1. Power test formula
The electric pen can be divided into AC and DC, and the bright is AC and dark DC. The AC poles are all bright, and the DC bright spot is at one end.
The detection of DC can be polarized, depending on where the bright spot is. The bright front is extremely positive, and the bright rear is negative.
(1) Explanation of formulas
Note that when inspecting AC power, the inspector can stand on the ground. This is because in the commonly used AC transmission lines, the ground is connected to the neutral line (zero line) of the three-phase four-wire, so its phase line There is a certain potential difference (ie phase voltage, such as 220V) with the earth.
In the DC power supply system, the two transmission lines (positive and negative lines) are generally not grounded, so there is no potential difference between them and the ground, that is, there is no voltage.
Therefore, it is not always possible to check whether it is charged by the method of checking the alternating current, which leads to a problem of how to test the charging of the DC circuit with a common low-voltage test pen.
(2) Method for checking whether the DC circuit is charged
When using an ordinary low-voltage electroscope to test whether the DC circuit is charged, generally, both ends of the electroscope should be directly or indirectly connected to the positive and negative electrodes of the circuit (a piece of insulated wire can be used to terminate the electroscope and the hand-contact electrode, and the other end another power cord).
In some DC circuits, if the hand-held end of the electroscope is grounded directly or through a certain resistance, the neon bulb of the electroscope can also emit light when the circuit has a certain voltage.
It should be pointed out that before using the wire to touch another power line, the method of checking the alternating current should be used to check whether the line is live (referring to alternating current), so as to prevent the mistaking the phase line of the alternating current as the direct current power line and cause serious contact accidents. .
