Do-it-yourself electrics in your home. "Initial electrician course" Methods for making contact connections
Electrical Engineer. Worked in electrical networks. He specialized in relay protection and electrical automation devices. Author of two books from the Electrician's Library series. Published in electrical engineering journals. Currently lives in Israel. 71 years old. Pensioner.
Ha-esh`har str., 8\6, Haifa, 35844, Israel
To the reader
There is probably no need to explain to you the importance of electricity for ensuring the normal functioning of every person. It will not be an exaggeration to say that today it is the same integral part of it as water, warmth, and food. And if the lights go out in the house, you, burning your fingers on a lit match, immediately call us.
Electricity travels a long and difficult path before it reaches your home. Produced from fuel at a power plant, it travels through transformer and switching substations, through thousands of kilometers of lines mounted on tens of thousands of poles.
Electricity today is advanced technology, reliable and high-quality power supply, care for the consumer and his service.
However, that's not all. The final link in the electrical chain is the electrical equipment of your home. And it, like anything else, requires some knowledge for its proper operation. Therefore, we urge you to cooperate with us and for this purpose we give some recommendations and warnings. Warnings are highlighted in red.
We will talk about the following:
1. Legal aspects. The subscriber must be familiar with his rights, duties and responsibilities in relation to the energy supply organization. The same applies to the energy supply organization’s attitude towards it.
2. Familiarity with residential electrical wiring, switching equipment and installation products.
4. Electricity requires not only certain knowledge, but also strict adherence to certain rules from the user. It poses a danger both for those who do not know how to use it and for undisciplined “craftsmen”. Therefore, we will introduce you to the basics of electrical safety.
We urge you to be understanding of our recommendations and warnings. We also hope that you will not cause damage to the network structures and electrical equipment mentioned above.
We wish you all the best, including those provided by electricity.
At present, it has already developed quite steadily services market, including in the region household electricians.
Highly professional electricians, with undisguised enthusiasm, try with all their might to help the rest of our population, while receiving great satisfaction from quality work and modest remuneration. In turn, our population also receives great pleasure from a high-quality, quick and completely inexpensive solution to their problems.
On the other hand, there has always been a fairly wide category of citizens who fundamentally consider it an honor - with his own hand solve absolutely any everyday issues that arise in your own place of residence. Such a position certainly deserves approval and understanding.
Moreover, all these Replacements, transfers, installations- switches, sockets, machines, meters, lamps, connection of kitchen stoves etc. - all these types of services most in demand by the population, from the point of view of a professional electrician, at all are not difficult work.
And to be honest, an ordinary citizen, without electrical engineering education, but having fairly detailed instructions, can easily cope with its implementation himself, with his own hands.
Of course, when performing such work for the first time, a novice electrician can spend much more time than an experienced professional. But it is not at all a fact that this will make it performed less efficiently, with attention to detail and no haste.
Initially, this site was conceived as a collection of similar instructions regarding the most frequently encountered problems in this area. But later, for people who had absolutely never encountered solving such issues, a “young electrician” course consisting of 6 practical lessons was added.
Features of installation of electrical sockets of hidden and open wiring. Sockets for electric kitchen stove. Connecting an electric stove with your own hands.
Switches.
Replacement and installation of electrical switches, hidden and exposed wiring.
Automatic machines and RCDs.
Operating principle of Residual Current Devices and circuit breakers. Classification of circuit breakers.
Electric meters.
Instructions for self-installation and connection of a single-phase meter.
Replacing wiring.
Indoor electrical installation. Installation features, depending on the material of the walls and the type of finishing. Electrical wiring in a wooden house.
Lamps.
Installation of wall lamps. Chandeliers. Installation of spotlights.
Contacts and connections.
Some types of conductor connections, most often found in “home” electrics.
Electrical engineering - basic theory.
The concept of electrical resistance. Ohm's law. Kirchhoff's laws. Parallel and serial connection.
Description of the most common wires and cables.
Illustrated instructions for working with a digital universal electrical measuring instrument.
About lamps - incandescent, fluorescent, LED.
About "money."
The profession of an electrician was definitely not considered prestigious until recently. But could it be called low-paid? Below you can see the price list of the most common services from three years ago.
Electrical installation - prices.
Electric meter pcs. - 650p.
Single-pole circuit breakers pcs. - 200p.
Three-pole automatic machines pcs. - 350p.
Difavtomat pcs. - 300p.
Single-phase RCD pcs. - 300p.
Single-key switch pcs. - 150p.
Two-key switch pcs. - 200p.
Three-key switch pcs. - 250p.
Open wiring panel up to 10 groups pcs. - 3400p.
Hidden wiring panel up to 10 groups pcs. - 5400p.
Laying open wiring P.m - 40p.
Corrugated wiring P.m - 150p.
Grooving in the wall (concrete) P.m - 300p.
(brick) P.m - 200p.
Installation of sub-socket and junction box in concrete pcs. - 300p.
brick pcs. - 200p.
plasterboard pcs. - 100p.
Sconce pcs. - 400p.
Spotlight pcs. - 250p.
Chandelier on hook pcs. - 550p.
Ceiling chandelier (without assembly) pcs. - 650p.
Installation of bell and bell button pcs. - 500p.
Installation of socket, open wiring switch pcs. - 300p.
Installation of a socket, hidden wiring switch (without installing a socket box) pcs. - 150p.
When I was an electrician "by advertisement", I was not able to install more than 6-7 points (sockets, switches) of hidden wiring on concrete - in an evening. Plus 4-5 meters of grooves (on concrete). We carry out simple arithmetic calculations: (300+150)*6=2700p. - these are for sockets with switches.
300*4=1200 rub. - this is for the grooves.
2700+1200=3900 rub. - this is the total amount.
Not bad for 5-6 hours of work, isn’t it? Prices, of course, are Moscow prices; in Russia they will be less, but not more than twice.
Taken as a whole, the monthly salary of an electrician-installer currently rarely exceeds 60,000 rubles (not in Moscow)
Of course, there are also particularly gifted people in this field (as a rule, with excellent health) and practical acumen. Under certain conditions, they manage to raise their earnings to 100,000 rubles and above. As a rule, they have a license to carry out electrical installation work and work directly with the customer, taking on “serious” contracts without the participation of various intermediaries.
Electricians - industrial repairmen. equipment (at enterprises), electricians - high-voltage workers, as a rule (not always) - earn somewhat less. If the enterprise is profitable and funds are invested in “re-equipment”, additional sources of income may open up for electricians-repairers, for example, installation of new equipment carried out during non-working hours.
Highly paid but physically difficult and sometimes very dusty, the work of an electrician-installer is undoubtedly worthy of all respect.
By doing electrical installation, a novice specialist can master basic skills and abilities and gain initial experience.
Regardless of how he builds his career in the future, you can be sure that the practical knowledge obtained in this way will definitely come in handy.
Use of any materials from this page is permitted provided there is a link to the site
CONTENT:
INTRODUCTION
TYPE OF WIRE
PROPERTIES OF CURRENT
TRANSFORMER
HEATING ELEMENTS
ELECTRICITY HAZARD
PROTECTION
AFTERWORD
POEM ABOUT ELECTRIC CURRENT
OTHER ARTICLES
INTRODUCTION
In one of the episodes of "Civilization" I criticized the imperfection and cumbersomeness of education, because it, as a rule, is taught in a studied language, stuffed with incomprehensible terms, without clear examples and figurative comparisons. This point of view has not changed, but I am tired of being unfounded, and I will try to describe the principles of electricity in simple and understandable language.
I am convinced that all difficult sciences, especially those describing phenomena that a person cannot comprehend with his five senses (vision, hearing, smell, taste, touch), for example, quantum mechanics, chemistry, biology, electronics, should be taught in the form of comparisons and examples. And even better - create colorful educational cartoons about invisible processes inside matter. Now in half an hour I will turn you into electrically and technically literate people. And so, I begin to describe the principles and laws of electricity using figurative comparisons...
VOLTAGE, RESISTANCE, CURRENT
You can rotate the wheel of a water mill with a thick jet with low pressure or a thin jet with high pressure. The pressure is the voltage (measured in VOLTS), the thickness of the jet is the current (measured in AMPERES), and the total force striking the wheel blades is the power (measured in WATTS). A water wheel is figuratively comparable to an electric motor. That is, there can be high voltage and low current or low voltage and high current, and the power in both options is the same.
The voltage in the network (socket) is stable (220 Volts), but the current is always different and depends on what we turn on, or rather on the resistance that the electrical appliance has. Current = voltage divided by resistance, or power divided by voltage. For example, on the kettle it is written - Power 2.2 kW, which means 2200 W (W) - Watt, divided by voltage (Voltage) 220 V (V) - Volt, we get 10 A (Ampere) - the current that flows at operation of the kettle. Now we divide the voltage (220 Volts) by the operating current (10 Amperes), we get the resistance of the kettle - 22 Ohms (Ohms).
By analogy with water, resistance is similar to a pipe filled with a porous substance. To push water through this cavernous tube, a certain pressure (voltage) is required, and the amount of liquid (current) will depend on two factors: this pressure, and how permeable the tube is (its resistance). This comparison is suitable for heating and lighting devices, and is called ACTIVE resistance, and the resistance of the electrical coils. motors, transformers and electrical magnets work differently (more on this later).
FUSES, CIRCUIT MEASURES, TEMPERATURE REGULATORS
If there is no resistance, then the current tends to increase to infinity and melts the wire - this is called a short circuit (short circuit). To protect email from this. fuses or automatic switches (automatic circuit breakers) are installed in the wiring. The principle of operation of the fuse (fuse link) is extremely simple; it is a deliberately thin place in the electrical circuit. chains, and where they are thin, they break. A thin copper wire is inserted into a ceramic heat-resistant cylinder. The thickness (section) of the wire is much thinner than the electric one. wiring. When the current exceeds the permissible limit, the wire burns out and “saves” the wires. In operating mode, the wire can become very hot, so sand is poured inside the fuse to cool it.
But more often, to protect electrical wiring, it is not fuses that are used, but circuit breakers (circuit breakers). The machines have two protection functions. One is triggered when too many electrical appliances are connected to the network and the current exceeds the permissible limit. This is a bimetallic plate made of two layers of different metals, which when heated do not expand equally, one more, the other less. The entire operating current passes through this plate, and when it exceeds the limit, it heats up, bends (due to inhomogeneity) and opens the contacts. It is usually not possible to turn the machine back on right away because the plate has not cooled down yet.
(Such plates are also widely used in thermal sensors that protect many household appliances from overheating and burnout. The only difference is that the plate is not heated by an exorbitant current passing through it, but directly by the heating element of the device itself, to which the sensor is tightly screwed. In devices with desired temperature (irons, heaters, washing machines, water heaters), the shutdown limit is set by the handle of the thermostat, inside of which there is also a bimetallic plate. It then opens and then closes the contacts maintaining the set temperature. As if, without changing the strength of the fire of the burner, then set there is a kettle on it, then remove it.)
There is also a coil of thick copper wire inside the machine, through which all the operating current also passes. When there is a short circuit, the force of the magnetic field of the coil reaches a power that compresses the spring and retracts the movable steel rod (core) installed inside it, and it instantly turns off the machine. In operating mode, the coil force is not enough to compress the core spring. Thus, the machines provide protection against short circuits (short circuits) and long-term overloads.
TYPE OF WIRE
Electrical wiring wires are either aluminum or copper. The maximum permissible current depends on their thickness (section in square millimeters). For example, 1 square millimeter of copper can withstand 10 Amps. Typical wire cross-section standards: 1.5; 2.5; 4 "squares" - respectively: 15; 25; 40 Amps is their permissible long-term current load. Aluminum wires withstand current less than one and a half times. The bulk of the wires have vinyl insulation, which melts when the wire overheats. The cables use insulation made of more refractory rubber. And there are wires with fluoroplastic (Teflon) insulation, which does not melt even in fire. Such wires can withstand higher current loads than wires with PVC insulation. Wires for high voltage have thick insulation, for example on cars in the ignition system.
PROPERTIES OF CURRENT
Electric current requires a closed circuit. By analogy with a bicycle, where the leading star with pedals corresponds to the electrical source. energy (generator or transformer), the star on the rear wheel is an electrical appliance that we plug into the network (heater, kettle, vacuum cleaner, TV, etc.). The upper section of the chain, which transfers force from the drive to the rear sprocket, is similar to the potential with voltage - phase, and the lower section, which passively returns - to zero potential - zero. Therefore, there are two holes in the socket (PHASE and ZERO), as in a water heating system - an incoming pipe through which boiling water flows, and a return pipe through which the water leaves, giving off heat in the batteries (radiators).
There are two types of currents - constant and alternating. Natural direct current that flows in one direction (like water in a heating system or a bicycle chain) is produced only by chemical energy sources (batteries and accumulators). For more powerful consumers (for example, trams and trolleybuses), it is “rectified” from alternating current using semiconductor diode “bridges”, which can be compared to the latch of a door lock - it is let through in one direction, and locked in the other. But such a current turns out to be uneven, but pulsating, like a machine-gun burst or a jackhammer. To smooth out the pulses, capacitors (capacitance) are installed. Their principle can be compared to a large, full barrel, into which a “ragged” and intermittent stream is poured, and from its tap at the bottom, water flows out steadily and evenly, and the larger the volume of the barrel, the better the quality of the stream. The capacitance of capacitors is measured in Farads.
In all household networks (apartments, houses, office buildings and in production) the current is alternating, it is easier to generate it at power plants and transform (lower or increase). And most el. engines can only work on it. It flows back and forth, as if you take water into your mouth, insert a long tube (straw), immerse its other end in a full bucket, and alternately blow out and draw in water. Then the mouth will be similar to potential with voltage - phase, and a full bucket - zero, which in itself is not active and not dangerous, but without it the movement of liquid (current) in the tube (wire) is impossible. Or, as when sawing a log with a hacksaw, where the hand will be the phase, the amplitude of the movement will be the voltage (V), the force of the hand will be the current (A), the energy will be the frequency (Hz), and the log itself will be the electric power. a device (heater or electric motor), only instead of sawing - useful work. Sexual intercourse is also suitable for figurative comparison, a man is a “phase”, a woman is ZERO!, amplitude (length) is voltage, thickness is current, speed is frequency.
The number of oscillations is always the same, and always the same as that produced at the power plant and supplied to the network. In Russian networks, the number of oscillations is 50 times per second, and is called the alternating current frequency (from the word often, not purely). The unit of frequency measurement is HERZ (Hz), that is, in our sockets it is always 50 Hz. In some countries, the frequency in networks is 100 Hertz. The rotation speed of most electric devices depends on the frequency. engines. At 50 Hertz the maximum speed is 3000 rpm. - on three-phase power supply and 1500 rpm. - on single-phase (household). Alternating current is also needed to operate transformers that step down high voltage (10,000 Volts) to normal household or industrial voltage (220/380 Volts) in electrical substations. And also for small transformers in electronic equipment that reduce 220 Volts to 50, 36, 24 Volts and below.
TRANSFORMER
The transformer consists of electrical iron (assembled from a package of plates), on which a wire (varnished copper wire) is wound through an insulating coil. One winding (primary) is made of thin wire, but with a large number of turns. The other (secondary) is wound through a layer of insulation on top of the primary (or on an adjacent coil) from thick wire, but with a small number of turns. A high voltage comes to the ends of the primary winding, and an alternating magnetic field appears around the iron, which induces current in the secondary winding. How many times there are fewer turns in it (the secondary one) - the voltage will be lower by the same amount, and how many times the wire is thicker - how much more current can be drawn. As if, a barrel of water will be filled with a thin stream, but with enormous pressure, and from below, a thick stream will flow out of a large tap, but with moderate pressure. Similarly, transformers can be the opposite - step-up.
HEATING ELEMENTS
In heating elements, unlike transformer windings, the higher voltage will correspond not to the number of turns, but to the length of the nichrome wire from which the spirals and heating elements are made. For example, if you straighten the spiral of an electric stove at 220 Volts, then the length of the wire will be approximately 16-20 meters. That is, to wind a spiral at an operating voltage of 36 Volts, you need to divide 220 by 36, which is 6. This means that the length of the wire of a 36 Volt spiral will be 6 times shorter, approximately 3 meters. If the coil is intensively blown by a fan, then it can be 2 times shorter, because the air flow blows heat away from it and prevents it from burning out. And if, on the contrary, it is closed, then it is longer, otherwise it will burn out from lack of heat transfer. You can, for example, turn on two heating elements of 220 Volts of the same power in series at 380 Volts (between two phases). And then each of them will be under a voltage of 380: 2 = 190 Volts. That is, 30 Volts less than the calculated voltage. In this mode, they will heat up a little (15%) less, but they will never burn out. The same with light bulbs, for example, you can connect 10 identical 24 Volt light bulbs in series and turn them on as a garland to a 220 Volt network.
HIGH VOLTAGE POWER LINES
It is advisable to transmit electricity over long distances (from a hydro or nuclear power plant to a city) only under high voltage (100,000 Volts) - this way the thickness (cross-section) of wires on the supports of overhead power lines can be kept to a minimum. If electricity were transmitted immediately under low voltage (as in sockets - 220 Volts), then the wires of the overhead lines would have to be made as thick as logs, and no reserves of aluminum would be enough for this. In addition, high voltage more easily overcomes the resistance of the wire and connection contacts (for aluminum and copper it is negligible, but over a length of tens of kilometers it still builds up significantly), like a motorcyclist rushing at breakneck speed who easily flies over holes and ravines.
ELECTRIC MOTORS AND THREE-PHASE POWER
One of the main needs for alternating current is asynchronous electric power. engines that are widely used due to their simplicity and reliability. Their rotors (the rotating part of the engine) do not have a winding and a commutator, but are simply blanks made of electrical iron, in which the slots for the winding are filled with aluminum - in this design there is nothing to break. They rotate due to the alternating magnetic field created by the stator (the stationary part of the electric motor). To ensure proper operation of the electrical For motors of this type (and the vast majority of them), 3-phase power supply prevails everywhere. The phases as three twin sisters are no different. Between each of them and zero there is a voltage of 220 Volts (V), the frequency of each is 50 Hertz (Hz). They differ only in the time shift and “names” - A, B, C.
The graphical representation of alternating current of one phase is depicted in the form of a wavy line that wags like a snake through a straight line - dividing these zigzags in half into equal parts. The upper waves reflect the movement of alternating current in one direction, the lower ones - in the other direction. The height of the peaks (upper and lower) corresponds to the voltage (220 V), then the graph drops to zero - a straight line (the length of which reflects the time) and again reaches the peak (220 V) on the lower side. The distance between waves along a straight line expresses the frequency (50 Hz). The three phases on the graph represent three wavy lines superimposed on each other, but with a lag, that is, when the wave of one reaches its peak, the other is already declining, and so on one by one - like a gymnastics hoop or a pan lid that has fallen to the floor. This effect is necessary to create a rotating magnetic field in three-phase asynchronous motors, which spins their moving part - the rotor. This is similar to bicycle pedals, on which the legs press alternately like phases, only here there are, as it were, three pedals located relative to each other at an angle of 120 degrees (like the Mercedes emblem or a three-blade airplane propeller).
Three electrical windings motor (each phase has its own) are depicted in the diagrams in the same way, like a propeller with three blades, some ends connected at a common point, the other to the phases. The windings of three-phase transformers at substations (which reduce high voltage to household voltage) are connected in the same way, and ZERO comes from the common connection point of the windings (the neutral of the transformer). Generators producing electricity. energy have a similar pattern. In them, the mechanical rotation of the rotor (via a hydro or steam turbine) is converted into electricity in power plants (and in small mobile generators - via an internal combustion engine). The rotor, with its magnetic field, induces electric current in the three stator windings with a lag of 120 degrees around the circumference (like the Mercedes emblem). The result is a three-phase alternating current with multi-time pulsation, creating a rotating magnetic field. Electric motors, on the other hand, convert three-phase current through a magnetic field into mechanical rotation. The wires of the windings have no resistance, but the current in the windings limits the magnetic field created by their turns around the iron, like the force of gravity acting on a cyclist riding uphill and preventing him from accelerating. The resistance of the magnetic field limiting the current is called INDUCTION.
Due to the phases lagging behind each other and reaching their peak voltage at different instants, a potential difference is obtained between them. This is called line voltage, and in household networks it is 380 Volts (V). Linear (phase-to-phase) voltage is always 1.73 times greater than phase voltage (between phase and zero). This coefficient (1.73) is widely used in calculation formulas for three-phase systems. For example, the current of each phase of the electric. motor = power in Watts (W) divided by line voltage (380 V) = total current in all three windings, which we also divide by the coefficient (1.73), we get the current in each phase.
Three-phase power supply creating a rotational effect for the electric power. engines, due to the universal standard, provides power supply to domestic buildings (residential, office, commercial, educational buildings) - where there is electricity. engines are not used. As a rule, 4-wire cables (3 phases and zero) come to general distribution panels, and from there they disperse in pairs (1 phase and zero) to apartments, offices, and other premises. Due to the inequality of current loads in different rooms, the common zero, which comes to the electric power supply, is often overloaded. shield If it overheats and burns out, it turns out that, for example, neighboring apartments are connected in series (since they are connected by zeros on a common contact strip in the electrical panel) between two phases (380 Volts). And if one neighbor has powerful electric power. appliances (such as a kettle, heater, washing machine, water heater), and the other has low-power ones (TV, computer, audio equipment), then the more powerful consumers of the first, due to low resistance, will become a good conductor, and in sockets another neighbor, instead of zero, a second phase will appear, and the voltage will be over 300 Volts, which will immediately burn out his equipment, including the refrigerator. Therefore, it is advisable to regularly check the reliability of the contact of the zero coming from the supply cable with the general electrical distribution board. And if it gets hot, then turn off the circuit breakers in all apartments, clean off the carbon deposits and thoroughly tighten the common zero contact. With relatively equal loads on different phases, a larger share of reverse currents (through the common connection point of consumer zeros) will be mutually absorbed by neighboring phases. In three-phase electric In motors, the phase currents are equal and completely disappear through adjacent phases, so they do not need zero at all.
Single-phase electric motors operate from one phase and zero (for example, in household fans, washing machines, refrigerators, computers). In them, to create two poles, the winding is divided in half and located on two opposite coils on opposite sides of the rotor. And to create a torque, a second (starting) winding is needed, also wound on two opposite coils and with its magnetic field intersects the field of the first (working) winding at 90 degrees. The starting winding has a capacitor (capacitance) in the circuit, which shifts its pulses and, as it were, artificially emits a second phase, due to which a torque is created. Due to the need to divide the windings in half, the rotation speed of asynchronous single-phase electric. engines cannot be more than 1500 rpm. In three-phase electric In engines, the coils can be single, located in the stator every 120 degrees around the circumference, then the maximum rotation speed will be 3000 rpm. And if they are each divided in half, then you get 6 coils (two per phase), then the speed will be 2 times less - 1500 rpm, and the rotation force will be 2 times greater. There may be 9 or 12 coils, respectively 1000 and 750 rpm, with an increase in force the same times as the number of revolutions per minute is lower. The windings of single-phase motors can also be cut more than in half, with a similar reduction in speed and increase in force. That is, a low-speed engine is more difficult to hold onto the rotor shaft with anything than a high-speed engine.
There is another common type of email. engines - commutator. Their rotors carry a winding and a contact collector, to which voltage is supplied through copper-graphite “brushes”. It (the rotor winding) creates its own magnetic field. Unlike the passively untwisted iron-aluminum “blank” of asynchronous electric. engine, the magnetic field of the rotor winding of the commutator motor is actively repelled from the field of its stator. Such emails engines have a different operating principle - like the two poles of a magnet of the same name, the rotor (the rotating part of the electric motor) tends to push off from the stator (the stationary part). And since the rotor shaft is firmly fixed by two bearings at the ends, out of “despair” the rotor is actively twisted. The effect is similar to a squirrel in a wheel, the faster it runs, the faster the drum spins. Therefore, such emails motors have much higher speeds and can be adjusted over a wide range than asynchronous ones. In addition, with the same power, they are much more compact and lighter, do not depend on frequency (Hz) and operate on both alternating and direct current. They are usually used in mobile units: electric train locomotives, trams, trolleybuses, electric cars; as well as in all portable el. devices: electric drills, grinders, vacuum cleaners, hair dryers... But they are significantly inferior in simplicity and reliability to asynchronous machines, which are used mainly on stationary electrical equipment.
ELECTRICITY HAZARD
Electric current can be converted into LIGHT (by passing through a filament, luminescent gas, LED crystals), HEAT (overcoming the resistance of a nichrome wire with its inevitable heating, which is used in all heating elements), MECHANICAL WORK (through the magnetic field created by electric coils in electric motors and electric magnets, which respectively rotate and retract). However, el. current is fraught with mortal danger for a living organism through which it can pass.
Some people say: “I was hit by 220 volts.” This is not true because it is not the voltage that causes damage, but the current that passes through the body. Its value, at the same voltage, can differ tens of times for a number of reasons. The path it takes is also of great importance. In order for current to flow through the body, you must be part of an electrical circuit, that is, become its conductor, and for this you must touch two different potentials at the same time (phase and zero - 220 V, or two opposite phases - 380 V). The most common dangerous flow of current is from one hand to the other, or from the left hand to the legs, because this way the path will go through the heart, which can stop from a current of only one tenth of an Ampere (100 milliamps). And if, for example, you touch the bare contacts of the socket with different fingers of one hand, the current will pass from finger to finger, but will not affect the body (unless, of course, your feet are on a non-conductive floor).
The role of zero potential (ZERO) can be played by the ground - literally the soil surface itself (especially damp), or a metal or reinforced concrete structure that is dug into the ground or has a significant area of contact with it. It is not at all necessary to grab different wires with both hands; you can simply stand barefoot or in bad shoes on damp ground, concrete or metal floors and touch the exposed wire with any part of your body. And instantly from this part, an insidious current will flow through the body to the feet. Even if you go to relieve yourself in the bushes and accidentally hit the exposed phase with a stream, the current path will run through the (salty and much more conductive) stream of urine, the reproductive system and legs. If your feet are wearing dry shoes with thick soles or the floor itself is wooden, then there will be no ZERO and no current will flow even if you grab one exposed live PHASE wire with your teeth (a clear confirmation of this is birds sitting on uninsulated wires).
The magnitude of the current largely depends on the area of contact. For example, you can lightly touch two phases (380 V) with dry fingertips - it will hit, but not fatally. Or you can grab two thick copper rods, to which only 50 Volts are connected, with both wet hands - the contact area + dampness will provide conductivity tens of times greater than in the first case, and the magnitude of the current will be fatal. (I have seen an electrician whose fingers were so calloused, dry and calloused that he could easily work under voltage as if wearing gloves.) In addition, when a person touches the voltage with his fingertips or the back of his hand, he reflexively jerks away. If you grab hold of a handrail, then the tension causes contraction of the muscles of the hands and the person grabs with a force that he was never capable of, and no one can tear him off until the tension is turned off. And the time of exposure (milliseconds or seconds) to electric current is also a very significant factor.
For example, in the electric chair, a tightly tightened wide metal hoop is placed on a person’s previously shaved head (through a rag pad moistened with a special, well-conducting solution), to which one wire is connected - the phase one. The second potential is connected to the legs, on which (on the shins near the ankles) wide metal clamps (again with wet special pads) are tightly tightened. The condemned person is securely fixed to the armrests of the chair by his forearms. When you turn on the switch, a voltage of 2000 Volts appears between the potentials of the head and legs! It is understood that with the resulting current strength and its path, loss of consciousness occurs instantly, and the rest of the “afterburning” of the body guarantees the death of all vital organs. Only, perhaps, the cooking procedure itself exposes the unfortunate person to such extreme stress that the electric shock itself becomes a deliverance. But don’t be alarmed - there is no such execution in our state yet...
And so, the danger of electric shock. current depends on: voltage, path of current flow, dry or wet (sweat due to salts has good conductivity) parts of the body, area of contact with bare conductors, isolation of feet from the ground (quality and dryness of shoes, soil dampness, floor material), time exposure to current.
But you don’t have to grab a bare wire to get energized. It may happen that the insulation of the winding of the electrical unit is broken, and then the PHASE will end up on its body (if it is metal). For example, there was such a case in a neighboring house - on a hot summer day, a man climbed onto an old iron refrigerator, sat on it with his bare, sweaty (and therefore salty) thighs, and began drilling into the ceiling with an electric drill, holding onto its metal part near the chuck with his other hand... Either it got into the reinforcement (and it is usually welded to the general grounding loop of the building, which is equivalent to ZERO) of the concrete ceiling slab, or into its own electrical wiring?? He just fell down dead, struck on the spot by a monstrous electric shock. The commission discovered a PHASE (220 volts) on the body of the refrigerator, which appeared on it due to a violation of the insulation of the compressor stator winding. Until you simultaneously touch the body (with the hidden phase) and zero or “ground” (for example, an iron water pipe), nothing will happen (chipboard and linoleum on the floor). But, as soon as the second potential is “found” (ZERO or another PHASE), a blow is inevitable.
To prevent such accidents, GROUNDING is done. That is, through a special protective grounding wire (yellow-green) to the metal housings of all electrical devices. devices are connected to ZERO potential. If the insulation is broken and the PHASE touches the housing, a short circuit (short circuit) with zero will instantly occur, as a result of which the machine will break the circuit and the phase will not go unnoticed. Therefore, electrical engineering switched to three-wire (phase - red or white, zero - blue, ground - yellow-green wires) wiring in single-phase power supply, and five-wire in three-phase (phases - red, white, brown). In the so-called Euro-sockets, in addition to two sockets, grounding contacts (whiskers) were also added - a yellow-green wire is connected to them, and on Euro-plugs, in addition to two pins, there are contacts from which a yellow-green (third) wire also goes to the body electrical appliance.
To avoid short circuits, RCDs (residual current devices) have recently been widely used. The RCD compares the phase and zero currents (how much is in and how much is out), and when a leak appears, that is, either the insulation is broken, and the winding of the motor, transformer or heater spiral is “stitched” onto the housing, or a person actually touches the current-carrying parts, then the “zero” current will be less than the phase current and the RCD will instantly turn off. This current is called DIFFERENTIAL, that is, third-party ("left") and should not exceed a lethal value - 100 milliamps (1 tenth of an Ampere), and for household single-phase power supply this limit is usually 30 mA. Such devices are usually placed at the input (in series with circuit breakers) of the wiring supplying damp, hazardous rooms (for example, a bathroom) and protect against electric shock from hands - to the “ground” (floor, bathtub, pipes, water). Touching the phase and working zero with both hands (with a non-conducting floor) will not trigger the RCD.
The grounding (yellow-green wire) comes from one point with zero (from the common connection point of the three windings of a three-phase transformer, which is also connected to a large metal rod dug deep into the ground - GROUNDING at the electrical substation supplying the microdistrict). Practically, this is the same zero, but “exempt” from work, just a “guard”. So, in the absence of a ground wire in the wiring, you can use a neutral wire. Namely, in a Euro socket, place a jumper from the neutral wire to the grounding “whiskers”, then if the insulation is broken and there is a leak to the housing, the machine will operate and turn off the potentially dangerous device.
Or you can make grounding yourself - drive a couple of crowbars deep into the ground, pour it with a very salty solution and connect the grounding wire. If you connect it to the common zero at the input (before the RCD), then it will reliably protect against the appearance of a second PHASE in the sockets (described above) and the combustion of household equipment. If it is not possible to reach it to the common zero, for example in a private house, then you should install a machine at your zero, as in a phase, otherwise, if the common zero in the switchboard burns out, the neighbors' current will go through your zero to a homemade grounding. And with a machine gun, support for neighbors will be provided only up to its limit and your zero will not suffer.
AFTERWORD
Well, it seems that I have described all the main common nuances of electricity not related to professional activities. Deeper details will require an even longer text. How clear and intelligible it turned out is to judge by those who are generally distant and incompetent in this topic (was :-).
Low bow and fond memory to the great physicists of Europe, who immortalized their names in units of measurement of electric current parameters: Alexandro Giuseppe Antonio Anastasio VOLTA - Italy (1745-1827); Andre Marie AMPERE - France (1775-1836); Georg Simon OM - Germany (1787-1854); James WATT - Scotland (1736-1819); Heinrich Rudolf HERZ - Germany (1857-1894); Michael Faraday - England (1791-1867).
POEM ABOUT ELECTRIC CURRENT:
Wait, don’t rush, let’s talk a little.
Wait, don’t rush, don’t rush the horses.
You and I are alone in the apartment this evening.
Electric current, electric current,
Similar in tension to the Middle East,
From the moment I saw the Bratsk hydroelectric power station,
My interest in you has arisen.
Electric current, electric current,
They say you can be cruel at times.
Your insidious bite can take your life,
Well, let it be, I’m still not afraid of you!
Electric current, electric current,
They claim that you are a stream of electrons,
And besides, idle people chatter,
That you are controlled by the cathode and anode.
I don't know what "anode" and "cathode" mean,
I already have a lot of worries,
But while you're flowing, electric current
The boiling water in my pan will not run out.
Igor Irtenev 1984
Nowadays it is impossible to imagine life without electricity. This is not only light and heaters, but also all electronic equipment, from the very first vacuum tubes to mobile phones and computers. Their work is described by a variety of, sometimes very complex, formulas. But even the most complex laws of electrical engineering and electronics are based on the laws of electrical engineering, which are studied in the subject “Theoretical Foundations of Electrical Engineering” (TOE) in institutes, technical schools and colleges.
Basic laws of electrical engineering
- Ohm's law
- Joule-Lenz law
- Kirchhoff's first law
Ohm's law- the study of TOE begins with this law and not a single electrician can do without it. It states that current is directly proportional to voltage and inversely proportional to resistance. This means that the higher the voltage applied to the resistor, motor, capacitor or coil (holding other conditions constant), the higher the current flowing through the circuit. Conversely, the higher the resistance, the lower the current.
Joule-Lenz law. Using this law, you can determine the amount of heat generated by a heater, cable, electric motor power or other types of work performed by electric current. This law states that the amount of heat generated when electric current flows through a conductor is directly proportional to the square of the current, the resistance of that conductor, and the time the current flows. Using this law, the actual power of electric motors is determined, and also on the basis of this law, the electric meter works, according to which we pay for the electricity consumed.
Kirchhoff's first law. It is used to calculate cables and circuit breakers when calculating power supply circuits. It states that the sum of currents entering any node is equal to the sum of currents leaving that node. In practice, one cable comes in from the power source, and one or more go out.
Kirchhoff's second law. Used when connecting several loads in series or a load and a long cable. It is also applicable when connected not from a stationary power source, but from a battery. It states that in a closed circuit the sum of all voltage drops and all emfs is 0.
Where to start studying electrical engineering
It is best to study electrical engineering in special courses or in educational institutions. In addition to the opportunity to communicate with teachers, you can take advantage of the educational institution’s facilities for practical classes. The educational institution also issues a document that will be required when applying for a job.
If you decide to study electrical engineering on your own or you need additional material for classes, then there are many sites where you can study and download the necessary materials to your computer or phone.
Video lessons
There are many videos on the Internet that help you master the basics of electrical engineering. All videos can be watched online or downloaded using special programs.
Electrician video tutorials- a lot of materials telling about various practical issues that a novice electrician may encounter, about the programs that he has to work with and about the equipment installed in residential premises.
Basics of electrical engineering theory- here are video lessons that clearly explain the basic laws of electrical engineering. The total duration of all lessons is about 3 hours.
- zero and phase, connection diagrams for light bulbs, switches, sockets. Types of tools for electrical installation;
- Types of materials for electrical installation, electrical circuit assembly;
- Switch connection and parallel connection;
- Installation of an electrical circuit with a two-button switch. Model of power supply for the premises;
- Model of power supply for a room with a switch. Safety Basics.
Books
The best advisor there was always a book. Previously, it was necessary to borrow a book from the library, from friends, or buy it. Nowadays on the Internet you can find and download a variety of books that a beginner or an experienced electrician needs. Unlike video tutorials, where you can watch how this or that action is performed, in a book you can keep it nearby while doing the work. The book may contain reference materials that will not fit into a video lesson (like in school - the teacher tells the lesson described in the textbook, and these forms of teaching complement each other).
There are sites with a large amount of electrical engineering literature on a variety of issues - from theory to reference materials. On all these sites, you can download the book you need to your computer and later read it from any device.
For example,
mexalib- various types of literature, including electrical engineering
books for electrician- this site has a lot of advice for the novice electrical engineer
electric specialist- site for beginner electricians and professionals
Electrician's Library- many different books mainly for professionals
Online textbooks
In addition, there are online textbooks on electrical engineering and electronics with an interactive table of contents on the Internet.
These are such as:
Electrician Basic Course- textbook on electrical engineering
Basic Concepts
Electronics for Beginners- initial course and basics of electronics
Safety precautions
The main thing when performing electrical work is compliance with safety precautions. If incorrect operation can lead to equipment failure, then failure to comply with safety precautions can lead to injury, disability or death.
Main rules- this means not touching live wires with bare hands, working with tools with insulated handles, and when turning off the power, posting a sign “do not turn on, people are working.” For a more detailed study of this issue, you need to take the book “Safety Rules for Electrical Installation and Adjustment Work.”
Video version of the article:
Let's start with the concept of electricity. Electric current is the ordered movement of charged particles under the influence of an electric field. The particles can be free electrons of the metal if the current flows through a metal wire, or ions if the current flows in a gas or liquid.
There is also current in semiconductors, but this is a separate topic for discussion. An example is a high-voltage transformer from a microwave oven - first, electrons flow through the wires, then ions move between the wires, respectively, first the current flows through the metal, and then through the air. A substance is called a conductor or semiconductor if it contains particles that can carry an electric charge. If there are no such particles, then such a substance is called a dielectric; it does not conduct electricity. Charged particles carry an electric charge, which is measured as q in coulombs.
The unit of measurement of current strength is called Ampere and is designated by the letter I, a current of 1 Ampere is formed when a charge of 1 Coulomb passes through a point in an electrical circuit in 1 second, that is, roughly speaking, the current strength is measured in coulombs per second. And in essence, current strength is the amount of electricity flowing per unit time through the cross section of a conductor. The more charged particles running along the wire, the correspondingly greater the current.
To make charged particles move from one pole to another, it is necessary to create a potential difference or – Voltage – between the poles. Voltage is measured in volts and is designated by the letter V or U. To obtain a voltage of 1 Volt, you need to transfer a charge of 1 C between the poles, while doing 1 J of work. I agree, it’s a little unclear.
For clarity, imagine a water tank located at a certain height. A pipe comes out of the tank. Water flows through the pipe under the influence of gravity. Let water be an electric charge, the height of the water column be voltage, and the speed of water flow be electric current. More precisely, not the flow rate, but the amount of water flowing out per second. You understand that the higher the water level, the greater the pressure below will be. And the higher the pressure below, the more water will flow through the pipe because the speed will be higher.. Likewise, the higher the voltage, the more current will flow in the circuit.
The relationship between all three considered quantities in a direct current circuit is determined by Ohm's law, which is expressed by this formula, and it sounds like the current strength in the circuit is directly proportional to the voltage, and inversely proportional to the resistance. The greater the resistance, the less the current, and vice versa.
I'll add a few more words about resistance. It can be measured, or it can be counted. Let's say we have a conductor having a known length and cross-sectional area. Square, round, it doesn't matter. Different substances have different resistivities, and for our imaginary conductor there is this formula that determines the relationship between length, cross-sectional area and resistivity. The resistivity of substances can be found on the Internet in the form of tables.
Again, we can draw an analogy with water: water flows through a pipe, let the pipe have a specific roughness. It is logical to assume that the longer and narrower the pipe, the less water will flow through it per unit of time. See how simple it is? You don’t even need to memorize the formula, just imagine a pipe with water.
As for measuring resistance, you need a device, an ohmmeter. Nowadays, universal instruments are more popular - multimeters; they measure resistance, current, voltage, and a bunch of other things. Let's do an experiment. I will take a piece of nichrome wire of known length and cross-sectional area, find the resistivity on the website where I bought it and calculate the resistance. Now I will measure the same piece using the device. For such a small resistance, I will have to subtract the resistance of the probes of my device, which is 0.8 ohms. Just like that!
The multimeter scale is divided according to the size of the measured quantities; this is done for higher measurement accuracy. If I want to measure a resistor with a nominal value of 100 kOhm, I set the handle to the larger nearest resistance. In my case it is 200 kilo-ohms. If I want to measure 1 kilo-ohm, I use 2 ohms. This is true for measuring other quantities. That is, the scale shows the limits of the measurement you need to fall into.
Let's continue to have fun with the multimeter and try to measure the rest of the quantities we've learned. I'll take several different DC sources. Let it be a 12 volt power supply, a USB port and a transformer that my grandfather made in his youth.
We can measure the voltage on these sources right now by connecting a voltmeter in parallel, that is, directly to the plus and minus of the sources. Everything is clear with voltage; it can be taken and measured. But to measure current strength, you need to create an electrical circuit through which current will flow. There must be a consumer or load in the electrical circuit. Let's connect a consumer to each source. A piece of LED strip, a motor and a resistor (160 ohms).
Let's measure the current flowing in the circuits. To do this, I switch the multimeter to current measurement mode and switch the probe to the current input. The ammeter is connected in series to the object being measured. Here is the diagram, it should also be remembered and not to be confused with connecting a voltmeter. By the way, there is such a thing as current clamps. They allow you to measure current in a circuit without connecting directly to the circuit. That is, you don’t need to disconnect the wires, you just throw them on the wire and they measure. Okay, let's go back to our usual ammeter.
So I measured all the currents. Now we know how much current is consumed in each circuit. Here we have LEDs shining, here the motor is spinning and here... So stand there, what does a resistor do? He doesn't sing us songs, doesn't light up the room, and doesn't turn any mechanism. So what does he spend the whole 90 milliamps on? This won’t work, let’s figure it out. Hey you! Aw, he's hot! So this is where energy is spent! Is it possible to somehow calculate what kind of energy is here? It turns out that it is possible. The law describing the thermal effect of electric current was discovered in the 19th century by two scientists, James Joule and Emilius Lenz.
The law was called Joule-Lenz's law. It is expressed by this formula, and numerically shows how many joules of energy are released in a conductor in which current flows per unit time. From this law you can find the power that is released on this conductor; power is denoted by the English letter P and measured in watts. I found this very cool tablet that connects all the quantities we have studied so far.
Thus, on my table, electrical power is used for lighting, for performing mechanical work and for heating the surrounding air. By the way, it is on this principle that various heaters, electric kettles, hair dryers, soldering irons, etc. work. There is a thin spiral everywhere, which heats up under the influence of current.
This point should be taken into account when connecting wires to the load, that is, laying wiring to sockets throughout the apartment is also included in this concept. If you take a wire that is too thin to connect to an outlet and connect a computer, kettle and microwave to this outlet, the wire may heat up and cause a fire. Therefore, there is such a sign that connects the cross-sectional area of the wires with the maximum power that will flow through these wires. If you decide to pull wires, don’t forget about it.
Also, as part of this issue, I would like to recall the features of parallel and series connections of current consumers. With a series connection, the current is the same on all consumers, the voltage is divided into parts, and the total resistance of the consumers is the sum of all resistances. With a parallel connection, the voltage on all consumers is the same, the current strength is divided, and the total resistance is calculated using this formula.
This brings up one very interesting point that can be used to measure current strength. Let's say you need to measure the current in a circuit of about 2 amperes. An ammeter cannot cope with this task, so you can use Ohm's law in its pure form. We know that the current strength is the same in a series connection. Let's take a resistor with a very small resistance and insert it in series with the load. Let's measure the voltage on it. Now, using Ohm's law, we find the current strength. As you can see, it coincides with the calculation of the tape. The main thing to remember here is that this additional resistor should be as low resistance as possible in order to have minimal impact on the measurements.
There is one more very important point that you need to know about. All sources have a maximum output current; if this current is exceeded, the source can heat up, fail, and in the worst case, even catch fire. The most favorable outcome is when the source has overcurrent protection, in which case it will simply turn off the current. As we remember from Ohm's law, the lower the resistance, the higher the current. That is, if you take a piece of wire as a load, that is, close the source to itself, then the current strength in the circuit will jump to enormous values, this is called a short circuit. If you remember the beginning of the issue, you can draw an analogy with water. If we substitute zero resistance into Ohm's law, we get an infinitely large current. In practice, this of course does not happen, because the source has an internal resistance that is connected in series. This law is called Ohm's law for a complete circuit. Thus, the short circuit current depends on the value of the internal resistance of the source.
Now let's return to the maximum current that the source can produce. As I already said, the current in the circuit is determined by the load. Many people wrote to me on VK and asked something like this question, I’ll exaggerate it slightly: Sanya, I have a power supply of 12 volts and 50 amperes. If I connect a small piece of LED strip to it, will it burn out? No, of course it won't burn. 50 amperes is the maximum current that the source can produce. If you connect a piece of tape to it, it will take its well, let’s say 100 milliamps, and that’s it. The current in the circuit will be 100 milliamps, and no one will burn anywhere. Another thing is that if you take a kilometer of LED strip and connect it to this power supply, then the current there will be higher than permissible, and the power supply will most likely overheat and fail. Remember, it is the consumer who determines the amount of current in the circuit. This unit can output a maximum of 2 amps, and when I short it to the bolt, nothing happens to the bolt. But the power supply doesn’t like this; it works in extreme conditions. But if you take a source capable of delivering tens of amperes, the bolt will not like this situation.
As an example, let’s calculate the power supply that will be required to power a known section of LED strip. So, we bought a reel of LED strip from the Chinese and want to power three meters of this very strip. First, we go to the product page and try to find how many watts one meter of tape consumes. I couldn’t find this information, so there is this sign. Let's see what kind of tape we have. Diodes 5050, 60 pieces per meter. And we see that the power is 14 watts per meter. I want 3 meters, which means the power will be 42 watts. It is advisable to take a power supply with a 30% power reserve so that it does not operate in critical mode. As a result, we get 55 watts. The closest suitable power supply will be 60 watts. From the power formula, we express the current strength and find it, knowing that LEDs operate at a voltage of 12 volts. It turns out that we need a unit with a current of 5 amperes. For example, we go to Ali, find it, buy it.
It is very important to know the current consumption when making any USB homemade products. The maximum current that can be taken from USB is 500 milliamps, and it is better not to exceed it.
And finally, a short word about safety precautions. Here you can see to what values electricity is considered harmless to human life.