Need to find short circuit current can appear for check of the equipment for work in "stressful" conditions, for definition of suitability of means of automatic protection of the line, in means of protection from a thunderstorm. There is also some other cases when it is necessary to execute calculation or measurement of short circuit current.
It is required to you
- handle, piece of paper, calculator.
Instruction
1. In any electrical network the power supply is switched on consistently to a chain of consumers. In case of short circuit there is a replacement of consumers by the ordinary electric conductor. Draw the power supply, from it two wires to consumers. Specifically for your case learn what internal resistance of a source (in Ohms) and its tension (in Volts). Write it near the power supply.
2. Learn resistance of connecting wires to the place of short circuit. There are two ways: - theoretical: learn of what metal wires, their section and length are made. On a formula R=r*l/s find resistance where the r-specific resistance (table value), l is length of the conductor in meters, s is cross-sectional area in square meters; - practical: disconnect tension from network, close the site necessary to you and connect to it an ohmmeter, take readings from the device. Sign the calculated or measured value of resistance near a wire.
3. Calculate the general resistance of a chain at short circuit. For this purpose put resistance of a source and conductors. To reduce an error, you can measure and add resistance of connecting terminals. Find short circuit current from the law of Ohm: I=U/R where U is tension of a source (Paragraph 2), R is the general resistance of a chain (Paragraph 4).
4. If you want to define what "stopper" is required to be established in your apartment for effective protection against short circuit, use the special device. It and is called – the measuring instrument of short circuit current. Connect the device in network and pass into the mode of measurement of short circuit current. Resistance of the device will smoothly fall, and it will measure short circuit current if automatic protection does not work.