The terms "Medium Voltage" and "high voltage" have been used interchangeably by many people to describe fuses operating above 600 volts. Technically speaking, "medium voltage" fuses are those intended for the voltage range from 2,400 to 38,000 VAC. "High voltage fuses are for circuits carrying voltages greater than 38,000 VAC. "E" Rated fuses are considered to be general purpose fuses and can be used to protect against low and high values of fault current. "R" rated fuses are designed for back-up protection. They must be used in series with other devices, such as motor overload relays, in order to achieve both overload and short circuit protection.