Lee, True Dat...

by John Weinrich


When I was a kid learning electricity I thought that there was something special about the "ground". In the commercial world of TV, radio, automobiles, and whatnot engineers always used the chassis for a electrical return. So when I became and engineer I learned that it was for economy reasons, mostly. A lot of sensitive circuits have to be isolated from the chassis so that signal currents are not influenced by the other currents running through the chassis. In automobiles there is no real sensitive circuits. It is important to remember that "ground" is not perfect. Although a automobile frame and body is very massive relative to a wire, it still can present significant resistance and the subject problem shows up. Sometimes the money gained is significant. Imagine a signal repeater in the middle of the Atlantic ocean to boost telephone signals. A wire is run with the cable to power the booster. That wire needs to be large because of the loss incurred by the great distance. There maybe hundreds of thousands of dollars for that one wire. To save money they only run one wire to the booster to power it and use the salt water ocean for the return power. Yes they loose significant power in the resistance in the ocean but it is worth it...

Posted on Mar 18, 2012, 10:35 AM
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