Two-core wire: features of cables with a different number of cores, which is better - stranded or single-core

When designing and installing home electrical wiring, an important decision is the choice of the type of wire used. In order to find the best option, it is necessary to take into account all the nuances - electrical load, location, number of bends and resistance. Based on these initial data, it will be clear what kind of wire is needed - two-core, single-core or stranded, and what parameters it should have.

Types of wires and their characteristics

There are two broad categories of wires, depending on their design. Single-core products differ in that the metal core, through which the current flows, contains only one, then it is covered with one or more layers of insulating material. Stranded wires consist of two or more current-carrying elements, which are covered with insulation.

In addition to individual wires, cables are made. The main difference between a stranded wire and a stranded cable is that the conductive core in the wire contains several wires that are not insulated from each other - they are simply woven together and are solid conductor. The cable contains separate insulated conductors, which are then united by common insulation.

In addition to the indicators of the core length, the wires have other categories of differences. This is the type of metal that is used for the manufacture of conductors, the flexibility class of the finished product, as well as the material used for insulation. Depending on these features, the purpose and scope of these wires changes.

Product material

Regardless of the number of cores, copper or aluminum can be used for the production of a product; sometimes an alloy of these elements is used. However, aluminum wires are gradually being replaced by copper ones due to their greater functionality. In modern, not very high-quality technology, you can find steel veins covered with a copper layer, but this is the worst option, since such a wire is very brittle, brittle and difficult to solder and tinning. For example, such wires can be seen in inexpensive Chinese-made New Year's garlands.

Flexibility class

This indicator directly depends on the type of material, the number of wires in the core and their thickness. According to the state standard there is such a classification of wires according to the degree of flexibility:

• 1 - this class includes wires with a monolithic single-wire core or consisting of several wires of a rather large cross section and determines such resistance to bending, taking into account material of manufacture: copper wire is able to withstand 50 bends, aluminum - only 20, after which the deformation can no longer be restored, the wire breaks and can only be soldered. The first class is the most rigid wires, they are used in stationary structures with a minimum number of bends.
• Class 2 includes stranded copper and aluminum wires of the PV-2 brand, containing from 7 to 91 wires with a cross section of 0.5 mm². These options are already more flexible than the previous class.
• The third class no longer includes aluminum wires due to the deformation instability of this metal in comparison with copper. This category includes stranded wires of the PV-3 brand.
• The fourth class includes cables of the KG brand, consisting of several stranded conductors.
• Flexible wires of the fifth class have the PVA brand and consist of many very thin copper wires. These are very high quality products that can withstand up to 1 thousand. bending cycles.
• Highly flexible cables of the 6th class - the KOG brand - also contain thin conductive wires, united in cores, but their number is even greater than in the fifth class wires, which ensures the superflexibility of these cables.

When planning the use of a wire in a particular area, you should first of all pay attention to flexibility, so that the product does not fail shortly after installation.

Insulation layer composition

Wire insulation consists of a dielectric material that protects a person from electric shock, as well as prevents mechanical or other damage to the wire. Depending on the purpose, there are various modifications of the insulating material with a wide variety of characteristics and properties. High quality insulators should be as flexible as the inner core and have good strength values. The following materials are considered the most common on the market:

• Polyvinyl chloride (PVC). The advantages of this type of insulator include a wide low-temperature range, in which it retains all its performance characteristics, as well as a high elasticity, which allows it to be used in the most inaccessible places, and resistance to any environmental influences, including acids, moisture and mechanical deformation. However, it also has disadvantages - at high temperatures it loses some of its qualities, it can become brittle, and ultraviolet light generally accelerates the decomposition of polyvinyl chloride.
• Cross-linked polyethylene (XLPE) can differ in different levels of density, but at the same time it is equally resistant to negative external influences. There is a vulcanized form and a regular one. The first tolerates the effects of various critical temperatures, but the second reacts unstably to heat, which makes it unsuitable for use in high temperature conditions.
• Rubber insulation is characterized by a combined composition - it contains both natural components and elements of synthetic origin. This variety is prized for its high level of flexibility, which, however, decreases over time, which can cause the insulating layer to crack. In addition, this type of insulator does not have sufficient resistance to high temperatures and only withstands up to 65 degrees.
• PTFE insulation has unique properties - this insulating coating is considered to be very strong, resistant to absolutely any aggressive environmental influences and practically immune to mechanical damage. However, fluoroplastic is suitable exclusively for cores with a low flexibility class, since its strength does not allow for elasticity. The installation of such wires requires a professional approach and careful design.
• An insulator made of paper impregnated with a dielectric composition is nowadays used less and less - it is successfully replaced by more modern analogues. Oil, wax and rosin are used for impregnation; sulfate cellulose is taken as a base. This insulation is used only as one of the insulating layers of power cables. As an independent winding, a paper dielectric is not used, since it is completely unstable to external influences.

In each specific case of mounting the wiring, several options may be suitable at once, however, one should also make a start from the total cross-section of the wire.

Sectional features

One of the most important performance characteristics of any wire and cable is the cross-sectional area. This value directly depends on what load can be applied to the product without reducing the quality of the latter.

To calculate the total load, you can use the passport data of the devices that are supposed to be connected in a particular room. The current strength is calculated by the formula I = P / 220, where P is the total power of electrical appliances. The permissible load on a copper wire is 10 amperes per square millimeter, on an aluminum one - no more than 8 amperes.

If wiring is mounted hidden in a wall or a special tube, then these values ​​should be multiplied by 0.8, which will be a correction. But in general - there are special tables for different situations, where the details of the data are indicated with greater accuracy for each specific purpose of wires and cables.

Disadvantages and advantages of various types

It is impossible to say unequivocally which cable is better - single-core or multi-core, because both of them fulfill their functions and are successfully used in different situations. It all depends on the project, the technical characteristics of the given wire and the expected load on the wiring.

More detailed differences can be seen in the table below:

Stranded wire	Solid wire
Differences in characteristics and scope of application follow from the structural features:
Flexibility class: 3-6	1 and 2, depending on the cross-sectional area and material of manufacture of the cores.
Purpose: Temporary flexible connections	Stationary wiring.
Service life: less than 5 years	More than 30 years.
Convenience of installation: high flexibility allows you to lay the wire anywhere with any plane deformations - bends, twists, and so on.	Difficult installation due to low flexibility.
High price.	Lower price, more economical option.

Thus, we can conclude that the advantages of each type of wire are revealed only in their area of ​​application. For example, for movable joints of portable electrical appliances - kettles, irons and other "room" technicians, it would be better to use a more elastic wire with a stranded core and flexible insulation.

When laying a power cable for stationary use, you can, of course, also use stranded wire - it is more flexible, easy to install, however, based on its service life, this unprofitable. Otherwise, you will have to change the wiring after five years. Therefore, in such cases, it is better to use a mono-core.

Why is the service life of a stranded wire so short even in benign conditions? The fact is that small wires are oxidized in the process of repeated passage of current, which leads to a decrease in the working section of the current-carrying core. If you continue to apply the same load to such a wire, it will eventually fail and burn out. A single-core cable does not differ in this oxidation state, therefore it lasts much longer.

So, summarizing the information provided, you can give specific examples of use so that the question does not arise which is better - a stranded wire or a single-core wire.

Stranded conductor is used in the following situations:

• Laying wires in pipes and special cable ducts (as well as in industrial and private buildings) for temporary use, especially if the wiring has to overcome a large number of bends and deformations in the process installation. For these purposes, wires of such brands are used more often than others - PVS, ShVVP, PuGV.
• Connecting household appliances and any mobile electrical devices, as well as chandeliers, extension cords and non-stationary devices (Cable KG, Wires MGSHV, VVP, PVS).
• Wiring in the car and connecting audio systems - brands with increased resistance to vibration are best suited for this: PGVA, KRPT, PTL200, PuGV.
• Cables for connecting a telephone and the Internet, as well as alarms and external television antennas - UTP, FTP, PKSV, KSPV, TPPEP, TRP.

As for the use of solid wires, the scope of their use is limited to laying in concrete walls (brands VVG, NYM, PuV, AVVG), as well as in mines, tunnels and pipes (armored cables AVBbShv, ASB, SKl), in electric transport (MF, MK, NLF) and inside liquid concrete to accelerate its solidification by heating (PNSV, APV).

Therefore, for wiring equipment in an ordinary house or apartment, it is necessary to use rigid solid wires, the most popular brands of this type are VVG, VVGng, VVGng-LS and NYM. And in movable temporary connections, extension cords and home appliances, you will need to use a wire with stranded conductors, as well as cables of the same type - PVA and ShVVP.