How to determine electric power

Determination of electric power of the consumer can be made by means of the tester which is adjusted in a wattmeter operating mode. Rated power is specified in technical documentation of the device, it can be calculated on rated voltage if it is not specified.

It is required to you

  • - tester;
  • - current source;
  • - technical documentation on the consumer.


1. Connect the consumer or the site of a chain on which electric power to a current source is defined. Switch a tester to the mode of measurement of a wattmeter. At connection to the site of a chain on which there is a consumer consider that in that case the tester is at the same time connected both as the ampermeter, and as the voltmeter. Therefore close the corresponding terminal for current consistently to the consumer, and the conductor giving tension, establish parallel to this site. On the screen of a tester there will be a power consumption in the specified units. It can be W, MW, kW, etc.

2. If the tester does not allow to measure power directly, calculate it. For this purpose switch the device for measurement of current. Attach it consistently to the consumer and, having connected the consumer to a source, determine current in a chain in amperes. Then switch a tester to voltage measurement. Connect it parallel to the consumer and find value of voltage drop on it in volts.

3. After that calculate watts. If measurements it is made in a chain of a direct current, surely consider polarity of devices at connection. The positive pole of a source has to be connected to a positive pole of a tester.

4. It is possible to find the rated power (maximum power at which the consumer can work) if it is not specified in documentation having calculated it. For this purpose learn the rated voltage on which the consumer is calculated. It is specified on its case or in technical documentation.

5. Measure the electrical resistance of the consumer of current. For this purpose switch a tester to an operating mode of an ohmmeter and attach it to the consumer's clips. On the screen the value of its resistance will appear. Express it in Ohms. Calculate rated power, having divided the rated voltage squared on R resistance (P=U²/R).

Author: «MirrorInfo» Dream Team