Calculation of current by power and voltage
The inclusion of consumers in domestic or industrial electrical networks using a cable of less power than necessary can cause serious negative consequences. In the first place, this will cause the circuit breakers to constantly trip or the fuses to blow. In the absence of protection, the supply wire or cable may burn out. As a result of overheating, the insulation melts, and a short circuit occurs between the wires. To avoid such situations, it is necessary to pre-calculate the current by power and voltage, depending on the existing single-phase or three-phase electrical network.
Why do you need to calculate the current
The calculation of the magnitude of the current by power and voltage is carried out at the stage of designing the electrical networks of the facility. The data obtained allows you to choose the right power cable to which consumers will be connected. For current calculations, the value of the mains voltage and the full load of electrical appliances is used. In accordance with the magnitude of the current strength, the cross section of the cores of cables and wires is selected.
If all consumers in a house or apartment are known in advance, then the calculations are not particularly difficult. In the future, electrical work is greatly simplified. In the same way, calculations are made for cables supplying industrial equipment, mainly electric motors and other mechanisms.
Calculation of current for a single-phase network
The measurement is in amperes. To calculate the power and voltage, the formula is used I = P/ U, where P is the power or total electrical load, measured in watts. This parameter must be entered in the technical passport of the device. U - represents the voltage of the calculated network, measured in volts.
The relationship between current and voltage is clearly visible in the table:
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Electrical appliances and equipment |
Power consumption (kW) |
Current (A) |
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Washing machines |
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Stationary electric stoves |
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microwaves |
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Dishwashers |
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Refrigerators, freezers |
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Electric floor heating |
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Electric meat grinder |
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Electric kettle |
Thus, the relationship between power and current strength makes it possible to perform preliminary calculations of loads in a single-phase network. The calculation table will help you choose the required wire section, depending on the parameters.
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Conductor core diameters (mm) |
Copper conductors |
Aluminum conductors |
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Current (A) |
Power, kWt) |
Power, kWt) |
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Calculation of current for a three-phase network
In the case of using a three-phase power supply, the calculation of the current strength is carried out according to the formula: I = P/1.73U, in which P means the power consumed, and U is the voltage in the three-phase network. 1.73 is a special coefficient used for three-phase networks.
Since the voltage in this case is 380 volts, the whole formula will look like: I = P/657,4 .
In the same way as in a single-phase network, it can be determined using a table that reflects the dependence of these parameters on various loads.
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Conductor core diameters (mm) |
Conductor cross section (mm 2) |
Copper conductors |
Aluminum conductors |
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Current (A) |
Power, kWt) |
Power, kWt) |
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In some cases, the calculation of current by voltage and power should be carried out taking into account the total reactive power present in electric motors, welding and other equipment. For such devices, the power factor will be 0.8.
