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In automobile DC circuits, the chassis is typically connected to the negative battery terminal and, thus, the chassis provides the infrastructure for closing the DC circuit. In diagrams, this is often depicted with a symbol for the chassis ground. Unlike the Earth Ground wiring in a standard household AC system, the chassis ground is part of the electrical system (i.e., the circuit will not work without it), whereas the Earth Ground only becomes part of the circuit when certain other things malfunction (i.e., it is a safety device). My question is: Do automobile DC systems typically sport a safety device synonymous to the electrical infrastructure that we call Earth Ground wiring in standard household AC systems? Or is such infrastructure not needed in a car, and if it is not needed, why is it not needed? Obviously, there are breakers and fuses but those are also part of standard household AC systems. Therefore, I do not think that these components are the answer to my question. Also, while most of the time, you might be sitting in your vehicle, safely aloft your rubber tires, you might also hold or touch a connected electrical load while standing barefoot on nicely irrigated lawn outside of the vehicle.

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  • \$\begingroup\$ Quick comment to supplement the answers: an automobile battery is nominally only 12 VDC (maybe topping out at ~14 VDC. Whereas residential mains power is often 120 VAC or 240 VAC depending on the country. 12 V isn't considered hazardous. You don't even need to protect the wires from accidental finger contact! \$\endgroup\$
    – bitsmack
    Jul 30 at 10:12
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Also, while most of the time, you might be sitting in your vehicle, safely aloft your rubber tires, you might also hold or touch a connected electrical load while standing barefoot on nicely irrigated lawn outside of the vehicle.

And then what? No current flows through you, and you don't get hurt, because there's no circuit through the earth back to the battery negative terminal. The car is sitting on a nice set of insulators (tires), so the whole system is isolated from earth, and there is no need of (or benefit to) a protective ground.

It's possible to do the same with AC line power — to make a system where line and neutral are both isolated from ground, and there's no protective earth. In a trivial way, it's safer — a fault to ground won't pass any current (or just a tiny amount due to capacitive effects). But in such a system, a fault to ground also won't trip any breakers, make sparks, or do anything very noticeable, so it can pass undetected, and then a second fault to ground can easily be deadly. For this reason, and because of the logistical pain of keeping everything isolated in the first place, we don't normally do things this way. But for cars, airplanes, etc., it's a natural choice.

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Ground in electrical is anywhere you define as 0V, which in a car is the chassis. On the grid it is called “earth ground” or bonding.

Any voltage rise or noise from current drawn must be considered on grounds with appropriate connection for minimum R and L of the cable to stay as close to 0V as necessary to function.

The tires are good insulators and ESD from triboelectric friction cause charge the vehicle , like walking on nylon carpet with neoprene shoes, but contaminants and humidity discharge this for the most part.

I once asked my nephew , who is an exec. at Michelin if they added carbon to improve static dissipation. His research indicate there was none. I know that all tires are ionized with UHV GV radiation to crosslink the polymer for durability. This is also the same method to zap impurities in plastic to make them better insulators. So it seems to be a conflict between durability and electrical conductivity.

But for all onboard electronics, you just need a local ground to work like everything is floating at some point, even the earth! The grid is a much greater risk without earth bonding.

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