Current flows from $+$ to $-$ but electrons go the opposite direction.

When I connect the GND of a positive charged electric circuit board to earth, then the board accepts electrons from the earth until the board is neutral.

But let's look at another situation where

  1. the GND of a neutral board is not connected to anything

  2. I am negatively charged, after rolling and jumping on the carpet for a while

(1) What happens when I touch the $GND$ of the board? Will the board accept extra electrons from me until the board and I are at the same potential. (Both negatively charged.)

(2) If so, what happens when I stop touching $GND$ and I connect GND to earth again? Then, can the board donate the extra electrons back to earth? Isn't there a lot of circuitry (like diodes and stuff) controlling the direction of current towards $GND$ and (since electrons go the opposite direction) thus preventing the electrons going towards earth?

  1. Yes.

  2. Yes. There is leakage, and if you've charged yourself up statically, you stand a good chance of blowing diodes and transistors on either 1 or 2.

That's why there are such things as antistatic devices.

  • 2
    $\begingroup$ (1) Not quite: Marty and the board likely have different capacitances, so the board will accept electrons until Marty and the board have common potential, but not necessarily equal charge. $\endgroup$ – Ruslan Feb 24 '17 at 16:41
  • $\begingroup$ @Ruslan Thanks. Yes, you're right. Until there is zero potential between me and the board. I just edited my question. $\endgroup$ – Marty Feb 24 '17 at 17:04
  • $\begingroup$ @mike-dunlavey Thanks. Yes, things can get damaged, but before thinking of that, i am trying to understand some principles. So, it is true that when my body carries more electrons than protons, the surplus of electrons flows into the board, when i touch GND? Until there is zero potential between me and the board? Even when the board is neutral and not in need of any electrons? $\endgroup$ – Marty Feb 24 '17 at 17:13
  • $\begingroup$ @Marty: Right. Diodes are not simple one-way valves. Actually the current flow through them is exponential in voltage. So if the voltage is negative, they still leak. And transistors are just more complicated diodes. $\endgroup$ – Mike Dunlavey Feb 24 '17 at 19:30
  • $\begingroup$ @MikeDunlavey Thanks. I can understand me donating electrons to the board. But then, when i stop touching GND and i connect GND to earth? What happens to the surplus of electrons in the circuitry? They are attracted by earth, but the circuitry is not designed to let them move in that direction, towards GND. (Electrons are supposed to move the opposite direction. From GND to V+.) $\endgroup$ – Marty Feb 24 '17 at 19:42

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