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The choice of cross-section of wires and cables.

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

The length of the wire is calculated according to the wiring diagram. To do this, measure the distance between adjacent locations of the shields, plug sockets, switches, junction boxes, etc. on the circuit. Then, using the scale at which the circuit is drawn, calculate the length of the wire segments; at least 100 mm is added to the length of each segment (the need to connect wires is taken into account). The length of the wire can also be calculated by measuring directly on the shields, panels, walls, ceilings, etc. line segments along which the wires should be laid.

The cross section of the wire is calculated by the loss of voltage and the permissible continuous current load. If the calculated cross sections turn out to be unequal, then the value of the larger speech is taken as the final result. The voltage loss is due to a voltage drop in the wires connecting the current source to the power receiver. It should not exceed 2-5% of the rated voltage of the power source. The cross-section of wires for voltage loss is calculated when designing electrical networks from which power consumers of industrial enterprises, vehicles, large residential and public buildings, etc. are fed. When designing small electrical installations, such as electrical installations of individual rooms, home-made appliances, etc., voltage loss the wires can be neglected, since it is very small.

To calculate the cross-section of wires for permissible continuous 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 in the table:

Conductor cross section, mm sq.

Current, for wires and cables with copper conductors, A

Current, for wires and cables with aluminum conductors, A

One-

Two-core

Three-core

One-

Two-core

Three-core

When laying

air

air

Earth

air

Earth

air

air

Earth

air

Earth

1,5

23

19

33

19

27

-

-

-

-

-

2.5

thirty

27

44

25

38

23

21

34

19

29th

four

41

38

55

35

49

31

29th

42

27

38

6

fifty

fifty

70

42

60

38

38

55

32

46

10

80

70

105

55

90

60

55

80

42

70

16

one hundred

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

fifty

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: rated current is 50 A; the cross section of the copper core of the wire should be 6 mm square. The rated current and the permissible continuous current loads indicated in the table may not coincide in value. In this case, the cross section is found by the nearest higher rated current to the permissible continuous current load.

Example: a rated current of 74 A must pass through the wires; the closest largest largest 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 laying method), if its conductors are copper, or with a cross section of 10-25 mm square. (depending on the laying method), if aluminum conductors.

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