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So I'm testing a phase wire. When I touch the conductive screw top and use the tester like it's supposed to be used, it glows brightly. But when I'm only touching its plastic casing and not touching the screw at all, it still glows, albeit very faintly. What's happening?

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  • \$\begingroup\$ Apparently, ambient electric fields are high enough to reach the ionization voltage of the low-pressure neon gas inside the bulb. Once ionized, you see a glow for a portion of the AC cycle. Electric fields are affected by your body proximity. \$\endgroup\$
    – glen_geek
    Commented Nov 9, 2023 at 15:38

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When measuring AC current's there can still be a small amount of capacitance between test probes and other objects. This happens with most meters that can measure sub mA currents, but could also be happening with your meter. Because of the capacitance (usually in the pf range, but probably more if measuring close to the ground through the plastic in the unit you are measuring) a small amount of current can be detected and be enough to light the light. If you have a regular DMM turn it to AC mode mA and repeat the experiment, you should see some current.

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