Open and closed wiring. When to use open wiring

Vitaly
Good afternoon What explains such a significant difference in the permissible values of current flowing through a cable of the same cross-section when 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, suspended ceiling and behind hemmed walls. Wires with rubber insulation allow long-term heating of their cores, not exceeding 65 °C, and wires with plastic insulation - 70 °C. The cross-section of the current-carrying 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 carry out 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 influence of electric field. The most convincing evidence of the electronic nature of current in metals was obtained in experiments with the inertia of electrons (the experiment of Tolman and Stewart):

A coil with a large number of turns of thin wire (Fig. 9.1) was driven into rapid rotation around its axis. The ends of the coil were connected using flexible wires to a sensitive ballistic galvanometer. The untwisted coil was sharply slowed down, 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 acted upon by a braking force, which plays the role of an external force, that is, a force of non-electric origin:

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

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

During the braking 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, and 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 the electronic theory of metal conductivity. This theory was developed in the works of the Dutch physicist H. Lorentz and is called classical electronic theory. According to this theory, electrons in metals behave like an electron gas, much like an ideal gas. Electron gas fills the space between the ions that form the metal's crystal lattice. Due to interaction with ions, electrons can leave the metal only by 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 thermal movement, like the molecules of a monatomic ideal gas. This allows us to estimate the average speed of thermal motion of electrons using the formulas of molecular kinetic theory:

When an external electric field is applied to a metal conductor, in addition to the thermal movement of electrons, their ordered movement (drift), that is, an electric current, occurs. The electron drift velocity is in the range of 0.6 – 6 mm/s. Thus, the average speed of ordered movement of electrons in metal conductors is many orders of magnitude less average speed their thermal movement. The low drift speed does not contradict the experimental fact that the current in the entire circuit direct current installs almost instantly. Closing the circuit causes the electric field to propagate at a speed c= 3·10 8 m/s. After time (l is the length of the chain), a stationary distribution of the electric field is established along the chain and the ordered movement of electrons begins in it.
In the classical electronic theory of metals, it is assumed that the movement of electrons obeys Newton's laws of 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 with each collision the electron transfers to the lattice all the energy accumulated in it. electric field energy and therefore after the collision it begins to move with zero drift speed. Despite the fact that all these assumptions are very approximate, the classical electronic theory qualitatively explains the laws electric current in metal conductors: Ohm’s law, Joule–Lenz’s law and explains the existence electrical resistance metals
Ohm's law:

Electrical resistance of the conductor:

Joule-Lenz law:

However, in a number of issues, the classical electronic 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 equal to 3R (Dulong and Petit's law). Classical electronic theory also cannot explain the temperature dependence resistivity metals: theory gives, while from experiment the dependence ρ ~ T is obtained. The most striking example of the discrepancy between theory and experiment is superconductivity. The qualitative difference between metals and semiconductors (dielectrics) lies in the nature of the dependence of specific conductivity on temperature. For metals, the conductivity decreases with increasing temperature, while for 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, and 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 manner. Moreover, according to the Pauli principle, there can be no more than one electron in one quantum state. As a result, electrons are not collected at any one energy level, but sequentially fill the allowed energy levels in the atom, forming its electron shells. When approaching large number atoms and the formation of a crystal structure, chemical bonds between atoms are formed due to electrons located in the outer, valence, electronic shells.
According to the Pauli principle, atoms cannot bunch together into a dense mass, since in this case there would be many particles with half-integer spin in one quantum state - the intrinsic angular momentum (L = ħ/2). Such particles are called fermions, and they include, in particular, electrons, protons, and neutrons. They are named after the Italian physicist E. Fermi, who was the first to describe the peculiarities of the behavior of groups of such particles. When a large number of atoms come together within solid the initial energy level of the valence electron in the atom is split into N sublevels, where N is the number of atoms forming 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, in silver atoms outer shell 5s1 there is one electron, while, according to the Pauli principle, there could be two electrons with different spin orientations, but there is simply no second electron in the outer shell of the silver atom. When N Ag atoms approach each other and the outer energy level 5 splits s 1 1 into N sublevels, each of them is 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. Distance between adjacent energy levels DE is very small because N is very large, up to.
e F ~ 1¸10 eV, Δ E=eF/ 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, turning it on, for example, in a closed circuit with an EMF source, then electrons will begin to move from a point in the conductor 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 the electron, and according to quantum concepts, a transition to a higher energy level of an electron is possible if this neighboring level is free. In metals, there are quite enough such free levels for electrons located near the Fermi level, so 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 /T g, Where T g= 5×10 4 K– degeneration temperature.

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The option of hidden electrical wiring has become a standard in construction, however, there are situations when installing wires when open wiring is used, for example, electrical wiring in an old house. After all, hidden electrical wiring, for all its design advantages, still has some disadvantages - wall chipping, labor-intensive work, the formation of debris and dust during installation, as well as difficult diagnostics and replacement of individual sections of wires.

All these disadvantages develop into the advantages of open wiring and are used in certain cases, namely:

When installing electrical wiring in an old house.
Laying wiring in wooden houses.
When replacing old wiring.
If you want to have retro-style wiring in your apartment or house.
If electrical wiring is installed in the event of a change of homeowners.

In one case or another, the installation technology, parts and devices of open wiring will differ from its hidden counterpart. In short, we can highlight the following basic materials used when laying open electrical wiring:

Porcelain insulators in the form of rollers.
Plastic staples.
Corrugated plastic and metal pipes.
Cable trays and europlinths.
Twisted copper wire.
Surface-mounted switches and sockets.

Now we will briefly describe each case when open wiring is used.

Installation of electrical wiring in an old house

Can you imagine old brick walls in an old house or apartment that need to be chipped to install hidden wiring? In this case, you can destroy certain sections of the wall, damage the communications of water pipes, and create a lot of dirt and dust. Moreover, in such houses you will have to apply for permission to carry out work from the relevant authorities. All this can be avoided by installing open wiring, which will fit perfectly into the interior of old premises.

Open wiring in wooden houses

For fire safety purposes, in houses made from, exclusively open wiring is used while maintaining an air gap between the wall and the wire. If it is necessary to install the wire through the wall, metal tubes are used.

This is done so that fire-hazardous dust does not accumulate in the transition areas around the wiring, and also to prevent damage to the wires by rodents. Using this principle, parts for sockets and switches are manufactured with varying degrees of protection from dust and moisture.

Replacing old wiring with open wiring

If the old hidden wiring often fails, then replacing it with the same closed wiring is fraught with high costs, destruction of established communications, destruction of wallpaper and ceramic tiles in the bathtub and kitchen. The only rational solution would be to replace hidden electrical wiring with open wiring.

Exposed wiring in retro style

Currently, the number of apartment and house owners who prefer retro style in their premises is growing. One element of this style is exposed stranded wire wiring on porcelain insulators.

This kit includes porcelain sockets and switches for each individual light bulb or household appliance. Moreover, the retro style is used in one or two rooms, while the rest of the rooms can be decorated in Scandinavian or.

When property owners change

There are options when there is a change of homeowners and in order to have reliable, new electrical wiring they resort to the open method. And indeed, try to figure out where and how the closed-type wiring was previously carried out.

Types of electrical wiring

Typically, experts distinguish between only two types of wiring - hidden and open. In this article we will also talk about the third type - open decorative wiring.

The most commonly used type of electrical wiring. With hidden wiring, all its elements are located inside the structures. Distribution boxes and wires are mounted in specially prepared holes (grooves and sockets). On the outer part of the walls there are only switch control keys and socket openings; the inside of these devices is also hidden in the wall openings.

The advantages of this type of electrical wiring are that most of its elements are invisible, and they do not affect the appearance of the room.
The disadvantages are that this type of electrical wiring requires disruption of the surface of structures, and this, firstly, is a separate type of work for construction or installation teams (and requires appropriate payment), and, secondly, the holes made must be subsequently closed ( prime, putty, sand, prime again, etc.). But that is not all. Since the wiring is done in a hidden way, it often happens that residents do not know where it goes, and by making any hole in the wall (to hang a picture, secure furniture), they can damage it. The consequences of such actions can be disastrous - to repair the wiring, you will have to again disturb the surface of the walls, and then restore their decorative coating.

Its peculiarity is that all electrical wiring elements are mounted outside the structure. Junction boxes, wires, switches and sockets remain visible. This type of wiring is most often used in country houses, country houses, garden houses and industrial enterprises. Where design and appearance are not of paramount importance.

The advantages of this type of wiring are that there is no need to make holes in structures; it requires less time and material costs. It’s also hard to imagine that someone would accidentally break the integrity of the wiring done in an open way. But if it is necessary to restore or change it, this work will not require subsequent repairs of the structures.
The disadvantages of open wiring are that its appearance can damage the design of the room as a whole.
And now it’s time to talk about the third type of electrical wiring - open decorative wiring!

Open decorative wiring.

This type of wiring is also carried out outside structures, but with the help of decorative electrical appliances. Twisted wires, retro switches, retro sockets and even retro junction boxes - all this becomes not just a functional element, but an element of style and decor of your room!

Open decorative wiring has all the advantages of simple open electrical wiring and does not have its only disadvantage - it does not worsen the appearance of the room, but, on the contrary, shapes it. But at the same time it acquires its own disadvantage - the cost of its elements is noticeably higher than the cost of simple electrical appliances. In addition, we have not yet encountered decorative wires and sockets suitable for high-power electrical appliances (electric stoves, hobs, ovens, microwave ovens), so the use of this type of wiring in kitchen areas is not yet acceptable.

So, we told you about the existing types of electrical wiring. Now you can answer the question for yourself which one is suitable for your premises. We just remind you that the determining factor is the purpose of the room. Where design is not paramount, simple exposed wiring should be used. Where design is very important - hidden or open decorative.
I would also like to add that it is quite possible to use different types of wiring in one room. For example, you have fenced off part of the room for a wardrobe - you can have open wiring in the wardrobe, and closed wiring in the main part of the room. Or so - you bought an apartment with a fine finish. We have done zoning in one of the rooms, which you would like to emphasize with light. But you have no desire to ditch and then repair the ceiling. Move the ceiling light using an inconspicuous cable channel to the place you need, thus combining hidden and open wiring in one room! And you liked the idea of open decorative wiring, but you don’t want to spend a lot of money on its elements - do the wiring in this way only in the most noticeable areas of the room, and the rest in a closed or simple open way.

The specialists of the Provodka-EKB company are always happy to help you find the right solution, as well as to carry it out for you in a qualified manner!

http://provodka-ekb.ru

Hidden wiring

Hidden wiring is found in almost all residential buildings and apartments. Usually, to make wiring, small grooves are knocked out in the walls and ceilings, and electrical wires are laid in them. Then these grooves are simply plastered over with cement or alabaster. Furrows are not made if the wiring is only being carried out in a house under construction. The wires are attached using nails that are driven between the bricks. You can also attach the wires to the wall using alabaster. And after that the room is plastered, and the wires end up under a layer of plaster.

All twists of wires are hidden in special junction boxes, which are installed in the places where the wires are connected. These boxes must be installed flush with the wall surface. They are closed with plastic lids. This is necessary for safety reasons, and just for beauty. Junction boxes are also used to install switches and sockets. The boxes are made of plastic or steel. Sockets and switches are also used when working for hidden wiring. They almost do not protrude above the surface of the walls.

For hidden wiring, two types of wire are usually used: copper and aluminum. The cross-section of the copper wire is at least 1mm2, and the aluminum wire is at least 2.5mm2. Installation of hidden wiring in apartments is done in special channels that are built in the walls. Therefore, when switching electrical wires, as well as when replacing switches and sockets, you need to be careful. To replace or extend an electrical wire, you need to get to the place where they connect, and to do this, if necessary, you even have to knock down a new tile or damage the wallpaper.

Open wiring

The difference between open and hidden wiring is that it is laid on the surface of ceilings and walls. For open wiring, use copper or aluminum wires, always with rubber insulation. In addition, copper and aluminum wires with insulation only made of polyvinyl chloride are used. But they can only be used if the wire has a separate base that separates one core of the wire from the other. The wires are secured using rollers made of porcelain, an insulating material. Each roller has a hole. A nail is inserted into this hole and attached to the ceiling or wall with wires attached to it.

During installation, use copper wire with a cross-section of 1 mm2, or aluminum with a cross-section of 2.5 mm2. Along the walls, the wires are laid parallel to the intersection lines of the walls and ceiling. In this case, the distance from the cornice or ceiling should be 10-20 cm. The descents and ascents of the wires are made perpendicular to the ceiling. Near doors and windows, the wire is placed at a distance of 10 cm from the edge of the window or door. The wire fastening rollers should be 50 cm apart from each other.

With open wiring, all switches and sockets are fixed on the walls, on special pads made of dry wood. Such insulating pads are called socket boxes. First, use a long screw to screw the socket box to the wall. Then a socket or switch is attached to it with two small screws. When the wiring is open, switches and sockets are installed that are different from those installed when it is closed. They differ both in appearance and in the way they are installed. It is impossible to install a switch in the basement of a house, due to dampness, conductive walls and floors, so the switch is placed in the kitchen. Nowadays, open wiring in apartment buildings is quite rare, but for example, if the house is wooden, other wiring simply cannot be done.

One of two options for installing electrical wiring in a country house - open or closed - is chosen with reason. Having trouble with your arguments? And we will tell you!

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

In a stone cottage, closed wiring is undoubtedly more convenient. It is insulated 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 a retro setting or don’t 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 installed at the final stage of construction, before finishing work begins. Channels are hollowed out in the walls, cables wrapped in corrugated pipes are placed and fixed in them, and recesses are made for mounting boxes.

The laying of canals does not tolerate chaos. Just imagine the consequences of hardware getting into the cable when trying to “drive a nail” into the wall! For this reason, experienced electricians lay wires strictly horizontally or vertically from sockets and switches. If the wiring is placed in the floor, laying is done around the perimeter of the room at a distance of 10 cm from the walls, and the cable does not interfere with the fastening of the baseboard.

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

✓ Please note
When installing electricity into a house or changing wiring, it is dangerous to skimp on equipment and installation. It is better to entrust the selection of cables, 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. In this case, it is wrong to focus only on price; it is not an absolute indicator of quality. If for one reason or another the choice falls on retro-style 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

Electrical wiring embedded in a stone wall does not pose a particular fire hazard. Of course, an outlet 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 electrical failure may well cause a fire. Meanwhile, hidden wiring in a country house often becomes the object of attention of rodents. In addition, wood dust accumulates in the voids of wooden houses where wiring is laid, which instantly ignites from a spark. Therefore, in accordance with current Russian standards, electrical wiring on a combustible base is carried out openly.

The advantages of open wiring are obvious. It is easy to install, maintain and control; if necessary, the route can be moved, supplemented or repaired. There are also “cons”. The open installation method eats up part of the space: you cannot hang a shelf on top of the cable, and sometimes you cannot place a cabinet close to the wall.

Open wiring – retro + progress

Traditionally, open wiring was done with stranded wire on ceramic insulators. This is the way today. most suitable for retro style, easy to replicate using modern twisted three-core or two-core wire and ceramic holders. Styling will cost more than exposed wiring from a regular cable on plastic or metal brackets. But in any case, the distance between the holders should be no more than 50 cm, and in difficult areas they are placed more often.

To protect exposed wiring from a regular cable from accidental damage, cable ducts and plastic skirting boards are used. Their internal space may have partitions that allow both low-current and power cables to be laid inside the boxes at the same time. The removable upper part provides the ability to monitor the condition of the route and its modernization.

✓Note
The protective ground in the 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 grounding loop. In general, this is a separate independent project that takes into account the properties of the soil, the occurrence of groundwater, and the meteorological features of the region.

Electrical wiring begins with a project

The power supply of a country house should be carried out according to a project carried out in a specialized organization that has official permission and approved by the Rosenergonadzor authorities. But before ordering a project, you need to draw up technical specifications. To do this, you will need to obtain information about the power allocated to an apartment or house (a certificate is issued by the operating company), draw a diagram of the location of sockets, switches and lighting fixtures (or order a design project), and also count the expected consumers of electricity. The power supply system installed according to the project is tested, after which it is accepted into operation by an Energonadzor inspector. Only this approach guarantees the electrical and fire safety of the house. In practice, an electrical project is often 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.

Protection against electric shock

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

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

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

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

Installation of panels

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

An input switch and differential circuit breakers are located on its mounting profiles or DIN rails. Each of them is responsible for a specific group. Let's say one is for lighting, the other is for sockets.

In addition to protective devices, there is also room for auxiliary modules: load limiting relays, relays that monitor the quality of incoming electricity.

The distribution board is selected in such a way that after assembly there remains at least 30% of free space, because over time the needs for power supply may increase. In wooden houses, mounted dust- and moisture-proof power panels with an impact-resistant lid that is locked with a lock are installed. In stone, as well as in city, apartments, built-in wardrobes are usually used.

✓Expert opinion
If the customer voices the task of gradually replacing the wiring in the house, then at the design stage of the distribution board it is noted 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 switchboard diagram: some consumers will connect to the home’s power supply system, and for others, backup outgoing lines will be provided in the switchboard.
Then in the future it will be possible to complete the wiring and connect new groups of consumers through the “backup” lines of the input panel. But we do not recommend dividing the work of replacing electrical wiring into stages. At a minimum, shields must be installed throughout the entire house and power cables must be installed.