Originally Posted by auondicz
Can you explain further the context of your question? I get you like to use the water analogy, but that only works to help explain how electricity "Flows" , and the effect of pressure(volts) and (rate of) flow (current).
I am getting a kick out of some of the new "therory" of electricity I have seen, or more correctly, the perception of electricity and how it works. Once I learn what you are trying to understand or how to use the information, I can help with better explanation than I am about to provide, and diagrams to help illustrate what is going to be difficult to explain here.
Some of the comments made I feel I need to mention and correct:
Single phase is just that, therefore, the "phases" are not 180 deg apart. A single phase circuit is the complete phase, 360 deg.
The confusion comes from the perception of the typical residential 120/240 volt Edison Three wire system everyone has in their homes. The single phase is the 240 volts, the sine wave begins at 0 volts, rises to +240 volts, descends back to 0 V, continues on down to -240 volts, and back to 0. This is a total of 360 deg.
Alternating current changes from 0 to +volts to 0 to - volts to 0 volts, it does this 60 times per second in a 60 cycle system.
The 240 volts comes from a single transformer coil and the voltage does just what I stated above, 60 cycles or times per second.
The 120 volts is nothing but a center tap in the actual center of the 240 volt coil, and the voltage does the same cycle of sine wave, again 60 times per second.
The center tap is the "return" (neutral)for the 120 volt from only one of the hot legs. The neutral is grounded, otherwise there would be two hot legs in a 120 volt outlet. This is done here in North America for safety, so there is only one hot leg at the outlet. If the outlet was not grounded, then both wires would be "hot".
Do you know that Europe uses a 230 volt system, at each outlet, and one leg is grounded! For the same reason, just all their appliances, TV' computers, hair dryers, everything, is rated 230 volts! This is why there is a switch on the back of most personal computers to chose from 115 or 230 volts, so the computer can be sold either here or in Europe.
The ground connection is not for the purpose of requiring the electricity to do work. It is a redundant safety wire attached only to the metal housings of appliances, only to be used in the event the wires inside the appliance come in contact, or "short out' to the metal case. Otherwise the metal case would become live and stay that way until someone comes along and touches it, possibly completing the circuit, and getting shocked.
Electricity is not spent, and there is no drain. One law of physics is that energy cannot be neither created nor destroyed, only transformed into another form of energy. The voltage from one hot leg of a 240 volt system, returns back to the other 240 volt hot leg to form a circuit, and it does go back and forth , (or change from + to -) 120 times due to the 60 cycles.
I think we need to get you to understand the 240 volt portion of this before we go further with the Neutral, which is nothing more than a "shortcut" return for the one leg of a 240 volt system, thus 120 volts. The Neutral is "zero volts" simply because it is grounded, but still is a return.
For the water diagram you are seeking for 240 volts, simply take a hose, connect both ends, cause water to flow in the circle, and there you go. Draw a line at the center diameter connecting the hose at the center points, and there is the neutral.
I felt I had to clear up some of the misconceptions presented here so far, but not sure if I did a good job at explaining it, without confusing you even more. Again, if you can explain exactly what you are seeking ,and more importantly, how the information is to be used, I can provide some better explanations and direct you to some diagrams to show how the current flows, and why.