How to find rated current

How to find rated current

To find rated current for a certain conductor, use the special table. It is specified in it at what values of current the conductor can collapse. For finding of rated current for electric motors of various designs, use special formulas. If the question concerns the safety lock, then, knowing the power on which it is calculated, find its rated current.

It is required to you

  • For carrying out measurements and calculations take the voltmeter, a caliper, the table of dependence of rated current on section, the registration certificate of electric motors.


1. Determination of rated current Determine material of which the wire is made by the section of a wire. Most often wires from copper and aluminum meet round cross section. Measure its diameter by a caliper, and then find cross-sectional area, having increased diameter square by 3.14 and having divided into 4 (S=3.14•D²/4). Define wire type (single-core, two-core or three-vein). After that determine rated current for this wire by the special table. Excess of this value will lead to burn-out of a wire.

2. Determination of rated current of a predokhranitelyan the fuse is surely specified the power on which it is calculated with a stock approximately in 20%. Learn tension in network where the safety lock has to be inserted if it is not known, measure it by means of the voltmeter. To find rated current, it is necessary the maximum rated power of the safety lock in watts, to divide into tension in network in volts. In case current increases more than the face value, the conductor in the safety lock will collapse.

3. Determination of rated current of the electric motor to find rated current for the direct current motor, learn its rated power, source tension where it is connected and also its efficiency. These data have to be in technical documentation of the electric motor, and measure tension of a source by the voltmeter. Then consistently divide power in watts into tension in volts and efficiency in single shares (I=P / (U•η). The rated current in amperes will be result. For the three-phase engine of alternating current in addition learn the nominal power factor of the engine, and count rated current by the same technique, only divide result into nominal power factor (Cos(φ)).

Author: «MirrorInfo» Dream Team