Thermocouples are sensors that measure temperature across a wide range of applications in most industrial environments, and thermocouple extension wires used to create a hardwearing connection between the thermocouple probe to a readout instrument. These extension wires are used to extend a thermocouple signal back to the instrument and cannot be used in a thermocouple probe. At RS Components, we have a curated range of thermocouple extension wires suitable for J, K, L, N, R/S, RTD, S and T thermocouples from leading brands in the industry, including Jumo, Keysight Technologies, Reckmann and our own RS PRO.
Thermocouple extension wire is made from a lower grade of wire than that used in thermocouple probes, so is more economical when used at length. It's typically made with colour-coded (usually PVC) insulation applied to each wire leg. The negative lead is usually insulated in red and the positive lead is the colour of the thermocouple. For added durability and flexibility, a metal overbraid is applied to the insulated wire. For PVC wire this is a tinned copper overbraid, and for PFA it's stainless steel. This added layer protects the wire against abrasion.
Thermocouple extension wire is only used to extend the distance between a thermocouple probe and the instrument reading the signal and cannot be used as part of the probe itself. Thermocouple grade wire is used instead to make the sensing point of the thermocouple, as extension wire has a lower ambient temperature limit, which means may return a signal representing higher temperature readings than those that would be returned by a proper thermocouple probe, and therefore extension wire can't be used in a thermocouple's sensing point. Thermocouple wire can be used as an extension if necessary.