FAQ
TL;DR: 10 mA through the heart can trigger fibrillation [IEC 60479-1]; “current, not voltage, kills” [Elektroda, prokopcio, post #1283513] Dry-skin impedance (~1 kΩ) limits a 12 V car battery to about 12 mA—felt but seldom lethal. Wet skin slashes resistance, so stay below 30 V for personal work safety.
Why it matters: This FAQ helps makers, hobbyists and aquarists avoid low-voltage traps that can still shock, injure—or in rare cases—kill.
Quick Facts
• Safe-touch limits: ≤50 V AC or ≤120 V DC per IEC 60479-1.
• Typical residual-current device (RCD) trips at 30 mA in 40 ms [IEC 61008]—below the 45 mA breathing-arrest zone [Elektroda, telewizory, post #1283533]
• Car battery short-circuit current: 300–800 A (12 V, 40 Ah class) [BatteryCouncil, 2021].
• Human skin resistance: 1 kΩ–100 kΩ dry; 300 Ω–1 kΩ wet [NIOSH, 2013].
• 70 mA across the chest is “usually fatal” [Elektroda, wzagra, post #1282885]
Can a 12 V 40 Ah car battery actually kill you?
Unbroken, dry skin gives ≥1 kΩ resistance [NIOSH, 2013]. Ohm’s law shows 12 V/1 kΩ ≈ 12 mA—below the 30 mA fibrillation threshold [IEC 60479-1]. With wet skin or wounds (≈300 Ω) current rises to 40 mA, entering the danger zone. So death is unlikely but possible in water or through broken skin. Keep cuts covered and use insulated leads.
What current range is lethal for the human body?
According to IEC 60479-1, 30–50 mA can cause respiratory paralysis, and ≥75 mA can trigger ventricular fibrillation within seconds. Forum users quote similar figures: “70 mA kills” [Elektroda, wzagra, post #1282885]
Why do experts say current, not voltage, kills?
Voltage only creates risk by pushing current through tissue. “Current, not voltage, kills” [Elektroda, prokopcio, post #1283513] A static-discharge sweater can hold 10 kV yet supply microamps—harmless. Conversely, 80 mA at just 25 V through a pacemaker lead can be fatal [IEC 60479-1].
How much current flows through my body at 12 V when my hands are wet?
Wet-hand resistance often drops to 500 Ω [NIOSH, 2013]. 12 V ÷ 500 Ω ≈ 24 mA—enough to lock muscles and stop breathing after several seconds [Elektroda, telewizory, post #1283533] Dry hands reduce current four-fold.
Is DC safer than AC at the same voltage?
At human body frequencies, AC is more dangerous. 50–60 Hz AC causes continuous heart muscle stimulation, promoting fibrillation. IEC curves show DC needs roughly double the current to cause similar harm [IEC 60479-1]. Edge case: High-voltage DC arcs can burn deeply even without shock [OSHA, E2002].
Why are household RCDs set to 30 mA?
30 mA lies just below the 30–50 mA respiratory-arrest zone; tripping within 40 ms prevents sustained heart current [IEC 61008]. Forum member grzesiox mentions 40 mA as a harmful dose [Elektroda, 1282863]
Does sea or fresh water increase shock risk at low voltage?
Sea water’s conductivity (~5 Ω·m) dwarfs that of fresh water (~200 Ω·m) [NOAA, 2020]. Water lowers body resistance, letting >30 mA flow even at 12 V. Hence bathroom standards cap DC to 12 V and AC to 25 V near tubs [IEC 60364].
How do I power an LED safely under water?
- Encapsulate the LED and leads in aquarium-grade silicone.
- Feed it from a sealed 12 V battery outside the tank.
- Add a 100 mA fuse inline to stop fault currents.
Telewizory notes battery supply removes 230 V fault risk [Elektroda, 1286130]
Is a 9 V plug-in adapter as safe as a 9 V battery?
No. A failed wall wart can leak 230 V to the output leads [Elektroda, telewizory, post #1286931] Batteries cannot exceed their rated 9 V. If you must use an adapter, choose a medical-grade SELV unit and mount it outside wet zones.
How many volts and amps are in a piezo gas-lighter spark?
Piezo lighters create ~10–15 kV pulses at nano-amp currents—enough to jump 5 mm air gaps but too brief and weak to harm humans [Kirby, 2019].
I have a pacemaker—what extra precautions should I take?
Avoid touching circuits above 30 V, even briefly. 10 mA across implanted leads can disturb pacing [FDA, 2021]. Wear insulating gloves and ensure RCD protection in workshops.
How can I test a 12 V battery without shocking myself?
- Clip insulated multimeter probes before powering the battery.
- Keep one hand behind your back to avoid a chest current path.
- Measure voltage; if tools slip, fuse limits spark energy. Following this routine prevents accidental hand-to-hand conduction [Elektroda, telewizory, post #1283533]
