There are several special situations when using an electroscope:
1. The test pen has been verified to be good. The neon tube does not emit light when the device is tested, which does not mean that the device has no electricity. For example, when the AC voltage is lower than 50V and the DC voltage is lower than 90V, the electroscope does not emit light. Electric shock may still occur when the human body touches the device, because the safe voltage should be lower than 36V (AC).
2. When a person stands on the insulating pad and uses an electroscope to test the 220V AC voltage, the neon tube glows; but when a person stands on a well-insulated ground and uses an electroscope to test a DC voltage higher than the ignition voltage, the neon tube does not emit light. If one end of the DC power supply is grounded, the neon tube glows.
3. When a good metal casing without protective grounding (connected to zero) is detected with an electroscope, sometimes the neon tube will emit weak light.
Because the normal insulation resistance of low-voltage electrical equipment is less than 1MΩ, there is still a large distributed capacitance between the shell of some equipment and the conductor, while the current limiting resistance of the electroscope is 1~3MΩ. The flow resistance and the human body are connected to the ground, and the voltage applied to the neon tube exceeds its ignition voltage, so the electroscope emits light.
Since the leakage current is at the microamp level, it is harmless to the human body. Will not cause electric shock accident.
However, if the brightness of the neon tube is strong, it may be due to poor insulation of the equipment, serious leakage, and danger of electric shock. At this time, you need to use a megohmmeter or a multimeter to check the insulation of the equipment, and must not be paralyzed.
