In security engineering, we sometimes inevitably encounter some problems due to negligence or other reasons, such as: when we need to distinguish between positive and negative poles, we find that there is no multimeter.
Generally in the engineering power supply installation, must be equipped with multimeter and other tools, if you can not distinguish between the output positive and negative poles, the multimeter is the most effective tool to use, the multimeter test pen itself has positive and negative points, positive and negative test after two times, after the multimeter will have positive and negative two sets of data, so it is easy to distinguish the positive and negative poles of the power supply.
But if there is no multimeter, how do we distinguish the positive and negative poles of the power supply DC line?
Distinguished from wire color
The positive and negative poles of the wire can first be distinguished from the color: red is the positive pole, black is the negative pole, which is the standard stipulated by the state.
Distinguish from symbol labels
Secondly, we can distinguish between the symbols marked on the wires: "+" is the positive electrode and "-" is the negative electrode.
Other ways to differentiate
As shown in the following figure:
The circle is the positive pole, and there is a dotted line on the wire; the other one is the negative pole.
Although we said at the beginning that it was premised on "the situation without a multimeter", after thinking about it, I still felt that it was necessary to say that the multimeter judged the use of positive and negative poles:
Measure with multimeter DC file: when the test is positive, the test end of the red meter pen is positive, the test end of the black meter pen is negative, and conversely, when the test is negative, the test end of the red meter pen is negative, and the test end of the black meter pen is positive.
It should be noted that the positive and negative poles are only found in DC circuits; in AC circuits, the phase line "L" and the zero line "N" (also often called fire "L" line and zero line "N"), these two should not be confused.
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