Normal life situation - it is necessary to install a new switch or outlet in the country.All this is - socket, wire, fasteners, chose the site for installation.Take it and do it.But no!I forgot to check whether it is possible to use the existing wire?To determine a possible need to use a term such as current density, and found it permissible value.
What is this figure, and why is it so important?It is believed that under normal conditions of the electric current passes through the entire volume of the conductor.Simplistically - the value of the current flowing through the cross section of the conductor, its density is considered.For its measurement in the SI system is used such a unit is amperes per square meter (A / m), and it serves to establish permissible when flowing through the wire current value.
Where such requirements?Everything is very simple.Any wire resists the current flow, resulting in "lost" part of it.This "lost" current causes heating of the conductor.If the losses are big, then followed by excessive heating of the conductor, and he melted.To this was not, for each type of instrument is set allowable current density, compliance with which will ensure reliable operation of the wiring.
It should be clear that if a section of the conductor is chosen correctly, ieis supposed to use the load consumes much power, or both include several household appliances (kettle, computer, TV, etc.), the current flow will cause significant heating of wires and they melt.Or serve the cause of the fire.
That is why when choosing a cable cross-section, or in any other case, when it is planned to connect the load, it is necessary to take into account the allowable current density.When the design work for these purposes by engineers using special formulas and tables.However, the calculation section of the wire on the permissible current density gives a perfectly acceptable from a practical point of view the result.
For this purpose it is not necessary to use complex formulas and cumbersome spreadsheets.It is only necessary to take into account the same value - the current density in the copper wire should not exceed six to ten amperes per square meter.millimeter.The data is valid for copper.As now used mainly copper wires of said data should be sufficient to determine the possibility of its application.
need to understand these figures as follows.When continuous operation the current density in the chain should not exceed 6 A / sq.mm.Then the wiring will run in lite mode, and it can be used for a long time.However, it can be operated in the mode of 10 A / sq.mm, but such a regime should be short-lived.
how to apply it in practice?It is necessary to define the maximum connected load.Let it be, for example, at the same time it included a chandelier with five lights of 100 watts, TV, computer, refrigerator.The total capacity of not more than 5 kW, divide this figure by the line voltage, 5000 watts divided by 220, we get round figures 23A.So, in order to ensure the passage of the short-time current needs copper wire 2.5 sq.millimeter.
can approach this issue in a different way.If the outlet is written that it is designed for current 6A, the use of copper wire more than one square.mm unnecessary outlet burned before.Just for your information - as if the conductive material is aluminum, the allowable current density is equal to 4.6 A / square.mm.So, using these figures can determine what section of the wire to be used for electrical devices.
In the above material is given the definition of "current density".It described the need for its use to select the section of wires.The practical recommendations on the use of this parameter in operation.
