Ok, so I've been wrestling with the concept of ground for the past two weeks. I'm in an electrical engineering program at college, and let me preface this by saying I have no difficulty dealing with ground in a practical sense and understand its general function very well. That being said, I've posed a few hypothetical scenarios about ground to a few of my professors and none of them can really give me a straight answer. So the crux of the issue is whether ground acts as an infinite source/sink of electrons, or whether it acts as a return path for current. Based on my musings, the two seem to be mutually exclusive. Take hypothetical scenario A. So we have a DC power source, let's say it's a battery, but it could really be any power supply, not necessarily a battery. If you were to hook one end of the supply up to ground, and the other end to a long wire up to the moon with a light bulb on the end, and grounded it on the moon, would current not flow? For the purpose of this hypothetical, let's assume the moon is at 0v, or earth ground potential. My thoughts are that it would work because electricity flows from a higher potential to a lower potential, but if electricity needs a complete circuit, then this would seem to be impossible. Here's a crappy little diagram: http://dl.dropbox.com/u/3372365/earthtomoon.jpg [Broken] Ok, so if scenario A doesn't work, than does scenario B work? In this case the power supply is using two points on earth ground to complete the circuit. http://dl.dropbox.com/u/3372365/scenB.png [Broken] If neither of these two would work, than it seems like earth ground has absolutely no use, so one of them must work. If current doesn't in fact flow THROUGH ground, then ground must be an infinite source/sink for current. But if scenario A doesn't work because it needs a return path, than scenario B must work because it's using earth as a ground return. If scenario B would work, then it would seem to follow that scenario C would not work, but convention indicates that it would, because otherwise how would you ever get electrocuted by making a connection to ground? http://dl.dropbox.com/u/3372365/scenC.png [Broken] General feedback has said the first and third options are incorrect, yet isn't the whole point of grounding in the first place to prevent shock hazard? If ground needs a return path in order to conduct, then what's the point of grounding circuits in the first place? It would seem like it only allows people to be electrocuted more easily since essentially the surface of the planet becomes a return point for any electric current, whereas without grounding at all electricity can never escape the circuit except to bridge to another point in the same circuit. Furthermore, if the ground DOES act as a return path, how does it know where to travel to? If nearly all points connected to ground anywhere are at 0V, how does the current see a return path. Assuming both actual earth ground wires would measure 0V with reference to ground, so the potential difference between the respective grounding wires would be 0V, or some negligible voltage across some amount of resistance so no current would flow. If after reading everything so far, you're about to say "well earth does not act as a ground return, it just acts as a sink/source" then why wouldn't this last scenario actually turn the bulb off? http://dl.dropbox.com/u/3372365/scenD.png [Broken] I'm almost 100% positive the last scenario would not work, because you can't drain a battery by hooking one terminal up to ground. Someone clarify this for me if you can. I've run these past several people including two analog electronic instructors, an electrical physics instructor, several classmates and my Dad who knows quite a bit about electricity and everyone is giving me conflicting answers or is just plain confused by it altogether. tldr: Does current travel through the actual ground or does the ground simply sink and source current when appropriate?