For a three-phase 380-volt network with a 15-kilowatt resistive load, the current is approximately 22.8 amperes. This indicator is the basis for selecting protective automation and the cross-section of conductors. When calculating, it is necessary to take into account the power factor (cos φ), which for industrial equipment is often equal to 0.8, which increases the operating current to 28.5 amperes. Accurate knowledge of these parameters prevents overheating of the wiring and false triggering of input circuit breakers.
Owners of garages and private houses are often faced with the need to connect powerful electrical equipment, such as electric welding machines or charging stations for electric vehicles. An error in determining the rating of the machine can lead to constant power outages at the most inopportune moment. Therefore, the question “15 kW how many amperes is 380” requires not just a theoretical answer, but a practical application of formulas taking into account real operating conditions.
Formula for calculating current for a three-phase network
The basis for any calculations in electrical engineering is Ohm's law and the total power formula for a three-phase circuit. To find out how many amperes falls on 15 kW, it is necessary to divide the power by the product of voltage, root of three and cosine phi. For a 380 volt network, the formula looks like this: I = P / (√3 × U × cos φ). If we neglect the reactive component and take cos φ equal to unity, we get a simplified calculation, but it does not always reflect reality.
Let's consider a detailed calculation for standard conditions. With a power of 15,000 Watts and a voltage of 380 Volts, if the load is active (for example, heating elements), the current will be about 22.8 A. However, if an asynchronous motor or switching power supply is connected, reactive power comes into play. In this case full power increases, and with it the current in the wires.
If instead of 380 volts the outlet is 360 volts, the current will increase to maintain the same power. That is why engineers always include a safety margin. To accurately determine the parameters, use a calculator or lookup tables that take into account various coefficients.
- ⚡ Active load (heating, light) - cos φ ≈ 1, current ~22.8 A.
- ⚡ Inductive load (motors) - cos φ ≈ 0.8, current ~28.5 A.
- ⚡ Mixed load (computers, drivers) - cos φ ≈ 0.9, current ~25.3 A.
Selecting a 15 kW circuit breaker
After determining the calculated current at 22.8–28.5 amperes, the question arises of choosing a rating circuit breaker. The standard range of machines includes values of 16, 20, 25, 32 amperes. You cannot select a device with a rating equal to the rated current - it will operate at the limit and may turn off during short-term inrush currents.
The optimal choice for a load of 15 kW with a three-phase input would be an automatic machine with a rating of 25 or 32 amperes. If you have a purely active load (for example, an electric boiler), it will be enough 25A. For equipment with electric motors, where starting currents can exceed operating currents by 5-7 times, it is better to install a machine with characteristic “D” or increase the rating to 32A, but only if the cable cross-section allows this.
⚠️ Attention: Installing a machine with a larger rating than the cable cross-section allows is strictly prohibited. This can lead to melting of the insulation and a fire, since the machine will not operate until the critical wire temperatures are reached.
When choosing, pay attention to the breaking capacity. For garage cooperatives and private homes, it is recommended to use circuit breakers with a breaking capacity of at least 6 kA (6000 Amperes). This ensures that the device does not stick if there is a short circuit on the input.
☑️ Check before installing the machine
Cable cross-section for connection 15 kW
Safe transmission of power with a power of 15 kW requires the correct selection of the cross-section of copper or aluminum conductors. For a current of about 28-30 amperes, the minimum permissible cross-section of a copper cable is 4 mm², but taking into account the length of the route and the safety margin, professionals recommend using 6 mm² or even 10 mm². The aluminum wire should be thicker - at least 10 mm², and preferably 16 mm².
The table below will help you navigate the choice of cross-section depending on the installation method and conductor material. Data is based on continuous load and standard cooling conditions.
| Material | Section (mm²) | Allowable current (A) | Max. power (kW) |
|---|---|---|---|
| Copper | 4.0 | ~30-35 | ~16-19 |
| Copper | 6.0 | ~40-45 | ~22-25 |
| Aluminum | 10.0 | ~35-40 | ~19-22 |
| Aluminum | 16.0 | ~50-55 | ~28-30 |
If a cable is buried in the ground or in a bundle with other wires, its ability to dissipate heat is reduced. In such cases, it is necessary to apply reduction factors or increase cable section. Also take into account the length of the line: at a distance of more than 50 meters from the panel to the consumer, a voltage drop may occur, which will require an increase in the thickness of the cores.
Effect of temperature on cable
When laying in conditions of high temperatures (for example, in hot workshops or under the scorching sun in closed boxes), the permissible current is reduced. Use special heat-resistant cables or increase the cross-section by one step.
Features of connection in the garage and private house
Garage co-ops often have problems with power quality. The voltage of 380 volts can “walk” in the range from 340 to 410 volts. At low voltage, the current increases, which causes heating of the contacts and wiring. Therefore, to connect 15 kW in a garage, it is critical to use high-quality terminal blocks and regularly tighten the connections.
Private houses usually have a more stable network, but here the issue of load distribution across phases comes into play. If you connect 15 kW, this does not mean that you can “hang” the entire load on one phase. The three-phase load must be symmetrical. A phase imbalance of more than 30% can lead to failure of three-phase equipment and tripping of the protection.
To organize the input of 15 kW, a circuit with a three-phase meter and a differential circuit breaker or a combination of “automatic machine + RCD” is often used. Residual current device (RCD) must be designed for a current of at least the nominal value of the machine, and the leakage current for a garage or wet room is selected at 30 mA.
- 🔌 Use three-phase 3P+PE+N type sockets for safe connection.
- 🔌 Install voltage control relays to protect against surges.
- 🔌 Ensure reliable grounding of the circuit before starting operation.
Tip: Before final connection of powerful equipment, check the tightness of all screw connections in the panel. A loose contact at 30 amps is a guaranteed source of heat and potential fire.
Electricity consumption calculation
Understanding how many amps your load draws is important not only for safety, but also for savings. Knowing the current strength, you can calculate the approximate consumption and compare it with the meter readings. For 15 kW, 15 kWh of electricity is consumed per hour of operation.
If the tariff is, for example, 5 rubles per kWh, then an hour of equipment operation will cost 75 rubles. With round-the-clock operation (for example, ventilation or heating), the amount per month will be impressive. Therefore, installing timers or smart relays that turn off power during idle hours becomes economically feasible.
It is also worth considering inrush currents. If you run a powerful compressor several times an hour, this creates short-term peaks in consumption. Modern electronic meters take into account both active and reactive power (for industrial tariffs), so a low cosine phi can cost money.
⚠️ Attention: Do not try to “deceive” the meter or increase the power limit without agreement with the energy sales company. This is fraught with huge fines and disconnection from the network.
Frequent errors during installation and operation
One of the most common mistakes is using twists instead of terminal connections. At currents above 16 amperes, the twist oxidizes, heats up and burns out. Always use screw terminals, sleeves or welding to connect wires.
The second mistake is ignoring color coding. In a three-phase network, it is important to observe the phase order (L1, L2, L3), especially for motors. By mixing up the phases, you can run the engine in the opposite direction, which will lead to damage to the mechanism (for example, a pump or compressor).
The third mistake is saving on materials. A cheap machine or cable “not in accordance with GOST” (where the core cross-section is underestimated by 20-30%) is a time bomb. A load of 15 kW does not forgive negligence. Always check the cable markings and certifications.
Main conclusion: For 15 kW at 380V you need a 25-32A automatic, a copper cable of 6-10 mm² and mandatory grounding. Saving on protection components is unacceptable.
Is it possible to connect 15 kW to a single-phase 220V network?
Theoretically it is possible, but the current will be about 68-70 amperes (taking into account cos φ). This will require a 100A input and very thick wires (minimum 16mm² copper). Most household networks and meters are not designed for such current in one phase. Three-phase connection (380V) for 15 kW is the only correct and safe solution.
Which machine to choose: 25A or 32A?
The choice depends on the type of load and cable cross-section. For a resistive load (heating elements) and a 4-6 mm² cable, 25A is enough. For motors or if the cable is 10 mm² and there is input margin, it is better to use 32A to avoid false alarms during startup.
Is a three-phase RCD necessary if the load is single-phase?
If you distribute single-phase loads across three phases (for example, sockets in a garage), then a three-phase RCD at the input will protect the entire network. If you have strictly one consumer of 15 kW (three-phase), an RCD is still necessary to protect against leaks to the housing.
What to do if the machine keeps knocking out?
Check the total power of the switched on devices. You may have exceeded the 15 kW limit. Also check the tightness of the contacts - poor contact heats up the thermal release of the machine. If the current is normal, but the machine heats up and turns off, it is possible that the device itself is defective or the mechanism is aging.