Build Daily


August 26, 2016 23:11

How to calculate the cable cross-section , so that it does not overheat

Before connecting the load to the network it is important to ensure sufficient thickness of live power cable.In the event of a significant excess of the allowable power possible destruction of insulation and even the veins due to its overheating.

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cable cross-section calculation power and amperage

Before producing the cable cross-section calculation power is necessary to calculate the amount of electrical power connected.Most modern apartments main customers are:

  • Refrigerator 300W
  • Washing Machine 2650 W
  • Computer 550W
  • Lighting 500W
  • Electric 1150 W
  • Microwave 700 W
  • TV 160W
  • heater 1950 W
  • cleaner 600W
  • Iron 1750W
  • Total 10310 W = 10,3 kW

In sum, most of the modern apartments consume about 10 kW.Depending on the time of day, this option can significantly decrease.However, when choosing a section of the conductor is important to be guided by a large amount.

You need to know the following: The cable cross-section calculation for single and three phase networks varies.But in fact, and in another case to consider first of all the three parameters:

  • amperage (I),
  • voltage (U),
  • power consumption (P).

There are also several other variables, their value is different for each case.

section calculations were performed for the single-phase network

section calculation of wire for power is carried out using the following formula:


  • I - current;
  • P - power consumption of all electrical appliances in the amount;
  • Ki - simultaneity factor, usually for payments accepted standard value of 0.75;
  • U - phase voltage, it is 220 (B), but can range from 210 to 240 (B);
  • Cos (φ) - for residential single-phase devices, this value remains unchanged and equal to 1.

If necessary, you can quickly calculate the current lower value cos (φ), and even Key.The resulting value will be different in the smaller side (15%) in the case of the use of such formula:

Finding current calculated by the formula, you can safely proceed to the selection of the supply cable.Specifically, its sectional area.There are special tables that present data to compare the amount of current, power consumption and cable cross-section.

These are very different for conductors made from different metals.To date, for the residential electrical wiring is usually used only the hard copper wire, aluminum is almost never used.While many of the old houses all the lines laid it with aluminum.

selectable cross-section of copper cable on the following parameters:

Calculation of conductor cross-section of the apartment - Table

Calculation of wire cross-section of the apartment - Table

It often happens that as a result of calculations obtained by the current, located between the two values ​​given in the table.In this case, use the next higher value.If the result of the calculation current value is equal to a single-core wire 25 (A), it is necessary to choose the cross section of 2.5 mm2 or more.

cable cross section calculation for three-phase network

To calculate the cross-section of the supply cable used in the three-phase network, you must use the following formula:


  • I - current, on which will be selected cross-sectional area of ​​the cable;
  • U - phase voltage, 220 (B);
  • Cos φ - phase angle;
  • P - measure the total power of all the appliances.

Cos φ in this formula is very important.Since a direct impact on the current.For a variety of equipment it is different, most often this option can be found in the technical documentation, or it is indicated on the housing.

Total power of consumers is very simple: all the facilities are added, the resulting value is used for calculations.

distinctive feature of selecting the cable cross-sectional area for use in the three-phase network is that the thinner core can withstand a greater load.We select the section required by the type plate.

The choice of cable cross sections for the three-phase network - Table

Cable Sizing for the three-phase network - Table

calculation-section for three-phase power is performed with the use of such a magnitude as √3 .This value is necessary to simplify the appearance of the formula.

Thus it is possible to replace the root of the product and, if necessary phase voltage for voltage linear.This value is 380 (B) (Ulineynoe = 380).

When selecting cable cross sections, for both three-phase and single-phase for the need to consider allowable continuous current .This parameter indicates the strength of the current (measured in amperes), which conductor can withstand for an unlimited amount of time.Determined it on special tables are available in SAE.For aluminum and copper conductors are significantly different data.

Permissible current duration - Table

Permissible current duration - Table

When exceeding the specified values ​​in the table begins to heat conductor.The heating temperature is inversely proportional to the current intensity.

temperature at a particular site can be increased not only due to improperly matched cross-section, but also because of poor contact. example, in place of twisted wires.Quite often, this happens as a result of direct contact between aluminum and copper cables.oxidized metal surface is covered with an oxide film, which significantly impairs the contact.At this point, the cable is heated.