Thermocouple wire can be separated into two basic categories – bare and insulated.  Bare thermocouple wire consists of the metal wire (a conductor) only and is primarily used to make a thermocouple. The principal operating theory of a thermocouple is when combining 2 dissimilar metals at a junction and subjecting the metals to a temperature which will be produce a small voltage. Since its discovery in 1826, industry; through research and experimentation, has standardized on about 10 metal combinations categorized by “types.” Types are designated by specific letters of the alphabet. Bare thermocouple wire is divided into two groupings by gauge: fine and standard. Fine gauge, bare thermocouple wire diameters range from .0005 to .015. Standard gauge, bare thermocouple diameters range from .003 up to .125. Fine gauge wire material is iron, chromel, constantan, copper, and alumel commonly referred to as the base metal. Precious metals materials for fine guage are platinum and platinum composites. Typical metal materials are designated as Type J, Type K, Type T, and Type N. Insulated thermocouple wire use non-conductive material to “jacket” the metal wire and are combined with the corresponding metal material which is also categorized by the Type. The most common jacket material that insulates the metal are polyvinyl (PVC), glass braid, Kaypton, and Teflon. The most important factor in thermocouple wire is their temperature ratings. Often specified as continuous or single reading, temperature ranges vary from 200°C to 870°C. Most of the wires are color coded and set by ANSI standards.   

The most common thermocouple connector is the rounded pin which is available in a plug (male) version or a jack (female) version. It is a popular industry standard that offers users easy connect-ability to sensor elements or extension wire. The majority of the round pin plug is a 2 pole, hollow pin type with optional solid pins including a 3 pin version. The pins are polarized and marked by polarity to prevent connection errors. Most frequently used is the “assembled” body type that allows the user easy access to the terminations inside the body of the plug or jack.

The plug bodies are colored coded to ANSI MC 96.1-1982 specification to make identification quick and easy. Color codes are as follows: Yellow – Type K, Black – Type J, Type T- Blue, Type E – Purple, Type N – Purple, Type N – Orange, Type R/S – Green, Type C – Red. This style thermocouple connector accepts solid, stranded, overbraid, RSC coil cord, and TWSH wire.  The maximum diameter wire or is 0.80”. There are optional cable clamps and weatherproof covers to protect against wet environments. They are available in 410°F (210°C), 660°F (350°C), or 1200°F (650°C) temperature ratings.

The most common RTD connector is the rounded pin type (“standard plug”). RTD connectors are also available in a plug version (male) or a jack version (female). Its’ popularity comes from its easy connect-ability to sensor elements or extension wire. The majority of the round pin plug is a 2 pole, hollow pin type with optional solid pins including a 3 pin version. Like the thermocouple version, the RTD connector pins are polarized and have a special identifying mark for polarity to avoid assembly mistakes. The “assembled” body type is also the most popular RTD connector style. This allows users easy access to the connection terminations located inside the body of the plug or jack.

Unlike thermocouples, RTD connector bodies are not colored coded; however, they are generally white in color. Since RTD wire is nickel plated copper, connectors need only accept solid, stranded, and overbraided for genral.  The maximum diameter wire or is 0.80”. There are optional cable clamps and weatherproof covers to protect against wet environments. The standard plug (or jack), rounded pin style is typically rated at 400°F (200°C).