The direct current system of generating and distributing electric power was invented by Thomas Edison, one of America’s foremost inventors and businessmen. Edison, who also famously invented the light bulb, was a staunch proponent of direct current and promoted it fiercely over its rival alternating current.
In the early days of electric power, there was no practical way to change the voltage from the generator to the load, its intended source. Because incandescent lights were the primary target for electricity, most DC voltages were kept around 100 watts. This low voltage allowed for safe electricity distribution and minimized insulation needs. Gradually, alternating current, or AC, became the dominant form of power transmission because of its ability to vary voltages and transmit over longer distances.