![]() ![]() This issue occurs with all chargers, laptop computers, and mobile phones that have metallic covers. However, this does not mean that the voltage is high enough to be dangerous. ![]() After the AC input terminal (fire line, zero line, or grounding end of a power grid) of the external power adapter is isolated through the built-in transformer, there is a potential difference between the output of the power adapter (connected to the metal case of the notebook when charging) and the earth, so the metal case of the notebook is a relatively high voltage and impedance source for the human body.īecause of this potential difference, the voltage tester will light up. Your computer comes with a 2-pin power adapter that lacks a ground connection. A voltage tester lights up when it touches the metallic part of my computer.Whether the user is earthed or not, the voltage tester will always emit light because the human body and earth are equivalent to a capacitor which can run an AC current. When the electric potential difference between the two ends of the voltage tester is greater than 50 V, the neon gas in the neon gas tube will become ionized and emit light and will continue to do so as long as the AC current through the pen is greater than 0.001 mA, which is far less than the safe limit of 0.25 mA. Voltage testers contain a neon gas tube which is connected in series with a large resistor.
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