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Thermocouple and Extension Wire - General lnformation

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Therrnocouple Wire - Thermocouple grade wire is typically used to make the actual thermocouple element. Note that thermocouple grade wire can be used as extension wire, but the outer jacket insulation may have a different color code and in some cases it may be much more expen- sive than using exlension grade wire. Depending on the applications service temperature range, environmental conditions, and phys- ical constraints, a wire gauge, calibration type, and insulation material can be specified. Each of the calibration types have their own insulation standard color code for easy identification. See the thermocouple wire color code table located in this catalog. To aid in the installation of the thermocouple, the RED wire is always the NEGATIVE leg of the element. lf the thermocouple wires are installed incorrectly the instrument in the circuit will give backwards readings. Thermocouple grade wire is offered with solid or stranded con- ductors and in a wide range of gauges. lf the thermocouple wire will be in an application where it is subjected to repeated flexing, a stranded wire should be used to prevent conductor fatigue and failure. Thermocouple wire is available in AWG wire gauges from 40 (0.0031 inches) to 6 (0.1620 inches) in bare wire form or insulated with any of the common insulation materials. lnsulation materials for thermocouple grade wire are available to cover temperature ranges from -190"F to 2000'F (-123'C to 1093"G). Extension Wire - Extension grade wire is used to complete the thermocouple circuit from the thermocouple element to the temperature instrument. Note that extension grade wire should not be used to make thermocouple elements. Extension wires can be divided into two categories. Category 1 extension wires are made with conductors which are the same as the thermocouple. Category 2 extension wires are made with conductors which are different from the the thermocouple. The base metal thermocouples are used with Category 1 extension wires. Noble metal and a few nonstandardized thermocouples are used with Category 2 extension wires. The extension wire and thermocouple wire musf both be of the same calibration typelo maintain the accuracy of the thermocouple. The polari- ty of each set of wires must also be maintained during installation in order for the thermocouple circuit to function properly. The RED wire is always the NEGATIVE leg of the extension wire. Extension grade wire is also color coded to help with identification and instal- lation. See the extension grade wire color code table in this catalog. lf the extension wire will be subject to repeated flexing, a strand- ed wire should be used to prevent fatigue and failure. For typical, non-flexing, ambient temperature, indoor use, a 20 gauge (1 .3mm) solid conductor with PVC insulation wire is an exceilent choice. Note: Never install extension wire in the same conduit as power lrnes. This will cause interference and errors in the temperature readings. lt is a good practice to keep the extension wire at least 1 foot away from power lines to maintain an accurate thermocouple circuit.

Limits of Error for Thermocouple & Extension Wire. The limits of error for the calibration types listed in this catalog have been extracted from standards set by the American National Standards lnstitute, lnc. as shown in ASTM Standard E 230. All thermocouple grade and extension grade wire are tested and matched in our own calibration laboratories to insure that they are within these standards or better.

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