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Here's what I'm asking: if the electricity flows from the hot wire to device X, then to the neutral wire which ultimately carries the signal to ground/earth at the panel then how does electricity "get back to" hot? Like, what "bridges the gap" between ground at the end of the circuit and hot at the beginning of the circuit?

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Neutral doesn't carry the power to earth. It is connected back to the power source, i.e. the power plant. –  Eli Iser Dec 5 '13 at 7:00
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The answer to this question may be useful. –  BMitch Dec 5 '13 at 12:21
    
Perhaps this Wikipedia article will help –  Steven Dec 6 '13 at 0:18
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4 Answers

The gap is bridged by the power company driving the current through your wires.

You can think of it as a remote generator pushing the current through your house, but in actuality there are several transformers isolating the current between generation and your house. So the current itself recirculates at the transformer near your house, and that current is driven by current in the transformer's primary coils.

If all is working properly (and nominally), there is no current to earth. That connection is there only to guarantee that each loop—including your house current loop—never has a potential voltage to ground greater than 120 volts. If a loop were not grounded, that portion could conceivably float to any voltage through static effects or other processes.

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The connection to earth also provides a path for stray voltages (e.g. lightning, power surges, etc.). –  Tester101 Dec 5 '13 at 10:22
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(USA system, single phase) The transformer at your pole (or on the ground if you have underground power feed) provides 240VAC with a center tap. Three wires run to your house - L1, N, L2 (or hot neutral, hot, if you like.)

240 V loads have a complete circuit from L1 to the load returning through L2

120V loads have a complete circuit from L1 or L2, returning through Neutral.

If multiple 120V loads are running from L1 and L2, the neutral current is reduced, as the two 120V loads are a 240V load to the extent of the lesser current (the remaining current from the higher current load returns through Neutral.)

Tying neutral to ground, in the USA, is done at the service entrance to the house - some in meter box, some in main circuit breaker panel. No service current flows through the ground. It flows through the neutral wire, back to the service transformer.

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The neutral wire does not carry the signal to ground/earth at the panel. It carries it to the neutral wire from the utility company's transformer. This wire bridges the gap back to the hot at the transformer. The ground connections are for safety.

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The actual correct answer is that alternating current, unlike direct current, does not require a complete circuit, it simply requires a displacement current path. Such a path is provided when the line is connected to the a large charge holder, like ground (Earth).

Though it's often convenient to think of every point on Earth as being electrically-connected (and thus providing a conduction path), that's actually not true, and not why it works. This fact even trips up many electrical engineers!

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Not, in fact, how actual electric systems work. Ground return hasn't been used since some VERY early telephone systems. –  Ecnerwal Dec 5 '13 at 16:22
    
@Ecnerwal: The line is grounded at the transformer, and again at the panel. –  BlueRaja - Danny Pflughoeft Dec 5 '13 at 17:29
    
This does not answer the question at all: The OP is not asking if incomplete circuits are possible. –  wallyk Dec 5 '13 at 18:37
    
A/C generators are 2 pole devices (minimum), The EMF induces the current to flow (back and forth. I guarantee without a return path, no generator can produce electric current out of thin air (Van de Graff generators, too) –  HerrBag Dec 5 '13 at 18:57
    
"without a return path, no generator can produce electric current" - The return-path is the same as the incoming path. Please see my first link. –  BlueRaja - Danny Pflughoeft Dec 5 '13 at 22:15
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