Resistance of Humans

Humans are conductors of electricity and have electrical resistance similar to any other material. The human body's resistance to current flow varies depending on:

  • internal and external moisture;
  • exposed sub-epidermal tissue;
  • and skin thickness.

Human resistance is about 10,000 ohms on the high side and as little as 1,000 ohms if the person is wet. Remember, ohms is the unit of measure of a material's resistance or impedance to current flow. Current flow is obviously higher as the resistance goes down.

Shocking SAM GraphicAs an example, let's see how much current flows through a person if he or she contacts a typical 120 volt household circuit. On the high side, with human resistance around 10,000 ohms, we can compute the current flow by dividing the voltage, 120, by the resistance, 10,000. This yields .012 amps, or 12 milliamps.

This is well above the perception level of 1 milliamp, and slightly below the 15 milliamp "let go" threshold. We feel it, but we can let go and have no lasting physical damage.

If we are wet or standing in water, we become a much better conductor, thereby offering less resistance. The current flow is again found by dividing the voltage, 120, by the lowered resistance of 1,000 ohms, which yields 0.12 amps, or 120 milliamps, of current flow. This is easily enough current to send the heart into fibrillation and cause electrocution.