical wiring in an apartment and a private house, stationary electrical equipment, electrical panels, etc.
For stationary grounding, it is acceptable to use both multiwire (flexible) copper three-core cables of BBG, PVG, and multi-strand single-wire - for example, NYM. They must have a grounding conductor with a yellow-green color of the insulation. There are cases when a cheaper three-wire PPV cable is used without the yellow-green insulation of the ground wire, which is used as an average core. However, when using such a cable, there is a high probability of confusion when connecting or following.
Also, separate copper single-core stranded (flexible) wires can be used for an earth conductor in an apartment and a private house. For example, the wire of the brand ESUY (Germany). In this case, the wiring (phase + zero) is carried out by a two-wire copper cable, plus a grounding single-core wire, for example, ESUY, is also laid here.
Brief characteristics of some cable brands and wires for grounding
Cable for electrical wiring and grounding NYM
The cable is intended for transmission and distribution of electrical energy in stationary installations
for AC voltage up to 0.66 kV at a frequency of 50 Hz, including in electrical installations of buildings and structures for the safe use of electrical equipment of protection class 1 for electrical safety. The cable can be used for laying power and lighting networks, even in explosive areas of classes B1b, B1g, VPa, and also for lighting networks in explosive zones of class B1a.
Distinctive features of NYM:
- copper core;
- Intermediate shell;
- coloring of cores in accordance with the norms of the EE;
- convenience of cutting and installation.
Cable VVG
Material: cores - copper of I or II class of twisting, insulation - polyvinyl chloride, shell - polyvinyl chloride, armor - two steel tapes, outer covering - winding with fiberglass with watering bituminous composition.
The cable sheath is resistant to solar radiation and does not spread combustion.
Cables are made of 1-, 2-, 3-, 4-and 5-wire, with zero core or earth conductor.
Isolated strands of multicore cable have a distinctive coloring. The insulation of the neutral conductors is blue or light blue, the insulation of the earth conductors is carried out in two-color - green-yellow.
Wire ПВ-3
Cable ПВ-3 is, on a design, one vein from the braided wires of soft copper. In the cross-sections 0.5 ... 1.5 mm square - the class of conductors No. 2, 3 or 4; for sections within 2.5 ... 4 mm square. - Class of conductor - No.4; for cross-sections within 6 ... 95 mm kV - the core class - №3. The core of the cable is covered with insulation from one layer of polyvinyl chloride plastic. When the installation of the cable takes place and the ends are cut off, this sheath must break away from the twisted core without breaking. If insulation breaks are observed, that is, it sticks to the vein, this means that during storage or production, terms, conditions or technology were violated. Output cable sections in mm sq .: 0.5; 0.75; 1; 1.5; 2.5; 4; 6; 10; 16; 25; 35; 50; 70; 95; 120; 185; 240. The cable is painted in 11 different colors: white, blue, black, red, green, yellow, etc. If the cable is used to ground equipment or installations, then the color of the insulating jacket should be only yellow-green.
Wire ПВ-6
The conductor core is copper, multiwire, class 6 according to GOST 22483.
Insulation is made of transparent PVC compound, which provides visual control over the integrity and quality of the conductive core.
ПВ 6-Зп - Wire with a copper vein of high flexibility with insulation from transparent PVC plastic compound for portable grounding.
Wires are resistant to ambient temperatures: -40 ° C to + 50 ° C
Insulation stand: to deformation at temperature (50 ± 2) ° С; to cracking at a temperature of (120 ± 2) ° C.
The wires are resistant to the action of alternating bends by an angle of not more than 180 ° at a bend radius (50 ± 5) mm.
ESUY wire
The ESUY grounding cable is used for grounding protection systems from. Special application of grounding cable for repair work in systems with high currents EVU, railway installations, in distribution systems, AC systems, transmission and distribution systems as protection in installations.
For this cable, there are special requirements, for example, light weight, increased flexibility over a wide temperature range and temperature resistance. The cable sheath has an important function of protecting against mechanical and chemical influences.
Feature: for this cable, the nominal voltage is not normalized, because this cable is used as a ground cable.
Earthing can be natural and artificial. Natural earthing switches are: metal structures of buildings and structures connected to the ground, metal pipelines laid in the ground (with the exception of pipelines of flammable liquids and combustible gases); Lead casing of cables laid in the ground, if there are at least two of them.
In the event that resistance of the grounding device when using natural earthing switches will meet the requirements of the PUE, there is no need to arrange additional artificial earthing.
Vertically clogged steel pipes with a wall thickness of at least 3.5 mm, angular steel, steel rods with a diameter of at least 6 mm, horizontally laid steel strips with a thickness of at least 4 mm and a total cross-section of at least 48 mm 2, etc., are used as artificial earths. etc. The resistance of the earthing of earthing switches is determined mainly by the resistivity of the soil, the size and shape of the earthing switch, the depth of its placement in the ground.
The specific resistance of the soil depends on its composition, density, humidity and temperature and ranges from 0.3 x 10 4 to 1. 3 x 10 4 ohms per centimeter.
The internal network of grounding in the premises of the RU is implemented in the form of a grounding line and branches from them to separate bodies of the apparatus.
Sequential connection of earthing enclosures of electrical equipment to the earthing main not allowed. The main earthing bus is connected to the earthing switch by at least two branches connected to the earthing switch and various places.
The main earthing bar and branches to the grounded parts are laid open. Openly laid grounding conductors are painted black. When painting them in a different color at the points of connections and branches, it is necessary to draw two bands of black color at a distance of 150 mm from each other.
Cross-sections of earthing conductors are chosen in such a way that when the currents of single-phase earth faults flow, the temperature of the grounding conductors in installations above 1000 V with high ground-fault currents does not exceed 400 ° C, in installations up to and above 1000 V with low currents, the cross-section of grounding conductors should be at least 1/3 of the cross-section phase conductors, but not less than indicated in the tables below.
Minimum dimensions of steel earthing conductors and grounding conductors.
In electrical installations with voltages up to 1000V, copper and aluminum conductors are used as grounding conductors, the minimum cross-sections of which are given in the table below.
Minimum cross sections of copper and aluminum grounding conductors
in electrical installations with voltages up to 1000V
Note. Laying bare aluminum conductors in the ground is not allowed
Earthing conductors are connected with each other by welding. To grounded structures they are also connected by welding, and to the bodies of machines, machines - by welding or bolts. Soldered conductors are connected to the metal sheaths of cables and wires.
Passes earthing conductors through the walls and floors are performed in pipes, steel clips or open apertures.