Thermocouple Wires From A to Z: All About Different Types of Thermocouples
A thermocouple wire is an integral part of a thermocouple device, which is a device used to measure temperature. The device consists of two wires made of different conductive metals or metal alloys that are interconnected twice and united with insulation. One of the wires is negative, and the other is positive, and together they create an electrical circuit.
Thermocouples are used across industries, including in food processing, in motors of cars, airplanes, spaceships, and other machines, in industries that produce metal, in furnacing, and in many different applications.
Common Types of Thermocouples and How They Differ + Thermocouple Color Codes
Depending on the metal alloys that comprise the wire, there are nine types of thermocouple wire.
The three most common ones are Type T, Type J, and Type K, with the last one being by far the most common of all. Other types that are found less often are B, R, E, N, C, and S.
! All negative thermocouple wires in the United States are color-coded in red!
Type K thermocouple wire is the most widespread subtype of a thermocouple. It is a very reliable high-quality thermocouple wire. The approximate temperature range of this thermocouple is −200°C to +1350°C. Its two conductors are nickel-chromium and nickel-alumel. It is used in the widest range of thermocouple applications, some notable being nuclear plants and oil refineries.
The positive wire is yellow, and the negative one is red.
The second most popular type of thermocouple cable, Type J thermocouple wire, is a budget-friendly variation that is a great compromise between price and quality. The temperature range of this one is -40°C to 760°C, and the conductors are iron and constantan. The positive wire is either white or black.
Thermocouple types T are another reliable type with a temperature range of −200°C to +350°C, not designed for high temperatures. Because of this, these cables are more suitable for freezers and food processing as they demonstrate excellent performance in low temperatures. The conductors are made of copper and constantan. A positive wire is color-coded in blue.
Type N thermocouple wire is a better-quality, more costly analog of Type K with nicrosil and nisil legs and a −270°C to +1300°C temperature range. The color of the positive wire is orange.
Type E Thermocouple is the most accurate one out of the existing thermocouples, with a −50°C to +740°C range and nickel-chromium / constantan legs, combining the best of two words of type J and Type K.
The positive wire of Type E is color-coded in purple.
Type B Thermocouple has two platinum-rhodium legs with an extremely high range of 600 to 1704°C. This makes it excellent for glass plants.
Type R Thermocouple has another high temperature range of 0 °C to 1450 °C, one platinum-rhodium leg, and another leg made out of platinum. A positive wire is green.
The rarest types of thermocouples are G, D, and C. They are made of different variations of tungsten-rhenium alloys and have an extreme maximum continuous operating temperature of 2,320°C. These thermocouples are used in the space industry.
Common Thermocouple Wire Insulations
- Teflon (Most often, PTFE) is common budget-friendly insulation of thermocouple wires. PTFE insulated thermocouple wire is by far the most common.
- Fiber Glass Glass Braid insulation is the most flexible.
- Stainless steel is strong and durable insulation that is more expensive.
