Tips on using an electric tester
1. The mnemonic for determining AC and DC power: Use an electric pen to determine AC and DC power. AC power should be bright and DC power should be dark. The AC neon tube should be lit up, and one end of the DC neon tube should be lit up.
Explanation: Firstly, it is important to inform the reader that before using a low-voltage tester, it must be tested on a confirmed charged body; Do not use the test pen until it is confirmed to be functioning properly. When distinguishing between AC and DC electricity, it is best to make a comparison between the "two electricity", so that it is very clear. When measuring AC power, both ends of the neon tube light up simultaneously, while when measuring DC power, only one end of the neon tube is extremely bright.
2. Formula for determining the positive and negative poles of direct current: Use an electric pen to determine the positive and negative poles. Observe the neon tube carefully, with a bright front end indicating the negative pole and a bright back end indicating the positive pole.
Explanation: The front end of the neon tube refers to the tip of the measuring pen, and the back end of the neon tube refers to the end held by the hand. A bright front end indicates a negative pole, while a bright front end indicates a positive pole. Attention should be paid during testing: the power supply voltage should be 110V or above; If a person is insulated from the earth, with one hand touching either pole of the power source and the other holding a measuring pen, the metal head of the pen touches the other pole of the tested power source, and the front end of the neon tube lights up, indicating that the tested power source is negative; If the rear end of the neon tube is extremely bright, the measured power source is the positive electrode, which is based on the principle of unidirectional DC flow and electron flow from the negative electrode to the positive electrode.
3. The mnemonic for determining whether a DC power supply is grounded or not, and the difference between positive and negative grounding: the DC coefficient of the substation, the electric pen does not light up when touched; If the light is close to the tip of the pen, there is a ground fault on the positive electrode; If the light is close to the finger end, the grounding fault is at the negative pole.
Explanation: The DC coefficient of power plants and substations is insulated from the ground. When a person stands on the ground and touches the positive or negative pole with a voltage tester, the neon tube should not light up. If it lights up, it indicates that the DC system is grounded; If the light shines on the end close to the pen tip, it is the positive pole grounded; If the light shines on the end close to the finger, it is negative ground.
4. The mnemonic for determining the same and different phases: Determine if two lines are the same but different. Hold a pen in each hand, keep both feet insulated from the ground, touch one of the lines with each pen, and observe one pen with your eyes. If the pen is not lit and the same phase is lit, it is considered different.
Explanation: During this test, remember to keep both feet and the ground insulated. Due to the majority of 380/220V power supply in our country and the widespread use of neutral point direct grounding for transformers, insulation must be maintained between the human body and the ground during testing to avoid forming a circuit and avoid misjudgment; During testing, the two pens display the same whether they are lit or not, so only one pen can be viewed.
5. The mnemonic for determining the grounding fault of the phase line of the 380/220V three-phase three wire power supply line is: star shaped connection of the three-phase line, two of which are bright when touched by the electric pen, and the remaining one is weak in brightness, indicating that the phase wire has been grounded; If there is almost no light, there is a fault in the metal grounding.
Explanation: The secondary side of power transformers is generally connected in a Y-shape. In a three-phase three wire system where the neutral point is not grounded, when using a voltage tester and three phase wires, if two of them are slightly brighter than usual and the brightness on the other one is weaker, it indicates that the weak phase wire is grounded, but not too severely; If two are very bright and the remaining one is almost invisible, it is a metal grounding fault in this phase wire.
