The online cable cross-section calculator will help you calculate the optimal conductor cross-section based on power, line length and load current.
Calculate the optimal conductor cross-section for electrical wiring
The online cable cross-section calculator will help you calculate the optimal conductor cross-section based on power, line length and load current. The tool is suitable for selecting cables when designing electrical wiring in a house, apartment, garage or office. The type of current (single-phase/three-phase), conductor material (copper or aluminum) and permissible voltage loss are taken into account.
The calculator uses proven formulas for calculating cable cross-section in accordance with GOST and international standards (IEC). The calculation takes into account the load power or current, network voltage, line length, conductor material, installation method, ambient temperature and permissible voltage loss. This allows you to obtain accurate results for designing electrical wiring of any complexity.
Let's look at practical examples of calculating cable cross-sections for various use cases:
Single-phase network 220V, load 3.5 kW, length 20 m
Входные данные:
Power: 3.5 kW
Voltage: 220 V
Length: 20 m
Material: Copper
Network type: Single phase
cosφ: 0.9Расчёт:
Current: I = 3500 / (220 × 0.9) = 17.7 A
For copper, permissible current density: 10 A/mm²
Section: S = 17.7 / 10 = 1.77 mm²
Standard cross-section: 2.5 mm²
Voltage loss: ΔU = 2 × 17.7 × 0.0175 × 20 / 1000 = 0.012 V (0.005%)Результат:
Recommended cable: 2.5 mm² (copper)
Тип:
Sockets in the apartment
Cross-section 2.5 mm² is standard for sockets, withstands current up to 25 A
Single-phase network, load 1.2 kW, length 30 m
Входные данные:
Power: 1.2 kW
Voltage: 220 V
Length: 30 m
Material: Copper
Network type: Single phase
cosφ: 0.95Расчёт:
Current: I = 1200 / (220 × 0.95) = 5.74 A
For lighting, permissible current density: 8 A/mm²
Section: S = 5.74 / 8 = 0.72 mm²
Standard cross-section: 1.5 mm²
Voltage loss: ΔU = 2 × 5.74 × 0.0117 × 30 / 1000 = 0.004 V (0.002%)Результат:
Recommended cable: 1.5 mm² (copper)
Тип:
Lighting
A cross-section of 1.5 mm² is sufficient for lighting, the minimum for sockets is 2.5 mm²
Single-phase network, 7 kW stove, length 15 m
Входные данные:
Power: 7 kW
Voltage: 220 V
Length: 15 m
Material: Copper
Network type: Single phase
cosφ: 1.0Расчёт:
Current: I = 7000 / (220 × 1.0) = 31.8 A
For powerful devices, permissible current density: 9 A/mm²
Section: S = 31.8 / 9 = 3.53 mm²
Standard cross-section: 4 mm² (or 6 mm²)
Voltage loss: ΔU = 2 × 31.8 × 0.0044 × 15 / 1000 = 0.0042 V (0.002%)Результат:
Recommended cable 4-6 mm² (copper)
Тип:
Electric stove
Electric stoves require a separate line with a cross-section of at least 4 mm²
Three-phase network 380V, load 15 kW, length 50 m
Входные данные:
Power: 15 kW
Voltage: 380 V (three phase)
Length: 50 m
Material: Copper
Network type: Three-phase
cosφ: 0.9Расчёт:
Phase current: I = 15000 / (√3 × 380 × 0.9) = 25.3 A
For a three-phase network, permissible density: 8 A/mm²
Section: S = 25.3 / 8 = 3.16 mm²
Standard cross-section: 4 mm²
Voltage loss: ΔU = √3 × 25.3 × 0.0044 × 50 / 1000 = 0.0096 V (0.003%)Результат:
Recommended cable 4 mm² (copper) for each phase
Тип:
Three-phase line
For a three-phase network, a 4-6 mm² cable per phase is required
Single-phase network, load 5 kW, length 40 m, aluminum
Входные данные:
Power: 5 kW
Voltage: 220 V
Length: 40 m
Material: Aluminum
Network type: Single phase
cosφ: 0.9Расчёт:
Current: I = 5000 / (220 × 0.9) = 25.25 A
For aluminum permissible current density: 6 A/mm²
Section: S = 25.25 / 6 = 4.21 mm²
Standard cross-section: 6 mm² (aluminum)
Voltage loss: ΔU = 2 × 25.25 × 0.0027 × 40 / 1000 = 0.0055 V (0.002%)Результат:
Recommended cable 6 mm² (aluminum)
Тип:
Aluminum cable
Aluminum cable requires a larger cross-section, but is cheaper than copper
Single-phase network, load 2 kW, length 100 m, permissible losses 5%
Входные данные:
Power: 2 kW
Voltage: 220 V
Length: 100 m
Material: Copper
Network type: Single phase
cosφ: 0.9
Allowable losses: 5%Расчёт:
Current: I = 2000 / (220 × 0.9) = 10.1 A
Maximum loss: ΔU = 220 × 0.05 = 11 V
Resistance: R = 11 / (2 × 10.1) = 0.545 Ohm
Section: S = (2 × 0.0175 × 100) / 0.545 = 6.42 mm²
Standard cross-section: 10 mm²Результат:
10 mm² cable (copper) recommended
Тип:
Long line
Long lines require larger cross-sections to compensate for voltage losses
The calculator uses standard formulas for calculating cable cross-section:
Our cable size calculator provides many benefits for accurate electrical wiring calculations.
The calculator uses proven formulas in accordance with GOST and international standards (IEC), taking into account all parameters: power, current, voltage, line length, conductor material, laying method and permissible losses for the most accurate results.
Selecting the correct cable size helps avoid wastage of expensive cables and ensures safety, which significantly reduces project costs and material costs.
Knowing in advance the required cable cross-section, you will be able to properly plan purchases, select circuit breakers and protective devices, avoiding installation errors.
A simple interface and quick calculations allow you to get all the necessary data in a few seconds without complex calculations and formulas.
To select the correct cable cross-section, it is important to take into account many factors affecting the safety and reliability of the power supply.
To calculate the cable cross-section by power, use the formula: I = P / (U × cosφ), where I - current (A), P - power (W), U - voltage (V), cosφ - power factor. Then cross section S = I / J, where J is the permissible current density (8-10 A/mm² for copper). The calculator automatically performs all calculations.
Yes, the calculator automatically calculates the voltage drop using the formula: ΔU = 2 × I × R × L / 1000, where R is the resistivity, L is the line length. If the losses exceed the permissible values (5% for residential, 3% for industrial), the calculator will increase the cable cross-section.
Copper cable is preferable: it has lower resistance (1.6 times), conducts current better, is safer and more durable. Aluminum cable requires a larger cross-section (1.6 times) and is used mainly for outdoor installation due to its lower cost.
Yes, the calculator supports calculations for a three-phase 380V network. For three-phase systems, the current is calculated using the formula: I = P / (√3 × U × cosφ). Each phase requires the same cable cross-section, typically 4-6 mm² for loads of 10-15 kW.
Yes, the calculator calculates the current automatically using the formula: for a single-phase network I = P / (U × cosφ), for a three-phase network I = P / (√3 × U × cosφ). Then the required cable cross-section is determined based on the current, taking into account the permissible current density.
Calculations are performed according to GOST R 50571.5.52-2011, GOST 31996-2012 and international standards IEC 60364-5-52. Allowable currents for various installation methods, current density and standard cable cross-sections (1.5, 2.5, 4, 6, 10, 16, 25, 35, 50 mm²) are taken into account.
Power factor (cosφ) shows the proportion of active power to total power. For active loads (lamps, heaters) cosφ = 1.0, for electric motors cosφ = 0.7-0.85, for household appliances cosφ = 0.8-0.9. A lower cosφ requires more current for the same power.
For sockets in the apartment, a copper cable with a cross-section of at least 2.5 mm² is used. This section can withstand current up to 25 A (power up to 5.5 kW at 220V) and ensures safety. Aluminum cable for sockets requires a cross-section of 4 mm². The 1.5 mm² section is used for lighting only.
For lighting, a copper cable with a cross-section of 1.5 mm² is sufficient, which can withstand current up to 19 A (power up to 4 kW). For long lighting lines (more than 30 m), it is recommended to use a 2.5 mm² cable to compensate for voltage losses.
An electric stove with a power of 7-10 kW requires a separate line with a copper cable with a cross-section of 4-6 mm². Load current: I = 7000 / 220 = 31.8 A. Section 4 mm² can withstand current up to 38 A, section 6 mm² - up to 46 A. Use a 25-32 A circuit breaker.
The length of the cable directly affects the voltage loss: the longer the line, the greater the loss. For lines up to 30 m, a standard section is sufficient. For lines 30-50 m, it is recommended to increase the cross-section by one size. For lines over 50 m, be sure to check the voltage loss - it may be necessary to increase the cross-section by 1.5-2 times.
For input into a private house with a single-phase 220V network with a power of 10-15 kW, a cable with a cross-section of 10-16 mm² (copper) is used. For a three-phase 380V network with a power of 15-20 kW - 6-10 mm² cable for each phase. Internal wiring: sockets 2.5 mm², lighting 1.5 mm², electric stove 4-6 mm².
According to the PUE (Electrical Installation Rules), only copper cable is allowed in residential premises. Aluminum cable can only be used for external installation, in entrances and for entry into the house. Inside the apartment, be sure to use a copper cable with a cross-section of 2.5 mm² for sockets.
For direct current, the calculation is simpler: I = P / U, where U is the direct current voltage. The cross section is calculated in the same way: S = I / J. For DC, the permissible current density is higher: 12-15 A/mm² for copper. There is no voltage loss since there is no reactance.
The permissible current density is the maximum current per unit cross-sectional area of the cable. For copper with an open gasket: 8-10 A/mm², with a closed gasket: 6-8 A/mm². For aluminum: 5-6 A/mm². The density depends on the installation method, ambient temperature and the number of wires in the cable.
The circuit breaker is selected according to the permissible cable current: for a cable 1.5 mm² - 10 A, for 2.5 mm² - 16-20 A, for 4 mm² - 25 A, for 6 mm² - 32 A, for 10 mm² - 40-50 A. The rated current of the circuit breaker should not exceed the permissible current of the cable for overload protection.
For a garage with a load of 5-7 kW, a copper cable with a cross-section of 4-6 mm² is used for input. Inside the garage there are 2.5 mm² sockets, 1.5 mm² lighting. If you have a welding machine or compressor, you need a separate line of 4-6 mm². Aluminum cable can be used for outdoor installation, but the cross-section must be 1.6 times larger.
Allowable voltage losses: for residential premises - no more than 5% of the rated voltage (11 V for 220V), for industrial facilities - no more than 3% (11.4 V for 380V), for lighting lines - no more than 3%. If losses exceed, it is necessary to increase the cable cross-section or reduce the line length.
For a three-phase motor, the current is calculated: I = P / (√3 × U × cosφ × η), where η is the motor efficiency. The cross section is selected according to the current, taking into account the starting currents (5-7 times more than the rated current). For example, 3 kW motor at 380V: I = 3000 / (√3 × 380 × 0.85 × 0.9) = 6 A, 1.5-2.5 mm² cable required.
No, you cannot use a cross section smaller than the calculated one. This will lead to overheating of the cable, destruction of insulation, short circuit and fire. The cross section should be no less than the calculated one, preferably with a margin of 15-20%. Minimum sections according to the PUE: for lighting 1.5 mm², for sockets 2.5 mm².
VVG - copper cable with PVC insulation for stationary installation in walls and under plaster. PVS - flexible multi-core cable for connecting household appliances. NYM is a German standard, an analogue of VVG with an additional protective layer. For stationary wiring use VVG or NYM, for transfers - PVS.
For an office, the load is usually 50-100 W/m². With an area of 100 m², the load is 5-10 kW. For input for a single-phase network - a cable of 10-16 mm², for a three-phase network - 6-10 mm² per phase. Inside the office: sockets 2.5 mm², lighting 1.5 mm². Consider turning on computers and air conditioners at the same time.
Yes, the installation method affects the permissible current. When laid open, the cable is cooled better, the current can be 20-30% higher. When the installation is closed in a wall or corrugation, the cooling is worse and a larger cross-section is required. When laid in a bundle (several cables together), the permissible current is reduced by 15-20%.
An electric boiler with a power of 6-12 kW requires a separate line. Current: I = 8000 / 220 = 36.4 A for 8 kW. We recommend a copper cable with a cross section of 6 mm² (withstands current up to 46 A) with a 32-40 A circuit breaker. For boilers 12-15 kW - a 10 mm² cable, for 18-24 kW - 16 mm² or a three-phase connection.
For baths and saunas, a heat-resistant cable with insulation that does not support combustion (brand VVGng or NYM) is required. The section is selected as usual, but due to high temperature and humidity it is recommended to increase the section by one size. Use only copper cable, circuit breakers and RCDs.
An air conditioner with a power of 1.5-3 kW (split system) requires a separate line with a 2.5 mm² copper cable and a 16 A circuit breaker. Powerful 5-7 kW air conditioners require a 4 mm² cable and a 25 A circuit breaker. Consider the starting current of the compressor, which is 3-5 times higher than the rated current.
For a storage water heater with a power of 2-2.5 kW, a 2.5 mm² cable (copper) with a 16 A automatic is sufficient. Instantaneous water heaters with a power of 6-8 kW require a 4-6 mm² cable and a 32 A automatic. For powerful instantaneous heaters 10-15 kW - a 10 mm² cable or a three-phase connection.
For a greenhouse with lighting and heating (2-3 kW), a copper cable with a cross-section of 2.5 mm² is used for input. Inside the greenhouse the lighting is 1.5 mm². Due to high humidity, use moisture-protected cable (VVG or VVGng), circuit breakers and RCDs with a tripping current of 30 mA to protect against electric shock.
At ambient temperatures above 30°C, the permissible cable current is reduced: at 35°C - by 10%, at 40°C - by 15%, at 45°C - by 20%. At temperatures below 25°C, the permissible current can be increased by 5-10%. The calculator takes temperature into account when choosing cable cross-section.
Yes, you can use different sections in one line, but the section should only increase in the direction from the source to the load. You cannot reduce the cross-section of a section of the line - this will lead to overload and overheating. For example, the input is 16 mm², then the main is 6 mm², then the outlets are 2.5 mm².
To charge an electric vehicle with a power of 7-11 kW (single-phase charging), a 6-10 mm² cable (copper) and a 32-40 A circuit breaker are required. For fast charging 22 kW (three-phase) - a 10 mm² cable for each phase. Be sure to use a cable with overheat protection and type B RCD.
For street lighting, a cable with protection from UV radiation and moisture is used (for example, an AVVG cable or a special street cable). The cross section is selected as usual: for one lamp 1.5 mm², for several lamps 2.5 mm². The line length can be large, so check the voltage loss - a cross-section of 4-6 mm² may be required.
For a showcase with backlighting with a power of 1-2 kW, a 2.5 mm² cable is sufficient. If the line length is more than 20 m or there are many luminaires, check the voltage loss. For large display cases with powerful lighting (5-7 kW), use a 4-6 mm² cable and a 25-32 A circuit breaker.
The PUE table shows permissible currents for standard cable cross-sections for various installation methods. Select a section where the permissible current is at least 25% greater than the calculated load current. For example, with a current of 20 A for a 2.5 mm² cable (copper, open laying), the permissible current of 27 A is suitable.
Yes, you can connect several sockets to one 2.5 mm² cable if the total load does not exceed 5.5 kW (25 A). When connecting, take into account the simultaneity factor - not all sockets work at the same time. For a kitchen with many appliances, it is better to use several 2.5 mm² lines.
For an electric heated floor with a power of 1-2 kW per room, a 2.5 mm² cable (copper) and a 16 A automatic circuit breaker are sufficient. Powerful 3-4 kW floor heating systems require a 4 mm² cable and a 25 A automatic circuit breaker. Keep in mind that the heated floor operates for a long time, so a cross-sectional reserve is required.