How does the chassis neutralize the excess of electrons from a lightning strike?
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1\$\begingroup\$ Read .. what is a Faraday Cage \$\endgroup\$– D.A.S.Commented Sep 23, 2018 at 2:32
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\$\begingroup\$ It doesn't, it just provides an easier path for electrons to flow to ground. \$\endgroup\$– Long PhamCommented Sep 23, 2018 at 2:35
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\$\begingroup\$ Tests have shown safe results with an occupant inside a car exposed to a 1 million volt discharge but there may be exceptional situations. \$\endgroup\$– D.A.S.Commented Sep 23, 2018 at 2:43
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2 Answers
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Tests** have shown safe results with an occupant inside a car exposed to a 1 million volt discharge but there will be exceptional situations. (e.g. open sunroof and with roof antenna.)
Those tests**, which you may search on Youtube, were even performed on a dry car. A wet car makes it easier for the >1kV/m E field stress as water is 80x stronger as a capacitor to conduct the charge to ground. It is minute contaminants in the medium that cause the arc to bifurcate and change direction slightly or "fork" in the general direction of opposite polarity.
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How does the chassis ground on an automobile protect against lightning and how does the chassis neutralize the excess of electrons from a lightning strike?
Specifically what the chassis is doing is providing a low impedance path for current to travel around you rather than through you. Because the chassis is a cage arrangement of metal fully surrounding the passengers, it qualifies as a Faraday Cage, which is a device generally used to protect people or areas from electricity and or electromagnetic radiation. Because the chassis is also insulated from ground by the rubber of the tires and air beneath the car, it could also be considered to be protecting you, not only by being a better path for current than you, but also by being a potentially less good path than other nearby objects which might be taller or overall better conductors, like posts, wet trees, buildings, towers, lightning rods, larger vehicles.
Note that during a lightning strike, the electricity is not the only danger. There is also heat, fire, flash, flashburn, and potential explosion to consider, so being in a car when it is hit by lightning could still really suck and or be destructive or lethal.
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\$\begingroup\$ The windows prevent the car's "fully surrounding" the humans. \$\endgroup\$ Commented Sep 23, 2018 at 4:46
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\$\begingroup\$ @analogsystemsrf This is why it is referred to as a Faraday Cage rather than a Faraday Box. A Faraday Cage meant to block EMP or EM interference would likely actually have several layers of varying size meshes to effectively block different frequency waves. A car happens to be a Faraday Cage, one of the purposes of which is to divert current around the object contained, but if it were designed primarily as a Faraday Cage and secondarily as transportation it would be a very different looking beast. \$\endgroup\$– K HCommented Sep 23, 2018 at 4:52
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\$\begingroup\$ I'm looking for a better way to phrase that though. "fully surrounding with holes not larger than will pass the largest permitted wavelength" seems similarly lacking. No part of the objects protected may pass the boundaries of the cage, but the cage need not be solid. \$\endgroup\$– K HCommented Sep 23, 2018 at 4:57
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\$\begingroup\$ @KH you did not ask how to write about it, you asked how does it work... \$\endgroup\$ Commented Sep 23, 2018 at 6:19
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\$\begingroup\$ @SolarMike I think you mean OP asked how it works. With my second comment I'm acknowledging that I could probably have phrased better than "fully surrounding" which is only accurate combined with the assumption that a "continuous" cage can be composed both of conductive matter and the less conductive voids between. Is this what you mean? \$\endgroup\$– K HCommented Sep 23, 2018 at 6:25