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1. Where does the electric current come from?
Directory / Electrician in the house The range of influences of a home electrician is possible only within the limits of the electrical wiring to the meter. Repair is only permissible if there is no current in the wiring. An encounter with an electric current threatens the incompetent with death! Most people have no idea how the current from the power plant gets to their meter. And this is necessary to know both from a safety point of view and for everyday reasons. Apartments on the same landing of a multi-storey building, for example, receive power through different wires. Therefore, in one apartment there is light, in another - not. The same thing occurs in nearby rural houses. Let's consider the transmission scheme. Generators are current producers. They are installed at the power plant. The rotation of the generators is carried out by water, steam or other types of “forces”. The current voltage that generators or a generator produce lies in the range from 3000 to 24 V. The symbol for voltage is V, and 000 V is 1000 kV. Generator power is a determinant of a particular voltage. Step-up transformers are located next to the power plant. They raise the current voltage created by the generators to 1 V, 110 V. This will ensure less energy loss in the overhead line wires. The enormous voltage at the point where the current is used is reduced twice. The first group of transformers reduces the voltage to 6000...20 V, the second - to 000 V. The time has come to remind you of the concepts of “phase” and “ground”. Much of the explanation will be conditional. But without this, it will not become clear how generators, transformers, and inputs into a house or apartment are connected. In everyday life, we are accustomed to dealing with cords that have two conductors. Sconces, table lamps, TVs, etc. have such cords with plugs for plugging into an outlet. A phase is an electric current flowing through one conductor of a cord. Having completed work in a radio, light bulb, etc., the current returns through the second conductor of the cord to the ground. The current voltage that drives our household appliances is approximately 220 V. Transformers helped produce 400 V. How does 220 V come about? The power plant's generators produce three-phase current. It “flows” through three large cross-section conductors to step-up transformers. The enormously increased voltage current from these transformers along overhead lines (as overhead lines are called) rushes over long distances again along three conductors. Four or five conductors appear only after the last transformer. The “ground” and lighting wire complemented the three phase wires. Five wires on support poles are visible in rural areas, say, in garden plots. Two wires from the pole are stretched to each house on the plots. One of these wires is a phase with current, the second is ground. A voltage of 220 V operates in the electrical wiring of the house. But in garden plots there is also a room in which electric motors are installed. They rotate the pumps that supply water. Four wires from the pole go to the pump house: three phase wires and ground. A voltmeter is a device for determining the voltage value. If its clamps are applied to two phase wires, the arrow will indicate a voltage in the range of 370... 390...400 V. Electric motors rotate this voltage. Conventionally, the voltage between phases is considered to be 380 V. The difference between 380 V and 400 V goes to various losses. Phase wires, as a rule, are placed highest on poles from a safety point of view. The ground wire is attached to the insulator below. Lighting lamp wire - the first or second on the pole on the side of the sidewalk or roadway. A lamp on a pole with ground and lamp wires is connected at insulators. The lighting wire is also a phase wire with a known number of light bulbs. The load of this wire is therefore known. Electrical active load. Resistive load characterizes the energy consumed in the circuit (for mechanical work, heat, etc.) and is expressed in watts (W). The three upper (closer to the sky) phase wires on the pole, however, with a relatively undefined load. In order to equalize the loads on each wire to some extent, branches to garden houses, for example, are alternated. So the outlet from the topmost phase wire is directed to the house next to it. The branch from the middle, second, phase wire is connected to the next house. The third phase wire is in contact with another house. The second wire for each house will lead from the same “ground” wire on the pole. We will again connect the fourth house on Garden Street to the topmost phase wire... Let's look at a specific example. Electric wires are stretched between support poles on a rural street or in a collective gardening partnership. Current-carrying bushings are extended from these wires into houses. Electrical wires and inputs between support posts to the wall and roof of the house, as a rule, lack insulation. When these external wires carried through the air are touched by an “object”, the electric current will flow through it to one degree or another. Safety precautions prohibit even short-term human contact with these wires through any thing. However, the tops of trees and branches constantly or periodically “stroking” the wires in the wind when they grow nearby. And here another prohibition comes into play. Branches and trunks of trees in a wet state on the surface are conductors for electric current and 220...380 V. A person who is on the ground next to or on a tree is struck by an electric shock. What to do if the owner of a garden plot or estate receives an order? Energosbyt will require the tree or trees growing under the wires to be “shortened by a head.” Of course, no one will turn off the electric current during the cutting period. The solution is to choose the situation. A clear, windless, dry day is conducive to the “operation”. When it comes to cutting down a tree, the first thing to do is break off or cut down the branches in close proximity to the wires. This is done with rubber gloves and from a dry ladder or while on the tree itself. Be sure to wear shoes with rubber soles. Sneakers, but not sneakers, are more likely to resist slipping. It is not at all easy to make a cut so that the branches or trunk of the tree do not disfigure the worker. A branch is sometimes more substantial than another tree trunk. Two main rules should be observed when sawing off large branches of a standing tree: 1) no one should stand under the branch being sawed off; 2) make the cut from above. A rope tied to a branch in advance will provide a shallower cut. However, this cut usually covers 2/3 of the branch diameter. The person pulling or pulling the rope should not stand under a tree branch on the roots. And of course, the sawer is not sitting on the same branch... When shortening of branches occurs in the spring, one should not forget about the advantages of birch trees. What is tastier than birch sap? Therefore, in spring you should not cut more than two branches from a birch tree. This is done so that it is convenient to place or hang dishes under the wound or wounds. There are utility poles in every city. However, in most cases you will not notice the wires on them. The pillars are topped with lamps. Wiring to the lamps is through the hollow core of the pillars. How does electric current penetrate to poles and houses? The answer is short - through cables laid in the ground under asphalt or other types of covering. The cable is usually introduced into the house through a pipe made of non-conducting material (asbestos cement, plastic, etc.). The hole for the pipe in the wall or foundation is left during the construction of the house or is punched. The gaps between the pipe and the hole, as well as the pipe and the cable, are sealed with packing and cement against the penetration of moisture. The cable entry into a multi-storey building, as a rule, is located below the level of the ground and its covering. Houses built a long time ago have a panel room in the basement. The entrance door is covered with roofing steel. Inscriptions and drawings on the door warn of danger. The door lock can only be installed by electricians. Metal cabinets cover one of the walls of the room. One wall! So that the electrician does not accidentally rest his back against the equipment of the open cabinet. The input cable enters the metal cabinet from the back. A three-phase current meter, a switch, current transformers, and circuit breakers are mounted inside the cabinet. The holes on the front panel of the cabinet allow you to pass the handles of the listed devices through them. A special viewing window is for taking readings from the meter scale. The cable cores are connected to the switch from the knife side. The ends of the cores of another cable or wire are clamped into the contacts of the fixed jaws. This will ensure that the circuit can be broken and the power supply stopped if necessary. The internal cable leads to the meter and from it to the circuit breakers. Each circuit breaker is “responsible” for the entrance to the house. The electrical wiring riser in the entrance penetrates all floors of the house in the area of the staircase landings. The riser wires and branches to the apartments are hidden for safety in the thickness of the wall. The beginning of the riser is at the contacts of the circuit breaker. Three conductors with three phases are switched, that is, closed and opened, by a switch. Opening - automatic when overloaded, or forced by the handle, say, when repairing a circuit. The riser ground wire is laid in addition to the circuit breaker. There is an electrical panel on the wall of the landing of each entrance floor. The panel doors block access to the riser wiring. Apartments in “ancient” houses, according to the date of construction, received two wires from the switchboard: phase and ground. The meter and fuses of the apartment were mounted inside it, near the exit door. This had its pros and cons. There were also fuses behind the panel door. They were placed on the branches of phase wires to apartments from the riser. The peculiar shape of the fuse gave it the name “frog”. The disadvantages were that this arrangement of the meter led to abuse and sometimes to concealing the actual consumption of electricity. The owner or owners of the apartment were required to maintain the electrical wiring, starting with the meter. The main advantage was the integrity of the meter and fuses. Their condition depended only on the owners of the apartment and natural wear and tear. Multi-storey buildings of modern construction have a slightly different installation of electrical devices. The switch room is usually on the first floor of the middle entrance. If this is a house, say, a sixteen-story building with one entrance, then the switchboard is right in the entrance lobby. Rooms for a switchboard are not always allocated. Metal cabinets are installed openly somewhere in a dead end, but they are, of course, closed to the curious. The automatic riser switch in the entrance is placed on the first floor in a special niche behind a metal door. The riser has exits through shields on the walls of the landings. The apartment panel here is overflowing with devices and is designed for all apartments facing the landing. The meters are placed behind a separate door that, unfortunately, is not always closed. This is one of the reasons for their disappearance. Obviously, there are observation windows in the switchboard door for taking meter readings. A separate compartment of the shield is “dedicated” to overload and short circuit protection devices. Three switches control the power supply to each apartment. A batch or automatic switch allows you to immediately turn off the electrical outlet and lighting lines in the apartment. Single-phase circuit breakers are mounted on the panel fittings and are located on the named lines. The wiring of lines into the apartment, therefore, begins with a shield on the wall of the landing. Electricians servicing a house are required to ensure the supply of electric current to it without entering the apartment. Back (Table of contents) Forward (Selection and replacement of incandescent electric lamps)
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