Understanding Chassis Ground in Car Electrical Systems

[fran1942]

I was just wondering about chassis ground in the context of a cars electrical system.
If the return path back to the battery is through the metal chassis of the car, then what stops you from receiving a shock when you touch the car chassis ?

Thanks.

 

[gneill]

Ignoring the fact that a 12V potential difference is a bit low to produce a shock response, can you draw a diagram (schematic) that would show the required closed circuit path from the chassis, through the person, and back to the positive terminal of the battery?

 

[fran1942]

OK thanks. I can imagine how to draw the path. That leads me to think that the current would take the path of least resistance which would be though the metal chassis, rather than though human skin ?
So, that coupled with the fact that 12V is low to produce shock, would explain why it is safe to touch a car chassis that is acting as a return path to the battery ?

Thanks

 

[gneill]

Pushing current through any conductor, the human body included, is a matter of potential difference. The car chassis, due to the low resistance of metals, is essentially all at one potential. How would you establish a potential difference across your body? Perhaps you could elaborate on that path you've imagined...

 

[fran1942]

I thought that because the person was standing on the ground with bare feet that when he touched the chassis, a potential difference would be formed through the person (i.e between the chassis, through the body and into the Earth ground), thus resulting in current passing through the body.
(The same way that if a bird stands with one leg on a power line and the other leg on the earth, the bird will also get a shock).
What exactly prevents this happening ?

Thanks.

 

[gneill]

I thought that because the person was standing on the ground with bare feet that when he touched the chassis, a potential difference would be formed through the person (i.e between the chassis, through the body and into the Earth ground), thus resulting in current passing through the body.
(The same way that if a bird stands with one leg on a power line and the other leg on the earth, the bird will also get a shock).
What exactly prevents this happening ?

Thanks.

What is the path back to the + terminal of the battery? A current requires a circuit -- a closed path (unless we're talking about static electricity, where a potential difference can lead to a very brief but potent "snap" of current). Also, consider that the car is sitting on rubber tires, which are non-conductive.