From GardenWeb.com's Home Electrical Wiring section:
"I'm trying to understand those wires in my house (I haven't been paying attention in school :-) and I have one question: where does the neutral wire come from? My understanding that the power company only supplies the hot wires, and the neutral is tied to the ground wire at the main service panel, but looking at the diagram below there's a white neutral coming in."
Response from an astute "electrician":
"The neutral wire is the return path for the spent electrons to return to the transformer for re-energizing. The neutral completes the path so that the transformer can keep functioning. There are two types of power distribution: Wye and Delta. Wye, more common and newer, uses 3 phases plus a neutral conductor. The neutral is grounded both at the substation and at every power pole. Delta uses 3 phases and no neutral. In Delta there is only a single voltage, between two phases (phase to phase), while in Wye there are two voltages, between two phases and between a phase and neutral (phase to neutral). For further reading do a Google search on AC power generation and distribution."
Wow...
"Almost" Good Answers: