I mostly deal with residential 120V/240V systems. What I'm wondering is the specifics of how electricity flows. I have read some basic texts that try to explain it, and perhaps they do, but I'm still a bit confused. Let me explain how I think it works and any of you can feel free to add to it or correct me.

A pot transformer steps down 6kVA or what ever to 240V with a secondary side tap in the middle to achieve 120V from either leg.
Question: Since the tap is to earth from the transformer, why isn't there a short or something at the tap? Every drawing I've seen shows the secondary winding being connected to in the center. It seems this would still carry a voltage and would short when it is connected to earth.

For 220V dryers, ovens, etc. It is my understanding that the electrons in each leg move back and forth at whatever the amps pull. So there is no direction for the current going from negative to positive because there is no positive as in DC. Does the current get "consumed" or is there a loss due to heat or whatever that is measurable.

For 120V applications, it seems that the current only moves in one direction; since the neutral doesn't have the same potiential as a negative "hot" to carry current because it is tied back to earth at the panel. It seems that the electricity in this example continually moves toward the neutral from the hot, and the voltage is only gained from the upper half of the sine wave created by the AC generator. As opposed to the top and bottom halves of the sine wave creating 240V between them. So, the only current that the neutral carries is the unbalanced load.

Speaking of unbalanced loads, in the case of 120V applications, where is the unbalanced load comming from? Also, why does it vary in amperage?

Any comments that will help clear these issues up would be appreaciated. I'm looking forward to learning as much as I can.

Thanks,
Byron