A motor generator (M–G set) is a rotary device for converting an electrical power supply to another form. Motor–generator sets are used to convert frequency, voltage, or phase of power. They may also be used to isolate electrical loads from the electrical power supply line. A motor–generator consists of an electric motor mechanically coupled to an electric generator (or alternator). The motor runs on the electrical input current while the generator creates the electrical output current. At times, MG sets are referred to as rotary converters.