Grounding is necessary to provide protection against the dangerous action of electric current by reducing the touch voltage to a level that is safe for humans and animals. To fulfill these conditions, an earthing loop is installed. Its device consists of a group of electrodes installed vertically at a certain depth, and also connected by welding with a horizontal metal strip for grounding.
Content
- Outer contour
- Grounding application
- How the protective device works
- Installation
Outer contour
For the device of a protective structure, natural or artificial elements installed in the ground are used, which is the grounding circuit. This design includes conductors located inside the room on the walls and connected to the outer loop.
Metal structures installed in the soil allow for a large area of contact with the ground and have little resistance. Highways made of metal pipes are widely used as natural ground electrodes, except for those intended for the transportation of explosive and combustible substances. This also includes:
- elements of metal pipes used for the arrangement of drilling channels;
- metal frame details in reinforced concrete elements of houses;
- cable elements of overhead wiring, connected to zero with re-grounding.
All these earthing switches are connected to the protective circuit in two places. The connection is carried out using a welding machine. In this case, the welding seam must be continuous and made along the entire length of the section of the metal rod. All welding places are processed anticorrosive bitumen varnish. If it is impossible to apply welding, then clamps are used for the connection.
Grounding application
If it is impossible to use natural grounding conductors, then the structure is made of different materials, selected according to special rules for the operation of electrical installations.
Moreover, they are divided by type and they are: horizontal, vertical, recessed. The following items must be grounded:
- housings of control switchboards and electrical installations casings;
- metal elements of cable sleeves, pipes for the installation of electrical wires;
- secondary windings of transformers.
At the same time, it is not required to install a protective device for supporting cable insulators, devices on grounded platforms, instrument cases located inside the shields. For the manufacture of horizontal elements of the protective device, metal strips with a thickness of at least 4 mm and a width of more than 10 mm are used.
The strips are laid in a horizontal direction and vertical electrodes are tied to them. With a recessed version of the location of the protection, a similar structure is made, which is installed on the bottom of the pit during the installation of power line supports.
Usually, such elements are prepared in advance in assembly shops, using metal stripes or fittings. Pipes, rolled metal products or reinforcing pins are driven into the ground as electrodes.
How the protective device works
Grounding can protect a person from electric shock, and the devices he uses - from breakdown or voltage breakdown on the case. Such a device is necessary for the safe and smooth operation of electrical units.
On an industrial scale, it is used for the continuous operation of electrical equipment, and in domestic conditions, devices are grounded through an outlet with such an outlet. But still, some household devices require deaf protection. These include:
- washing units with a large capacity;
- microwave ovens with a special grounding terminal;
- electric ovens with oven;
- stationary computers, to the case of which a protective device is connected.
Sometimes it is impossible to equip all protection on one ground, since the ground is not a linear conductor of electricity. The protection resistance is determined by the value of the operating voltage and the contact area with the contour element.
Moreover, if a distance of 1.2-1.5 m is maintained between the two structures, then the area of interaction with the elements increases almost a hundred times. The contours cannot be spread over a greater distance, since this will entail a break in the potential field and a reduction in the area of interaction.
It is not recommended to take out protective elements and connect them to contacts that have not been trained. In addition, it should be borne in mind that any metal has its own potential, and under wet conditions it is subject to corrosion and destruction.
It is also not recommended to connect several electrodes in series on one bus. In this case, the emergency state of one device will provoke the failure of other electrical units.
When choosing a soil for placing the contour, you should pay attention that the most suitable are clay soils, loams or peat soil. It is practically impossible to install a protective device in rocky soil, and especially in rocky formations.
Installation
To equip a private house with a protective structure, it is placed at the entrance to the building, which is re-grounding. This is due to the fact that the building is supplied with electricity via an overhead line and secondary grounding is performed in accordance with special rules for electrical installations.
First, they plan the place for installing the structure, the shape and dimensions of the contour. Usually they are made in the form of a triangle, rectangle or line. Determine the number of electrodes that will be bound by the metal strip.
When installing horizontal structures, the depth of the trench should be within 0.5-0.8 m, and vertical devices deepened at least 3.5-3.8 m. The length of the electrodes is chosen taking into account the characteristics of the soil, the depth of its freezing and relative humidity.
The distance between the pins should be approximately equal to the length of one instance. If this distance is made smaller, the performance of the protective device will decrease. At the beginning of work, the territory where the contour will pass is marked with pegs.
According to the breakdown, trenches at least 30 cm wide are dug and softer and crumbly soil 25 cm thick is laid on their bottom. This part of the earth will directly interact with the grounding elements.
In trenches, steel strips are welded together, leaving a certain margin at the edges. When installing the strips, it is not recommended to stretch them, as they must be in a free state. Next, after a certain distance, electrodes are welded to the strips.
Welding points on strip structures are painted with bituminous varnish, while the rods cannot be coated with paint. When the structure is ready, it is upset to the required depth. To facilitate this procedure, the soil can be spilled with water. Then, the protective structure is connected with the input and the control box.
