120240volt

120/240 volt service, commonly referred to as 120/240 V or split-phase power, is the standard electrical distribution system used in most residential buildings in the United States and Canada. It provides two 120-volt legs that are 180 degrees out of phase, with a neutral conductor that is typically connected to earth ground at the service entrance. The voltage between the two hot legs is 240 V nominal, while each hot leg to neutral is 120 V.

Originating from a center-tapped transformer at the service entrance, the electrical panel houses circuit breakers that split the supply into individual circuits. The neutral conductor serves all 120 V circuits and is bonded to the grounding electrode system. Modern houses usually use four-wire service (two hots, a neutral, and a grounding conductor); older installations may use three-wire configurations without a separate ground. Most household appliances and outlets run on 120 V, while larger appliances like ranges, dryers, and some air conditioners use 240 V circuits.

Voltage, frequency, and safety are governed by standards in North America. The standard frequency is 60 Hz. The system must be properly grounded, and protective devices such as circuit breakers or fuses protect against overloads. For wet locations and other sensitive equipment, GFCI or AFCI protection is used. Wiring requires correct conductor gauge for the amperage, and improper handling can cause electrical shock, fire, or equipment damage.

Historically, the 120/240 V split-phase system was adopted in the early 20th century as part of broader standardization of electrical distribution. It provided a versatile and efficient means of delivering both high and low voltage services to residences and small commercial buildings.