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Selection of wire and cable sections.

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

The length of the wire is calculated according to the wiring diagram. To do this, the diagram measures the distances between adjacent locations of shields, receptacles, switches, junction boxes, etc. Then, using the scale in which the circuit is drawn, calculate the length of the wires; 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 panels, panels, walls, ceilings, etc., the segments of the lines along which the wires are to be laid.

The wire cross section is calculated from the voltage loss and the permissible continuous current load. If the calculated sections are not identical, then the final result is taken as the magnitude of the larger utterance. The voltage loss is due to the voltage drop in the wires connecting the current source to the receiver. It should not exceed 2-5% of the rated voltage of the power supply. The wire cross section for voltage loss is calculated in the design of electrical networks that feed electrical receivers of industrial enterprises, transport, large residential and public buildings, etc. When designing small electrical installations, such as electrical installations of individual premises, homemade appliances, etc., voltage loss in wires can be neglected, since it is very small.

To calculate the cross-section of wires for a permissible long-term 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 from the table:

The cross section of the conductor, mm square.

Current, for wires and cables with copper conductors, A

Current, for wires and cables with aluminum conductors, A

Single

Two-core

Three-core

Single

Two-core

Three-core

When laying

air

air

land

air

land

air

air

land

air

land

1.5

23

nineteen

33

nineteen

27

-

-

-

-

-

2.5

thirty

27

44

25

38

23

21

34

nineteen

29

four

41

38

55

35

49

31

29

42

27

38

6

50

50

70

42

60

38

38

55

32

46

ten

80

70

105

55

90

60

55

80

42

70

sixteen

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: rated current is 50 a; the cross section of the copper conductor of the wire should be 6 mm square. The rated current and permissible continuous current loads shown in the table may not be the same in magnitude. In this case, the cross section is found at the nearest higher rated current permissible continuous current load.

Example: a wire must pass a rated current of 74 A; the closest largest permissible long-term current load of 80, 75 A (see table); This means that a wire with a cross section of 10 - 16 mm square is required. (depending on the method of installation), if its copper conductors, or a section of 10-25 mm square. (depending on the method of installation), if the conductors are aluminum.

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