Thermocouple Wire Color Code ISA Symbol Jacket Color Insulation Color Code (+) Insulation Color Code (-) E Brown Purple / Chromel Red / Constantan J Brown White / Iron Red / Constantan K Brown Yellow / Chromel Red / Alumel T Brown Blue / Copper Red / Constantan EX Purple Purple / Chromel Red / Constantan JX Black White / Iron Red / Constantan KX Yellow Yellow / Chromel Red / Alumel TX Blue Blue / Copper Red / Constantan *First four ansi types (E,J,K,T) are thermocouple grade. Last four ansi types (EX,JX,KX,TX) are thermocouple extension grade.