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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 conductor wire should 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.