Just to add to the description of the 120/240V 3-wire system, in American homes you'll find both 120 and 240V appliances.
All your general-purpose wall receptacles are 120V, connected between one of the hot lines and the neutral. Some circuits will be on one hot leg, some on the other to balance the load.
Many large appliances are designed to run on 240V and are thus connected across the two hot wires (via a double-pole breaker). In many cases (range, dryer etc.) the neutral is also run to the appliance so that 120V is available for lights, timer clocks, and so on.
Contrast this with the British system where everything is run at 240V and thus you have just a single hot and neutral on the service.
The EGC (Equipment Grounding Conductor) in America is equivalent to what you would know from Britain as either the CPC (Circuit Protective Conductor) or ECC (Earth Continuity Conductor), depending upon how long ago you left these shores!
Bonding and grounding/earthing arrangements are where the U.S. differs considerably from British practice. All U.S. services are equivalent to British PME (TN-C-S) for example, but the point of the bond is at the main panel instead of before the meter as in England.
