Shock effects for DC and different AC frequencies

Effects of electric shock

Current through the body causes tingling and pain (about 1 mA), muscular contraction and inability to let go (about 10–20 mA), breathing difficulty (about 25–60 mA), ventricular fibrillation (about 60–100 mA and above), cardiac arrest and burns at higher currents, plus nerve damage and secondary injuries from falls.

Why and how DC and AC of different frequencies differ

The body's nerves and heart work on electrical signals of low frequency. The effect depends on how strongly the current repeatedly stimulates nerves and heart muscle.

1. DC: a steady current stimulates nerves mainly when it is switched on or off, so muscles do not stay in continuous spasm. The let-go and fibrillation thresholds are about 2–4 times higher than for 50 Hz AC (let-go roughly 50–90 mA). DC can still cause burns and electrolysis of body fluids.
2. AC at 50–60 Hz: this is the most dangerous range. Each cycle restimulates the muscles, causing continuous tetanic contraction, so the victim grips the conductor and cannot let go, and the heart is easily thrown into fibrillation.
3. Higher frequency (above about 1 kHz): nerves cannot respond to each cycle, and current tends to flow near the surface of the body (skin effect). Thresholds of perception, let-go and fibrillation rise with frequency. At very high frequency (above about 100 kHz) the main danger is heating and burns rather than fibrillation.