Electric communication cable is a cable which contains one or more isolated electric circuit in the sheath. Depending on laying conditions and usage environment it can have a special protective covering above.
Electric cables are classified by the areas of application, transmission frequency spectrum, laying and usage conditions.
According to the areas of use cables are divided into trunk cables, areal or intraregional cables, local cables (town and country), office cables, structure (intrafacility) cable systems.
Depending on transmission frequency spectrum cables are classified as low-frequency (up to 10 KHz) and high-frequency (more than 10 KHz).
Because of laying conditions and usage areas, there exist buried cables (placed in ductbank), cables for stringing on airline holdups, underwater cables, station cables, cables for in-house phone networks and structure systems.
Сircuits of electric cables can be symmetrical or coaxial – it depends on construction and relative positions of electrical conductors.
Symmetry circuit (symmetrical pair) consists of two insulated conductors with similar structural and electric properties.
Coaxial circuit (pair) has an inner conductor which concentrically placed in outer conductor that has a shape of cored cylinder. Inner conductor insulated from outer with different layers (washers, balloon, insulating cord, continuous layer).
For easy of classification and using electric communication cables assigned with alphanumeric name – cable mark, which allows to recognize the structure and appropriation. Different countries have different marks, though each holds the same principle: every letter of cable mark means a structural member and they ordered in the “from in to out” way.
For example, in Russia the very first group of letters shows the field of use: trunk cable, areal cable, intra-areal cable, low-frequency phone cable.
The second place filled with letter that means low-frequency station cable type: inside or distribution.
As a rule, cables have pair twisting threads. But it doesn’t mentioned in the marking.
Next one shows the type of insulation: cord-polystyrene, polyethylene. If there are no letter, it means paper insulation.
Another letter refers to the sheath material. Absence means lead covering.
The very last gives an information about the cable protection.
Group of figures means cable capacitance and its diameter of threads.
Here were given the main well-established marks that widely used in Russian cable industry, though nowadays new marks that means manufacturing enterprise and other distinctive features are being added.