Touch Voltage / Body Current

V = I × R_body

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Result
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Formula

V_touch = I_body × R_body

Description

Touch voltage safety analysis uses Ohm's law to determine the current flowing through a person who contacts an energized surface. The IEC 61140 standard limits touch voltage to 50V AC RMS or 120V DC in normal conditions. Human body resistance varies widely depending on skin moisture, contact area, and voltage level, but 1000Ω is commonly used as a conservative estimate for wet conditions (IEC 60479-1). At 50V across 1000Ω body resistance, the current is 50 mA, which is at the threshold of ventricular fibrillation.

Variables

  • V — Touch voltage (V)
  • R — Human body resistance (Ω)
  • I — Current flowing through the body (A)

Practical Notes

IEC 60479-1 body impedance ranges: dry conditions ~2000-5000Ω hand-to-hand, wet conditions ~500-1000Ω. Currents above 10 mA cause involuntary muscle contraction (cannot let go), above 30 mA risk respiratory arrest, and above 75 mA risk ventricular fibrillation. Equipment Class I (grounded) and Class II (double insulated) protection schemes are designed to keep touch voltage below safe limits.

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