AC, DC, and How They're Used
Alternating current, or AC, has been the electric power transmission system of choice over direct current (DC) since George Westinghouse and Thomas Edison conducted their war of the currents (pun intended) in the late 1800s. Westinghouse’s AC triumphed over DC due to its ability to transmit electricity efficiently over long distances. The fundamental difference between AC and DC is the direction of electron flow. Alternating current periodically changes direction between a positive and a negative direction, while direct current flows in only one direction.
AC currently accounts for the great majority of electrical power installed in buildings, from the incoming service through the substation to distribution panels, outlets, lighting, motors, etc. DC is produced by power sources such as batteries, solar panels, and fuel cells. Because of its consistent voltage delivery, it has long been primarily used in electronic devices like cell phones, TVs, and televisions. Since the early 2000s, Power over Ethernet (PoE) has been used to transmit DC power over Ethernet cables for things like WAPs, IP cameras, and VoIP. More recently, PoE is increasingly being used for LED lighting in commercial and residential markets.