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.

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