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I have a laptop, connected to the wall socket. A separate USB charger is also connected to the (same) wall socket.

I have noticed, when my arm touched the USB ground, it hurt a little bit.

When I measure the difference between my laptop aluminium plate, and my USB charger ground, the difference is 84.5V AC. AC uA measurement is 76 uA.

Why does this happen?
Is this dangerous?
Do I need to do anything to alleviate this "issue"?

enter image description here

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  • \$\begingroup\$ Y-capacitor leakage. Set it to measure current instead and move the lead. It should be in the 100 uA range. \$\endgroup\$
    – winny
    May 25, 2021 at 12:48
  • \$\begingroup\$ USB charger may be isolated not grounded, and you may be seeing AC via its RF suppression capacitors. IF so, this is normal and on the AC current range you'll see a few (tens of) microamps. This is normal. If not... \$\endgroup\$
    – user16324
    May 25, 2021 at 12:49
  • \$\begingroup\$ it seems to measure 0.3 uA DC, 0 on AC. \$\endgroup\$
    – Gizmo
    May 25, 2021 at 12:50
  • \$\begingroup\$ Does this answer your question? How does low impedance measurement reveals ghost voltage? \$\endgroup\$
    – winny
    May 25, 2021 at 12:51
  • \$\begingroup\$ is the laptop actually conductive? ... have you measured the resistance between two points on the laptop? \$\endgroup\$
    – jsotola
    May 25, 2021 at 12:51

2 Answers 2

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This is normal RF leakage winding capacitance current through SMPS floating charger. If you wish to avoid this , don’t touch it with most sensitive part of body or connect a VGA port to an earth grounded monitor or similar retrofit of earth ground. It is not unsafe.

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Maybe you don't have real ground to supply your laptop (unconnected in wall socket). It's potentially dangerous for devices. I had similar situation with my PC when ground wasn't connected in socket - it was 180V :)

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