When repairing and designing electrical equipment there is a need to choose the right wires. You can use a special calculator or directory. But for this you need to know the parameters of the load and the features of the cable laying.

What is the calculation of the cable cross section

The following requirements are presented to electrical networks:

• safety;
• reliability;
• efficiency.

If the selected cross-sectional area of \u200b\u200bthe wire is small, then the current loads on cables and wires will be large, which will lead to overheating. As a result, an emergency situation may arise, which will harm all electrical equipment and will be dangerous to the life and health of people.

If the wires are mounted with a large cross-sectional area, then safe use is provided. But from a financial point of view will be the costs of funds. Right choice wire section is a pledge of long-term safe operation and rational use Financial means.

The cable cross section is calculated in power and current. Consider at the examples. To determine which wire section is needed for 5 kW, you will need to use PUE tables ("rules of the electrical installation device"). This reference book is a regulatory document. It indicates that the selection of the cable cross section is made in 4 criteria:

1. Power supply (single-phase or three-phase).
2. Explorer material.
3. Load current measured in amperes (A), or power - in kilowatts (kW).
4. Location of cable.

There is no value of 5 kW in PUE, so you have to choose the next greater value - 5.5 kW. For mounting in the apartment today it is necessary to use a wire of copper. In most cases, the installation occurs through the air, therefore a section of 2.5 mm² is suitable from reference tables. At the same time, the highest permissible current load will be 25 A.

The above reference is also regulated by the current to which the introductory automatic (VA) is calculated. According to the "Rules of the Electrical Installation Device", with a load of 5.5 kW of the current of the BA should be 25 A. The document states that the rated current of the wire that comes to the house or apartment should be an order of magnitude more than that of WA. In this case, after 25 A, there are 35 A. The latter value and must be taken for the calculated one. The current 35 A corresponds to a cross section of 4 mm² and a power of 7.7 kW. So, the selection of the cross-section of the copper wire is completed: 4 mm².

To find out what a wire section is needed for 10 kW, we will use the directory again. If we consider the case for open wiring, then you need to decide on the cable material and with the feed voltage. For example, for aluminum wire and voltage 220 in the nearest high power will be 13 kW, the corresponding cross section is 10 mm²; For 380 in power will be 12 kW, and the cross section is 4 mm².

We choose the power

Before choosing a cable cross section for power, it is necessary to calculate its total value, to make a list of electrical appliances located in the territory to which the cable is paved. Each of the devices should be indicated power, the corresponding units of measurement will be written near it: W or kW (1 kW \u003d 1000 W). Then it will be necessary to fold the power of all equipment and it will turn out to be the total.

If the cable is selected for connecting one device, then enough information is only about its power consumption. You can choose the cross section of the wire in power in the PUE tables.

Table 1. Selection of the cable cross section for cable with copper cores

	For cable with copper veins
	Voltage 220 B.		Voltage 380 B.
	Talk, A.	power, kWt	Talk, A.	power, kWt
1,5	19	4,1	16	10,5
2,5	27	5,9	25	16,5
4	38	8,3	30	19,8
6	46	10,1	40	26,4
10	70	15,4	50	33
16	85	18,7	75	49,5
25	115	25,3	90	59,4
35	135	29,7	115	75.9
50	175	38.5	145	95,7
70	215	47,3	180	118,8
95	260	57,2	220	145,2
120	300	66	260	171,6

Table 2. Selection of cable cross-section for cable with aluminum veins

Conductive vein section, mm²	For cable with aluminum veins
	Voltage 220 B.		Voltage 380 B.
	Talk, A.	power, kWt	Talk, A.	power, kWt
2,5	20	4,4	19	12,5
4	28	6,1	23	15,1
6	36	7,9	30	19,8
10	50	11,0	39	25,7
16	60	13,2	55	36,3
25	85	18,7	70	46,2
35	100	22,0	85	56,1
50	135	29,7	110	72,6
70	165	36,3	140	92,4
95	200	44,0	170	112,2
120	230	50,6	200	132,2

In addition, it is necessary to know the network voltage: three-phase corresponds to 380 V, and single-phase - 220 V.

In PUE, information is given for aluminum, and for copper wires. Both have their advantages and disadvantages. The advantages of copper wires:

• high strength;
• elasticity;
• oxidation resistance;
• the electrical conductivity is greater than that of aluminum.

Lack of copper conductors - high cost. In Soviet homes, it was used with the construction of aluminum wiring. Therefore, if a partial replacement occurs, it is advisable to put aluminum wires. The exception is only those cases when it is installed new instead of the entire old wiring (before the distribution shield). Then it makes sense to apply copper. It is unacceptable that copper with aluminum in contact directly, since it leads to oxidation. Therefore, the third metal is used for their compound.

You can independently calculate the cross section of the wire for the power for the three-phase chain. To do this, use the formula: i \u003d p / (u * 1.73), where P is power, W; U - voltage, in; I - current, A. Then from the reference table selected the cable cross section depending on the calculated current. If there is no reasonable value, then the nearest, which exceeds the calculated one is selected.

How to calculate

The value of the current passing through the conductor depends on the length, width, resistivity of the latter and on temperature. When heated, the electric current decreases. reference Information indicated for room temperature (18 ° C). To select a cable cross section using PUE tables.

Table3. Electric current for copper wires and cords with rubber and PVC insulation

Square Conductor cross section, mm²
	open	in one trumpet
		two single-cores	three single-cores	four single-cores	one two-tier	one triple
0,5	11	-	-	-	-	-
0,75	15	-	-	-	-	-
1	17	16	15	14	15	14
1,2	20	18	16	15	16	14,5
1,5	23	19	17	16	18	15
2	26	24	22	20	23	19
2,5	30	27	25	25	25	21
3	34	32	28	26	28	24
4	41	38	35	30	32	27
5	46	42	39	34	37	31
6	50	46	42	40	40	34
8	62	54	51	46	48	43
10	80	70	60	50	55	50
16	100	85	80	75	80	70
25	140	115	100	90	100	85
35	170	135	125	115	125	100
50	215	185	170	150	160	135
70	270	225	210	185	195	175
95	330	275	255	225	245	215
120	385	315	290	260	295	250
150	440	360	330	-	-	-
185	510	-	-	-	-	-
240	605	-	-	-	-	-
300	695	-	-	-	-	-
400	830	-	-	-	-	-

To calculate aluminum wires apply a table.

Table4. Electric current for aluminum wires and cords with rubber and PVC insulation

Explorer cross section, mm²	Current, and, for wires, laid
	open	in one trumpet
		two single-cores	three single-cores	four single-cores	one two-tier	one triple
2	21	19	18	15	17	14
2,5	24	20	19	19	19	16
3	27	24	22	21	22	18
4	32	28	28	23	25	21
5	36	32	30	27	28	24
6	39	36	32	30	31	26
8	46	43	40	37	38	32
10	60	50	47	39	42	38
16	75	60	60	55	60	55
25	105	85	80	70	75	65
35	130	100	95	85	95	75
50	165	140	130	120	125	105
70	210	175	165	140	150	135
95	255	215	200	175	190	165
120	295	245	220	200	230	190
150	340	275	255	-	-	-
185	390	-	-	-	-	-
240	465	-	-	-	-	-
300	535	-	-	-	-	-
400	645	-	-	-	-	-

Besides electric currentYou will need to choose the material of the conductor and the voltage.

To approximately calculate the cable cross section, it is necessary to divide by 10. If the table is not obtained, then it is necessary to take the nearest greater value. This rule is suitable only for those cases where the maximum allowable current for copper wires does not exceed 40 A. for the range from 40 to 80 and the current must be divided into 8. If aluminum cables are installed, then it is necessary to divide on 6. This is explained by the fact that for Provide identical loads The thickness of the aluminum conductor is greater than copper.

Calculation of the cable cross section for power and length

The length of the cable affects the loss of voltage. Thus, at the end of the conductor, the voltage can decrease and turn out to be insufficient for the operation of the electrical appliance. For household power grids, these losses can be neglected. It will be enough to take a 10-15 cm cable longer. This stock is spent on switching and connecting. If the ends of the wire are connected to the shield, the spare length must be even more, since the protective automata will be connected.

When laying a cable over long distances, have to take into account the voltage drop. Each conductor is characterized by electrical resistance. This parameter affects:

1. The length of the wire, the unit of measurement - m. When it increases, losses are growing.
2. The cross-sectional area is measured in mm². When it is increased, the voltage drop decreases.
3. Specific resistivity (reference value). Shows the resistance of the wire, the dimensions of which 1 square millimeter per 1 meter.

The voltage drop is numerically equal to the product of resistance and current. It is permissible that the specified value does not exceed 5%. Otherwise, you must take a larger cable. Algorithm for calculating the cross section of the wire at maximum power and length:

1. Depending on the power P, the voltage U and the coefficient COSF we find the current according to the formula: I \u003d P / (U * COSF). For power grids, which are used in everyday life, COSF \u003d 1. In industry, COSF is calculated as the ratio of active power to full. The latter consists of active and reactive capacity.
2. Using the PUE tables, determine the cross-section of the current wire.
3. We calculate the resistance of the conductor by the formula: RO \u003d ρ * L / S, where ρ is the specific resistance of the material, L is the length of the conductor, S is the cross-sectional area. It is necessary to take into account the current fact that the current goes on the cable not only in one direction, but also back. Therefore, the overall resistance: R \u003d RO * 2.
4. We find the voltage drop from the ratio: ΔU \u003d i * r.
5. Determine the voltage drop in percent: ΔU / U. If the resulting value exceeds 5%, then select the immediate cross-section of the conductor from the reference book.

Open and closed wire laying

Depending on the placement, the wiring is divided into 2 types:

• closed;
• open.

Today in the apartments hidden wiring. In the walls and ceilings are created special recesses intended for placing the cable. After installing the conductors of the recess plaster. Copper is used as wires. Everything is planned in advance, since with time to build electrical wiring or replace items you will have to dismantle the finish. For hidden finishes, wires and cables that have a flat form are used more often.

With open laying, the wires are installed along the surface of the room. Benefits give flexible conductors who have a round form. They are easy to install in cable channels and skip through the corrugation. When the load on the cable is calculated, then the method of laying the wiring is taken into account.

In the process of repair, they usually always replace the old wiring. This is due to the fact that many useful household appliances have recently appeared, which facilitate the life of housewives. Moreover, they consume quite a few energy, which is old wiring, just may not stand. To such electrical appliances include washing machines, electric ovens, electric kettle, microwaves, etc.

Locking the electric pipe, you should know what section the wire should be paved to power the electrical appliance or group of electrical appliances. As a rule, the choice is carried out both by power consumption and the strength of the current, which consume electrical appliances. At the same time, it is necessary to take into account how the laying method and the length of the wire.

It is quite simple to select the secting of the cable paved for load power. This may be one load or totality of loads.

Each household appliance, the more new, is accompanied by a document (passport), where its main technical data is indicated. In addition, the same data is available on special signs attached to the body of the product. On this plate, which is located on the side or back of the device, is indicated by the country of manufacturer, its factory number and, of course, its power consumption in wats (W) and current that consumes the device in amperes (A). On products of the domestic producer, power may be indicated in watts (W) or kilowatts (kW). In import models there is a letter W. In addition, the power consumption is indicated as "that" or "that max".

An example of such a sign, where the main information on the device is indicated. Such a sign can be found on any technical device.

In the event that you cannot recognize the desired information (the inscription fell on the plate or household appliances no yet) you can find out about what power have the most common appliances. All this data is actually found in the table. Basically, the electrical appliances are standardized by power consumed and there is no special data scatter.

The table selects those electrical appliances that are planned to be purchased and their consumed current and power are recorded. From the list it is better to choose indicators that have maximum values. In this case, it will not be possible to calculate and wiring will be more reliable. The fact is that the thicker the cable, the better because the wiring is warm much less.

How to choose from

When the wire is selected, all loads should be summed up to this wire. At the same time, it should be monitored so that all the indicators are discharged or in watts, or kilowatts. To translate the indicators to one value, the numbers are followed or divided, or multiply by 1000. For example, to translate into watts, all numbers follow (if they are in kilowatts) to multiply by 1000: 1.5 kW \u003d 1.5x1000 \u003d 1500 W. When reverse rendering actions are made in reverse order: 1500 W \u003d 1500/1000 \u003d 1.5 kW. Usually, all calculations are made in wats. After such calculations, the cable is selected by using the corresponding table.

You can use the table as follows: Find the corresponding column, where the supply voltage is indicated (220 or 380 volts). In this column there is a digit that corresponds to the power of consumption (you need to take a little greater value). In the line that corresponds to the power consumption, the first column shows the cross section of the wire that is allowed to be used. Going to the store for the cable, you should search for the wire, the cross section of which corresponds to the records.

What wire is to use - aluminum or copper?

In this case, it all depends on power consumption. In addition, the copper wire withstands the load twice as much as aluminum. If the load is large, it is better to give preference to the copper wire, as it will be thinner and easier to lay it. In addition, it is easier to connect it to electrical equipment, including to sockets, and to switches. Unfortunately, the copper wire has a significant minus: it is much more expensive than the wire from aluminum. Despite this, he will serve much longer.

How to calculate the current cable cross section

Most of the masters calculate the diameters of the current consumption. Sometimes it simplifies the task, especially if you know which current withstands a wire having one or another thickness. To do this, write all the indicators of the current consumed and summing up. The wire section can be chosen along the same table, only now you need to look for a column where the current is specified. As a rule, the greater value is always selected for reliability.

For example, to connect hobswhich can consume maximum current up to 16a, the copper wire is required. By contacting the table, the desired result can be found in the third column on the left. Since there is no value 16a, then choose the nearest, greater - 19a. By this current is suitable for the cable cross section, equal to 2.0 mm square.

As a rule, connecting powerful household appliances, they are powered by separate wires, with the installation of individual inclusion machines. This greatly simplifies the process of selection of wires. In addition, this is part modern demands To wiring. Plus, it is practical. In an emergency, you do not have to turn off the electricity completely, in the whole housing.

It is not recommended to choose wires along a smaller value. If the cable will constantly work at maximum loads, then this may lead to emergency situations in the electrical network. The result can be a fire if automatic switches are incorrectly selected. At the same time, you should know that they are not protected from the shell ignition, and it is not possible to choose exactly the current so that it can protect the wires from overload. The fact is that they are not regulated and manufactured on a fixed current value. For example, on 6a, on 10a, on 16a, etc.

The selection of the wire with a margin will allow you to further install another electrical appliance on this line or even a few if it will correspond to the current consumption rate.

Calculation of power cable and length

If you take into account the average apartment, then the length of the wires does not reach such values \u200b\u200bto take into account this factor. Despite this, there are cases when when choosing a wire should be taken into account and their length. For example, you need to connect a private house From the nearest pillar, which can be at a considerable distance from the house.

With significant consumption currents, the long wire can influence the quality of the power. This is associated with losses in the Wire itself. The more the length of the wire, the greater the loss in the wire itself. In other words, the more the length of the wire, the greater the voltage drops in this area will be. With regard to our time, when the quality of the power supply leaves much to be desired, such a factor plays a significant role.

To know this, you will have to refer to the table, where you can determine the cross section of the wire, depending on the distance to the power point.

Table of determining the thickness of the wire, depending on the power and distance.

Open and closed wire laying method

The current passing through the conductor causes it to heat up, as it has a certain resistance. So, the larger the current, the more heat on it it is distinguished, under conditions of the same cross section. With the same current consumption, heat is released on extensions of a smaller diameter greater than on conductors with a greater thickness.

Depending on the laying conditions, the amount of heat released on the conductor changes. When the gasket is open, when the wire is actively cooled with air, you can give preference to a thin wire, and when the wire is laid closed and cooling it minimized, it is better to choose thicker wires.

Such information can also be found in the table. The principle of choice is the same, but taking into account another factor.

And finally, the most important thing. The fact is that in our time the manufacturer is trying to save on everything, including on the material for wires. Very often, the claimed section does not respond true. If the seller does not inform the buyer, then it is better to measure the thickness of the wire, if it is critical. To do this, it is enough to take with me the caliper and measure the thickness of the wire in millimeters, after which it is to calculate its cross section along the simple formula 2 * pi * d or pi * r in the square. Where Pi is a constant number of equal to 3.14, and D is the diameter of the wire. In another formula, respectively, pi \u003d 3.14, and R in the square is a radius in a square. The radius is very simple, a diameter is enough to share for 2.

Some sellers directly indicate the inconsistency of the stated section and valid. If the wire is selected with a large margin - it is not at all significantly. The main problem is that the price of the wire, compared with its cross section, is not underestimated.

Calculation of the cable cross section (wires) is an equally important stage when designing an electrical scheme of an apartment or at home. The safety and stability of electricity consumers work depends on the correctness of the choice and quality of electrical installation. On the initial stage It is necessary to take into account such source data as the planned power of consumption, the length of the conductors and their type, the generation of the current, the installation method of the wiring. For clarity, consider the method of determining the section, main tables and formulas. Also, you can take advantage of a special calculation program presented at the end of the main material.

Calculation of the cross section

The optimal cross-section area allows you to skip the current without possible overheating of wires. Therefore, when designing an electrical wiring, first of all, the optimal cross-section of the wire is found depending on the power consumption. To calculate this value, calculate the total power of all devices that are planned to be connected. At the same time, consider the fact that not all consumers will connect simultaneously. Analyze this frequency to select the optimal diameter of the conductor's core (more in the following paragraph "Load Calculation").

Table: Approximate power of consumption of household electrical appliances.

Name	Power, W
Lighting	1800-3700
TVs	120-140
Radio and audio equipment	70-100
Refrigerators	165-300
Freezers	140
Washing machines	2000-2500
Jacuzzi	2000-2500
Vacuum cleaners	650-1400
ElectricUags	900-1700
Electrocuffs	1850-2000
Water Heated Dishwasher	2200-2500
Electro-confer	650-1000
Electromasuines.	1100
Juicer	200-300
Toasters	650-1050
Mixers	250-400
Electrophen	400-1600
microwaves	900-1300
Expanded filters	250
Fans	1000-2000
Grilled stoves	650-1350
Stationary electric stoves	8500-10500
Electric saunas	12000

For a home network with a voltage of 220 volts, the value of the current force (in amperes, A) is determined by the following formula:

I \u003d p / u,

where P is the electrical full load (presented in the table and, also, is indicated in the technical passport of the device), W (Watt);

U is the voltage of the electrical network (in this case 220), in (volt).

If the voltage in the network is 380 volts, then the calculation formula is as follows:

I \u003d p / √3 × u \u003d p / 1.73 × u,

where P is the total power consumption, W;

U - voltage in the network (380), V.

The permissible load at the copper cable is 10 A / mm², and in aluminum - 8 A / mm². To calculate, the resulting current value ( I.) To divide by 10 or 8 (depending on the selected conductor). The value obtained and will be the estimated size of the required section.

Load calculation

On the initial stage It is recommended to make a load correction. It was mentioned above, but still repeat that there are rarely situations in everyday life when all energy consumers turn on simultaneously. Most often alone devices work, while others are not. Therefore, to clarify the resulting section, multiplying the demand coefficient ( Ks.). If you are confident that you will exploit all the devices immediately, you do not need to use the specified coefficient.

Table: The demand ratio of various consumers (kC).

Influence of the length of the conductor

The length of the conductor is important in the construction of industrial networks, when the cable must be pulled at considerable distances. During the passage of current on the wires, power losses (DU) occur, which are calculated by the following formula:

where I is the current strength;

p is a resistivity (for copper - 0.0175, for aluminum - 0.0281);

L - cable length;

S is the calculated area of \u200b\u200bthe conductor cross section.

According to the technical conditions, the maximum value of the voltage drop in the wire length should not exceed 5%. If the fall is significantly, then you should pick up another cable. This can be done using tables, where the dependence of the power and current force from the section is already reflected.

Table: selection of wires at a voltage of 220 V.

Cross-section of veins wires, mm 2	Conductor core diameter, mm	Copper cores		Aluminum cores
		Talk, A.	Power, W	Talk, A.	power, kWt
0,50	0,80	6	1300
0,75	0,98	10	2200
1,00	1,13	14	3100
1,50	1,38	15	3300	10	2200
2,00	1,60	19	4200	14	3100
2,50	1,78	21	4600	16	3500
4,00	2,26	27	5900	21	4600
6,00	2,76	34	7500	26	5700
10,00	3,57	50	11000	38	8400
16,00	4,51	80	17600	55	12100
25,00	5,64	100	22000	65	14300

Example of calculation

Planning the wiring scheme in the apartment, you first need to determine the places where the sockets and lighting devices will be. It is necessary to determine which devices will be involved and where. Next can be made up general scheme Connections and calculate the cable length. Based on the data obtained, the size of the cable cross section is considered above the formulas above.

Suppose we need to determine the size of the cable to connect the washing machine. We take the power from the table - 2000 W and define the current strength:

I \u003d 2000 W / 220 V \u003d 9.09 A (rounded to 9 a). To increase the safety reserve, you can add a few amps and choose depending on the type of conductor and the laying method corresponding to the cross section. The considered example will suit a three-core cable with a cross section of copper veins from 1.5 mm².

Conducting Copper Conductor, mm²	Permissible long load current, and	Maximum power of single-phase load for voltage 220 V, kW	Rated current automatic protection, and	Limit of the current automatic protection, and	Possible consumes
1,5	19	4,1	10	16	lighting and Alarm Groups
2,5	27	5,9	16	25	outlet groups and electric floors
4	38	8,3	25	32	water heaters and air conditioning
6	46	10,1	32	40	electric stoves and brass cabinets
10	70	15,4	50	63	introduction supply lines

CABLE 2.1 calculation program

After reading the calculation methodology and special tables, for convenience, you can use this program. It will save you from independent computing and select the optimal cross section of the cable according to the specified parameters.

The Cable 2.1 program has two types of calculation:

1. Calculation of the cross section for a given power or current.
2. Calculation of the maximum current and power in cross section.

Consider each of them.

In the first case you need to enter:

• Power value (in the considered example of 2 kW).
• Select the current, the type of conductor, the laying method and the amount of live.
• By clicking the "Calculate" button, the program will display the desired section, the current strength, the recommended circuit breaker and the protective shutdown device (UZO).

Calculation of section for specified power or current

In the second case, on a certain cross section of the conductor, the program selects the most allowed:

• Power.
• Current strength.
• Recommended current protection vehicle.
• Recommended RCD.

Calculation of maximum current and power in cross section

As you can see, the calculator interface is rather simple, and the final results are useful and informative.

Installation is not required. Open the archive and run the file "Cable.exe".

Video on this topic

On the cable it is impossible to skip more than a certain amount of current. Designing and mounting wiring in an apartment or house, select the correct cross section of the conductor. This will continue to avoid overheating of wires, short circuit and unplanned repair.

In order for the wiring to function impeccably, it is important to choose the proper section of the wires and make a competent power calculation, because other characteristics depend on these indicators. The current moves along the wires in the same way as water comes through the pipes.

The safety of the entire premises depends on the quality of electrical installation works. It is especially important to choose the correctly choose such a parameter as the cable cross section. In order to carry out the calculation of the cable cross-section for power, it is necessary to know the technical characteristics of all consumers of electricity that will be connected to it. You should also consider the length of the wiring and how it will be installed.

The current moves along the wires just as water flows through the pipe. How in water pipe You can not put a larger liquid and the cable cannot be skipped more than a certain amount of current. In addition, the cost of the cable directly depends on its cross section. The more the cross section, the price of the cable will be higher.

The plumbing pipe on the cross section is large than necessary, it is more expensive, and too narrow will not miss the desired amount of water. The same thing happens with a current with the only difference that the selection of the cable, in cross section, less than the specified value is much more dangerous. Such a wire overheats all the time, the power of the current in it increases. Because of this, the light in the room will arbitrarily cut down, and in the worst case there will be a short circuit, a fire will begin.

The fact that the selected cable cross section will be more necessary, there is nothing terrible. On the contrary, wiring, where power and section exceed the desired value will last much longer, but the cost of all electrical work will immediately increase at least 2-3 times, because the main costs of power supply are precisely in the cost of wires.
The correct selected section will allow:

• avoid overheating wires;
• prevent short circuit;
• save at the cost of repair.

Calculation with the help of formulas

A sufficient cross-sectional area will give the opportunity to pass the maximum current on the wires without overheating. Therefore, when designing wiring, first of all, the optimal cross-section of the wire is found depending on the power consumption. To calculate this value, the total current should be calculated. It is determined, based on the power of all devices connected to the cable.

To select the optimal wire section, knowing the power, the Ohm law should be remembered, as well as the rules of electrodynamics and other electromechanical formulas. So, current (i) strength for a network of 220 volts voltage, namely, this voltage is used for the home network, calculated by the formula:

I \u003d (p1 + p2 + ... + pn) / 220, where:

(P1 + P2 + ... + Pn) - the total power of each used electrical appliance.

For voltage networks 380 volts:

I \u003d (p1 + p2 + ... + pn) / √3 / 380.

Power indicators of some household electrical appliances

Electrical appliance	Power, W	Electrical appliance	Power, W
Blender	up to 500.	Heated towel rail	900-1700
Fan	750-1700	Dishwasher	2000
Video recorder	up to 500.	A vacuum cleaner	400-2000
Accumulator water heater	1200-1500	Juicer	up to 1000.
Water heater flowing	2000-5000	Washer	3000
Hood (ventilation)	500-1000	Washing machine with dryer	3500
Grill	1200-2000	Drying for hand	800
Oven	1000-2000	Television	100-400
A computer	400-750	Toaster	600-1500
Air conditioning	1000-3000	Humidifier	200
Coffee maker	800-1500	Iron	500-2000
Food processor	up to 100.	Hair dryer	450-2000
Microwave	850	Fryernitsa	1500
Microwave combined	2650	Refrigerator	200-600
Mixer	up to 500.	Electric Shaver	up to 100.
Meat grinder	500-1000	Electromamp	20-250
Heater	1000-2400	Electric stove	8000-10000
Double boiler	500-1000	Electric kettle	1000-2000

But these are blurry formulas and simplified calculation. In detailed computing, the value of permissible loads is taken into account, which for the copper cable will be 10a / mm², and for aluminum - 8 A / mm². The load determines which strength of the current can pass through the unit area freely.

Correction of power indicators

Also, when calculating is added amendment in the form of a demand ratio (KC). This coefficient shows which devices are used on the network constantly, and which for a certain time. Special calculator and tables, where the calculation of power is shown, simplify all these calculations.

Receiver Receiver Research Receiver (KC)

But what to do if the characteristics indicate 2 types of power: active and reactive? And the first one measures them in the usual KV, and the second - kVA. In our networks flows alternating current, the value of which varies in time. Therefore, for all consumers there is an active power, which is calculated as the average value of all instantaneous current and power variables. The instruments with active power include incandescent bulbs, electric heaters. In such consumers, the energy and voltage phase energy coincide. If, in the electrical circuit, aggregates accumulating energy, such as transformers or electric motors, are involved, then they are possible by amplitude deviations. Due to this phenomenon and reactive power occurs.

For networks where there is a reactive and active power, it is necessary to take another correction - the power coefficient (cosφ) or the reactive component.

Thus, the formula is obtained:

S \u003d kc * (p1 + p2 + ... + pn) / (220 * cosφ * RD), where:

• S - cross section area
• RD is the permissible load value.

In addition, the current current loss of current, which occurs during the passage along the wires. When using a cable with several cores, you need to multiply the amount of losses on the number of these lived.

Important! For all these calculations, it will be necessary not just a calculator, but also deep knowledge in the field of physics. Make accurate calculation immediately without theoretical knowledge will not work.

Search area diameter

Sometimes even a scrupulous calculation does not help, a short circuit occurs in the chain. This is due to the fact that the stated technical characteristics often do not correspond to the actual value. Therefore, to learn how to make the calculation of power, it is important to be sure that the store will offer a suitable electrically conduction. To do this, use the simple formula:

S \u003d 0.785D 2, where:

• d is the diameter of the vein;
• S is the cross-sectional area.

It is possible to determine the accurate, make the calculation of the section using a caliper or micrometer, more precisely.

If the cable consists of several thin wires, then first look at the diameter of one of them, and then the data obtained is multiplied by their number:

Singch \u003d n * 0,785di 2, where:

• dI is an individual wire area;
• n - the number of wires;
• Singch - the total area of \u200b\u200bthe cross section.

Tables for calculations

Each time to resort to complex calculations for the calculation is not entirely correct. Industry produces wires of a certain section. If, after accurate calculations and calculations, the cable cross section is obtained by a power of 3.2 square millimeters, then it will not be possible to find such a wire, because there are wires in cross section 2.5 mm 2, 3 or 4 mm 2.

Attention! In order to find out the cable cross sections, a table is required, where all data is regulated, as well as compiled in accordance with Pue - the rules of the electrical installation device.

In order to determine the cable cross section at a well-known load, it is necessary:

• calculate current strength;
• round up to a larger value according to the table;
• then find the closest standard amount of section.

Permissible long-term current for wires and cords with rubber and polyvinyl chloride insulation with copper conductors

Cross section provocative Wearing veins, mm 2		Current, and, for wires, laid
	Open that		in one trumpet
		two one- Household	three single Household	four single Household	one two- core	one three- core
0,5	11	-	-	-	-	-
0,75	15	-	-	-	-	-
1	17	16	15	14	15	14
1,2	20	18	16	15	16	14,5
1,5	23	19	17	16	18	15
2	26	24	22	20	23	19
2,5	30	27	25	25	25	21
3	34	32	28	26	28	24
4	41	38	35	30	32	27
5	46	42	39	34	37	31
6	50	46	42	40	40	34
8	62	54	51	46	48	43
10	80	70	60	50	55	50
16	100	85	80	75	80	70
25	140	115	100	90	100	85
35	170	135	125	115	125	100
50	215	185	170	150	160	135
70	270	225	210	185	195	175
95	330	275	255	225	245	215
120	385	315	290	260	295	250
150	440	360	330	-	-	-
185	510	-	-	-	-	-
240	605	-	-	-	-	-
300	695	-	-	-	-	-
400	830	-	-	-	-	-

Make such a calculation simply. First you need to determine the total power of all the electrical appliances used in the network. To do this, you need a table, and the missing data for each electrographation can be taken from the passport of products. The resulting amount must be multiplied by 0.8 - the demand coefficient, if the electrical appliances will not be used immediately, or leave unchanged during continuous operation. Now you need to divide the value to the voltage in the network and add a constant value 5. This will be the necessary current indicator. Suppose the current is 20a.

Note! In the residential premises, a three-in-room electrically conductive and closed wiring are used. It must be remembered when the calculation is done on the table.

Next will need a table from PUE. We take a column where the values \u200b\u200bof the current for the three-core core are given, and select the closest: 17 and 22. It is better to take a cross section with a margin, therefore in the example of the example, the desired value will be equal to 22. As you can see, this value corresponds to a three-in-a-cable in cross section 2 mm 2 .

You can additionally consider how this calculation is made for an aluminum cable according to PUE, although such wires cannot be used in residential facilities. In old houses, aluminum wiring is still preserved, but during overhaul It is recommended to replace it. In addition, the aluminum electrical wire is crumbled on bends and has a smaller conductivity at the joints. The bare parts of aluminum are quickly oxidized in air, which leads to significant electricity losses in the connection places.

Calculator

Today, non-only table, but also a special calculator applies specialists to determine the section. This calculation greatly simplifies calculations. Calculator is easy to find on the Internet. For calculations of size by section, you need to know the following parameters:

• a variable or permanent current is used;
• wire material;
• power of all devices used;
• network voltage;
• power supply system (one or three-phase);
• wiring type.

These indicators are loaded into the calculator and get the required wire value by cross section.

Calculation of length

Calculate the length in length is important in the construction of industrial scale networks, when the plots are subjected to a constant heavy load, and the cable must be pulled at considerable distances. After all, during the passage of current on the wires, power losses occur associated with electrical resistance in the chain. Power loss (DU) is calculated as follows:

du \u003d i * p * l / s, where:

• I - current strength;
• p - specific resistance (copper - 0.0175, aluminum - 0.0281);
• L - cable length;
• S - already calculated by the cross-sectional area.

According to the technical conditions, the maximum voltage drop in the wire length should not exceed 5 percent. Otherwise, you should choose a wire with a larger cross section.

Features

There are certain standards according to which the cable calculation is carried out in cross section. If there is no certainty, which electrical wiring is necessary, you can use these rules: the electrical appliances in the apartment are divided into the lighting group and the rest; for powerful electrical appliances, for example, washing machines or electrical furnaces use connection from individual wires; The standard cross-section of the wire for the lighting group in the apartment is 1.5 mm 2, and for the remaining wires - 2.5 mm 2. Such standards are used because the regulatory power of the incoming current cannot be greater.

The three-phase current is necessary when the high-power production values \u200b\u200bare used. Therefore, to determine the cable cross section at enterprises, it is necessary to accurately calculate all the additional coefficients, as well as be sure to take into account the power loss and voltage fluctuations. For electrical work in an apartment or private house, such complex computations are not conducted.

For mounting acoustic equipment, wires with minimal resistance are used. This is necessary in order to maximize the distortion and improve the quality of the transmitted signal. Therefore, for acoustic systems, cables are better suited for a size of 2x2.5 or 2x1.5 at a length of at least 3 meters, and the subwoofer is connected by the shortest cable 2.5-4 mm 2.

Examples

Consider a common scheme for selecting a cable cross section in the apartment:

• First you need to determine the places where the sockets and lighting devices will be;
• Next, you need to determine which devices will be involved at each output;
• Now you can create a general connection scheme and calculate the length of the cable, adding at least 2 cm for wire connections;
• Based on the data obtained, we consider the size of the cable cross section according to the formulas above.

I \u003d 2400W / 220V \u003d 10,91A, round and get 11a.

As we already know, different coefficients are used to accurately determine the cross-sectional area, but almost all of these data refer to the network with voltage in 380V. To increase the margin of the strength to add to our current of the current more 5a:

For apartments use three-cable cables. The table will show the current value close to our 16A, it will be 19a. We get that to install one washing machine We need a wire with a cross section of at least 2 mm 2.

General Theory

To determine the optimal cable cross section for household needs, generally use the following rules:

• for sockets needed wires with a cross section of 2.5 mm²;
• for lighting - 1.5 mm²;
• for devices with increased power - 4-6 mm².

If there are doubts about calculating the section, then the PUE table is used. To determine accurate data on the cable cross section, all factors affect the passage of the circuit current are taken into account. These include:

• type of wire isolation;
• length of each site;
• laying method;
• temperature regime;
• humidity;
• permissible overheating value;
• the difference in the power of current receivers in one group.

All these indicators allow you to increase the efficiency of the use of electricity on an industrial scale, as well as avoid overheating.

Select section. Video

In this video, their experience in the sequence of the cable and the nominal machine is divided by a master. It indicates possible errors and gives seld advice novice.

If, after reading the article, there were still some doubts, the table or calculator described above will help you find the exact cross-section of the power wire.

The standard apartment wiring is calculated on the maximum consumption current with a long load 25 amp (there is a circuit breaker to be selected and the circuit breaker, which is installed on the input of the wires in the apartment) is performed by copper wire with a cross section of 4.0 mm 2, which corresponds to the diameter of the wire 2.26 mm and Load capacity up to 6 kW.

According to the requirements of p 7.1.35 Pue the cross-section of copper veins for the apartment wiring must be at least 2.5 mm 2, What corresponds to the diameter of the conductor 1.8 mm and the load current 16 A. to such electrical wiring, you can connect the electrical appliances with a total capacity of up to 3.5 kW.

What is the cross section of the wire and how to determine it

To see the wire section, it is enough to cut across and look at the slice from the end. Cutting area and there is a wire section. The more, the greater current strength can transfer the wire.

As can be seen from the formula, the wire section is easily in its diameter. It is sufficient to multiply the diameter of the conductivity of the wires of the wire and 0.785. To cross section of the stranded wire, it is necessary to calculate the cross section of the same vein and multiply to their number.

The diameter of the conductor can be determined using a caliper with an accuracy of 0.1 mm or a micrometer with an accuracy of 0.01 mm. If there is no appliance at hand, then an ordinary ruler will help.

Select section
Copper wire electrical wiring for current power

The magnitude of the electric current is denoted by the letter " BUT"And measured in amperes. When choosing a simple rule, the wire section is more, the better, this is round the result in the big face.

Table for secting and diameter of copper wire depending on the strength of the current
Maximum current, and	1,0	2,0	3,0	4,0	5,0	6,0	10,0	16,0	20,0	25,0	32,0	40,0	50,0	63,0
Standard section, mm 2	0,35	0,35	0,50	0,75	1,0	1,2	2,0	2,5	3,0	4,0	5,0	6,0	8,0	10,0
Diameter, mm.	0,67	0,67	0,80	0,98	1,1	1,2	1,6	1,8	2,0	2,3	2,5	2,7	3,2	3,6

My data given in the table is based on personal experience and guarantee reliable operation of electrical wiring under the most unfavorable conditions for its gasket and operation. When choosing a cross-section of a wire largest value, the variable is a current or permanent. The magnitude and frequency of voltage in the electrical wiring also do not matter, this can be the onboard network of a DC car by 12 V or 24 V, an aircraft at 115 in the frequency of 400 Hz, electrical wiring 220 V or 380 in a frequency of 50 Hz, high voltage line Power transmission per 10000 V.

If the electric appliance consumption current is not known, but the supply voltage and power are known, then you can calculate the current using the following online calculator.

It should be noted that at frequencies of more than 100 Hz in the wires in the flow of electric current begins to manifest the skin effect, which consists in the fact that with increasing the frequency of the current begins "pressing" to external surface Wires and actual cross-section of the wire decreases. Therefore, the selection of the cross-section for high-frequency circuits is performed according to other laws.

Determination of the load capacity of the electrical wiring 220 V
made of aluminum wire

In long built houses, wiring, as a rule, is made of aluminum wires. If connections in the junction boxes are performed correctly, the service life of aluminum wiring can be a hundred years. After all, aluminum is practically no oxidized, and the service life of the wiring will be determined only by the service life of plastic isolation and the reliability of contacts in the deposit places.

In the case of connecting additional energy-intensive electrical appliances in an apartment with an aluminum wiring, it is necessary to determine the ability to withstand additional power through the cross section or diameter. According to the table below, it is easy to do.

If your wiring in the apartment is made of aluminum wires and there is a need to connect the newly installed outlet in the camshaft with copper wires, then such a connection is performed in accordance with the recommendations of the article and the connection of aluminum wires.

Calculation of the cross section of the wiring wire
By power of connected electrical appliances

To select a section, the cable wires live when laying wiring in an apartment or a house need to analyze the fleet of existing electrical appliances in terms of their simultaneous use. The table presents a list of popular household electrical appliances with an indication of the current consumed depending on the power. You can find out the power consumption of your models yourself from the labels on the products yourself or passports, often the parameters indicate the packaging.

In the event that the power of the current consumed by the electrical appliance is not known, it can be measured using an ammeter.

Table of power consumed and current consumption with household electrical appliances
With a supply voltage of 220 V

Usually, the power consumption of electrical appliances is indicated on the housing in watts (W or VA) or kilowatts (kW or KVA). 1 kW \u003d 1000 W.

Table of power consumed and current consumption with household electrical appliances
Household electrical appliance	Power consumption, kW (KBA)	Current power, and	Current Consumption Mode
Incandescent light bulb	0,06 – 0,25	0,3 – 1,2	Constantly
Electric kettle	1,0 – 2,0	5 – 9	Up to 5 minutes
Electric stove	1,0 – 6,0	5 – 60	Depends on the mode of operation
Microwave	1,5 – 2,2	7 – 10	Periodically
Electrompala	1,5 – 2,2	7 – 10	Depends on the mode of operation
Toaster	0,5 – 1,5	2 – 7	Constantly
Grill	1,2 – 2,0	7 – 9	Constantly
Coffee grinder	0,5 – 1,5	2 – 8	Depends on the mode of operation
Coffee maker	0,5 – 1,5	2 – 8	Constantly
Electrophovka	1,0 – 2,0	5 – 9	Depends on the mode of operation
Dishwasher	1,0 – 2,0	5 – 9
Washer	1,2 – 2,0	6 – 9	Maximum from the moment of inclusion before water heating
Tumble dryer	2,0 – 3,0	9 – 13	Constantly
Iron	1,2 – 2,0	6 – 9	Periodically
A vacuum cleaner	0,8 – 2,0	4 – 9	Depends on the mode of operation
Heater	0,5 – 3,0	2 – 13	Depends on the mode of operation
Hair dryer	0,5 – 1,5	2 – 8	Depends on the mode of operation
Air conditioning	1,0 – 3,0	5 – 13	Depends on the mode of operation
Stationary computer	0,3 – 0,8	1 – 3	Depends on the mode of operation
Power tools (drill, jigsaw, etc.)	0,5 – 2,5	2 – 13	Depends on the mode of operation

The current consumes the refrigerator, lighting, radiotelephone, chargers, a TV in the duty state. But in the amount, this power is not more than 100 W and when calculating it can not be taken into account.

If you enable all the electrical appliances available in the house at the same time, it will be necessary to choose a wire cross section capable of missing the current 160 A. The wire will need a thick thicker! But such a case is unlikely. It is difficult to imagine that someone is able to simultaneously grind meat, ironing the iron, vacuuming and drying the hair.

Example of calculation. You got up in the morning, turned on the electric kettle, microwave, toaster and coffee maker. Current consumed accordingly will be 7 a + 8 A + 3 A + 4 A \u003d 22 A., taking into account the lighting, the refrigerator and in addition, for example, the TV, the current consumed can reach 25 A.

For network 220 V

You can select the wire section not only by the power of the current but also by the amount of power consumed. To do this, make a list of all electrical wiring planned to connect to this section of electrical wiring, determine which power it consumes each of them separately. Next, fold the data obtained and use the table below.

For network 220 V
Power of electrical appliance, kW (KBA)	0,1	0,3	0,5	0,7	0,9	1,0	1,2	1,5	1,8	2,0	2,5	3,0	3,5	4,0	4,5	5,0	6,0
Standard section, mm 2	0,35	0,35	0,35	0,5	0,75	0,75	1,0	1,2	1,5	1,5	2,0	2,5	2,5	3,0	4,0	4,0	5,0
Diameter, mm.	0,67	0,67	0,67	0,5	0,98	0,98	1,13	1,24	1,38	1,38	1,6	1,78	1,78	1,95	2,26	2,26	2,52

If there are several electrical appliances and for some known consumption current, and for other power, then you need to determine the cross-section of the wire for each of them from the tables, and then fold the results.

Selecting a copper wire in power
For from the onboard network of the car 12 in

If, when connected to the on-board network of a car, only its consumption power is known, then you can determine the cross section of the additional wiring using the table below.

Single selection table and copper wire diameter for power For the onboard network of the car 12 V
Electrical Appliance Power, Watt (BA)	10	30	50	80	100	200	300	400	500	600	700	800	900	1000	1100	1200
Standard section, mm 2	0,35	0,5	0,75	1,2	1,5	3,0	4,0	6,0	8,0	8,0	10	10	10	16	16	16
Diameter, mm.	0,67	0,5	0,8	1,24	1,38	1,95	2,26	2,76	3,19	3,19	3,57	3,57	3,57	4,51	4,51	4,51

Selecting a wire section for connecting electrical appliances
to three-phase network 380 V

When operating electrical appliances, for example, an electric motor connected to a three-phase network, the current consumed flows no longer on two wires, but in three and, therefore, the magnitude of the flowing current in each individual wire is slightly smaller. This allows you to use a smaller wire to connect the electrical appliances to the three-phase network.

To connect the electrical appliances to the three-phase voltage of 380 V, for example, the electric motor, the wire cross section for each phase is 1.75 times less than for connecting to a single-phase network of 220 V.

Attention, when choosing a wire section for connecting an electric motor in power, it should be noted that the maximum mechanical power is indicated on the motility nameplate, which the engine can create on the shaft, and not consumed electric power. The electric power consumption with an electric motor with, accounting for efficiency and Cos φ is about two times more than being created on the shaft, which must be considered when choosing a wire section based on the engine power specified in the plate.

For example, you need to connect the electric motor that consumes the power from a 2.0 kW network. The total consumption current of the electric motor of such power in the three phases is 5.2 A. on the table, it turns out that we need a wire with a cross section of 1.0 mm 2, taking into account the above 1.0 / 1.75 \u003d 0.5 mm 2. Consequently, to connect an electric motor with a capacity of 2.0 kW to the three-phase network 380 V, it will take a copper three-core cable with a cross section of each vein 0.5 mm 2.

It is much easier to select a wire section for connecting a three-phase motor, based on the current consumption current, which is always indicated on the nameplate. For example, in the nameplate shown in the photo, the motor consumption current of 0.25 kW for each phase with a 220 V power supply voltage (the engine winding is connected according to the triangle scheme) is 1.2 A, and at a voltage of 380 V (the engine winding is connected by Scheme "Star") Total 0.7 A. Take the current specified on the nameplate, on the table to select the wire section for the apartment wiring, select the wire with a cross section of 0.35 mm 2 when the electric motor windings are connected according to the triangle scheme or 0.15 mm 2 When connected according to the "Star" scheme.

About choosing a brand of cable for domestic wiring

Making an apartment wiring made of aluminum wires at first glance seems cheaper, but operating costs due to the low reliability of contacts with time multiple times will exceed the cost of electrical wiring of copper. I recommend to make the wiring exclusively from copper wires! Aluminum wires are indispensable when laying air wiring, as they are light and cheap and with the right connection serve reliably for a long time.

And which wire is better to use when installing electrical wiring, single-core or stranded? From the point of view of the ability to carry out a current per unit section and installation, one-core better. So for domestic wiring you need to use only a single-core wire. Multi-apected multiple bends, and the thinner the conductors in it, the more flexible and more durable. Therefore, stranded wires are used to connect nonstationary electrical appliances to the power grid, such as electrophane, electric shaver, electricity and all others.

After making a decision on the cross section of the Wire, the issue of cable brand for wiring is faced. Here the choice is not large and is represented by just a few cable stamps: PUNP, VVGNG and NYM.

PUNP cable since 1990, in accordance with the decision of the GlavgosEnergoneadzor "On the prohibition of the use of wires of such an ATSN, PPBN, PEN, PUNP, and others produced by TU 16-505. 610-74 Instead of Wires of APV, ADPV, PV and PPV according to GOST 6323-79 * »For use is prohibited.

Cable WG and VVGng - copper wires in double polyvinyl chloride insulation, flat shape. Designed to work at temperatures ambient from -50 ° C to + 50 ° C, to perform wiring inside buildings, outdoors, in the ground when laying in tubes. Service life up to 30 years. The letters "NG" in the designation of the brand say the non-combustible isolation of the wire. Two-, three- and four-core, with a cross section, lived from 1.5 to 35.0 mm 2. If the letter A (AVVG) is standing in the designation of the cable before UG, then the veins in the aluminum wire.

NYM cable (his Russian analogue - cable VVG.), with copper veins, round shape, with non-combustible insulation, corresponds to the German standard VDE 0250. Specifications and the scope, almost the same with the IWG cable. Two-, three- and four-cylinders with a cross section lived from 1.5 to 4.0 mm 2.

As you can see, the selection for laying the wiring is not large and determined depending on which form cable is more suitable for mounting, round or flat. Round-shaped cable is more conveniently locked through the walls, especially if you enter the street to the room. It will take to drill a hole slightly more cable diameter, and with a greater thickness the wall it becomes relevant. For internal wiring it is more convenient to use a flat cable of the VG.

Parallel wire connection of electrical wiring

There are hopeless situations when urgently need to pave the wiring, and there are no wires of the required cross section. In this case, if there is a wire smaller than necessary, sections, then you can make the wiring from two or more wires, connecting them in parallel. The main thing is that the sum of the sections of each of them was not less than the calculated one.

For example, there are three wires with a cross section 2, 3 and 5 mm 2, and is needed by 10 mm 2 calculations. Connect them all in parallel, and the wiring will withstand a current of up to 50 amps. Yes, you yourself have repeatedly seen a parallel connection of a larger number of thin conductors for transmitting high currents. For example, a current is used for welding to 150 a and in order for the welder to control the electrode, you need a flexible wire. It is made from hundreds parallel to the connected thin copper wires. In the car, the battery to the on-board network is also connected using the same flexible stranded wire, since during the start of the engine starter consumes the current from the battery to 100 A. and when installing and removing the battery, the wires must be removed to the side, that is, the wire must be quite flexible .

The method of increasing the cross-section of the electric conduction by parallel connection of several wires of different diameters can only be used in extreme cases. When laying a home wiring, it is permissible to connect in parallel only the wires of the same cross section taken from one bay.

Online calculators for calculating the cross section and diameter of the wire

With the help of an online calculator, which presented below, you can solve the inverse problem - to determine the diameter of the conductor in cross section.

How to calculate the cross section of the stranded wire

The stranded wire, or as it is called still multi-way or flexible, is a reticent together single-core wires. To calculate the cross section of the multicore wire, you must first calculate the cross section of one wire, and then the result is multiplied by their number.

Consider an example. There is a stranded flexible wire in which 15 lived with a diameter of 0.5 mm. The cross section of one vein is 0.5 mm × 0.5 mm × 0.785 \u003d 0.19625 mm 2, after rounding, we obtain 0.2 mm 2. Since we have 15 wires in the wire, then to determine the cable cross section, multiply these numbers. 0.2 mm 2 × 15 \u003d 3 mm 2. It remains on the table to determine that such a stranded wire will withstand the current 20 A.

You can estimate the load capacity of the stranded wire without measuring the diameter of the individual conductor, measuring the total diameter of all the penetration of wires. But since the wires are round, then there are air gaps between them. To exclude the area of \u200b\u200bgaps, the result obtained by the result of the cross section of the wire is multiplied by the coefficient of 0.91. When measuring diameter, you need to trace so that the stranded wire is not flattened.

Consider on the example. As a result of measurements, the multicore wire has a diameter of 2.0 mm. Calculate its cross section: 2.0 mm × 2.0 mm × 0.785 × 0.91 \u003d 2.9 mm 2. On the table (see below), we determine that this stranded wire will withstand the current of up to 20 A.