Sure. Here's an exerpt.
Electricity from the local utility company is typically supplied through three overhead or underground wires called service conductors. An electric service or feed consists of two "hot" leads (wires) each carrying 120 volts, and one "neutral" lead. Two hot leads are used together to provide 240 volts when needed. The wires pass through a meter and into the service panel of the building where they connect to metal strips called buss bars (9.1). The neutral wire and another "safety ground" or "green" wire (often bare copper) connect from the service panel to a copper rod driven into the earth. Three wires, hot, neutral, and safety ground make up the connections found in a typical outlet receptacle.
You may wonder why both the safety ground wire and neutral are needed since both ultimately connect to the same ground rod. Actually, the safety ground wire isn't needed as evidenced by the large number of electrical appliances which only use only two (hot and neutral) prongs. But, in electrical equipment which has a safety ground connection (a three pronged plug), the round grounding prong is always connected to any exposed metal parts of the equipment. That way, if an exposed part of the equipment becomes energized due to a wiring fault inside the equipment the safety ground connection causes the hot connection to be directly connected to earth, and the fuse or circuit breaker would shut down power to the circuit. Equipment with two-prong plugs usually has a non-conducting plastic case so errant electricity cannot pass to a person or horse touching the case.
