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I had a question, can you answer it: as you can see in the picture I uploaded, the single-phase alternating current flows in one wire at one moment and in the next moment from another wire as in the picture, but why when you connect the phase meter(voltage tester or neon screwdriver ) to the phase wire When we hit it, it light on, but it doesn't light on in the neutral wire? I think the AC current flows only in one wire as the second photo or does the three-phase current become it after the transformer? One picture: pic one AC current->-<

Two pictures: two pictures AC phase

In the first picture, it shows the ac current. At the first moment, the direction of the electrons from the wire is forward and at the next moment, it is backward. The phase wire makes a circuit by connecting to the neutral wire. Now, according to the first figure, the ac current flows once from phase to neutral and once from neutral to phase? In this case, the voltage tester light should be lit on both the phase and neutral wires!

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  • \$\begingroup\$ OP's image shows current. A neon bulb depends on voltage to light up. It needs an electric field between it's two posts. \$\endgroup\$
    – glen_geek
    Commented Sep 8, 2023 at 18:26
  • \$\begingroup\$ Mahdi - Hi, Please remember the site rule which says that when a post includes content (e.g. text, image, photo etc.) copied or adapted from elsewhere, that content must be correctly referenced. For online content, the source webpage or PDF etc. should be linked as a minimum (references for books / articles should include title, author(s), publisher, edition, page numbers etc. - a typical citation). Therefore please can you edit your question to include the original source webpage/PDF links for those images. Thanks. \$\endgroup\$
    – SamGibson ♦
    Commented Sep 10, 2023 at 14:31

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The neon line tester lights up when it completes the circuit, across the line and neutral, in series with the human body and ground.

enter image description here

It doesn't when it's in a closed circuit with the human body and ground but with no source.

enter image description here

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It connects the phase wire through your body with ground, which is connected to neutral at the transformer. You are part of the circuit.

If you touched neutral with the screwdriver tip instead, you had connected neutral with neutral. No voltage between those.

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It doesn't matter if the voltage is going up and down between active and neutral, because you connect your screwdriver just between neutral and also neutral (through your body), so the relative voltage is always zero. It's like connecting both sides of the led to the same point.

But if you put the screwdriver in the active side, then it is connected between active and (through your body) neutral, so there is a voltage. This is my understanding.

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If you have a load, electrons go both ways because current alternates.

If you don't have a load, no current flow at all.

It's the voltage on the live wire that lights up the detector because it causes current. You being effectively the 0V neutral or ground so very small current goes from live wire through the lamp and you to ground.

The neutral has 0V as it is connected to ground and you are also approximately at 0V ground potential. There is no voltage over the lamp so no current and it won't glow.

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Look at it this way. There is small conductor plate on the back of the screw driver. You are pressing the screw driver on the live point while your thumb is connected to that conductor plate. You are making the circuit complete through your body, and capacitance/resistance down to earth. If you remove your thumb the connection breaks and the bulb will not light up.

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