Pursuing my goal to learn more about electricity, I stumbled upon this idea. As I've learned, a current will travel from a high voltage source to a low voltage destination.

Since there's air between a live electrical socket and various ground paths, I'm wondering if a tiny current occurs from any electrical socket through the air.

Given a 240V outlet and if we assume the air has a resistance of 2e+13 ohms, then the current should be 1.2e-11 amps.
Does this happen in reality?

  • 5
    \$\begingroup\$ Your logic is impeccable, but in reality, the current that's due to the capacitive coupling between the conductors of your typical Romex cable is many orders of magnitude larger than that, so it is of no practical significance. \$\endgroup\$
    – Dave Tweed
    Commented Aug 13, 2021 at 3:17
  • 1
    \$\begingroup\$ When I was about 6, I would go around the house switching off all the sockets - so the electricity did not leak out and collect in a puddle on the floor. \$\endgroup\$
    – Solar Mike
    Commented Aug 13, 2021 at 6:44
  • 1
    \$\begingroup\$ @SolarMike that would be shockingly slippery. \$\endgroup\$
    – Andy aka
    Commented Aug 13, 2021 at 8:18
  • \$\begingroup\$ @Andyaka took my mum a while to work out why things did not work :) \$\endgroup\$
    – Solar Mike
    Commented Aug 13, 2021 at 8:52

1 Answer 1


Electrons will enter the air when the voltage gradient is high enough (cold arcing) or by thermo-electronic emission (and perhaps a few more exotic mechanisms like quantum tunneling).

Thankfully, under normal circumstances, the voltage gradient is insufficient for cold arcing. The current from that mechanism is zero.

At room temperature, and with normal materials, thermo-electronic emission, and to a lesser extent quantum tunneling, do occur, but the resulting current is negligible.

Thermo-electronic emission occurs because electrons have thermal energy. At any given moment, some electrons may have more energy than others. At a given temperature, a certain fraction of electrons will have enough energy to leave the material in which they were located and enter the air.

Quantum tunneling is a mechanism related to quantum uncertainty. Usually you will find electrons very close to the positively charged matrix of a material. However, there is a certain probability of finding them elsewhere.

Again, at room temperature, and with typical substances, thermo-electronic emission and quantum tunneling do occur, but the resulting current through the air is negligible.

  • \$\begingroup\$ Would I be correct to assume that it would happen at the breakdown voltage of the air? So realistically speaking if the distance between the hot and neutral conductors of the socket is 20mm then it would take 3kv * 20 = 60kv of electrical potential for an arc to occur through the air between the hot and neutral prongs (front face of the outlet)? \$\endgroup\$ Commented Aug 13, 2021 at 13:55
  • \$\begingroup\$ Yes, cold arcing will occur when the voltage between the conductors divided by the distance between the conductors reaches the breakdown "voltage" of air. (Actually it is the breakdown voltage gradient, not the voltage per se.) Depending upon moisture, temperature etc. you might easily require 60kV before a socket arcs. \$\endgroup\$ Commented Aug 13, 2021 at 14:02

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