In the United States,...
In countries whose standard phase to neutral voltage is 120 V, lighting and small appliances are connected between a live wire and the neutral. Large appliances, such as cooking equipment, space heating, water pumps, clothes dryers, and air conditioners are connected across the two live conductors and operate at 240 V, requiring less current and smaller conductors than would be needed if the appliances were designed for 120 V operation.[2]
A variation is the 240 V delta 4-wire system, also known as a high-leg or red-leg delta. This is a three-phase 240 V delta connected system, in which one winding of the transformer has a center tap which is connected to ground and used as the system neutral. This allows a single service to supply 120 V for lighting, 240 V single-phase for heating appliances, and 240 V three-phase for motor loads (such as air conditioning compressors). Two of the phases are 120 V to neutral, the third phase or "high leg" is 208 V to neutral.
