Re:Teenage schoolgirl 'electrocuted after rolling on to iPho...
by kec on Wednesday November 15, 2017 @01:25PM
(#15706280)
Amperage kills you, but it takes voltage to get to your heart first. 5VDC across your body's resistance (somewhere around 1MΩ in normal conditions) is nowhere near enough current to feel, let alone harm you.
Re:Teenage schoolgirl 'electrocuted after rolling on to iPho...
by klodolph on Wednesday November 15, 2017 @01:32PM
(#15706382)
Right, and the charger is plugged into the wall which provides 220VAC. The cheap chargers are unsafe because they don't have enough clearance between the high voltage and low voltage sides of the circuit, so the isolation can fail and energize the USB port with 220VAC, for example. This is a well-known failure mode of cheap phone chargers, and it should be obvious why these shortcuts are illegal in most countries.
Teardowns of cheap USB chargers online explain what I'm talking about, for example, https://www.youtube.com/watch?v=wi-b9k-0KfE
It takes 100 to 200 mA to kill someone. A typical charger would put out 1,000 mA in normal operation. Heating follows P = I^2 R law, so it should be obvious that you can kill someone without melting your USB cable. The problem here is with putting a high voltage through the USB cable, which might damage the cable since it's not designed for such a high voltage, but even the small amount of insulation in a USB cable can be enough that the attached person will die before the cable fails.