# Selection of the cross-section of wires and cables.

Electrical wiring must meet the requirements of safety, reliability and economy. Therefore, it is important to correctly calculate the length and cross-section of wires necessary for the installation of electrical wiring.

The length of the wire is calculated according to the wiring diagram. For this purpose, the distances between adjacent locations of flaps, plug sockets, switches, junction boxes, etc. are measured on the circuit. Then, using the scale in which the circuit is drawn, calculate the length of the wire segments; To the length of each segment add at least 100 mm (take into account the need to connect the wires). The length of the wire can also be calculated by measuring straight lines on the flaps, panels, walls, ceilings, etc., of the lines along which wires should be laid.

Wire cross-section is calculated by loss of voltage and permissible long-time current load. If the calculated cross sections are not the same, the larger result is taken as the final result. The voltage loss is caused by the voltage drop in the wires connecting the current source to the electric receiver. It should not exceed 2-5% of the rated voltage of the power supply. The cross-section of wires for loss of voltage is calculated in the design of electrical networks from which electric receivers of industrial enterprises, transport, large residential and public buildings, etc., are fed, etc. When designing small electrical installations, for example electrical installations of individual rooms, homemade devices, etc., In the wires can be neglected, since it is very small.

To calculate the cross-section of wires according to the permissible long-time current load, it is necessary to know the rated current that must pass through the designed electrical wiring. Knowing the rated current, the wire cross section is found by the table:

 Conductor cross-section, mm square. Current, for wires and cables with copper cores, A Current, for wires and cables with aluminum conductors, A One- Two-wire Three-wire One- Two-wire Three-wire When laying air air Earth air Earth air air Earth air Earth 1.5 23 19 33 19 27th - - - - - 2.5 thirty 27th 44 25 38 23 21 34 19 29 4 41 38 55 35 49 31 29 42 27th 38 6th 50 50 70 42 60 38 38 55 32 46 10 80 70 105 55 90 60 55 80 42 70 16 100 90 135 75 115 75 70 105 60 90 25 140 115 175 95 150 105 90 135 75 115 35 170 140 210 120 180 130 105 160 90 140 50 215 175 265 145 225 165 135 205 110 175 70 270 215 320 180 275 210 165 245 140 210 95 325 260 385 220 330 250 200 295 170 255 120 385 300 445 260 385 295 230 340 200 295 150 440 350 505 305 435 340 270 390 235 335 185 510 405 570 350 500 390 310 440 270 385 240 605 - - - - 465 - - - -

Example: the rated current is 50 A; The cross-section of the copper core must be 6 mm square. The rated current and permissible continuous current loads indicated in the table may not coincide in magnitude. In this case, the cross section is determined by the closest higher rated current to the permissible continuous current load.

Example: the wires should pass a rated current of 74 A; The nearest large permissible continuous current load of 80, 75 A (see Table); Therefore, a wire with a cross section of 10-16 mm square is required. (Depending on the method of laying), if its veins are copper, or a section of 10-25 mm square. (Depending on the method of laying), if the veins are aluminum.

If the rated current is not known in advance, then it can be determined by means of calculations of the circuit breakers indicated on the page.