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โก IEC 60479: Effects of Current on Humans โ The Physiological Boundary of Electrical Safety
📅 Standard: IEC TR 60479-5:2007 + COR1:2013 | 🔗 Prepared by: IEC TC 64 — Electrical Installations
What happens when electric current passes through the human body? From a mild tingling sensation to ventricular fibrillation to fatal shock — IEC 60479 systematically quantifies the physiological effects of current at different intensities, frequencies, pathways, and durations. This is the physiological foundation upon which all electrical safety standards (IEC 60364, IEC 60950, etc.) set their safety limits.
☢️ Why human effect data matters: Every RCD trip rating, every touch-voltage limit, every insulation requirement in electrical safety codes traces back to the time-current ventricular fibrillation curves defined in IEC 60479. Getting these numbers wrong in a standard means getting protection wrong worldwide.
📋 Key Thresholds of Current Effects
| ⚡ Threshold | 📋 Definition | 📐 Typical Value (50/60 Hz) |
|---|---|---|
| Perception threshold | Minimum current detectable by hand contact | ~0.5 mA |
| Let-go threshold | Maximum current from which a person can voluntarily release grip | ~10 mA |
| Ventricular fibrillation threshold | Current likely to induce VF (left-hand-to-foot path) | ~50 mA (> 1 s duration) |
| Cardiac arrest | Current causing heart standstill | > 5 A |
⚡ Engineering Insight
⚠️ Engineering Design Insight: The most important engineering derivation from IEC 60479 is the time-current safety zone. The ubiquitous 30 mA / 30 ms RCD trip characteristic is not arbitrary — it comes directly from the IEC 60479 ventricular fibrillation curve. At 30 mA, the human body can safely withstand approximately 200–300 ms of current flow (corresponding to the C1-C2 zone of the curve). The 30 ms tripping time provides roughly a 10× safety margin over this threshold. Understanding this curve is fundamental to protection design — every reduction in trip current or trip time directly corresponds to an increase in the safety margin protecting human life.
⚠️ Common Engineering Mistakes
❌ Mistake 1: Assuming Low Voltage Equals Absolute Safety
IEC 60479 explicitly notes: even at SELV levels (≤ 50V AC), if the contact area is large (full body immersion in water), body resistance drops to approximately 500Ω — 50V / 500Ω = 100 mA, well above the fibrillation threshold.
❌ Mistake 2: Ignoring Different Effects of High-Frequency Current
Above 100 kHz, current primarily produces thermal effects rather than shock effects — but this does not mean safety, as high-frequency burns are equally severe.
🔑 The bottom line: IEC 60479 is the fundamental science underlying all electrical safety engineering. Every RCD parameter, every grounding cable cross-section, every safety distance value — all find their physiological justification in this standard.
