Our civilization can no longer be imagined without electricity. The only reliable means of delivering electricity to any appliance or power plant is a cable. Copper and aluminum are excellent current conductors that suffer little from corrosion, but copper wire is more flexible and easy to work with, so professional electricians prefer to use copper cables. We will talk about what it is, how they differ from each other and where they are applied, below.
Cable: types and scopes.
One or more conductors (cores), having personal insulation and assembled in a common sealed sheath, is called a cable. Both the inner sheath of each core and the overall sheath can be made of various materials: rubber, PVC, aluminum or lead. If the operating conditions provide for the possibility of external influences, then the upper shell can be additionally armored with a steel coating.
A cable with one core is called single-core and has a rather limited scope. Stranded (2, 3, 4 cores) copper flexible cable is much more popular. Each of them has its own advantages and disadvantages, they differ in degree of flexibility, section, weight and price. The cross section of the cable corresponds to the strength of the current that it can pass.
A solid (single-core) copper cable (wire) is used in a situation where it will be motionless after installation. For example, in electric motors or internal wiring. If you need to power equipment with a large range of motion (for example, a gantry crane), if the wiring device requires a large number of bends, then it is best to use a flexible stranded copper cable, since it is softer. This is especially true for wires with a large cross-section of cores. As a rule, pure or tinned copper wire is used for the manufacture of flexible cables. It all depends on the required flexibility parameters so that the cable does not break when bent (flexibility class must be at least 5th).
The lower price segment is occupied by single-core wires without protection. The more lived in the cable and the stronger its protection (booking), the more expensive the cable. The weight also depends on the number of cores (from 1 to 37 with sections from 0.75 to 800 mm 2) and the braid. The cost of copper single-core cables is 3-4 times higher than aluminum ones.
There are classes of flexible copper cables and the specifics of use. For example, power has found its application in the creation of cable lines for the transmission and distribution of electricity in power electrical installations, lighting networks, as wiring in residential and industrial buildings. It is characterized by the presence of several cores of the same cross section, with the exception of the ground wire, which may have a smaller cross section. Copper multi-core cable must have stable mechanical, electrical and thermal characteristics, since the operating parameters of the power cable must remain unchanged when working under any conditions. Conventionally, they are divided into low voltage (up to 1 kV) and high voltage (up to 30 kV) cables, they have different external insulation materials (PVC, halogen-free, cross-linked polyethylene), differ in the presence of a screen, the type of cores, the nature of their twisting.
Copper cables come in different types:
- Control flexible cables are widely used in electrical work, automated transportation systems, security systems and control automation.
- Flame-retardant and halogen-free cables meet the requirements for increased fire resistance and non-flammability to maintain performance in the event of a fire and for fire alarm systems.
- Control cables are highly flexible for use in robots, conveyors and conveyor belts.
- Cables for data transmission with signal protection against external interference.
- Cables for frequency converters and servo drives.
- Data cables for office equipment, recording studios, external communication lines, for medical equipment. They have design features (pairwise twisted conductors, additional screens).
- Special heat-resistant cables with a silicone sheath that can withstand temperatures up to 800 degrees (refrigeration or heating installations, steel industry, shipbuilding and aviation industries, cement, glass industries, saunas and solariums).
- Crane cables that are necessary to ensure the operation of lifting mechanisms (cranes, hoists, elevators). They are highly resistant to mechanical stress, withstand twisting and tensile forces, and have a chemically resistant shell.
And many more - all-weather rubber cable, flat, compensation, coaxial (radio frequency), video cable, installation, telephone, BUS cable, cables with connectors, for alternative energy and media technologies, spiral and ship cables.
Marking of copper multicore cables.
The marking, which has a flexible stranded copper cable, contains alphabetic and numeric values. To select the right product, you need to navigate these notations.
The material of the cores is usually indicated by the first letter (usually the letter A, which stands for aluminum). The copper core is not marked.
The second letter indicates the material of the cable sheath. The third means the insulating coating of the cores:
- B or BP - PVC coating,
- P - polyethylene,
- R - rubber,
- H - nairite (from non-combustible rubber),
- F - folded (metal),
- K - kapron,
- O - polyamide silk braid,
- C - fiberglass,
- E - shielded,
- G - with a flexible core.
If the rubber insulation is protected by an additional sheath, then the abbreviated name of the coating may appear after the designation of the insulating material.
The fourth letter designation describes the design features: B - armored with tapes, K - armored with round wire, T - for laying in a pipe.
The numbers in the marking indicate (in order): the number of cores, the cross-sectional area, the rated voltage of the network.
For hidden or fixed outdoor wiring, the most commonly used flat copper cable is 2 or 3-core with single insulation (PPV) or round (up to 5 cores) with double insulation (PVA). Cords for connecting any household appliances to a power source usually come with double-insulated stranded copper wires (SHVVP). It is possible to lay a round copper four-core cable in double insulation VVG in the ground, and VVG in water. It is the VVG brand that is most in demand among builders, since it can be used for the installation of networks with a load of 0.6 to 6 kV. No less popular is the KG type - a copper flexible cable with rubber insulation. Moreover, the rubber coating with special additives makes it possible to lay it even in permafrost. For routes that are pulled in the ground, tunnels or in an open way, the armored cable VBBSHV, which has double PVC insulation and a protective coating of a metal tape in two layers, remains the most popular.
Parameters for choosing a power cable KG.
A universal solution for the installation of a power supply system is the use of a KG power cable, the purpose of which is the transmission and distribution of direct (up to 1000 V) or alternating (up to 660V / 400Hz) voltage. Indispensable, unlike most brands of power cables, it turns out to be for connecting consumers in open areas, in conditions of high humidity, water. Therefore, when choosing a KG cable, studying the marking, in addition to the cross section of the conductive cores, it is necessary to take into account the flexibility parameters and additional characteristics for specific operating conditions. But the flexibility indicators of such a cable can be found in its certificate, for example, a cable with a core cross section of up to 4 mm 2 is able to withstand 30,000 bending cycles without loss of operating parameters.
To operate the cable in tropical heat, you should choose products with a sheath that can withstand the action of fungi and mold (additional letter T in the marking - tropical version). For laying at low temperatures, there must be a KhL marking; with increased requirements for chemical resistance, resistance to oils and solvents, for fire safety, it is necessary to use the KG-N cable.
When purchasing such a cable, one should also take into account external loads. A 3-core cable with a cross section of 4 mm 2 can withstand a maximum tensile load of not more than 24 kgf.
An example of calculating a cable for home wiring.
The choice of cross-section of the power supply cable for internal wiring must be approached quite seriously. Before you buy a cable, you should determine the total load on it and the cross section of the wires that can transport such an amount of current. Safety depends on this, since the wrong choice can lead, at best, to overheating, and at worst, to insulation failure, short circuit or even fire. This can happen if a cable with a smaller gauge than necessary is selected for the wiring device.
The main indicator for the calculation is the total current load or, more simply, the amount of current that can be freely passed by the cable during long-term operation of all consumption points.
The number of electrical appliances that we operate daily is different for everyone. But each of them consumes a certain amount of current, which can be found in their passports. Adding all the indicators, we get the total power consumption in kW. You can determine the required current strength either using the tables, or by the formula (school physics course).
For example, in the morning the electric kettle, microwave oven, toaster and coffee maker were turned on at the same time. The total current consumption will be about 22 A. Taking into account the fact that other permanent consumers are also working: a TV or computer, a refrigerator and lighting, the consumption can increase to 25 A.
The electrical installation rules officially regulate the parameters of standard apartment wiring, which is calculated for a maximum current consumption of 25 A (automatic plugs on the input panel are designed for these values). Wiring is recommended to be carried out with a copper cable with a cross section of 5 mm 2 (corresponding to a cable diameter of 2.5 mm). In this case, the cross section of the core should not be less than 2.5 mm 2 (conductor diameter - 1.8 mm). For sockets, it is optimal to use a copper cable with a core cross section of 2.5 mm 2, for switches - 1.5 mm 2. If there are additional energy-consuming devices (electric stove or electric oven), a cable with a cross section of at least 4-6 mm 2 is connected to them.
This choice of cross-section of a copper stranded cable is very popular and common among electricians, since it is known that a copper cable with a cross section of 1.5 mm 2 is able to "withstand" a load of more than 4 kW (19 A), 2.5 mm 2 - 5.9 kW ( 27 A), 4 and 6 mm 2 - over 8 and 10 kW. This is quite enough to turn on the necessary electrical appliances, and in some cases even creates a certain reserve.