Calculation formulas when working with wire. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Amateur radio calculations

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Calculations by formulas are more accurate than by tables, and are necessary in cases where the tables do not contain the necessary data. Wire resistance (in ohms) is calculated by the formula

p-specific resistance (according to the table); I-wire length, m; s-cross-sectional area of ​​the wire, mm²; d-wire diameter,

The wire length from these expressions is determined by the formulas

The cross-sectional area of ​​the wire is calculated by the formula

The resistance R2 at temperature t2 can be determined by the formula

a-temperature coefficient of electrical resistance (from table 1), R1 - resistance at some initial temperature t1.

Usually, t1 is taken as 18°C, and in all the tables given, the value of R1 is shown for t1=18°C.

Permissible current strength at a given current density rate A/mm² is found from the formula

The required wire diameter for a given current strength is determined by the formula

if the load rate A \u2d XNUMX a / mm², then the formula takes the form:

The melting current for thin wires with a diameter of up to 0,2 mm is calculated by the formula

where d - wire diameter, mm; k is a constant coefficient equal to 0,034 for copper, 0,07 for nickel, and 0,127 for iron. The wire diameter from here will be:

Table 1

Basic data for the calculation of heating elements

Substituting the obtained values ​​into the formula

where l is the length of the wire, m; S-section of wire, mm²; R is the resistance of the wire. Ohm; p-specific resistance of the wire (for nichrome p \u1,1d 1,3, for fechral p \uXNUMXd XNUMX), Ohm * mm²/ m, we get the required wire length for the heating element.

When operating electro-radio equipment, it is necessary to know the cross section of the installation wires - depending on the amount of current passing through them. The table shows the maximum allowable load currents for copper wires of various sections.

Permissible load currents of copper wires (mounting).

Literature:

1. V.G.Bastanov. 300 practical tips. Moscow worker, 1986.

Publication: N. Bolshakov, rf.atnn.ru

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