Frequently Asked Questions: Thermocouple Wire

Thermocouple Wire

Thermocouple Wire

What is a thermocouple, and what is the wire used for?

It is a sensor used for determining temperature. It consists of diverse metals joined at the ends in a single connecting point. This connecting point generates electric energy when the temperature of one end differs from the other. The wire is commonly used to link the thermocouple to control instrumentation. It may also be used to build the sensing point.

What are the different types of thermocouple wire available?

This high temperature wire is produced using a wide range of materials, and is available with PVC, FEP, TFE, PFA, Fiberglass, and Ceramaflex insulation. However, if you see it referenced by "type" on a spec sheet, the description is referring to the kind of metal alloy used for the wire's conductor:

  • Type E = Chromel/Constantan
  • Type J = Iron/Constantan
  • Type K = Chromel/Alumel
  • Type N = Nicrosil/Nisil
  • Type T = Copper/Constantan

When an "X" follows the letter indicating which alloy was used in the cable, the cable is extension grade. In these cases, the types of cable are listed as Type EX, Type JX, Type KX, Type NX, or Type TX.

What is the difference between thermocouple grade wire and extension grade wire?

Thermocouple grade wire is wire that is used to make the sensing point of the instrument, where extension grade wire is only used to extend a thermocouple signal from a probe back to the instrument reading the signal.

How are insulated wires identified?

The insulation is usually color coded for easy identification. There are some common guidelines for the colors. For example, the negative lead in insulated wire is red. The positive lead has the color of the thermocouple as well as the overall color of insulated extension grade wire. The outer jacket of thermocouple grade wire is typically brown. For high temperature wire, it is common to have a color coded tracer thread in the white material. For information on usable temperature ranges for the insulation see the "Wire Insulation Identification" table. Other tables at this link are available for information on the metals used in the wire, insulation color codes, and more.

Can thermocouple wire be used at all temperatures?

For operations involving high temperature, this type of wire functions well. Although the service temperature of the wire varies depending on the specific wire type, the CERAMAFLEX insulated wire works to an extended high temperature of 1204 C. Check our catalog for more information about our wires and their service temperatures.

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