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What do beginners need to know about electricity?

We are often approached by readers who have not previously encountered work on electricity, but want to understand this. For this category the heading "Electricity for beginners" is created.

Figure 1. Movement of electrons in a conductor.

Before proceeding with work related to electricity, it is necessary to “savvy” a little theoretically in this matter.

The term "electricity" refers to the movement of electrons under the influence of an electromagnetic field.

The main thing is to understand that electricity is the energy of the smallest charged particles that move inside the conductors in a certain direction (Fig. 1).

Direct current practically does not change its direction and magnitude over time. Let's say that in a conventional battery there is direct current. Then the charge will flow from minus to plus, not changing until it runs out.

Alternating current is a current that changes direction and magnitude with a certain periodicity. Think of the current as a stream of water flowing through a pipe. After a certain period of time (for example, 5 s), the water will rush in one direction, then in the other.

Figure 2. Diagram of the transformer device.

With current, this happens much faster, 50 times per second (frequency 50 Hz). During one period of oscillation, the current rises to a maximum, then passes through zero, and then the reverse process occurs, but with a different sign. When asked why this happens and why such a current is needed, it can be answered that receiving and transmitting alternating current is much easier than direct current. Receiving and transmitting alternating current are closely related to a device such as a transformer (Fig. 2).

A generator that produces alternating current is much simpler in design than a direct current generator. In addition, alternating current is best suited for power transmission over long distances. With it, less energy is wasted.

With the help of a transformer (a special device in the form of coils), the alternating current is converted from low voltage to high voltage, and vice versa, as shown in the illustration (Fig. 3).

It is for this reason that most devices operate on a network in which the current is alternating. However, direct current is also used quite widely: in all types of batteries, in the chemical industry and in some other areas.

Figure 3. AC transmission diagram.

Many have heard such mysterious words as one phase, three phases, zero, ground or earth, and they know that these are important concepts in the world of electricity. However, not everyone understands what they mean and what relation they have to the surrounding reality. However, you need to know this.

Without going into technical details that a home master does not need, we can say that a three-phase network is a method of transmitting electric current when alternating current flows through three wires and returns one at a time. The above needs some clarification. Any electrical circuit consists of two wires. One by one, the current goes to the consumer (for example, to the kettle), and by the other it returns back. If such a circuit is opened, then the current will not flow. That's the whole description of a single-phase circuit (Fig. 4 A).

The wire through which the current flows is called phase, or simply phase, and through which it returns - zero, or zero. A three-phase circuit consists of three phase wires and one return. This is possible because the phase of the alternating current in each of the three wires is shifted with respect to the neighboring one by 120 ° (Fig. 4 B). A textbook on electromechanics will help answer this question in more detail.

Figure 4. Scheme of electrical circuits.

The transmission of alternating current occurs precisely with the help of three-phase networks. This is economically beneficial: two more neutral wires are not needed. Approaching the consumer, the current is divided into three phases, and each of them is given zero. So he gets into apartments and houses. Although sometimes a three-phase network is brought directly into the house. As a rule, we are talking about the private sector, and this state of affairs has its pros and cons.

Earth, or, more correctly, grounding, is the third wire in a single-phase network. In essence, it does not carry a workload, but serves as a kind of fuse.

For example, when electricity gets out of control (for example, a short circuit), there is a risk of fire or electric shock. To prevent this from happening (that is, the current value should not exceed a level that is safe for humans and devices), grounding is introduced. Through this wire, excess electricity literally goes into the ground (Fig. 5).

Figure 5. The simplest grounding scheme.

One more example. Let's say that a small breakdown occurred in the operation of the electric motor of the washing machine and part of the electric current falls on the outer metal shell of the device.

If there is no ground, this charge will wander around the washing machine. When a person touches it, he will instantly become the most convenient outlet for this energy, that is, he will receive an electric shock.

If there is a ground wire in this situation, the excess charge will drain through it without harming anyone. In addition, we can say that the neutral conductor can also be grounding and, in principle, it is, but only at a power plant.

The situation when there is no grounding in the house is unsafe. How to deal with it without changing all the wiring in the house will be described later.

ATTENTION!

Some craftsmen, relying on basic knowledge of electrical engineering, install the neutral wire as a ground wire. Never do that.

In the event of a break in the neutral wire, the housings of grounded devices will be energized with 220 V.

At present, it is already quite stable service market, including in the area household electrics.

Highly professional electricians, with undisguised enthusiasm, do their best to help the rest of our population, while receiving great satisfaction from the quality of work performed and modest remuneration. In turn, our population also gets great pleasure from a high-quality, fast 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 - personally resolve absolutely any domestic issues arising on the territory of their own place of residence. Such a position certainly deserves both approval and understanding.
Moreover, all these Replacements, transfers, installations- switches, sockets, automatic machines, counters, lamps, connecting kitchen stoves etc. - all these types of services most demanded by the population, from the point of view of a professional electrician, at all are not hard work.

And in truth, an ordinary citizen, without an electrical engineering education, but having sufficiently detailed instructions, may well cope with its implementation himself, with his own hands.
Of course, doing such work for the first time, a novice electrician can spend much more time than an experienced professional. But it’s not at all a fact that from this it will be performed less efficiently, with attention to detail and without any haste.

Initially, this site was conceived as a collection of similar instructions on the most common problems in this area. But in the future, for people who have absolutely never encountered the solution of such issues, the course "young electrician" of 6 practical classes was added.

Features of installation of electrical sockets hidden and open wiring. Sockets for electric cooker. Do-it-yourself electric stove connection.

Switches.

Replacement, installation of electrical switches, hidden and open wiring.

Automata and RCDs.

The principle of operation of Residual Current Devices and circuit breakers. Classification of automatic switches.

Electric meters.

Instructions for self-installation and connection of a single-phase meter.

Wiring replacement.

Indoor electrical installation. Features of installation, depending on the material of the walls and the type of their finish. Electrical wiring in a wooden house.

Lamps.

Installation of wall lamps. Chandeliers. Installation of spotlights.

Contacts and connections.

Some types of conductor connections, most commonly found in "home" electrics.

Electrical engineering-basics of theory.

The concept of electrical resistance. Ohm's law. Kirchhoff's laws. Parallel and series 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 underpaid? Below, you can find the price list of the most common services from three years ago.

Electrical installation - prices.

Electric meter pcs. - 650p.

Single-pole machines pcs. - 200p.

Three-pole circuit breakers pcs. - 350p.

Difamat pcs. - 300p.

RCD single-phase pcs. - 300p.

One-gang switch pcs. - 150p.

Two-gang switch pcs. - 200p.

Three-gang switch pcs. - 250p.

Board of open wiring up to 10 groups pcs. - 3400p.

Flush wiring board up to 10 groups pcs. - 5400p.

Laying open wiring P.m - 40p.

Postings in corrugation P.m - 150p.

Wall chasing (concrete) P.m - 300p.

(brick) P.m - 200p.

Installation of a socket and junction box in concrete pcs. - 300p.

brick pcs. - 200p.

drywall pcs. - 100p.

Sconce pcs. - 400p.

Spotlight pcs. - 250p.

Chandelier on hook pcs. - 550p.

Ceiling chandelier (without assembly) pcs. - 650p.

Bell and bell button installation pcs. - 500p.

Installing a socket, open wiring switch pcs. - 300p.

Installing a socket, flush-mounted switch (without installing a socket box) pcs. - 150p.

When I was an electrician "on an ad", I could not mount more than 6-7 points (sockets, switches) of hidden wiring, on concrete - in an evening. Plus, 4-5 meters of strobes (for concrete). We carry out simple arithmetic calculations: (300+150)*6=2700p. It's for sockets with switches.
300*4=1200r. - this is for the strobes.
2700+1200=3900r. is the total amount.

Not bad, for 5-6 hours of work, isn't it? Rates, of course, Moscow, in Russia they will be less, but not more than twice.
If taken as a whole, then the monthly salary of an electrician - installer, currently rarely exceeds 60,000 rubles (not in Moscow)

Of course, there are especially gifted people in this field (as a rule, with iron health) and a practical mind. Under certain conditions, they manage to raise their earnings to 100,000 rubles and more. As a rule, they have a license for the production of electrical work and work directly with the customer, taking "serious" contracts without the participation of various intermediaries.
Electricians - repairmen prom. equipment (at enterprises), electricians - high-voltage workers, as a rule (not always) - earn somewhat less. If the enterprise is profitable and it invests in "re-equipment" for electricians-repairmen, additional sources of income may be opened, for example, the installation of new equipment produced after hours.

Highly paid but physically difficult and sometimes very dusty, the work of an electrician-installer is undoubtedly worthy of all respect.
Being engaged in electrical installation, a novice specialist can master the basic skills and abilities, gain initial experience.
Regardless of how he will build his career in the future, you can be sure that the practical knowledge gained in this way will definitely come in handy.

The use of any materials on this page is allowed if there is a link to the site

In everyday life, we constantly deal with electricity. Without moving charged particles, the functioning of the instruments and devices we use is impossible. And in order to fully enjoy these achievements of civilization and ensure their long-term service, you need to know and understand the principle of work.

Electrical engineering is an important science

Electrical engineering answers questions related to the production and use of current energy for practical purposes. However, it is not at all easy to describe in an accessible language the world invisible to us, where current and voltage reign. So grants are in constant demand"Electricity for Dummies" or "Electrical Engineering for Beginners".

What does this mysterious science study, what knowledge and skills can be obtained as a result of its development?

Description of the discipline "Theoretical foundations of electrical engineering"

You can see the mysterious abbreviation "TOE" in the student's record books for technical specialties. This is precisely the science we need.

The date of birth of electrical engineering can be considered the period of the beginning of the XIX century, when the first direct current source was invented. Physics became the mother of the "newborn" branch of knowledge. Subsequent discoveries in the field of electricity and magnetism enriched this science with new facts and concepts that were of great practical importance.

It took its modern form, as an independent industry, at the end of the 19th century, and since then included in the curriculum of technical universities and actively interacts with other disciplines. So, for the successful study of electrical engineering, it is necessary to have a theoretical knowledge base from the school course of physics, chemistry and mathematics. In turn, such important disciplines are based on TOE, such as:

• electronics and radio electronics;
• electromechanics;
• energy, lighting engineering, etc.

The central focus of electrical engineering is, of course, the current and its characteristics. Further, the theory tells about electromagnetic fields, their properties and practical application. In the final part of the discipline, devices are covered in which energetic electronics work. Having mastered this science, he will understand a lot in the world around him.

What is the importance of electrical engineering today? Electrical workers cannot do without knowledge of this discipline:

• electrician;
• fitter;
• energy.

The omnipresence of electricity makes it necessary for a simple layman to study it in order to be a literate person and be able to apply his knowledge in everyday life.

It is difficult to understand what you cannot see and “feel”. Most electrical textbooks are full of obscure terms and cumbersome diagrams. Therefore, the good intentions of beginners to study this science often remain only plans.

In fact, electrical engineering is a very interesting science, and the main provisions of electricity can be stated in an accessible language for dummies. If you approach the educational process creatively and with due diligence, many things will become understandable and exciting. Here are some useful tips for learning electrics for dummies.

Journey into the world of electrons you need to start with the study of the theoretical foundations- concepts and laws. Get a tutorial, such as "Electrical Engineering for Dummies", which will be written in a language that you understand, or several of these textbooks. The presence of illustrative examples and historical facts will diversify the learning process and help to better assimilate knowledge. You can check your progress with the help of various tests, assignments and exam questions. Return once again to those paragraphs in which you made mistakes during the check.

If you are sure that you have fully studied the physical section of the discipline, you can move on to more complex material - a description of electrical circuits and devices.

Do you feel sufficiently "savvy" in theory? It's time to develop practical skills. Materials for creating the simplest circuits and mechanisms can be easily found in electrical and household goods stores. However, do not rush to immediately start modeling- first learn the section "electrical safety" so as not to harm your health.

To get practical benefit from your newfound knowledge, try repairing broken household appliances. Be sure to study the operating requirements, follow the instructions, or invite an experienced electrician to be your partner. The time for experimentation has not yet come, and electricity is not to be trifled with.

Try, do not rush, be inquisitive and diligent, study all available materials and then from the "dark horse" electric current will turn into a kind and faithful friend For you. And maybe you can even make an important electrical discovery and become rich and famous overnight.

Introduction

The search for new energy to replace smoky, expensive, low-efficiency fuels led to the discovery of the properties of various materials to accumulate, store, quickly transmit and convert electricity. Two centuries ago, methods of using electricity in everyday life and industry were discovered, investigated and described. Since then, the science of electricity has become a separate branch. Now it is difficult to imagine our life without electrical appliances. Many of us safely undertake to repair household appliances and successfully cope with it. Many are afraid to fix even the outlet. Armed with some knowledge, we will no longer be afraid of electricity. The processes occurring in the network should be understood and used for your own purposes.
The proposed course is designed for the initial acquaintance of the reader (student) with the basics of electrical engineering.

Basic electrical quantities and concepts

The essence of electricity is that the flow of electrons moves along a conductor in a closed circuit from a current source to a consumer and vice versa. Moving, these electrons perform a certain work. This phenomenon is called - ELECTRIC CURRENT, and the unit of measurement is named after the scientist who was the first to study the properties of current. The surname of the scientist is Ampere.
You need to know that the current during operation heats up, bends and tries to break the wires and everything through which it flows. This property should be taken into account when calculating circuits, i.e., the greater the current, the thicker the wires and structures.
If we open the circuit, the current will stop, but there will still be some potential at the terminals of the current source, always ready to work. The potential difference at the two ends of the conductor is called VOLTAGE ( U).
U=f1-f2.
At one time, a scientist by the name of Volt scrupulously studied electrical voltage and gave him a detailed explanation. Subsequently, the unit of measurement was given its name.
Unlike current, voltage does not break, but burns. Electricians say - punches. Therefore, all wires and electrical units are protected by insulation, and the higher the voltage, the thicker the insulation.
A little later, another famous physicist - Ohm, carefully experimenting, revealed the relationship between these electrical quantities and described it. Now every student knows Ohm's law I=U/R. It can be used to calculate simple circuits. Having covered the value we are looking for with our finger, we will see how to calculate it.
Don't be afraid of formulas. To use electricity, it is not so much they (formulas) that are needed, but an understanding of what is happening in the electrical circuit.
And the following happens. An arbitrary current source (let's call it for now - GENERATOR) generates electricity and transmits it by wire to the consumer (let's call it, for now, with a word - LOAD). Thus, we have obtained a closed electrical circuit "GENERATOR - LOAD".
While the generator is generating energy, the load consumes it and works (i.e., converts electrical energy into mechanical, light, or any other). By putting an ordinary knife switch in the wire break, we can turn the load on and off when we need it. Thus, we get inexhaustible possibilities of regulation of work. It is interesting that when the load is off, there is no need to turn off the generator (by analogy with other types of energy - extinguish a fire under a steam boiler, turn off the water in a mill, etc.)
It is important to observe the proportions GENERATOR-LOAD. The generator power must not be less than the load power. It is impossible to connect a powerful load to a weak generator. It's like harnessing an old horse to a heavy cart. Power can always be found in the documentation for the electrical appliance or its marking on a plate attached to the side or rear wall of the electrical appliance. The concept of POWER was introduced more than a century ago, when electricity went beyond the thresholds of laboratories and began to be used in everyday life and industry.
Power is the product of voltage and current. The unit is watt. This value shows how much current the load consumes at this voltage. P=U X

electrical materials. Resistance, conductivity.

We have already mentioned a quantity called OM. Now let's dwell on it in more detail. For a long time, scientists have paid attention to the fact that different materials behave differently with current. Some let it pass without hindrance, others stubbornly resist it, others let it pass only in one direction, or let it pass “on certain conditions”. After testing the conductivity of all possible materials, it became clear that absolutely all materials, to some extent, can conduct current. To assess the "measure" of conductivity, a unit of electrical resistance was deduced and called it OM, and materials, depending on their "ability" to pass current, were divided into groups.
One group of materials is conductors. Conductors conduct current without much loss. Conductors include materials with a resistance of zero to 100 ohm/m. These properties are mainly found in metals.
Another group- dielectrics. Dielectrics also conduct current, but with huge losses. Their resistance is from 10,000,000 ohms to infinity. Dielectrics, for the most part, include non-metals, liquids and various gas compounds.
A resistance of 1 ohm means that in a conductor with a cross section of 1 sq. mm and 1 meter long, 1 ampere of current will be lost..
The reciprocal of the resistance - conductivity. The value of the conductivity of a material can always be found in reference books. Resistivity and conductivity of some materials are shown in Table No. 1

TABLE #1

MATERIAL	Resistivity	Conductivity
Aluminum
Tungsten
Platinum-iridium alloy
Constantan
Chromonickel
Solid insulators	From 10 (to the power of 6) and above	10 (to the power of minus 6)
	10(to the power of 19)	10 (to the power of minus 19)
	10(to the power of 20)	10 (to the power of minus 20)
Liquid insulators	From 10 (to the power of 10) and above	10 (to the power of minus 10)
gaseous	From 10 (to the power of 14) and above	10 (to the power of minus 14)

From the table you can see that the most conductive materials are silver, gold, copper and aluminum. Due to their high cost, silver and gold are used only in high-tech schemes. And copper and aluminum are widely used as conductors.
It is also clear that no absolutely conductive materials, therefore, when calculating, it must always be taken into account that current is lost in the wires and voltage drops.
There is another, rather large and "interesting" group of materials - semiconductors. The conductivity of these materials varies with environmental conditions. Semiconductors begin to conduct current better or, conversely, worse if they are heated / cooled, or illuminated, or bent, or, for example, shocked.

Symbols in electrical circuits.

To fully understand the processes occurring in the circuit, it is necessary to be able to correctly read electrical circuits. To do this, you need to know the conventions. Since 1986, the standard has come into force, which largely removed the discrepancies in the designations that exist between European and Russian GOSTs. Now an electrical circuit from Finland can be read by an electrician from Milan and Moscow, Barcelona and Vladivostok.
In electrical circuits, there are two types of designations: graphic and alphabetic.
The letter codes of the most common types of elements are presented in table No. 2:
TABLE #2

	Devices	Amplifiers, remote controls, lasers…
	Converters of non-electrical quantities into electrical quantities and vice versa (except for power supplies), sensors	Loudspeakers, microphones, sensitive thermoelectric elements, ionizing radiation detectors, synchros.
	Capacitors.
	Integrated circuits, microassemblies.	Memory devices, logical elements.
	Miscellaneous elements.	Lighting devices, heating elements.
	Dischargers, fuses, protective devices.	Current and voltage protection elements, fuses.
	Generators, power supplies.	Batteries, accumulators, electrochemical and electrothermal sources.
	Indication and signaling devices.	Sound and light alarm devices, indicators.
	Relay contactors, starters.	Current and voltage relays, thermal, time relays, magnetic starters.
	Inductors, chokes.	Chokes for fluorescent lighting.
	Engines.	DC and AC motors.
	Devices, measuring equipment.	Indicating and recording and measuring instruments, counters, clocks.
	Switches and disconnectors in power circuits.	Disconnectors, short-circuiters, circuit breakers (power)
	Resistors.	Variable resistors, potentiometers, varistors, thermistors.
	Switching devices in control, signaling and measuring circuits.	Switches, switches, switches triggered by various influences.
	Transformers, autotransformers.	Current and voltage transformers, stabilizers.
	Converters of electrical quantities.	Modulators, demodulators, rectifiers, inverters, frequency converters.
	Electrovacuum, semiconductor devices.	Electronic tubes, diodes, transistors, diodes, thyristors, zener diodes.
	Microwave lines and elements, antennas.	Waveguides, dipoles, antennas.
	Contact connections.	Pins, sockets, collapsible connections, current collectors.
	mechanical devices.	Electromagnetic clutches, brakes, cartridges.
	End devices, filters, limiters.	Modeling lines, quartz filters.

Conditional graphic symbols are presented in tables No. 3 - No. 6. Wires in the diagrams are indicated by straight lines.
One of the main requirements in drawing up diagrams is the ease of their perception. An electrician, when looking at the diagram, must understand how the circuit is arranged and how one or another element of this circuit operates.
TABLE #3. Symbols for contact connections

detachable-
inseparable, collapsible
inseparable, inseparable

The point of contact or connection can be located on any section of the wire from one gap to another.

TABLE #4. Symbols of switches, switches, disconnectors.

	closing	opening
Single pole switch
Single pole disconnector
Three-pole switch
Three-pole disconnector
Three-pole disconnector with automatic return (slang name - "AUTOMATIC")
Single-pole disconnector with automatic reset
Push switch (so-called - "BUTTON")
Extract switch
Switch with return when the button is pressed again (can be found in table or wall lamps)
Single-pole travel switch (also known as "terminal" or "terminal")

The vertical lines crossing the moving contacts indicate that all three contacts close (or open) at the same time from one action.
When considering the diagram, it must be taken into account that some elements of the circuit are drawn in the same way, but their letter designation will be different (for example, a relay contact and a switch).

TABLE No. 5. Designation of contactor relay contacts

	closing	opening
with deceleration when actuated
slow down on return
with deceleration on operation and on return

TABLE No. 6. Semiconductors

zener diode
Thyristor
Photodiode
Light-emitting diode
photoresistor
solar cell
Transistor
Capacitor
Throttle
Resistance

DC electrical machines -

Asynchronous three-phase AC electrical machines -

Depending on the letter designation, these machines will be either a generator or an engine.
When marking electrical circuits, the following requirements are observed:

1. Sections of the circuit, separated by the contacts of devices, relay windings, devices, machines and other elements, are labeled differently.
2. Sections of the circuit passing through detachable, collapsible or non-separable contact connections are marked in the same way.
3. In three-phase AC circuits, the phases are marked: “A”, “B”, “C”, in two-phase circuits - “A”, “B”; "B", "C"; "C", "A", and in single-phase - "A"; "AT"; "WITH". Zero is denoted by the letter - "O".
4. Sections of circuits of positive polarity are marked with odd numbers, and negative polarity with even numbers.
5. Next to the symbol of power equipment in the drawings of plans, the equipment number according to the plan (in the numerator) and its power (in the denominator) are indicated with a fraction, and for lamps - the power (in the numerator) and the height of the installation in meters (in the denominator).

It must be understood that all electrical circuits show the state of the elements in the initial state, i.e. when there is no current in the circuit.

Electrical circuit. Parallel and serial connection.

As mentioned above, we can disconnect the load from the generator, we can connect another load to the generator, or we can connect several consumers at the same time. Depending on the tasks at hand, we can turn on several loads in parallel or in series. In this case, not only the circuit changes, but also the characteristics of the circuit.

At parallel connected, the voltage at each load will be the same, and the operation of one load will not affect the operation of other loads.

In this case, the current in each circuit will be different and will be summed up at the junctions.
Itot = I1+I2+I3+…+In
In this way, the entire load in the apartment is connected, for example, lamps in a chandelier, burners in an electric stove, etc.

At consistent switching on, the voltage is distributed in equal shares between consumers

In this case, the total current will pass through all the loads included in the circuit, and if one of the consumers fails, the entire circuit will stop working. Such schemes are used in New Year's garlands. In addition, when using elements of different power in a series circuit, weak receivers simply burn out.
Utot = U1 + U2 + U3 + ... + Un
Power, for any connection method, is summed up:
Rtot = P1 + P2 + P3 + ... + Pn.

Calculation of the cross section of wires.

The current passing through the wires heats them up. The thinner the conductor, and the greater the current passing through it, the stronger the heating. When heated, the insulation of the wire melts, which can lead to a short circuit and a fire. The calculation of the current in the network is not complicated. To do this, you need to divide the power of the device in watts by the voltage: I= P/ U.
All materials have acceptable conductivity. This means that they can pass such a current through each square millimeter (i.e. section) without much loss and heating (see table No. 7).

TABLE No. 7

cross section S(sq.mm.)	Permissible current I
		aluminum

Now, knowing the current, we can easily select the required wire section from the table and, if necessary, calculate the wire diameter using a simple formula: D \u003d V S / n x 2
You can go to the store for the wire.

As an example, we calculate the thickness of the wires for connecting a household stove: From the passport or from the plate on the back of the unit, we find out the power of the stove. Let's say the power (P ) is equal to 11 kW (11,000 watts). Dividing the power by the mains voltage (in most regions of Russia it is 220 Volts), we get the current that the stove will consume:I = P / U =11000/220=50A. If copper wires are used, then the wire cross sectionS must be at least 10 sq. mm.(see table).
I hope the reader will not be offended by me for reminding him that the cross section of a conductor and its diameter are not the same thing. The cross section of the wire is P(pi) timesr squared (n X r X r). Wire diameter can be calculated by taking the square root of the wire gauge divided by P and multiplying the resulting value by two. Realizing that many of us have already forgotten our school constants, let me remind you that Pi is equal to 3,14 , and the diameter is two radii. Those. the thickness of the wire we need will be D \u003d 2 X V 10 / 3.14 \u003d 2.01 mm.

Magnetic properties of electric current.

It has long been noticed that when current passes through conductors, a magnetic field arises that can act on magnetic materials. From a school course in physics, we may remember that opposite poles of magnets attract, and the same poles repel. This circumstance should be taken into account when laying wiring. Two wires carrying current in the same direction will attract each other, and vice versa.
If the wire is twisted into a coil, then, when an electric current is passed through it, the magnetic properties of the conductor will manifest themselves even more strongly. And if you also insert a core into the coil, then we get a powerful magnet.
At the end of the century before last, the American Morse invented a device that made it possible to transmit information over long distances without the help of messengers. This device is based on the ability of current to excite a magnetic field around the coil. By supplying power to the coil from a current source, a magnetic field arises in it, attracting a moving contact, which closes the circuit of another similar coil, and so on. Thus, being at a considerable distance from the subscriber, it is possible to transmit encoded signals without any problems. This invention has been widely used, both in communications and in everyday life and industry.
The described device has long been outdated and is almost never used in practice. It has been replaced by powerful information systems, but fundamentally they all continue to work on the same principle.

The power of any motor is disproportionately higher than the power of the relay coil. Therefore, the wires to the main load are thicker than to the control devices.
Let us introduce the concept of power circuits and control circuits. Power circuits include all parts of the circuit leading to the load current (wires, contacts, measuring and control devices). They are highlighted in color on the diagram.

All wires and equipment for control, monitoring and signaling are related to control circuits. They are shown separately in the diagram. It happens that the load is not very large or not particularly pronounced. In such cases, the circuits are conditionally divided according to the strength of the current in them. If the current exceeds 5 amperes - the power circuit.

Relay. Contactors.

The most important element of the already mentioned Morse apparatus is RELAY.
This device is interesting in that a relatively weak signal can be applied to the coil, which is converted into a magnetic field and closes another, more powerful contact, or group of contacts. Some of them may not close, but, on the contrary, open. This is also needed for different purposes. In the drawings and diagrams, this is depicted as follows:

And it reads like this: when power is applied to the relay coil - K, the contacts: K1, K2, K3, and K4 close, and the contacts: K5, K6, K7 and K8 open. It is important to remember that the diagrams show only those contacts that will be used, despite the fact that the relay may have more contacts.
Schematic diagrams show exactly the principle of building a network and its operation, so the contacts and the relay coil are not drawn together. In systems where there are many functional devices, the main difficulty is how to correctly find the contacts corresponding to the coils. But with the acquisition of experience, this problem is solved more easily.
As we have said, current and voltage are different matters. The current itself is very strong and it takes a lot of effort to turn it off. When the circuit is disconnected (electricians say - switching) there is a large arc that can ignite the material.
At a current strength of I = 5A, an arc 2 cm long occurs. At high currents, the dimensions of the arc reach monstrous sizes. You have to take special measures not to melt the contact material. One of these measures is ""arc chambers"".
These devices are placed at the contacts on the power relays. In addition, the contacts have a different shape than the relay, which allows you to split it in half even before the arc occurs. Such a relay is called contactor. Some electricians have dubbed them starters. This is wrong, but it accurately conveys the essence of the work of contactors.
All electrical appliances are manufactured in various sizes. Each size indicates the ability to withstand currents of a certain strength, therefore, when installing equipment, it is necessary to ensure that the size of the switching device matches the load current (table No. 8).

TABLE No. 8

Value, (conditional number of standard size)	Rated current	Rated power

Generator. Engine.

The magnetic properties of the current are also interesting in that they are reversible. If with the help of electricity you can get a magnetic field, then you can and vice versa. After not very long studies (only about 50 years), it was found that If the conductor is moved in a magnetic field, then an electric current begins to flow through the conductor . This discovery helped humanity overcome the problem of energy storage and storage. Now we have an electric generator in service. The simplest generator is not complicated. A coil of wire rotates in the field of a magnet (or vice versa) and a current flows through it. It remains only to close the circuit to the load.
Of course, the proposed model is greatly simplified, but in principle the generator differs from this model not so much. Instead of one turn, kilometers of wire are taken (this is called winding). Instead of permanent magnets, electromagnets are used (this is called excitement). The biggest problem in generators is how to take the current. The device for the selection of generated energy is collector.
When installing electrical machines, it is necessary to monitor the integrity of the brush contacts and their tightness to the collector plates. When replacing brushes, they will have to be ground.
There is another interesting feature. If you do not take current from the generator, but, on the contrary, apply it to its windings, then the generator will turn into an engine. This means that electric machines are completely reversible. That is, without changing the design and circuit, we can use electric machines, both as a generator and as a source of mechanical energy. For example, when moving uphill, an electric train consumes electricity, and downhill, it gives it to the network. There are many such examples.

Measuring instruments.

One of the most dangerous factors associated with the operation of electricity is that the presence of current in the circuit can only be determined by being under its influence, i.e. touching him. Up to this point, the electric current does not betray its presence. In connection with this behavior, there is an urgent need to detect and measure it. Knowing the magnetic nature of electricity, we can not only determine the presence / absence of current, but also measure it.
There are many instruments for measuring electrical quantities. Many of them have a magnet winding. The current flowing through the winding excites a magnetic field and deflects the arrow of the device. The stronger the current, the more the arrow deviates. For greater measurement accuracy, a mirror scale is used so that the view of the arrow is perpendicular to the measuring panel.
Used to measure current ammeter. It is included in the circuit in series. To measure the current, the value of which is greater than the nominal, the sensitivity of the device is reduced shunt(strong resistance).

Voltage measure voltmeter, it is connected in parallel to the circuit.
A combined instrument for measuring both current and voltage is called avometer.
Used to measure resistance ohmmeter or megger. These devices often ring the circuit to find an open or to verify its integrity.
Measuring instruments must be periodically tested. At large enterprises, measuring laboratories are created specifically for these purposes. After testing the device, the laboratory puts its stamp on its front side. The presence of a brand indicates that the device is operational, has an acceptable measurement accuracy (error) and, subject to proper operation, until the next verification, its readings can be trusted.
The electricity meter is also a measuring instrument, which also has the function of accounting for the electricity used. The principle of operation of the counter is extremely simple, as is its device. It has a conventional electric motor with a gearbox connected to wheels with numbers. As the current in the circuit increases, the motor spins faster, and the numbers themselves move faster.
In everyday life, we do not use professional measuring equipment, but due to the lack of the need for a very accurate measurement, this is not so significant.

Methods for obtaining contact compounds.

It would seem that there is nothing easier than connecting two wires to each other - twisted and that's it. But, as experience confirms, the lion's share of losses in the circuit falls precisely at the joints (contacts). The fact is that atmospheric air contains OXYGEN, which is the most powerful oxidizing agent found in nature. Any substance, coming into contact with it, undergoes oxidation, being covered first with the thinnest, and over time, with an increasingly thick oxide film, which has a very high resistivity. In addition, problems arise when connecting conductors consisting of different materials. Such a connection, as is known, is either a galvanic pair (which oxidizes even faster) or a bimetallic pair (which changes its configuration with a temperature drop). Several methods of reliable connections have been developed.
Welding connect iron wires when installing grounding and lightning protection equipment. Welding work is done by a qualified welder and electricians prepare the wires.
Copper and aluminum conductors are connected by soldering.
Before soldering, the cores are stripped of insulation up to a length of 35 mm, cleaned to a metallic sheen and treated with a flux in order to degrease and for better adhesion of the solder. The components of fluxes can always be found at retail outlets and pharmacies in the right quantities. The most common fluxes are shown in table No. 9.
TABLE No. 9 Compositions of fluxes.

Flux grade	Application area	Chemical composition %
	Soldering conductive parts made of copper, brass and bronze.	Rosin-30, Ethyl alcohol-70.
	Soldering of conductor products made of copper and its alloys, aluminum, constantan, manganin, silver.	Vaseline-63, Triethanolamine-6.5, Salicylic acid-6.3, Ethyl alcohol-24.2.
	Soldering of products made of aluminum and its alloys with zinc and aluminum solders.	Sodium fluoride-8, Lithium chloride-36, Chloride zinc-16, Potassium chloride-40.
Aqueous solution of zinc chloride	Soldering of steel, copper and its alloys.	Chloride zinc-40, Water-60.
	Soldering aluminum wires with copper.	Cadmium fluoroborate-10, Ammonium fluoroborate-8, Triethanolamine-82.

For soldering aluminum single-wire conductors 2.5-10 sq. mm. use a soldering iron. The twisting of the cores is performed by double twisting with a groove.


When soldering, the wires are heated until the solder begins to melt. Rubbing the groove with a solder stick, tin the strands and fill the groove with solder, first on one side and then on the other. For soldering aluminum conductors of large sections, a gas burner is used.
Single and stranded copper conductors are soldered with a tinned strand without a groove in a bath of molten solder.
Table No. 10 shows the melting and soldering temperatures of some types of solders and their scope.

TABLE No. 10

	Melting temperature	Soldering temperature	Application area
			Tinning and soldering the ends of aluminum wires.
			Soldering connections, splicing aluminum wires of round and rectangular cross section when winding transformers.
			Soldering by pouring aluminum wires of large cross section.
			Soldering of aluminum and its alloys.
			Soldering and tinning of conductive parts made of copper and its alloys.
			Tinning, soldering of copper and its alloys.
			Soldering parts made of copper and its alloys.
			Soldering semiconductor devices.
			Soldering fuses.
POSSu 40-05			Soldering of collectors and sections of electrical machines, devices.

The connection of aluminum conductors with copper conductors is carried out in the same way as the connection of two aluminum conductors, while the aluminum conductor is first tinned with “A” solder, and then with POSSU solder. After cooling, the place of soldering is isolated.
Recently, connecting fittings have been increasingly used, where the wires are connected by bolts in special connecting sections.

grounding .

From long work materials "get tired" and wear out. In case of oversight, it may happen that some conductive part falls off and falls on the body of the unit. We already know that the voltage in the network is due to the potential difference. On the ground, usually, the potential is zero, and if one of the wires falls on the case, then the voltage between the ground and the case will be equal to the mains voltage. Touching the body of the unit, in this case, is deadly.
A person is also a conductor and can pass current through himself from the body to the ground or to the floor. In this case, a person is connected to the network in series and, accordingly, the entire load current from the network will go through the person. Even if the network load is small, it still threatens with significant troubles. The resistance of the average person is approximately 3,000 ohms. A current calculation made according to Ohm's law will show that a current will flow through a person I \u003d U / R \u003d 220/3000 \u003d 0.07 A. It would seem a little, but it can kill.
To avoid this, do grounding. Those. deliberately connect the housings of electrical devices to earth in order to cause a short circuit in the event of a breakdown to the housing. In this case, the protection is activated and turns off the faulty unit.
Earthing switches they are buried in the ground, grounding conductors are attached to them by welding, which are bolted to all units whose housings may be energized.
In addition, as a protective measure, nulling. Those. zero is connected to the body. The principle of operation of protection is similar to grounding. The only difference is that grounding depends on the nature of the soil, its moisture content, the depth of the ground electrodes, the state of many connections, etc. etc. And zeroing directly connects the body of the unit to the current source.
The rules for the installation of electrical installations say that with a zeroing device, it is not necessary to ground the electrical installation.
grounding conductor is a metallic conductor or group of conductors in direct contact with earth. There are the following types of grounding conductors:

1. in-depth made of strip or round steel and laid horizontally on the bottom of building pits along the perimeter of their foundations;
2. Horizontal made of round or strip steel and laid in a trench;
3. vertical- from steel rods vertically pressed into the ground.

For ground electrodes, round steel with a diameter of 10 - 16 mm, strip steel with a cross section of 40x4 mm, pieces of angle steel 50x50x5 mm are used.
Length of vertical screwed-in and pressed-in earth electrodes - 4.5 - 5 m; hammered - 2.5 - 3 m.
In industrial premises with electrical installations with voltage up to 1 kV, grounding lines with a cross section of at least 100 square meters are used. mm, and with a voltage above 1 kV - at least 120 kV. mm
The smallest allowable dimensions of steel grounding conductors (in mm) are shown in table No. 11

TABLE No. 11

The smallest allowable dimensions of copper and aluminum grounding and neutral conductors (in mm) are given in table No. 12

TABLE No. 12

Above the bottom of the trench, vertical ground electrodes should protrude by 0.1 - 0.2 m for the convenience of welding connecting horizontal rods to them (round steel is more resistant to corrosion than strip steel). Horizontal ground electrodes are laid in trenches with a depth of 0.6 - 0.7 m from the level of the planning mark of the earth.
At the points of entry of conductors into the building, identification marks of the grounding conductor are installed. Grounding conductors and grounding conductors located in the ground are not painted. If the soil contains impurities that cause increased corrosion, earth electrodes with an increased cross section are used, in particular, round steel with a diameter of 16 mm, galvanized or copper-plated earth electrodes, or electrical protection of the earth electrodes against corrosion is carried out.
Grounding conductors are laid horizontally, vertically or parallel to sloping building structures. In dry rooms, grounding conductors are laid directly on concrete and brick bases with strips fastened with dowels, and in damp and especially damp rooms, as well as in rooms with an aggressive atmosphere - on linings or supports (holders) at a distance of at least 10 mm from the base.
Conductors are fixed at distances of 600 - 1,000 mm on straight sections, 100 mm at turns from the tops of corners, 100 mm from branch points, 400 - 600 mm from the floor level of the premises and at least 50 mm from the lower surface of the removable ceilings of the channels.
Openly laid grounding and neutral protective conductors have a distinctive color - a yellow strip along the conductor is painted over a green background.
It is the responsibility of electricians to periodically check the condition of the ground. To do this, the ground resistance is measured with a megger. PUE. The following resistance values ​​of grounding devices in electrical installations are regulated (Table No. 13).

TABLE No. 13

Grounding devices (grounding and grounding) at electrical installations are performed in all cases if the AC voltage is equal to or higher than 380 V, and the DC voltage is higher than or equal to 440 V;
At AC voltage from 42 V to 380 Volts and from 110 V to 440 Volts DC, grounding is carried out in rooms with increased danger, as well as in especially dangerous and outdoor installations. Grounding and grounding in explosive installations is performed at any voltage.
If the grounding characteristics do not meet acceptable standards, work is carried out to restore the grounding.

step voltage.

In the event of a wire breakage and its contact with the ground or the body of the unit, the voltage evenly “spreads” over the surface. At the point where the earth wire touches, it is equal to the mains voltage. But the farther from the center of contact, the greater the voltage drop.
However, with a voltage between potentials of thousands and tens of thousands of volts, even a few meters from the point where the ground wire touches, the voltage will still be dangerous to humans. When a person enters this zone, a current will flow through the human body (along the circuit: earth - foot - knee - groin - another knee - another foot - earth). It is possible, with the help of Ohm's law, to quickly calculate what kind of current will flow, and imagine the consequences. Since the tension occurs, in fact, between the legs of a person, it has received the name - step voltage.
You should not tempt fate when you see a wire hanging from a pole. Measures must be taken for a safe evacuation. And the measures are:
First, do not move in a big step. It is necessary with shuffling steps, without taking your feet off the ground, to move away from the place of contact.
Secondly, you can not fall and crawl!
And, thirdly, before the arrival of the emergency team, it is necessary to limit the access of people to the danger zone.

Three-phase current.

Above, we figured out how a generator and a DC motor work. But these motors have a number of disadvantages that hinder their use in industrial electrical engineering. AC machines have become more widespread. The current removal device in them is a ring, which is easier to manufacture and maintain. Alternating current is no worse than direct current, and in some respects surpasses it. Direct current always flows in the same direction at a constant value. Alternating current changes direction or magnitude. Its main characteristic is the frequency, measured in Hertz. Frequency indicates how many times per second the current changes direction or amplitude. In the European standard, the industrial frequency is f=50 Hertz, in the US standard, f=60 Hertz.
The principle of operation of motors and alternators is the same as that of DC machines.
AC motors have the problem of orienting the direction of rotation. It is necessary either to shift the direction of the current with additional windings, or to use special starting devices. The use of three-phase current solved this problem. The essence of his "device" is that three single-phase systems are connected into one - three-phase. Three wires supply current with a slight delay from each other. These three wires are always called "A", "B" and "C". The current flows in the following way. In phase "A" to the load and from it returns in phase "B", from phase "B" to phase "C", and from phase "C" to "A".
There are two three-phase current systems: three-wire and four-wire. We have already described the first. And in the second there is a fourth neutral wire. In such a system, current is supplied in phases, and removed in zero. This system proved to be so convenient that it is now used everywhere. It is convenient, including the fact that you do not need to redo something if you need to include only one or two wires in the load. Just connect / disconnect and that's it.
The voltage between the phases is called linear (Ul) and is equal to the voltage in the line. The voltage between the phase (Uf) and neutral wire is called phase and is calculated by the formula: Uf \u003d Ul / V3; Uph \u003d Ul / 1.73.
Each electrician has made these calculations for a long time and knows by heart the standard series of voltages (table No. 14).

TABLE No. 14

When connecting single-phase loads to a three-phase network, it is necessary to monitor the uniformity of the connection. Otherwise, it will turn out that one wire will be heavily overloaded, while the other two will remain idle.
All three-phase electrical machines have three pairs of poles and orient the direction of rotation by connecting the phases. At the same time, to change the direction of rotation (electricians say - REVERSE), it is enough to swap only two phases, any.
Likewise with generators.

Inclusion in the "triangle" and "star".

There are three schemes for connecting a three-phase load to the network. In particular, on the cases of electric motors there is a contact box with winding leads. The marking in the terminal boxes of electrical machines is as follows:
the beginning of the windings C1, C2 and C3, the ends, respectively, C4, C5 and C6 (leftmost figure).

A similar marking is also attached to transformers.
"triangle" connection shown in the middle picture. With such a connection, the entire current from phase to phase passes through one load winding and, in this case, the consumer operates at full power. The figure on the far right shows the connections in the terminal box.
star connection can "do" without zero. With this connection, the linear current, passing through two windings, is divided in half and, accordingly, the consumer works at half strength.

When connected ""in a star"" with a neutral wire, only phase voltage is supplied to each load winding: Uph = Ul / V3. The power of the consumer is less on V3.

Electric cars from repair.

A big problem is the old engines that have come out of repair. Such machines, as a rule, do not have plates and terminal outputs. The wires stick out of the cases, and look like noodles from a meat grinder. And if you connect them incorrectly, then at best, the engine will overheat, and at worst, it will burn out.
This happens because one of the three incorrectly connected windings will try to turn the motor rotor in the direction opposite to the rotation created by the other two windings.
To prevent this from happening, it is necessary to find the ends of the windings of the same name. To do this, with the help of a tester, all the windings are “ringed”, simultaneously checking their integrity (the absence of a break and a breakdown on the case). Finding the ends of the windings, they are marked. The chain is assembled as follows. We attach the proposed beginning of the second winding to the intended end of the first winding, connect the end of the second to the beginning of the third, and take the readings of the ohmmeter from the remaining ends.
We enter the resistance value in the table.

Then we disassemble the circuit, change the end and the beginning of the first winding in places and assemble it again. Like last time, the measurement results are entered in the table.
Then we repeat the operation again, swapping the ends of the second winding
We repeat these actions as many times as there are possible switching schemes. The main thing is to accurately and accurately take readings from the device. For accuracy, the entire measurement cycle should be repeated twice. After filling in the table, we compare the measurement results.
The diagram will be correct. with the lowest measured resistance.

Inclusion of a three-phase motor in a single-phase network.

There is a need when a three-phase motor must be plugged into a regular household outlet (single-phase network). To do this, by the method of phase shift using a capacitor, a third phase is forcibly created.

The figure shows the connection of the motor according to the "delta" and "star" scheme. “Zero” is connected to one output, to the second phase, a phase is also connected to the third output, but through a capacitor. To rotate the motor shaft in the desired direction, a starting capacitor is used, which is connected to the network in parallel with the working one.
At a mains voltage of 220 V and a frequency of 50 Hz, the capacitance of the working capacitor in μF is calculated by the formula, Srab \u003d 66 Rnom, where rnom is the rated motor power in kW.
The capacity of the starting capacitor is calculated by the formula, Descent \u003d 2 Srab \u003d 132 Rnom.
To start a not very powerful engine (up to 300 W), a starting capacitor may not be needed.

Magnetic switch.

Connecting the motor to the network using a conventional switch provides a limited possibility of regulation.
In addition, in the event of an emergency power outage (for example, fuses blow), the machine stops working, but after the network is repaired, the engine starts without a human command. This may lead to an accident.
The need to protect against the disappearance of current in the network (electricians say ZERO PROTECTION) led to the invention of a magnetic starter. In principle, this is a circuit using the relay already described by us.
To turn on the machine, use the relay contacts "TO" and button S1.
Push button relay coil circuit "TO" receives power and the relay contacts K1 and K2 close. The motor is powered and running. But, releasing the button, the circuit stops working. Therefore, one of the relay contacts "TO" use for shunting buttons.
Now, after opening the contact of the button, the relay does not lose power, but continues to hold its contacts in the closed position. And to turn off the circuit, use the S2 button.
A correctly assembled circuit, after turning off the network, will not turn on until the person gives a command to do so.

Mounting and circuit diagrams.

In the previous paragraph, we drew a diagram of a magnetic starter. This scheme is fundamental. It shows how the device works. It involves the elements used in this device (circuit). Although a relay or contactor may have more contacts, only those that will be used are drawn. Wires are drawn, if possible, in straight lines and not in a natural way.
Along with circuit diagrams, wiring diagrams are used. Their task is to show how the elements of the electrical network or device should be mounted. If the relay has several contacts, then all contacts are indicated. On the drawing, they are placed as they will be after installation, the wire connection points are drawn where they really should be attached, etc. Below, the left figure shows an example of a circuit diagram, and the right figure shows a wiring diagram of the same device.

Power circuits. Control circuits.

With knowledge, we can quickly calculate the required wire cross-section. The motor power is disproportionately higher than the power of the relay coil. Therefore, the wires leading to the main load are always thicker than the wires leading to the control devices.
Let us introduce the concept of power circuits and control circuits.
Power circuits include all parts that conduct current to the load (wires, contacts, measuring and control devices). In the diagram, they are marked with bold lines. All wires and equipment for control, monitoring and signaling are related to control circuits. They are marked with dotted lines in the diagram.

How to assemble electrical circuits.

One of the difficulties in the work of an electrician is understanding how the circuit elements interact with each other. Must be able to read, understand and assemble diagrams.
When assembling circuits, follow the easy rules:
1. Assembly of the circuit should be carried out in one direction. For example: we assemble the circuit clockwise.
2. When working with complex, branched circuits, it is convenient to break it into its component parts.
3. If the circuit has a lot of connectors, contacts, connections, it is convenient to break the circuit into sections. For example, first we assemble the circuit from a phase to a consumer, then we assemble it from a consumer to another phase, and so on.
4. Assembly of the circuit should start from the phase.
5. Each time you make a connection, ask yourself the question: What will happen if the voltage is applied now?
In any case, after assembly, we should get a closed circuit: For example, the socket phase - the switch contact connector - the consumer - the “zero” of the socket.
Example: Let's try to assemble the most common scheme in everyday life - connect a home chandelier of three shades. We use a two-button switch.
To begin with, let's decide for ourselves how the chandelier should work? When you turn on one key of the switch, one lamp in the chandelier should light up, when you turn on the second key, the other two light up.
In the diagram, you can see that both the chandelier and the switch go to three wires, while only a couple of wires go from the network.
To begin with, using an indicator screwdriver, we find the phase and connect it to the switch ( zero can not be interrupted). The fact that two wires go from the phase to the switch should not confuse us. We choose the place of connection of the wires ourselves. We screw the wire to the common rail of the switch. Two wires will go from the switch and, accordingly, two circuits will be mounted. One of these wires is connected to the lamp socket. We derive the second wire from the cartridge, and connect it to zero. The circuit of one lamp is assembled. Now, if you turn on the switch key, the lamp will light up.
We connect the second wire coming from the switch to the cartridge of another lamp and, just as in the first case, we connect the wire from the cartridge to zero. When the switch keys are alternately turned on, different lamps will light up.
It remains to connect the third light bulb. We connect it in parallel to one of the finished circuits, i.e. we remove the wires from the cartridge of the connected lamp and connect it to the cartridge of the last light source.
It can be seen from the diagram that one of the wires in the chandelier is common. It usually differs from the other two wires in color. As a rule, it is not difficult, without seeing the wires hidden under the plaster, to connect the chandelier correctly.
If all the wires are of the same color, then we proceed as follows: we connect one of the wires to the phase, and we call the others one by one with an indicator screwdriver. If the indicator glows differently (in one case it is brighter, and in the other it is dimmer), then we have not chosen a “common” wire. Change the wire and repeat the steps. The indicator should glow equally brightly when both wires are “ringing”.

Schema Protection

The lion's share of the cost of any unit is the price of the engine. Overloading the motor leads to its overheating and subsequent failure. Great attention is paid to the protection of motors from overloads.
We already know that when running, motors draw current. During normal operation (operation without overloads), the motor consumes normal (rated) current, during overload, the motor consumes very large amounts of current. We can control the operation of motors with devices that respond to changes in current in the circuit, for example, overcurrent relay and thermal relay.
An overcurrent relay (often referred to as a "magnetic release") consists of several turns of very thick wire on a movable core loaded with a spring. The relay is installed in the circuit in series with the load.
The current flows through the winding wire and creates a magnetic field around the core, which tries to move it. Under normal motor operating conditions, the force of the spring holding the core is greater than the magnetic force. But, with an increase in the load on the engine (for example, the hostess put more laundry in the washing machine than the instructions require), the current increases and the magnet “overpowers” ​​the spring, the core shifts and acts on the drive of the NC contact, the network opens.
Overcurrent relay with works with a sharp increase in the load on the electric motor (overload). For example, a short circuit has occurred, the machine shaft is jammed, etc. But there are cases when the overload is insignificant, but it lasts a long time. In such a situation, the engine overheats, the insulation of the wires melts and, in the end, the engine fails (burns out). To prevent the development of the situation according to the described scenario, a thermal relay is used, which is an electromechanical device with bimetallic contacts (plates) that pass an electric current through them.
With an increase in current above the nominal value, the heating of the plates increases, the plates bend and open their contact in the control circuit, interrupting the current to the consumer.
For the selection of protection equipment, you can use table No. 15.

TABLE No. 15

			I nom of the machine	I magnetic release	I rated thermal relay	S alu. veins

Automation

In life, we often come across devices whose name is combined under the general concept - "automation". And although such systems are developed by very smart designers, they are maintained by simple electricians. You should not be afraid of this term. It only means "WITHOUT HUMAN INVOLVEMENT".
In automatic systems, a person gives only the initial command to the entire system and sometimes disables it for maintenance. The rest of the work for a very long time the system does itself.
If you look closely at modern technology, you can see a large number of automatic systems that control it, reducing human intervention in this process to a minimum. A certain temperature is automatically maintained in the refrigerator, and a set reception frequency is set on the TV, the light on the street lights up at dusk and goes out at dawn, the supermarket door opens in front of visitors, and modern washing machines “independently” perform the entire process of washing, rinsing, spinning and drying underwear. Examples can be given endlessly.
At its core, all automation circuits repeat the circuit of a conventional magnetic starter, to one degree or another improving its speed or sensitivity. Instead of the “START” and “STOP” buttons, we insert contacts B1 and B2 into the already known starter circuit, which are triggered by various influences, for example, temperature, and we get the refrigerator automation.


When the temperature rises, the compressor turns on and drives the cooler into the freezer. When the temperature drops to the desired (set) value, another such button will turn off the pump. Switch S1 in this case plays the role of a manual switch to turn off the circuit, for example, during maintenance.
These contacts are called sensors" or " sensitive elements". Sensors have a different shape, sensitivity, setting options and purpose. For example, if you reconfigure the refrigerator sensors and connect a heater instead of a compressor, you get a heat maintenance system. And, by connecting the lamps, we get a lighting maintenance system.
There can be infinitely many such variations.
Generally, the purpose of the system is determined by the purpose of the sensors. Therefore, different sensors are used in each individual case. Studying each specific sensing element does not make much sense, as they are constantly being improved and changed. It is more expedient to understand the principle of operation of sensors in general.

Lighting

Depending on the tasks performed, lighting is divided into the following types:

1. Working lighting - provides the necessary illumination in the workplace.
2. Security lighting - installed along the boundaries of protected areas.
3. Emergency lighting - is intended to create conditions for the safe evacuation of people in case of emergency shutdown of working lighting in rooms, passages and stairs, as well as to continue work where this work cannot be stopped.

And what would we do without Ilyich's ordinary light bulb? Previously, at the dawn of electrification, lamps with carbon electrodes shone on us, but they quickly burned out. Later, tungsten filaments began to be used, while air was pumped out of the bulbs of the lamps. Such lamps lasted longer, but were dangerous due to the possibility of rupture of the bulb. An inert gas is pumped inside the bulbs of modern incandescent lamps; such lamps are safer than their predecessors.
Incandescent lamps with flasks and socles of various shapes are produced. All incandescent lamps have a number of advantages, the possession of which guarantees their use for a long time. We list these advantages:

1. Compactness;
2. Ability to work with both AC and DC.
3. Unaffected by the environment.
4. The same light output throughout the entire service life.

Along with the listed advantages, these lamps have a very short service life (approximately 1000 hours).
Currently, due to the increased light output, tubular halogen incandescent lamps are widely used.
It happens that the lamps burn out unreasonably often and, it would seem, for no reason. This can happen due to sudden voltage surges in the network, with uneven distribution of loads in the phases, as well as for some other reasons. This "disgrace" can be put an end to if you replace the lamp with a more powerful one and include an additional diode in the circuit, which allows you to reduce the voltage in the circuit by half. At the same time, a more powerful lamp will shine in the same way as the previous one, without a diode, but its service life will double, and the electricity consumption, as well as the fee for it, will remain at the same level.

Tubular fluorescent low pressure mercury lamps

according to the spectrum of emitted light are divided into the following types:
LB - white.
LHB - cold white.
LTB - warm white.
LD - day.
LDC - daylight, correct color rendering.
Fluorescent mercury lamps have the following advantages:

1. High light output.
2. Long service life (up to 10,000 hours).
3. Soft light
4. Wide spectral composition.

Along with this, fluorescent lamps have a number of disadvantages, such as:

1. The complexity of the connection scheme.
2. Big sizes.
3. The impossibility of using lamps designed for alternating current in a direct current network.
4. Dependence on the ambient temperature (at temperatures below 10 degrees Celsius, the ignition of the lamps is not guaranteed).
5. Decrease in light output towards the end of service.
6. Pulsations harmful to the human eye (they can only be reduced by the combined use of several lamps and the use of complex switching circuits).

High pressure mercury arc lamps

have a higher light output and are used to illuminate large spaces and areas. The advantages of lamps include:

1. Long service life.
2. Compactness.
3. Resistance to environmental conditions.

The disadvantages of lamps listed below hinder their use for domestic purposes.

1. The spectrum of lamps is dominated by blue-green rays, which leads to incorrect color perception.
2. Lamps work only on alternating current.
3. The lamp can only be turned on through the ballast choke.
4. The lamp stays on for up to 7 minutes when turned on.
5. Re-ignition of the lamp, even after a short-term shutdown, is possible only after it has almost completely cooled down (i.e., after about 10 minutes).
6. The lamps have significant pulsations of the luminous flux (greater than those of fluorescent lamps).

Recently, metal halide (DRI) and metal halide mirror (DRIZ) lamps, which have better color rendering, as well as sodium lamps (DNAT), which emit golden-white light, are increasingly being used.

Electrical wiring.

There are three types of wiring.
open- laid on the surfaces of walls of ceilings and other elements of buildings.
Hidden- laid inside the structural elements of buildings, including under removable panels, floors and ceilings.
Outdoor- laid on the outer surfaces of buildings, under canopies, including between buildings (no more than 4 spans of 25 meters, off roads and power lines).
With an open wiring method, the following requirements must be observed:

• On combustible bases, asbestos sheet with a thickness of at least 3 mm is placed under the wires with a protrusion of the sheet due to the edges of the wire of at least 10 mm.
• Wires with a dividing wall can be fastened with nails with ebonite washers placed under the hat.
• When the wire is turned on an edge (i.e. 90 degrees), a separating film is cut out at a distance of 65 - 70 mm and the core closest to the turn is bent inside the turn.
• When attaching bare wires to insulators, the latter should be installed with the skirt down, regardless of where they are attached. The wires in this case should be out of reach for accidental contact.
• With any method of laying wires, it must be remembered that the wiring lines should only be vertical or horizontal and parallel to the architectural lines of the building (an exception is possible for hidden wiring laid inside structures with a thickness of more than 80 mm).
• Routes for power outlets are located at the height of the outlets (800 or 300 mm from the floor) or in the corner between the partition and the top of the ceiling.
• Descents and ascents to switches and lamps are performed only vertically.

Wiring devices are attached:

• Switches and switches at a height of 1.5 meters from the floor (in schools and preschool institutions 1.8 meters).
• Plug connectors (sockets) at a height of 0.8 - 1 m from the floor (in school and preschool institutions 1.5 meters)
• The distance from grounded devices must be at least 0.5 meters.
• Above-plinth sockets installed at a height of 0.3 meters and below must have a protective device that closes the sockets when the plug is removed.

When connecting electrical installation devices, it must be remembered that zero cannot be broken. Those. only the phase should be suitable for switches and switches, and it should be connected to the fixed parts of the device.
Wires and cables are marked with letters and numbers:
The first letter indicates the core material:
A - aluminum; AM - aluminum-copper; AC - made of aluminum alloy. The absence of letters means that the conductors are copper.
The following letters indicate the type of core insulation:
PP - flat wire; R - rubber; B - polyvinyl chloride; P - polyethylene.
The presence of subsequent letters indicates that we are not dealing with a wire, but with a cable. The letters indicate the material of the cable sheath: A - aluminum; C - lead; N - nairite; P - polyethylene; ST - steel corrugated.
Core insulation has a designation similar to wires.
The fourth letters from the beginning speak about the material of the protective cover: G - without cover; B - armored (steel tape).
The numbers in the designations of wires and cables indicate the following:
The first digit is the number of cores
The second digit is the cross section of the core in square meters. mm.
The third digit is the rated voltage of the network.
For example:
AMPPV 2x3-380 - wire with aluminum-copper conductors, flat, in PVC insulation. Two wires with a cross section of 3 square meters. mm. each, rated at 380 volts, or
VVG 3x4-660 - a wire with 3 copper conductors with a cross section of 4 square meters. mm. each in polyvinyl chloride insulation and the same sheath without a protective cover, designed for 660 volts.

Providing first aid to victims of electric shock.

If a person is struck by an electric current, urgent measures must be taken to quickly release the victim from its effects and immediately provide the victim with medical assistance. Even the slightest delay in providing such assistance can lead to death. If it is impossible to turn off the voltage, the victim should be freed from live parts. If a person is injured at a height, before turning off the current, measures are taken to prevent the victim from falling (the person is taken on his hands or pulled under the place of the alleged fall with a tarpaulin, strong fabric, or soft material is placed under it). To free the victim from live parts at mains voltages up to 1000 volts, dry improvised objects are used, such as a wooden pole, board, clothes, rope or other non-conductive materials. The person providing assistance should use electrical protective equipment (dielectric mat and gloves) and take only the victim’s clothes (provided that the clothes are dry). At a voltage of more than 1000 volts, an insulating rod or tongs must be used to release the victim, while the rescuer must wear dielectric boots and gloves. If the victim is unconscious, but with a stable breathing and pulse, he should be comfortably laid on a flat surface, unbuttoned clothes, brought to consciousness by smelling ammonia and sprinkled with water, provide fresh air and complete rest. Immediately and simultaneously with the provision of first aid, a doctor should be called. If the victim is breathing poorly, infrequently and spasmodically, or breathing is not monitored, CPR (cardiopulmonary resuscitation) should be started immediately. Artificial respiration and chest compressions should be performed continuously until the doctor arrives. The question of the advisability or futility of further CPR is decided ONLY by the doctor. You must be able to perform CPR.

Residual current device (RCD).

Residual current devices designed to protect a person from electric shock in group lines supplying plug sockets. Recommended for installation in power circuits of residential premises, as well as any other premises and objects where people or animals can be. Functionally, an RCD consists of a transformer whose primary windings are connected to the phase (phase) and neutral conductors. A polarized relay is connected to the secondary winding of the transformer. During normal operation of the electrical circuit, the vector sum of the currents through all windings is zero. Accordingly, the voltage at the terminals of the secondary winding is also zero. In the event of a leakage "to earth", the sum of the currents changes and a current appears in the secondary winding, causing the operation of a polarized relay that opens the contact. Once every three months it is recommended to check the operability of the RCD by pressing the "TEST" button. RCDs are divided into low-sensitivity and high-sensitivity. Low sensitivity (leakage currents 100, 300 and 500 mA) to protect circuits that do not have direct contact with people. They work when the insulation of electrical equipment is damaged. Highly sensitive RCDs (leakage currents of 10 and 30 mA) are designed for protection when it is possible for service personnel to touch the equipment. For the comprehensive protection of people, electrical equipment and wiring, in addition, differential circuit breakers are produced that perform the functions of both a residual current device and a circuit breaker.

Current rectification circuits.

In some cases, it becomes necessary to convert alternating current to direct current. If we consider an alternating electric current in the form of a graphic image (for example, on an oscilloscope screen), we will see a sinusoid crossing the ordinate with an oscillation frequency equal to the frequency of the current in the network.

Diodes (diode bridges) are used to rectify alternating current. The diode has one interesting property - to pass current in only one direction (it, as it were, “cuts off” the lower part of the sinusoid). There are the following AC rectification circuits. A half-wave circuit, the output of which is a pulsating current equal to half the mains voltage.

A full-wave circuit formed by a diode bridge of four diodes, at the output of which we will have a constant current of the mains voltage.

A three-half-wave circuit is formed by a bridge consisting of six diodes in a three-phase network. At the output, we will have two phases of direct current with a voltage Uv \u003d Ul x 1.13.

transformers

A transformer is a device that converts alternating current of one magnitude into the same current of another magnitude. The transformation occurs as a result of the transmission of a magnetic signal from one winding of the transformer to another through a metal core. To reduce losses during conversion, the core is assembled with plates made of special ferromagnetic alloys.


The calculation of the transformer is simple and, in essence, is a solution to the ratio, the basic unit of which is the transformation ratio:
K =UP/Uin =WP/Win, where UP and U in - respectively, the primary and secondary voltage, WP and Win - respectively, the number of turns of the primary and secondary windings.
After analyzing this ratio, you can see that there is no difference in the direction of the transformer. It's just a matter of which winding to take as the primary.
If one of the windings (any) is connected to a current source (in this case it will be primary), then at the output of the secondary winding we will have a greater voltage if the number of its turns is greater than that of the primary winding, or less if the number of its turns is less, than the primary winding.
Often there is a need to change the voltage at the output of the transformer. If there is “not enough” voltage at the output of the transformer, it is necessary to add turns of wire to the secondary winding and, accordingly, vice versa.
The calculation of the additional number of turns of wire is as follows:
First you need to find out what voltage falls on one turn of the winding. To do this, we divide the operating voltage of the transformer by the number of turns of the winding. Suppose a transformer has 1000 turns of wire in the secondary winding and 36 volts at the output (and we need, for example, 40 volts).
U\u003d 36/1000 \u003d 0.036 volts in one turn.
In order to get 40 volts at the output of the transformer, 111 turns of wire must be added to the secondary winding.
40 - 36 / 0.036 = 111 turns,
It should be understood that there is no difference in the calculations of the primary and secondary windings. Just in one case, the windings are added, in the other, they are subtracted.

Applications. Selection and application of protective equipment.

Circuit breakers provide protection of devices against overload or short circuit and are selected based on the characteristics of the wiring, the breaking capacity of the switches, the value of the rated current and the tripping characteristic.
The breaking capacity must correspond to the value of the current at the beginning of the protected section of the circuit. When connected in series, a device with a low short-circuit current value can be used if a circuit breaker is installed closer to the power source upstream of it, with an instantaneous breaker cut-off current lower than that of subsequent devices.
Rated currents are selected so that their values ​​are as close as possible to the rated or rated currents of the protected circuit. The tripping characteristics are determined taking into account that short-term overloads caused by inrush currents must not cause them to trip. In addition, it should be taken into account that the circuit breakers must have a minimum opening time in the event of a short circuit at the end of the protected circuit.
First of all, it is necessary to determine the maximum and minimum values ​​​​of the short-circuit current (SC). The maximum short circuit current is determined from the condition when the short circuit occurs directly on the contacts of the circuit breaker. The minimum current is determined from the condition that the short circuit occurs in the farthest section of the protected circuit. A short circuit can occur both between zero and phase, and between phases.
For a simplified calculation of the minimum short circuit current, you should know that the resistance of the conductors as a result of heating increases to 50% of the nominal value, and the voltage of the power supply decreases to 80%. Therefore, for the case of a short circuit between phases, the short circuit current will be:
I = 0,8 U/ (1.5r 2L/ S), where p is the specific resistance of the conductors (for copper - 0.018 ohm sq. mm / m)
for the case of a short circuit between zero and phase:
I =0,8 Uo/(1.5 p(1+m) L/ S), where m is the ratio of the cross-sectional areas of the wires (if the material is the same), or the ratio of the zero and phase resistances. The machine must be selected according to the value of the rated conditional short-circuit current not less than the calculated one.
RCD must be certified in Russia. When choosing an RCD, the connection diagram of the zero working conductor is taken into account. In the TT grounding system, the sensitivity of the RCD is determined by the grounding resistance at the selected safe voltage limit. The sensitivity threshold is determined by the formula:
I= U/ Rm, where U is the limiting safety voltage, Rm is the grounding resistance.
For convenience, you can use the table number number 16

TABLE No. 16

RCD sensitivity mA	Ground resistance Ohm
	Maximum safe voltage 25 V	Maximum safe voltage 50 V

To protect people, RCDs with a sensitivity of 30 or 10 mA are used.

Fused fuse
The current of the fusible link must not be less than the maximum current of the installation, taking into account the duration of its flow: In =Imax/a, where a \u003d 2.5, if T is less than 10 sec. and a = 1.6 if, T is greater than 10 sec. Imax =InK, where K = 5 - 7 times the starting current (from the motor nameplate data)
In - rated current of the electrical installation for a long time flowing through the protective equipment
Imax - maximum current flowing through the equipment for a short time (for example, starting current)
T - the duration of the maximum current flow through the protective equipment (for example, the acceleration time of the motor)
In household electrical installations, the starting current is small; when choosing an insert, you can focus on In.
After calculations, the nearest higher current value is selected from the standard range: 1,2,4,6,10,16,20,25A.
Thermal relay.
It is necessary to choose such a relay so that In of the thermal relay is within the regulation range and is greater than the network current.

TABLE No. 16

	Rated currents	Correction limits
	2,5 3,2 4,5 6,3 8 10.
	5,6 6,8 10 12,5 16 25

We offer a small material on the topic: "Electricity for beginners." It will give an initial idea of ​​the terms and phenomena associated with the movement of electrons in metals.

Term Features

Electricity is the energy of small charged particles moving in conductors in a certain direction.

With direct current, there is no change in its magnitude, as well as the direction of movement for a certain period of time. If a galvanic cell (battery) is chosen as the current source, then the charge moves in an orderly manner: from the negative pole to the positive end. The process continues until it completely disappears.

Alternating current periodically changes the magnitude, as well as the direction of movement.

AC transmission scheme

Let's try to understand what a phase in a word is, everyone has heard it, but not everyone understands its true meaning. We will not go into details and details, we will choose only the material that the home master needs. A three-phase network is a method of transmitting electric current, in which current flows through three different wires, and it returns through one. For example, there are two wires in an electrical circuit.

On the first wire to the consumer, for example, to the kettle, there is a current. The second wire is used for its return. When such a circuit is opened, there will be no passage of an electric charge inside the conductor. This diagram describes a single-phase circuit. in electricity? A phase is a wire through which an electric current flows. Zero is the wire through which the return is made. In a three-phase circuit, there are three phase wires at once.

The electrical panel in the apartment is necessary for the current in all rooms. consider it economically feasible, since they do not need two. When approaching the consumer, the current is divided into three phases, each with zero. The earthing switch, which is used in a single-phase network, does not carry a working load. He is a fuse.

For example, if a short circuit occurs, there is a threat of electric shock, fire. To prevent such a situation, the current value should not exceed a safe level, the excess goes to the ground.

The manual "School for an electrician" will help novice craftsmen to cope with some breakdowns of household appliances. For example, if there are problems with the operation of the electric motor of the washing machine, the current will fall on the outer metal case.

In the absence of grounding, the charge will be distributed throughout the machine. When you touch it with your hands, a person will act as a ground electrode, having received an electric shock. If there is a ground wire, this situation will not occur.

Features of electrical engineering

The manual "Electricity for Dummies" is popular with those who are far from physics, but plan to use this science for practical purposes.

The beginning of the nineteenth century is considered the date of the appearance of electrical engineering. It was at this time that the first current source was created. The discoveries made in the field of magnetism and electricity have managed to enrich science with new concepts and facts of great practical importance.

The "School for an Electrician" manual assumes familiarity with the basic terms related to electricity.

Many collections of physics contain complex electrical circuits, as well as a variety of obscure terms. In order for beginners to understand all the intricacies of this section of physics, a special manual “Electricity for Dummies” was developed. An excursion into the world of the electron must begin with a consideration of theoretical laws and concepts. Illustrative examples, historical facts used in the book "Electricity for Dummies" will help novice electricians learn knowledge. To check progress, you can use tasks, tests, exercises related to electricity.

If you understand that you do not have enough theoretical knowledge to independently cope with the connection of electrical wiring, refer to the manuals for "dummies".

Safety and practice

First you need to carefully study the section on safety. In this case, during work related to electricity, there will be no emergencies hazardous to health.

In order to put into practice the theoretical knowledge gained after self-study of the basics of electrical engineering, you can start with old household appliances. Before starting repairs, be sure to read the instructions that came with the device. Do not forget that electricity is not to be trifled with.

Electric current is associated with the movement of electrons in conductors. If a substance is not capable of conducting current, it is called a dielectric (insulator).

For the movement of free electrons from one pole to another, a certain potential difference must exist between them.

The intensity of the current passing through a conductor is related to the number of electrons passing through the cross section of the conductor.

The current flow rate is affected by the material, length, cross-sectional area of ​​​​the conductor. As the length of the wire increases, its resistance increases.

Conclusion

Electricity is an important and complex branch of physics. The manual "Electricity for Dummies" considers the main quantities that characterize the efficiency of electric motors. Voltage units are volts, current is measured in amperes.

Everyone has a certain amount of power. It refers to the amount of electricity generated by the device in a certain period of time. Energy consumers (refrigerators, washing machines, kettles, irons) also have power, consuming electricity during operation. If you wish, you can carry out mathematical calculations, determine the approximate fee for each household appliance.