Mineral Insulated Thermocouple also konwn as MI Thermocouple is mineral insulated cable used to insulate thermocouple wires from one another and from the metal sheath that surrounds them. MI Cable has two for simplex and four for duplex thermocouple wires running in the tube. The tube is then filled with magnesium oxide powder and compacted to ensure the wires are properly insulated and separated. MI cable helps to protect the thermocouple wire from corrosion and electrical interference.