Electronic – Why don’t we get shocked when we touch a car

automotivebatteries

According to this answer to a question about car batteries:

[…] so the entire chassis is an extension of the minus terminal of the battery.

If this is the case, I would expect that you'd get shocked when you touch something metal on a started vehicle if you're grounded.

I've read that 10mA passing through the heart at a high enough voltage is enough to kill a human, but only if the voltage is high enough (which in the case of most car batteries is only 12V.)

Is the voltage simply too low to produce an electric shock?

Best Answer

You don't get shocked because you're talking about DC with no connection path back to the positive terminal of the battery.

If you touch something metal on the vehicle you're now at the potential of the negative terminal of the battery (or the car's ground voltage). If you're also touching earth ground, then a very slight current will flow to balance out earth ground and car ground. But after that's balanced, there's no difference in potential across you and no current flows.

It's kind of akin to a bird resting on a high voltage power line. They don't get shocked much because there's no completed circuit.