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Selection of cable cross-section for power and current. Calculation of cable and wire cross-sections based on power and current. Basic calculation formula

For correct and safe installation of wiring cables, it is imperative to make a preliminary calculation of the expected power consumption. Failure to comply with the requirements for selecting the cross-section of the cable used for wiring can lead to insulation melting and fire.

Calculating the cable cross-section for a specific electrical wiring system can be divided into several stages:

breakdown of electricity consumers by groups;
determining the maximum current for each segment;
selection of cable cross-section.

All consuming electrical appliances should be divided into several groups so that the total power consumption of one group does not exceed approximately 2.5-3 kW. This will allow you to select a copper cable with a cross-section of no more than 2.5 square meters. mm. The power ratings of some major household appliances are shown in Table 1.

Table 1. Power values of major household appliances.

Consumers combined into one group must be geographically located in approximately the same place, since they are connected to the same cable. If the entire connected object is powered by a single-phase network, then the number of groups and distribution of consumers do not play a significant role. If the power supply is three-phase, then it is recommended to divide consumers into groups so that each phase receives approximately the same power.
Then the percentage of discrepancy can be calculated using the formula = 100% — (Pmin/Pmax*100%), where Pmax is the maximum total power per phase, Pmin is the minimum total power per phase. The lower the power discrepancy percentage, the better.

Calculation of the maximum current for each consumer group

Once the power consumption has been found for each group, the maximum current can be calculated. It is better to take the demand coefficient (Kc) equal to 1 everywhere, since the use of all elements of one group at the same time is not excluded (for example, you can turn on all household appliances belonging to one group of consumers at the same time). Then the formulas for single-phase and three-phase networks will look like:

Icalc = Pcalc / (Unom * cosφ)
for a single-phase network, in this case the network voltage is 220 V,

Icalc = Pcalc / (√3 * Unom * cosφ)
for three-phase network, network voltage 380 V.

When installing electrical wiring in recent decades, the method using. This is explained by a whole set of properties that a corrugated pipe has, but at the same time, when working with it, you must adhere to certain rules.

You can often come across both in theory and in practice the terms delta and star connection, phase and linear voltage - an interesting one will help you understand their differences.

The cosine value for household appliances and incandescent lighting is assumed to be 1, for LED lighting - 0.95, for fluorescent lighting - 0.92. The arithmetic mean cosine is found for the group. Its value depends on the cosine of the device that consumes the most power in a given group. Thus, knowing the currents in all sections of the wiring, you can begin to select the cross-section of wires and cables.

Selection of cable cross-section based on power

Once the calculated maximum current is known, you can begin selecting cables. This can be done in two ways, but the easiest way is to select the desired cable cross-section using the tabular data. The parameters for selecting copper and aluminum cables are given in the table below.

Table 2. Data for selecting the cross-section of a cable with copper conductors and a cable made of aluminum.

When planning electrical wiring, it is preferable to choose cables from the same material. Connecting copper and aluminum wires using conventional twisting is prohibited by fire safety rules, since when temperature fluctuates, these metals expand differently, which leads to the formation of gaps between the contacts and the generation of heat. If there is a need to connect cables made of different materials, then it is best to use terminals specially designed for this.

Video with formulas for calculating cable cross-section

When designing the circuit of any electrical installation and installation, choosing the cross-section of wires and cables is a mandatory step. In order to correctly select the power wire of the required cross-section, it is necessary to take into account the maximum consumption.

Wire cross-section is measured in square millimeters or "squares". Each “square” of aluminum wire is capable of passing through itself for a long time, heating up to permissible limits, a maximum of only 4 amperes, and copper wires 10 amperes of current. Accordingly, if some electrical consumer consumes power equal to 4 kilowatts (4000 watts), then at a voltage of 220 volts the current strength will be equal to 4000/220 = 18.18 amperes and to power it it is enough to supply electricity to it with a copper wire with a cross-section of 18.18/ 10=1.818 square. True, in this case the wire will work to the limit of its capabilities, so you should take a margin of at least 15% for the cross-section. We get 2.091 squares. And now we will select the nearest wire of standard cross-section. Those. We must conduct wiring to this consumer with a copper wire with a cross-section of 2 square millimeters, called the current load. Current values can be easily determined by knowing the rated power of consumers using the formula: I = P/220. The aluminum wire will be accordingly 2.5 times thicker.

Based on the calculation of sufficient mechanical strength, open power wiring is usually carried out with a wire with a cross-section of at least 4 square meters. mm. If you need to know with greater accuracy the long-term permissible current load for copper wires and cables, you can use the tables.

Copper conductors of wires and cables
	Voltage, 220 V		Voltage, 380 V
	current, A	power, kWt	current, 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	33,0
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	66,0	260	171,6

Aluminum conductors of wires and cables
Cross-section of current-carrying conductor, mm.	Voltage, 220 V		Voltage, 380 V
Cross-section of current-carrying conductor, mm.	current, A	power, kWt	current, 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	132,0

Permissible continuous current for wires and cords with rubber and polyvinyl chloride insulation with copper conductors, for example
Cross-section of current-carrying conductor, mm.	Open
Cross-section of current-carrying conductor, mm.	Open	Two single-core	Three single-core	Four single-core	One two-wire	One three-wire
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	-	-	-	-	-

Permissible continuous current for wires and cords with rubber and polyvinyl chloride insulation with aluminum conductors
Cross-section of current-carrying conductor, mm.	Open	Current, A, for wires laid in one pipe
Cross-section of current-carrying conductor, mm.	Open	Two single-core	Three single-core	Four single-core	One two-wire	One three-wire
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	-	-	-	-	-

Permissible continuous current for wires with copper conductors with rubber insulation in metal protective sheaths and cables with copper conductors with rubber insulation in lead, polyvinyl chloride, Nairite or rubber casing, armored and unarmored
Cross-section of current-carrying conductor, mm.	Current*, A, for wires and cables
	single-core		two-wire			three-wire
	when laying
	in the air	in the air		in the ground	in the air		in the ground
1,5	23	19		33	19		27
2,5	30	27		44	25		38
4	41	38		55	35		49
6	50	50		70	42		60
10	80	70		105	55		90
16	100	90		135	75		115
25	140	115		175	95		150
35	170	140		210	120		180
50	215	175		265	145		225
70	270	215		320	180		275
95	325	260		385	220		330
120	385	300		445	260		385
150	440	350		505	305		435
185	510	405		570	350		500
240	605	-		-	-		-

* Currents refer to cables and wires with and without a neutral core.

Permissible continuous current for cables with aluminum conductors with rubber or plastic insulation in lead, polyvinyl chloride and rubber sheaths, armored and unarmored
Cross-section of current-carrying conductor, mm.	Current, A, for wires and cables
	single-core		two-wire			three-wire
	when laying
	in the air	in the air		in the ground	in the air		in the ground
2,5	23	21		34	19		29
4	31	29		42	27		38
6	38	38		55	32		46
10	60	55		80	42		70
16	75	70		105	60		90
25	105	90		135	75		115
35	130	105		160	90		140
50	165	135		205	110		175
70	210	165		245	140		210
95	250	200		295	170		255
120	295	230		340	200		295
150	340	270		390	235		335
185	390	310		440	270		385
240	465	-		-	-		-

Permissible continuous currents for four-core cables with plastic insulation for voltages up to 1 kV can be selected according to this table as for three-core cables, but with a coefficient of 0.92.

Summary table of wire cross-sections, current, power and load characteristics
Cross-section of copper conductors of wires and cables, sq. mm	Permissible continuous load current for wires and cables, A	Rated current of the circuit breaker, A	Maximum current of the circuit breaker, A	Maximum single-phase load power at U=220 V	Characteristics of an approximate single-phase household load
1,5	19	10	16	4,1	lighting and alarm group
2,5	27	16	20	5,9	socket groups and electric floors
4	38	25	32	8,3	water heaters and air conditioners
6	46	32	40	10,1	electric stoves and ovens
10	70	50	63	15,4	input supply lines

The table shows data based on the PUE for selecting cross-sections of cable and wire products, as well as rated and maximum possible currents of circuit breakers for single-phase household loads most often used in everyday life.

We hope this information was useful to you. We remind you that from us you can buy excellent quality at a low price.

Cable power table required to correctly calculate the cable cross-section, if the power of the equipment is large and the cable cross-section is small, then it will heat up, which will lead to the destruction of the insulation and loss of its properties.

To calculate the conductor resistance, you can use the conductor resistance calculator.

For the transmission and distribution of electric current, the main means are cables; they ensure the normal operation of everything related to electric current, and how good this work will be depends on the right choice cable cross-section by power. A convenient table will help you make the necessary selection:

Current cross-section conductive lived mm
	Voltage 220V		Voltage 380V
	Current. A	Power. kW	Current. A	Power, kWt

Section Toko- conductive lived mm	Aluminum conductors wires and cables
	Voltage 220V		Voltage 380V
	Current. A	Power. kW	Current. A	Power, kWt

But in order to use the table, you need to calculate the total power consumption of devices and equipment that are used in a house, apartment or other place where the cable will be laid.

Example of power calculation.

Let's say you are installing closed electrical wiring in a house using an explosive cable. You need to write down a list of equipment used on a piece of paper.

But how now find out power? You can find it on the equipment itself, where there is usually a label with the main characteristics recorded.

Power is measured in Watts (W, W) or Kilowatts (kW, KW). Now you need to write down the data and then add it up.

The resulting number is, for example, 20,000 W, which would be 20 kW. This figure shows how much energy all electrical receivers together consume. Next, you should consider how many devices will be used simultaneously over a long period of time. Let’s say it turns out to be 80%, in which case the simultaneity coefficient will be equal to 0.8. We calculate the cable cross-section based on power:

20 x 0.8 = 16 (kW)

To select a cross-section, you will need a cable power table:

Current cross-section conductive lived mm	Copper conductors of wires and cables
	Voltage 220V		Voltage 380V
	Current. A	Power. kW	Current. A	Power, kWt




10		15.4

If the three-phase circuit is 380 Volts, then the table will look like this:

Current cross-section conductive lived mm	Copper conductors of wires and cables
	Voltage 220V		Voltage 380V
	Current. A	Power. kW	Current. A	Power, kWt

				16.5


10		15.4

These calculations are not particularly difficult, but it is recommended to choose a wire or cable with the largest cross-section of conductors, because it may be that it will be necessary to connect some other device.

Additional cable power table.

Often, before purchasing cable products, there is a need to independently measure its cross-section in order to avoid deception on the part of manufacturers, who, due to savings and setting a competitive price, may slightly underestimate this parameter.

It is also necessary to know how the cable cross-section is determined, for example, when adding a new energy-consuming point in rooms with old electrical wiring that does not have any technical information. Accordingly, the question of how to find out the cross-section of conductors always remains relevant.

General information about cable and wire

When working with conductors, it is necessary to understand their designation. There are wires and cables that differ from each other in their internal structure and technical characteristics. However, many people often confuse these concepts.

A wire is a conductor that has in its design one wire or a group of wires woven together and a thin common insulating layer. A cable is a core or a group of cores that has both its own insulation and a common insulating layer (sheath).

Each type of conductor will have its own methods for determining cross sections, which are almost similar.

Conductor materials

The amount of energy that a conductor transmits depends on a number of factors, the main one of which is the material of the current-carrying conductors. The following non-ferrous metals can be used as the core material of wires and cables:

Aluminum. Cheap and lightweight conductors, which is their advantage. They are characterized by such negative qualities as low electrical conductivity, a tendency to mechanical damage, high transient electrical resistance of oxidized surfaces;
Copper. The most popular conductors, which have a high cost compared to other options. However, they are characterized by low electrical and transition resistance at the contacts, fairly high elasticity and strength, and ease of soldering and welding;
Aluminum copper. Cable products with aluminum cores coated with copper. They are characterized by slightly lower electrical conductivity than their copper counterparts. They are also characterized by lightness, average resistance and relative cheapness.

Important! Some methods for determining the cross-section of cables and wires will depend specifically on the material of their conductor component, which directly affects the throughput power and current strength (method of determining the cross-section of conductors by power and current).

Measuring the cross-section of conductors by diameter

There are several ways to determine the cross-section of a cable or wire. The difference in determining the cross-sectional area of wires and cables will be that in cable products it is necessary to measure each core separately and summarize the indicators.

For information. When measuring the parameter under consideration with instrumentation, it is necessary to initially measure the diameters of the conductive elements, preferably removing the insulating layer.

Instruments and measurement process

The measuring instruments can be a caliper or a micrometer. Mechanical devices are usually used, but electronic analogues with a digital screen can also be used.

Basically, the diameter of wires and cables is measured using a caliper, since it is found in almost every household. It can also measure the diameter of wires in a working network, for example, a socket or panel device.

The diameter of the wire cross-section is determined using the following formula:

S = (3.14/4)*D2, where D is the diameter of the wire.

If the cable contains more than one core, then it is necessary to measure the diameter and calculate the cross-section using the above formula for each of them, then combine the result obtained using the formula:

Stotal= S1 + S2 +…+Sn, where:

Stotal – total cross-sectional area;
S1, S2, …, Sn – cross sections of each core.

On a note. To ensure the accuracy of the results obtained, it is recommended to take measurements at least three times, turning the conductor in different directions. The result will be the average.

In the absence of a caliper or micrometer, the diameter of the conductor can be determined using a regular ruler. To do this, you need to perform the following manipulations:

Clean the insulating layer of the core;
Wind the turns around the pencil tightly to each other (there should be at least 15-17 pieces);
Measure the winding length;
Divide the resulting value by the number of turns.

Important! If the turns are not laid evenly on the pencil with gaps, then the accuracy of the obtained results of measuring the cable cross-section by diameter will be in doubt. To increase the accuracy of measurements, it is recommended to take measurements from different sides. It will be difficult to wind thick wires onto a simple pencil, so it is better to resort to a caliper.

After measuring the diameter, the cross-sectional area of the wire is calculated using the formula described above or determined using a special table, where each diameter corresponds to the cross-sectional area.

It is better to measure the diameter of the wire, which contains ultra-thin cores, with a micrometer, since a caliper can easily break it.

The easiest way to determine the cable cross-section by diameter is using the table below.

Table of correspondence between wire diameter and wire cross-section

Diameter of conductor element, mm	Cross-sectional area of the conductor element, mm2
0,8	0,5
0,9	0,63
1	0,75
1,1	0,95
1,2	1,13
1,3	1,33
1,4	1,53
1,5	1,77
1,6	2
1,8	2,54
2	3,14
2,2	3,8
2,3	4,15
2,5	4,91
2,6	5,31
2,8	6,15
3	7,06
3,2	7,99
3,4	9,02
3,6	10,11
4	12,48
4,5	15,79

Segment cable cross-section

Cable products with a cross-section of up to 10 mm2 are almost always produced in a round shape. Such conductors are quite sufficient to meet the domestic needs of houses and apartments. However, with a larger cross-section of the cable, the input cores from the external electrical network can be made in segment (sector) form, and it will be quite difficult to determine the cross-section of the wire by diameter.

In such cases, it is necessary to resort to a table where the size (height, width) of the cable takes the corresponding value of the cross-sectional area. Initially, it is necessary to measure the height and width of the required segment with a ruler, after which the required parameter can be calculated by correlating the obtained data.

Table for calculating the area of an electric cable core sector

Cable type	Sectional area of the segment, mm2
	S	35	50	70	95	120	150	185	240
Four-core segment	V	-	7	8,2	9,6	10,8	12	13,2	-
Four-core segment	w	-	10	12	14,1	16	18	18	-
Three-core segmental stranded, 6(10)	V	6	7	9	10	11	12	13,2	15,2
Three-core segmental stranded, 6(10)	w	10	12	14	16	18	20	22	25
Three-core segmental single-wire, 6(10)	V	5,5	6,4	7,6	9	10,1	11,3	12,5	14,4
Three-core segmental single-wire, 6(10)	w	9,2	10,5	12,5	15	16,6	18,4	20,7	23,8

Dependence of current, power and core cross-section

It is not enough to measure and calculate the cross-sectional area of the cable based on the diameter of the core. Before installing wiring or other types of electrical networks, it is also necessary to know the capacity of the cable products.

When choosing a cable, you must be guided by several criteria:

the strength of the electric current that the cable will pass;
power consumed by energy sources;

Power

The most important parameter during electrical installation work (in particular, cable laying) is throughput. The maximum power of electricity transmitted through it depends on the cross-section of the conductor. Therefore, it is extremely important to know the total power of the energy consumption sources that will be connected to the wire.

Typically, manufacturers of household appliances, appliances and other electrical products indicate on the label and in the documentation accompanying them the maximum and average power consumption. For example, a washing machine can consume electricity ranging from tens of W/h during rinsing mode to 2.7 kW/h when heating water. Accordingly, a wire with a cross-section that is sufficient to transmit electricity of maximum power must be connected to it. If two or more consumers are connected to the cable, then the total power is determined by adding the limit values of each of them.

The average power of all electrical appliances and lighting devices in an apartment rarely exceeds 7500 W for a single-phase network. Accordingly, the cable cross-sections in the electrical wiring must be selected to this value.

So, for a total power of 7.5 kW, it is necessary to use a copper cable with a core cross-section of 4 mm2, which is capable of transmitting about 8.3 kW. The cross-section of the conductor with an aluminum core in this case must be at least 6 mm2, passing a current power of 7.9 kW.

In individual residential buildings, a three-phase power supply system of 380 V is often used. However, most equipment is not designed for such electrical voltage. A voltage of 220 V is created by connecting them to the network through a neutral cable with an even distribution of the current load across all phases.

Electric current

Often the power of electrical equipment and equipment may not be known to the owner due to the absence of this characteristic in the documentation or completely lost documents and labels. There is only one way out in such a situation - to calculate using the formula yourself.

Power is determined by the formula:

P = U*I, where:

P – power, measured in watts (W);
I – electric current strength, measured in amperes (A);
U is the applied electrical voltage, measured in volts (V).

When the strength of the electric current is unknown, it can be measured with control and measuring instruments: an ammeter, a multimeter, and a clamp meter.

After determining the power consumption and electric current, you can use the table below to find out the required cable cross-section.

Calculation of the cross-section of cable products based on current load must be carried out to further protect them from overheating. When too much electric current passes through conductors for their cross-section, destruction and melting of the insulating layer can occur.

The maximum permissible long-term current load is the quantitative value of the electric current that can pass the cable for a long time without overheating. To determine this indicator, it is initially necessary to sum up the powers of all energy consumers. After this, calculate the load using the formulas:

I = P∑*Ki/U (single-phase network),
I = P∑*Kи/(√3*U) (three-phase network), where:

P∑ – total power of energy consumers;
Ki – coefficient equal to 0.75;
U – electrical voltage in the network.

Tablitz for matching the cross-sectional area of copper conductorsconductor products current and power *

Section of cable and wire products	Electrical voltage 220 V		Electrical voltage 380 V
	Current strength, A	power, kWt	Current strength, A	power, kWt
2,5	27	5,9	25	16,5
4	38	8,3	30	19,8
6	50	11	40	26,4
10	70	15,4	50	33
16	90	19,8	75	49,5
25	115	25,3	90	59,4
35	140	30,8	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

*Important! Conductors with aluminum conductors have different values.

Determining the cross-section of a cable product is a particularly important process in which miscalculations are unacceptable. You need to take into account all factors, parameters and rules, trusting only your calculations. The measurements taken must coincide with the tables described above - if they do not contain specific values, they can be found in the tables of many electrical engineering reference books.

Video

Calculation of wire cross-section is a very important component of high-quality and reliable electrical wiring. After all, these calculations include the power consumption of electrical equipment and the long-term permissible currents that the wire can withstand in normal operating mode. In addition, we all want to have a guarantee and be confident in the electrical and fire safety of electrical wiring, so wire cross section calculation is so important.

Let's see what the wrong choice of wire cross-section can lead to.

In most cases, electricians currently working on the market in this service sector do not bother themselves with performing any calculations at all, but simply overestimate or underestimate the cross-section of the wire. This is usually due to the fact that, after a long time after graduating from educational institutions, they do not remember how to do this, since the acquired knowledge was not consolidated in practice in a timely manner. For the most part, this knowledge is possessed by a certain portion of power engineers and chief engineers, and this is due to the fact that their knowledge is exploited in this direction every day.

If the wire cross-section is less than required

Let's consider an example if the wire cross-section is underestimated, that is, less power consumption is selected.

This case is the most dangerous of all those considered, as it can lead to damage to electrical equipment, fire, electric shock to people, and often death. Why this happens is very simple. Let's say we have an electric water heater with a power of 3 kW, but the wire installed by a specialist can withstand only 1.5 kW. When you turn on the water heater, the wire will become very hot, which will eventually lead to damage to the insulation, and subsequently to its complete destruction, and a short circuit will occur.

If the wire cross-section is larger than required

Now, let's look at an example with an oversized wire cross-section, chosen larger than what is required for the equipment. People even have all sorts of sayings about reserve, they say it’s not superfluous. Within reasonable limits, it is really not superfluous, but it will cost much more than required. For the 3 kW water heater given in the example above, according to calculations, we require a wire cross-section of 2.5 mm 2, look at table 1.3.4 given in the PUE (electrical installation rules). And in our case, let’s say a 6 mm 2 wire was used, the cost of this wire will be 2.5 times higher than 2.5 mm 2, let’s say 2.5 costs 28 rubles, and 6 costs 70 rubles per meter. We will need, say, 20 meters, in the first case we will spend 560 rubles, and in the second 1400 rubles, the difference in money is obvious. Just imagine, if you over-wire the entire apartment, how much money you will throw away. Hence the question, do you need such a reserve?

Summing up the interim results, we learned that incorrect calculation of the wire cross-section has very unpleasant, and in some cases, serious consequences, so it is simply necessary to approach the choice of wire cross-section correctly, competently and seriously.

Formula for calculating wire cross-section

I calculated =P/U nom

where I calculated – calculated current,

P – equipment power,

U nom – rated voltage = 220 volts

For example, let's calculate a 3 kW electric water heater.

3 kW = 3000 W, I calculated =3000/220=13.636363 ..., round I calculation = 14 A

There are also various correction factors depending on the environmental conditions and the laying of the wire, as well as the coefficient of repeated short-term switching on. To a greater extent, these coefficients are important in three-phase networks of 380 volts in production, where large starting currents are present. And in our case, we have household electrical appliances designed for a voltage of 220 volts, so we will not calculate it, but we will definitely take it into account and determine its average value equal to 5 A and add it to the calculated current.

As a result, I calculation = 14 +5 = 19 A,

The wire used is three-core copper (phase, neutral, ground), see the table.

Table of cross-section of copper wires according to long-term permissible current (PUE table 1.3.4)

If the value is in the interval between two currents of different sections, in our case 15 A and 21 A, we always take the larger one. The calculated wire cross-section required to connect a 3 kW water heater is 2.5 mm 2.

So, using the 3 kW water heater shown in the example, we calculated the cross-section of the wires and found out why it is impossible to underestimate and overestimate the cross-section of the wires. We learned how to determine long-term permissible currents, as well as choose the correct wire cross-section.

Similarly, according to the formula, you can also perform this, thanks to which you will achieve optimal illumination without straining your eyesight and high-quality distribution of light flux.

By calculating the wire cross-section with your own hands, you will save:

When purchasing wires, the cost of the wire increases with the cross-section. For example, 1 meter of a non-flammable wire of a brand that has proven itself quite well in the installation of internal electrical wiring with a cross-section of 1.5 squares costs 15 rubles, and the same wire with a cross-section of 2.5 squares costs 23 rubles, the difference is 8 rubles per meter, from 100 meters this is already 800 rubles.
On the purchase of protection devices, circuit breakers, RCDs. The higher the operating current of the device, the higher the price. For example, a single-pole circuit breaker for 16 Amps costs 120 rubles, and for 25 Amps it costs 160 rubles, a difference of 40 rubles. The average power panel has about 12 circuit breakers, each costing 40 rubles, the total will be 480 rubles. The difference in the cost of the RCD will be even greater, about 200-300 rubles.