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Select sections of wires and cables.
Electrical wiring must conform to the requirements of safety, reliability and efficiency. It is therefore important to calculate the length and cross section required for the installation of electrical wiring cables.
провода рассчитывают по монтажной схеме. The length of the wire is calculated by the circuit board. For this scheme to measure the distance between the locations adjacent shields, electrical outlets, switches, tap-off boxes, etc. Then, using a scale in which the plotted diagram, calculate the length of the wire segments, the length of each segment is added at least 100 mm (case the need for connection cables). The length of the wire can be calculated also by measuring directly on the panel, panels, walls, ceilings, etc. segments of lines along which the wires should be routed.
провода рассчитывают по потере напряжения и допустимой длительной токовой нагрузке. Conductor cross section is calculated by the loss of voltage and current long-term allowable stress. If the calculated cross section will vary, the final result for the value of taking a larger utterance. The loss of voltage due to voltage drop in the wires that connect the current source with a power-consuming equipment. It should not exceed 2-5% of the rated voltage of the power supply. Cross-section for the voltage loss is calculated in the design of electrical networks, which are fed from the power-consuming equipment of industrial enterprises, transport, large residential and public buildings, etc. When designing small electrical installations, electrical installations such as separate facilities, home-made devices, etc., the loss of voltage in the wires can be neglected, since it is very small.
To calculate the cross wires on the permissible duration of the current load is necessary to know the rated current, which must pass through the projected electrical wiring. Knowing the rated current, the wire cross section are on the table:
Cross section of conductor, sq mm. | The current for wires and cables with copper conductors, A | The current for wires and cables with aluminum conductors, A | ||||||||
One- | Two- | Three-core | One- | Two- | Three-core | |||||
When laying | ||||||||||
air | air | land | air | land | air | air | land | air | land | |
1.5 | 23 | 19 | 33 |
19 | 27 | - | - | - | - | - |
2.5 | 30 | 27 | 44 | 25 | 38 | 23 | 21 | 34 | 19 | 29 |
4 | 41 | 38 | 55 | 35 | 49 | 31 |
29 | 42 | 27 | 38 |
6 | 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, a section of copper conductor cables shall be 6 mm square. Rated current and valid long-term current loads specified in the table may not match in size. In this case the cross section is found by the next higher rated current allowable continuous current load.
Example: the wire must pass the rated current of 74 A, the nearest big-largest long-term permissible current load 80, 75 A (see table)., Then you want the wire cross section of 10 - 16 mm square. (Depending on the method of installation), if the conductor of brass, or a section of 10-25 mm square. (Depending on the method of installation), if the aluminum conductor.
If the rated current is not known beforehand, it can be determined by these calculations on a page of circuit breakers.
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