Hidden and open wiring. Internal - flush wiring Requirements for flush wiring

One of two wiring options country house- open or closed way - choose reasonably. Struggling with arguments? And we will advise you!

In wooden walls, it is cheaper and easier to comply with safety rules with an open method of laying electrical communications (although under certain conditions it is possible to install closed wiring). Today, it is no longer necessary to distance the cables from the walls by 2 cm, hanging them on ceramic insulators. They are fastened with plastic chopsticks directly to wooden crowns or laid in overhead cable channels.

In a stone cottage, closed wiring is undoubtedly more convenient. It is isolated from accidental damage, does not interfere with the arrangement of furniture and does not conflict with the style of the interior. However, if you prefer retro-entourage or do not want to ditch the walls, then open wiring will provide support.

closed wiring

Closed wiring is an important component of home life support systems. In stone buildings, it is mounted at the final stage of construction, before the start finishing works. Channels are hollowed out in the walls, they are placed and fixed in corrugated pipes cables, make recesses for mounting boxes.

Canal laying does not tolerate chaos. Just imagine the consequences of getting a hardware into the cable when trying to “hammer a stud” into the wall! For this reason, experienced electricians lay wires strictly horizontally or vertically from sockets and switches. If the wiring is located in the floor, laying is carried out along the perimeter of the room at a distance of 10 cm from the walls, and the cable does not interfere with the fixing of the skirting board.

IN wooden houses closed wiring is laid at the construction stage. It turns out that at this stage it is already necessary to have a design project that shows which electrical appliances and where will be located in the house.

✓ Note
When bringing electricity into the house or changing the wiring, it is dangerous to save on equipment and installation. It is better to entrust the choice of cable, protective modules, as well as sockets and switches to a specialist who will take into account all the nuances.
The issue of safety, especially when wiring in a wooden house, should come first. Focusing only on the price in this case is wrong, it is not an absolute indicator of quality. If, for one reason or another, the choice falls on retro-styled sockets and switches for open wiring, you need to understand that in terms of technology and safety, they are not inferior to other modern equipment.

open wiring

Immured in a stone wall electrical wiring poses no particular fire hazard. Of course, a socket may spark or a faulty electrical appliance may catch fire, but that, as they say, is a completely different story.

In wooden houses, a short circuit or other failure in the electrical network may well cause a fire. Meanwhile, hidden wiring in a country house often becomes the object of attention of rodents. In addition, 8 voids wooden houses where the wiring is laid, wood dust accumulates, which instantly ignites from a spark. Therefore, in accordance with the current Russian standards, electrical wiring on a combustible base is carried out openly.

The "pluses" of open wiring are obvious. It is easy to install, maintain and control; if necessary, the track can be moved, supplemented or repaired. There are also "cons". open way installation eats up part of the space: you can’t hang a shelf over the cable, sometimes you can’t put the cabinet close to the wall.

Open wiring - retro + progress

Traditionally, open wiring was arranged with twisted wire on ceramic insulators. Today this way. most suitable for retro style, easy to repeat using modern twisted three- or two-core wire and ceramic holders. Styling will cost more than open wiring from a conventional cable on plastic or metal brackets. But in any case, the step between the holders should be no more than 50 cm, and in difficult areas they are placed more often.

To protect open wiring from a conventional cable from accidental damage, cable channels and plastic skirting boards are used. Their internal space may have partitions that allow you to lay inside the boxes at the same time both low-current and power cables. The removable upper part provides the possibility of monitoring the condition of the track and its modernization.

✓Note
Protective grounding in a three-core cable must be connected to a galvanized steel ground loop buried in the ground near the house. The lightning protection system is also connected to the ground loop. In general, this is a separate independent project that takes into account the properties of the soil, the occurrence ground water, meteorological features of the region.

Wiring starts with a project

Power supply country house should be produced according to the project, carried out in a specialized organization that has official permission for that, and approved by the bodies of Rosenergonadzor. But before ordering a project, you need to draw up a technical task. To do this, you will need to obtain information about the power allocated to the apartment or house (the certificate is issued by the operating company), draw a diagram of the location of sockets, switches and lighting fixtures(or order a design project), as well as calculate the intended consumers of electricity. The power supply system installed according to the project is tested, after which it is accepted into operation by the inspector of Energy Supervision. Only this approach guarantees electrical and fire safety Houses. In practice, often an electrical project is carried out by an architect-developer of the general construction part, or even a designer who does not have not only the appropriate permits, but also the proper knowledge.

Electric shock protection

Circuit breakers protect the electrical network from overloads, including short circuits. Residual current devices or RCDs disconnect electrical circuit in case of current leakage, which can occur due to different reasons. For example, due to aging of the insulation or mechanical damage cable. In addition, the RCD de-energizes the network in the event of a fire.

Modern differential automata perform two functions at once: RCDs and circuit breakers.

And if the wiring is installed correctly, then 8 emergency protective devices will de-energize the network, preventing electric shock and fire in the home. If the power allocated to the house is not enough to simultaneously turn on all the necessary household appliances and heaters, it is recommended to install a load limit switch. A smart device will prioritize. For example, when a powerful vacuum cleaner or electric grill is running, the warm floors are temporarily turned off.

✓ Need to know
Natural shrinkage of 3 cm of a typical 2-storey house in the first years after construction will lead to squeezing and cracking of cable channels. The wiring will have to be redone!

Board mounting

According to the instructions of Energonadzor, two switchboards should be installed in country houses: one outside the house, the other inside. An external one is needed for an electric meter so that regulatory authorities can check the readings at any time. The inner shield is used to install electrical modules.

On its mounting profiles or DIN rails, an introductory switch and differential automata are located. Each of them is responsible for a specific group. Let's say one for lighting, the other for sockets.

Except protective devices there is also space for auxiliary modules: load limit relays, relays that control the quality of incoming electricity.

The switchboard is selected in such a way that after assembly there is at least 30% of free space left, because over time, power supply needs may increase. In wooden houses, hinged dust and moisture-proof power shields with a shock-resistant lid that is locked with a lock are installed. In stone, as well as in urban apartments, built-in wardrobes are usually used.

✓Expert opinion
If the customer voices the task of a phased replacement of wiring in the house, then at the design stage of the switchboard it is marked which groups of consumers should be connected to the power supply at the first, and which at the second (final) stage. This is taken into account in the single-line diagram of the shield: some consumers will be connected to the power supply system of the house, while for others, backup outgoing lines will be provided in the shield.
Then in the future it will be possible to complete the wiring and connect new groups of consumers through the "reserve" lines of the introductory shield. But we do not recommend breaking down the work of replacing electrical wiring into stages. At a minimum, shields should be installed throughout the house and a power cable should be routed.

There are 3 types of wiring installation, regardless of the cable laying conditions: open, closed and combined. Most in a simple way during installation is open wiring. It is convenient in that it allows you to easily change, add cables to common nodes, any of its sections are easily accessible for repair and connection of new pantographs. In this case, it will not be necessary to hammer the walls in case of damage to the cable and eliminate the cause, as with closed wiring. Typically, exposed cabling is used in office space where it is often necessary to lay new cables and wires. The disadvantage of this method is the low aesthetics, and in this regard, open wiring in residential premises is carried out very rarely. However, in the individual residential sector, in the country house and in utility rooms, it is used quite often, especially since there are modern ways aesthetic solutions. The stores sell skirting boards with cable channels, or you can purchase special PVC cable channels for any cable section.

The laying of electrical wires in protective channels is carried out in two ways:

Gasket with special fittings. With this method of mounting open wiring, special fittings are used for mounting electrical installation devices (switches and sockets), or a gasket with special fittings (insulation box system). Corners, bends, separation of wires in the shape of the letter "T" are performed using fittings that allow you to correct errors and uneven walls. In this way, it is easier to lay electrical wires and provide reliable protection from mechanical damage.
Laying without special fittings. In this case, the change in the direction of the wire (corners) is performed by cutting the conduits at an angle of 45 °. It must be remembered that the cuts are made carefully, with great care, leaving no gap between the joints. This should provide electrical wires with reliable protection. Laying without special fittings is possible only with a slight update of the wiring.

This wiring upgrade method is suitable for quick implementation, does not cause significant damage, and is reliable. But the wiring remains visible.

open wiring flat wires of the type APR, APPV, APRV on combustible bases are carried out on a layer of sheet asbestos with a thickness of at least 3 mm, protruding from each side of the wire by at least 5 mm.

Asbestos gaskets are fixed before the installation of wires with nails every 200 - 250 mm in a checkerboard pattern. When laying several groups of wires, the strip can be common, taking into account the distance between the wires of each group of at least 5 mm. For fastening wires, strips of tin 10 mm wide and 0.3 - 0.5 mm thick are used, attached to the asbestos layer. Between the metal strip and the wire, a gasket made of insulating cardboard is laid, protruding beyond the edges of the strip by 1.5-2 mm. When attaching the wire, the metal strip with the gasket should tightly wrap around the surface of the pre-tensioned wire. Bending of flat wires in the corners is performed by first cutting out a separating film between the wires at a length of 40-60 mm and taking them inside the corner (see figure).

Today, plastic products are sold for fastening flat wires of various sections. They can replace tin strips. The convenience of using plastic clamps lies in the fact that they can be fixed with BMK-5K glue and nails.

In addition, the ends of the wire inserted into branch boxes or installation boxes are cut off with a margin of approximately 65-75 mm, which makes it possible to reconnect the cores and conveniently replace the socket or switch. The wires are inserted into the box so that the section of the dividing base cut into them does not come out of the box. The cores of the wires are connected in boxes, the bare ends of the cores must be insulated with adhesive tape. The insulated ends of the wires are placed in boxes in such a way that they do not touch each other. The ends of the wires at the input to the box are fixed on the wall at a distance of 50mm from the box.

closed wiring- is considered the safest and is often used in residential areas. Its main drawback is the difficulty of accessing the wires. Cables are installed in hollowed out grooves right in the walls, and after laying the wires, these places are tightly cemented. Flat wires in walls, grooves or barbs are fixed by the “freezing” method with alabaster. They can also be attached with special plastic clamps. Fastening wires with nails is strictly prohibited! Hidden wiring is the most common and safe to use, as it is located in the thickness of fireproof material (there are no mechanical effects, air access to it is difficult). When laying under plaster on wooden wall under the wires enclose a layer of asbestos 3mm. Crossing flat wires with each other should be avoided. If it is necessary to cross, the insulation of the wires in this place is reinforced with three to four layers of electrical tape. Hidden wires lead to the surface of the ceiling walls (for connection to lamps) through insulating tubes or plastic tubes. It is allowed, with hidden wiring, to carry out branches of flat wires in the introductory boxes of switches, sockets or lamps.

If the wiring is done under a layer of drywall, then there is no need to punch grooves in the drywall board. Since the GKL is mounted on the wall on a special profile, there is a void between the sheet itself and the base. In this case, it will be enough to drill several holes in drywall (with a diameter of 30 to 40 mm) along the path of the electrical wiring. Wire loops are pushed through the holes, with the help of which they are pulled with reverse side wires. When repairing wiring, a faulty wire is often used as a conductor.

Combined wiring wires involves the application of the same rules and fastening of a complete set of devices for the construction of electrical wiring. This mounting method is used in rare cases and is more complex in terms of implementation.

When updating electrical wiring, professionals usually use this method. Its essence is as follows: a combination of laying electrical wires in insulating boxes and in walls in a hidden way. Parts of open wiring that look unaesthetic, for example, to power a lighting fixture, are made in a hidden way. In this case, insulating boxes are placed above the baseboards, around the door frames, and on top - along the junction lines of the ceiling and walls. All other branches of the wires are hidden.

After the electrical work the final look of the room is quite presentable. Upon completion of the painting, the insulating boxes are almost invisible against the background of the wall. This method of conducting electrical wiring complies with the standards in force for the installation of wires in walls and partitions, because chasing is applied partially.

Electrical wiring refers to all electrical wires and cables laid in a house or apartment. They are designed to supply electricity to household and lighting appliances. Today we are nowhere without technology, so let's take a closer look at all these cables and junction boxes.

Types of electrical wiring

There are two types of electrical wiring: hidden and open.The structure of the wiring itself, regardless of its type, is always the same: inapartment or house, the main power cable is introduced, which is connected to electric meter. Feeding branch cables run from the meter to all rooms. In rooms, cables branch out even more: to sockets, to switches, to lighting fixtures.

1. Hidden wiring

The name itself concealed wiring implies that electrical cables are hidden inside walls, partitions and ceilings, they are not visible. Only intermediate or end points are available to our gaze: junction boxes, switches, lighting fixtures, sockets and counters.

Concealed wiring is used in modern panel, monolithic and brick houses. Electric cables are located in special channels inside the walls or behind decorative or plasterboard panels.

The cable channel is an ordinary PVC tube, which is poured into the panel or laid in specially cut grooves in the walls or ceiling. Such channels usually terminate installation boxes, in which sockets and switches are mounted.

The main advantage of hidden wiring is its invisibility. But repair, replacement and redevelopment, especially in monolithic or brick houses, is a rather troublesome procedure: you have to open the walls, and after replacing them, cover and paint over them again.

2. Open wiring

Open wiring is located on top of a wall or ceiling. But open doesn't mean unprotected. For open wiring, either ready-made cable channels (cable runners) or PVC tubes are used in the same way, in which the wires are laid.In some cases, open wiring is made with cables in double or even triple insulation. So, for example, they make wiring in dachas and in country wooden cottages.For open wiring, special sockets, switches and junction boxes are used. They have a closed case, and are mounted directly on the wall.

Interior designers sometimes use exposed wiring as a decorative element, such as when implementing a steampunk, country or loft style project. For such projects, multi-colored wires and cables, fabric-braided wires, and special designer fasteners are used.

An important plus of open wiring is that its repair, replacement or connection of new branches is carried out without much labor: you do not need to hammer the walls and restore them after work. Minus - the wiring is visible, but for someone this minus can become a plus.

Wire types

Cables and wires are used for laying electrical wiring. For a non-specialist, there is not much difference between these concepts, but when laying wiring, it is important to know what it will be done with: a cable or a wire.

The wire

A wire is one solid wire metal core. Wires may be uninsulated or covered with a layer insulating material. They are also divided into dnovoloskovye (monolithic) and multi-hair (braided). The former are used for hidden wiring devices. Braided type wires are more flexible and break less with frequent bends and twists, so they are often used to power household appliances.

1. PVC wire

This wire is often used to repair electrical networks. It is also suitable for making extension cords and cords for any kind of technique. Flexibility and lightness make PVA indispensable assistant for lighting and installation of rosettes To.

2. PBPP wire

Flat electrical wire with two or three solid copper conductors. It is a universal conductor electric current, high quality: PBPP can be used when carrying out electrical work in a private house, apartment or country house. It is suitable for connecting lighting as well as mounting electrical sockets and switches.

Cable

A cable is several insulated wires in a common protective insulation. The number of wires in the cable can be different. For household electrical wiring, two-, three- and four-core cables with a cross section of 2.5 to 4 mm are used.

Wires and cables for household electrical wiring are made of copper or aluminum. In older houses, which are more than 15 - 20 years old, aluminum wiring used to be used. modern houses equipped with copper cables: with the same wire cross-section, copper cables are able to withstand a large electrical load. In addition, copper cables are more flexible and less prone to oxidation.

Important: try not to connect copper and aluminum wires. At the point of such contact, chemical reaction oxidation with release a large number heat. Possible fire. Wire with cables of the same material.

1. CableNYM

High-quality German cable, consisting of 1-5 cores. It is used for laying lighting and power networks both indoors and outdoors. outdoors. Its distinguishing feature is a high degree of security. This cable is also moisture and heat resistant, but does not like sunlight, so it must be protected from direct rays.

2. VVG cable

Cable with excellent insulating characteristics. It consists of a single core, making it convenient to lay inside the walls. Most often, VVG is used when they are independently involved in the installation or replacement of electrical wiring in an apartment. The service life of such a cable is at least 30 years.

Wiring for powerful equipment

For household electric stoves and electric ovens, it is recommended to lay a separate branch of electrical wiring. For this branch, more powerful cables with copper conductors in double insulation, with a cross section of at least 6 mm, are used, special power sockets are installed.

Distribution boxes

To organize the electrical network of a house or apartment, junction boxes, or, as they are also called, distribution boxes, are used. They are installed at the junctions, or, if you like, branchings of individual electrical cables. There are boxes like this in every room. Usually they are located under the ceiling. There are two types of junction boxes: For concealed and outdoor installation.

Hidden junction boxes are recessed into special sockets under the ceiling, at the convergence of several cable channels. The main power cable comes into the box, and cables for powering sockets, a cable for a switch, cables for powering lighting fixtures: chandeliers, sconces, spot sections, etc. branch off from it.Open boxes are mounted directly on the wall in the most convenient place for this.

The word "wiring" is familiar to everyone, but not everyone will correctly explain its meaning. For many, the concept is associated exclusively with wires. In fact, this is a whole system that includes:

insulated wires laid in the building;
unarmored cables;
their protective structures;
connecting and fastening elements.

And most importantly, this whole system called "wiring in the house" has a specific purpose - to deliver electricity from the power source and distribute it to consumers.

It's also important to understand the difference.

Electrical wiring is carried out in networks with a voltage of up to 1000 V: in buildings and structures (inside or outside), on the territories of institutions and enterprises, in courtyards and microdistricts, on construction sites and household plots.

Cables and wires with a voltage of over 1000 V, laid in special channels, wells, on poles, are already power transmission lines (TL).

TYPES AND TYPES OF ELECTRICAL WIRING

By placement, electrical wiring is of two types:

internal (mounted inside rear);
external (laid on outer walls structures).

According to the laying method, both external and internal wiring are also classified into hidden and open.

OPEN WIRING

With open wiring, cables and wires are laid along wall surfaces, ceilings and other building elements of the building.

There are several laying methods:

free suspension;
directly on the wall surface or ceiling;
in electrical plinth;
on strings;
in platbands;
on ropes;
in trays;
on rollerskates;
on insulators;
in boxes;
in pipes.

In turn, open wiring is divided into three subspecies:

Stationary.

This is wiring that is permanently connected and cannot be disconnected without the use of a special tool.

Portable.

The contacts of such wiring are interconnected using plug-in connectors (not twisted or soldered), that is, such wiring can be disconnected at any time.

Mobile.

It is used to connect mobile mechanisms to the electrical network.

The advantages of open wiring are as follows:

1. It is easy to install. Not even the most experienced electrician, but an ordinary man who understands electricity, can do such electrical wiring in an apartment with his own hands.

2. No additional equipment is required (such as a power tool for cutting strobes).

3. The integrity of ceilings and walls during installation is minimally disturbed.

4. Wiring is available at any time for inspection or damage repair.

5. It is mobile, if you need to move the switch or socket to another place, this can be done without problems.

Disadvantages of open wiring:

1. It is unattractive and does not always fit into the interior.

2. During installation, it is necessary to take into account the technical standards and requirements of the premises (not everywhere it can be used).

3. The open laying method is the most dangerous in terms of fires. If the load exceeds the permissible one, overheating of the wiring and fire is possible, which will immediately spread to the wallpaper or decor.

HIDDEN WIRING

Hidden wiring is laid inside structural elements buildings - in ceilings and foundations, in wall surfaces, under removable floors. There are several ways to lay a cable or wire:

in pipes;
in grooves for plaster;
in a flexible metal sleeve;
in the voids of the building structure;
in channels;
in boxes;
in niches of plasterboard structures.

Now it is rare, but in Soviet times such a method as embedding conductors in building structure during its manufacture.

Advantages of concealed wiring:

1. It is not visible, does not spoil the interior of the room and does not interfere with any finishing work.

2. This laying method is characterized by high level electrical safety. All conductors are hidden, which means that contact with live parts and electric shock are minimized.

3. Being under a layer of plaster, hidden wiring does not have air access, as a result of which it has high fire safety.

4. There is no solar and mechanical impact on the elements of hidden wiring, due to which its service life is increased.

Disadvantages of the hidden method of laying email. wiring:

1. It is practically impossible to repair such wiring. If a wire burns out somewhere, it will be very problematic to find the place of damage.

2. Labor-intensive installation.

3. It is necessary to immediately clearly think over the locations of sockets and switches, the ways of laying wires, since it will be difficult to change something in the future.

4. An accurate wiring diagram will be required. After all, when you need to drill a hole for attaching a picture or shelves, you need to be sure that you will not hit the wire with a drill. You can, of course, do without a circuit, but then you have to buy a special device to detect hidden wiring.

OUTDOOR WIRING

In another way, outdoor wiring is called street. It is laid outside the houses, along the walls of structures and buildings, as well as between them on special structures or supports.

Such wiring is necessary to supply voltage to lighting lamps, alarms, CCTV cameras and utility rooms(garage, workshop, barn, sauna, bath, swimming pool). All this must be taken into account at the stage of construction of buildings and structures.

External wiring in a country house is important no less than internal. In addition to the fact that it is necessary to provide sufficient lighting on the site, at any time you may need to connect a power tool in the yard (drill, grinder, lawn mower, pump). Do not pull carriers through the whole house and plot, it is better to plan places for installing 2-3 outlets when planning power supply.

The most important difference between outdoor wiring is that it is exposed to atmospheric factors - rain, snow, wind, Sun rays. Therefore, it must be reliably protected from precipitation, from mechanical influences and accidental human touches to current-carrying parts.

General requirements for electrical wiring.

These requirements are equally applicable for both apartments and private houses:

1. All boxes, sockets and switches must be located in such places that they always have free access.

2. All connections and branches are made only in boxes.

4. Grounding and grounding conductors are connected only by welding.

5. Zeroing of stationary plates is carried out by separate conductors.

According to the PUE (Rules for the Construction of Electrical Installations), the following are also regulated:

norms for the number of outlets per room;
distances at which sockets and switches should be placed in relation to the floor and communications;
wire laying standards (vertical and horizontal sections).

ELECTRICAL WIRING IN THE HOUSE AND APARTMENT

Apartment wiring is not as costly in terms of finances, effort and time as wiring in a private house. In multi-storey housing construction, each apartment has already been connected electrical network from a common switchboard to an introductory machine.

Do-it-yourself wiring in apartments is within the power of many and is carried out according to such an approximate plan:

You should start by drawing up a diagram.
Based on the scheme, it is necessary to make markings on the walls and calculate required amount wires, cables, switching devices and accessories.
Next come installation work- cutting strobes, laying conductors in them, installing boxes, switches and sockets, and connecting all elements.
The final stage– checking the operation of the assembled circuit.

Electrical wiring in a private house.

Wiring in a private house is also quite realistic to do with your own hands to a person who understands electricity. Just keep in mind that it is different from apartment option because it has additional requirements.

Power supply should be carried out from a 220 V or 380 V network, with a TN-C-S earthing system. It is forbidden to lay conductors on heated surfaces, as well as near a stove, chimney or fireplace (this rule is especially true for saunas and baths).

Of particular difficulty when laying wiring with your own hands in a private house is the installation of the input. First, you will have to go around several institutions to obtain permission and technical conditions.

There is a lot of work to be done on assembling the switchboard and laying the inlet line (digging a trench for a cable or installing a tap from an overhead power line). And only then you can proceed to the internal wiring according to the same plan as described above for the apartment version.

If you are not sure that you can mount a reliable and high-quality email. wiring in an apartment or a private house on your own in accordance with the requirements of the PUE, it is better to invite a specialist. Remember that 65% of all fires in electrical installations originate in the household electrical network.

* * *

Vitaly
Good afternoon What explains such a significant difference in the permissible values of the current flowing through the cable of the same section with open and closed types wiring?

Answer:

Wires or cables laid openly (exposed wiring) cool better than wires and cables (hidden wiring) laid in pipes or hidden under plaster, false ceiling and behind shelving walls. Wires with rubber insulation allow a long-term heating temperature of their cores, not exceeding 65 ° C, and wires with plastic insulation - 70 ° C. The cross section of the conductors is selected based on the maximum permissible heating of the conductors, at which the insulation of the wires is not damaged.

If you cannot perform electrical measurements yourself, then use the services of specialists from a mobile electrical laboratory.

Electric current in metals is the ordered movement of electrons under the action of electric field. The most convincing proof of the electronic nature of the current in metals was obtained in experiments with the inertia of electrons (the experiment of Tolman and Stewart):

Coil with a large number turns of thin wire (Fig. 9.1) was brought into rapid rotation around its axis. The ends of the coil were connected by means of flexible wires to a sensitive ballistic galvanometer. The untwisted coil was sharply decelerated, and a short-term current arose in the circuit, due to the inertia of the charge carriers. The total charge flowing through the circuit was measured with a galvanometer. When braking a rotating coil, each charge carrier e with mass m is affected by a braking force, which plays the role of an external force, that is, a force of non-electric origin:

The external force related to the unit of charge is, by definition, the field strength of the external forces:

Consequently, an electromotive force arises in the circuit when the coil is braked:

During the braking time of the coil, a charge q will flow through the circuit, equal to:

where is the length of the coil wire, I is the instantaneous value of the current in the coil, R is the total resistance of the circuit, is the initial linear speed of the wire. The good electrical conductivity of metals is explained by the high concentration of free electrons, equal in order of magnitude to the number of atoms per unit volume. The assumption that electrons are responsible for the electric current in metals arose much earlier than the experiments of Tolman and Stewart. Back in 1900, the German scientist P. Drude, based on the hypothesis of the existence of free electrons in metals, created an electronic theory of the conductivity of metals. This theory was developed in the works of the Dutch physicist H. Lorenz and is called the classical electron theory. According to this theory, electrons in metals behave like an electron gas, much like an ideal gas. The electron gas fills the space between the ions that form the crystal lattice of the metal. Due to interaction with ions, electrons can leave the metal only after overcoming the so-called potential barrier. The height of this barrier is called the work function.
At ordinary (room) temperatures, electrons do not have enough energy to overcome the potential barrier. According to the Drude-Lorentz theory, electrons have the same average energy of thermal motion as the molecules of a monatomic ideal gas. This makes it possible to estimate the average velocity of the thermal motion of electrons using the formulas of the molecular kinetic theory:

When an external electric field is applied in a metal conductor, in addition to the thermal motion of electrons, their ordered motion (drift), that is, an electric current, occurs. The value of the drift velocity of electrons is in the range of 0.6 - 6 mm/s. Thus, the average speed of the ordered motion of electrons in metallic conductors is many orders of magnitude less average speed their thermal motion. The low drift rate does not contradict the experimental fact that the current in the entire circuit direct current installed almost instantly. Closing the circuit causes the electric field to propagate at a speed c\u003d 3 10 8 m / s. After a time (l is the length of the chain), a stationary distribution of the electric field is established along the chain, and an ordered motion of electrons begins in it.
In the classical electronic theory of metals, it is assumed that the motion of electrons obeys the laws of Newtonian mechanics. In this theory, the interaction of electrons with each other is neglected, and their interaction with positive ions is reduced only to collisions. It is also assumed that during each collision, the electron transfers to the lattice all the energy accumulated in electric field energy and, therefore, after the collision, it begins to move with zero drift velocity. Despite the fact that all these assumptions are very approximate, the classical electronic theory qualitatively explains the laws of electric current in metal conductors: Ohm's law, the Joule-Lenz law and explains the existence of the electrical resistance of metals.
Ohm's law:

Conductor electrical resistance:

Joule-Lenz law:

However, in a number of issues the classical electron theory leads to conclusions that are in conflict with experiment. This theory cannot, for example, explain why the molar heat capacity of metals, as well as the molar heat capacity of dielectric crystals, is 3R (Dulong and Petit law). The classical electronic theory also cannot explain the temperature dependence of the resistivity of metals: the theory gives, while the dependence ρ ~ T is obtained from the experiment. The most striking example of the discrepancy between theory and experiments is superconductivity. The qualitative difference between metals and semiconductors (dielectrics) lies in the nature of the dependence of specific conductivity on temperature. In metals, the conductivity decreases with increasing temperature, while in semiconductors and dielectrics it increases. At T o K, pure metals have conductivity s o ¥. For semiconductors and dielectrics at T o K, s o 0. There is no qualitative difference between semiconductors and dielectrics in terms of electrical conductivity. The manifestation of metallic properties in some substances, while semiconductor and dielectric properties in others can be consistently explained only within the framework of quantum theory.
According to quantum concepts, the energy of electrons in an atom can change in a discrete way. Moreover, according to the Pauli principle, no more than one electron can be in one quantum state. As a result, electrons do not gather at any one energy level, but sequentially fill the allowed energy levels in the atom, forming its electron shells. With the approach of a large number of atoms and the formation of a crystal structure, chemical bonds between atoms are formed due to electrons in the outer, valence, electron shells.
According to the Pauli principle, atoms cannot clump together into a dense mass, since in this case there would be many particles with a half-integer spin - an intrinsic angular momentum (L = ħ/2) in one quantum state. Such particles are called fermions, and they include, in particular, electrons, protons, and neutrons. They are named in honor of the Italian physicist E. Fermi, who first described the features of the behavior of collectives of such particles. When a large number of atoms approach within a solid body, the initial energy level of the valence electron in the atom splits into N sublevels, where N is the number of atoms that form the crystal. As a result, a zone of allowed energy levels for electrons in a solid is formed (Fig. 9.2).

Fig.9.2
In metals, the outer valence shells are not completely filled, for example, silver atoms have one electron in the outer shell 5s1, while, according to the Pauli principle, there could be two electrons with different spin orientations, but the second electron in the outer shell of the silver atom is simply No. As N Ag atoms approach each other and the external energy level splits 5 s 1 1 into N sublevels, each of them is already filled with two electrons with different spin orientations. As a result, when N silver atoms approach each other, an energy band appears that is half filled with electrons. The energy corresponding to the last filled electronic level at 0 K is called the Fermi energy eF≈kTg. The distance between adjacent energy levels DE is very small, since N is very large, up to.
e F ~ 1¸10 eV, Δ E= e F / N << kT» 0.025 eV.

The distance between adjacent allowed levels of electrons in metals is much less than the energy of thermal motion of electrons even at the lowest temperatures. If you place a conductor in an electric field, including it, for example, in a closed circuit with an EMF source, then the electrons will begin to move from a conductor point with a lower potential to a point with a higher potential, since their charge is negative. But movement in an electric field means an increase in the energy of an electron, and according to quantum concepts, a transition to a higher energy level for an electron is possible if this neighboring level is free. In metals, such free levels are quite sufficient for electrons located near the Fermi level; therefore, metals are good conductors of electric current.
However, this conductivity is provided not by all free electrons of the metal, but only by those located near the Fermi level. The concentration of such electrons is approximately equal to nt /Tg, Where Tg\u003d 5 × 10 4 K is the degeneration temperature.

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