The last few miles of wire between the power grid and your socket
Electricity crosses the country at enormous voltages, but it would be lethal and useless at that level inside a house. Distribution is the final stage: substations and pole transformers step the power down in stages until it reaches homes at around 120 or 240 volts in the United States.
The handoff happens at a substation. Circuit breakers and switches let it cut loose from the transmission grid or isolate lines, and transformers lower voltages of 35,000 volts or more to a medium range of roughly 600 to 35,000. A thick conductor called a busbar then splits the flow among primary lines fanning out toward customers. Near the end, a distribution transformer on a pole or pad drops it again, and a service line and meter carry it indoors. City networks run mostly underground, rural ones on poles, and suburbs mix the two.
Most systems are radial, branching like a tree so that each customer has a single source, with emergency links that can reroute power around a fault or maintenance work. Dense city loads often use meshed networks fed from several sources at once. Long lines lose voltage along the way and need capacitors or regulators. Rural systems cover long distances at higher voltages, which lets them use strong galvanised steel wire and space poles widely; a single pole transformer may serve just one customer.
Until the 1880s electricity was usually made where it was used, and distribution only became necessary once central power stations appeared. The first city systems fed lighting. High-voltage arc lighting could run a string of lamps up to 11 kilometres from one station, since doubling the voltage lets a cable carry the same power four times as far with no extra loss, whereas low-voltage direct current struggled beyond short distances.
Workable transformers in the mid-1880s let alternating current be stepped up and down easily, and in the late 1880s the rivalry turned personal in the war of the currents, with Thomas Edison attacking George Westinghouse's AC systems by publicising deaths from high voltage. Better motors and systems linking older networks to large AC grids settled the contest in favour of alternating current.
Source: Electric power distribution
