Electric power devices and control methods are provided which automatically select a line voltage or phase voltage of an AC voltage supply. The electric power device includes a switchable circuit, a sensor and a switch control. The switchable circuit connects to the AC voltage supply, and includes multiple switchable elements. The sensor ascertains a voltage level of the AC voltage supply, and the switch control automatically establishes a configuration of the switchable circuit through control of the multiple switchable elements. The switch control couples the electric power device in a line-line (delta) configuration to the AC voltage supply when the voltage level is in a first voltage range, and a line-neutral (wye) configuration when the voltage level is in a second voltage range.