Physiological Effect Zones of AC Current (AC-1 to AC-4)

A classification in IEC/TR 60479-1 of the effect of alternating current (15-100 Hz) passing through the human body, plotted against current magnitude and duration, divided into four zones: AC-1 (usually no perceptible reaction), AC-2 (perceptible, usually no harmful physiological effect, though involuntary muscle contractions may occur above the let-go threshold), AC-3 (strong involuntary muscle contractions, breathing difficulties possible, usually no organ damage without cardiac disturbances), and AC-4 (increasing probability of ventricular fibrillation and other severe effects such as cardiac arrest or burns, with risk rising as current magnitude and duration increase). These curves form the scientific basis for the maximum touch voltages and disconnection times found in NEN 1010, and underpin the rated residual current and tripping time of RCD protection.