In the early days of electrical distribution in the U.S., most utilities operated three-wire ungrounded delta 2300 volt distribution systems. After 1925, many of these systems were converted to 2300/4000 V four-wire wye circuits, some were left at 2300 volts, and other were converted to 4800 volt delta. Some of these ungrounded systems are still in operation. Other higher voltage ungrounded distribution systems were also used. Three-wire distribution systems are still the norm in Europe, Japan, and other parts of the world.