How do I identify a thermocouple cable?
If you encounter a thermocouple cable on site, it is usually easy enough to identify the type (K, T, J, N etc.) by the fact that thermocouple cables are usually colour coded, In the UK and Europe that usually means colour coded in accordance with IEC60584-3, details of which can be found here.
The cable will have two cores and the colour of the negative leg of all thermocouple cable is white and the positive leg is the same as the outer insulation which is different for each thermocouple type as shown below.
If the thermocouple is uninsulated or perhaps insulated with ceramic beads then there are few tests that can be done to determine the type, other than to connect the thermocouple to an instrument which will accept all thermocouple inputs and have the sensor sit in an ice bath or in boiling water. However, there are a few details which may help to identify the thermocouple; the positive leg of a Type J thermocouple is magnetic. The negative leg of a type K thermocouple is slightly magnetic. You may be able to determine that the positive leg of a Type T thermocouple is copper by its colour.
Identifying thermocouple cable by colour