Thermocouple Wire Extension and Multicable

Types BX, EX, JX, KX, NX, RSX, and TX.

General Information -

Richards Extension wire completes the circuit from the thermocouple element to the temperature instrument. The extension wire and the thermocouple wire must both be of the same calibration type to maintain the accuracy of the thermocouple. The polarity of each set of wires must also be maintained during the installation or errors will be introduced into the circuit.

Color Codes -

The RED wire is always the NEGATIVE leg of the extension wire. The wire is also color coded to help with identification and installation. See the color coding chart below under the tables. If the wire will be subject to repeated flexing, a stranded wire should be used to prevent conductor breakage.

Types of Conductors -

To specify stranded conductors, add an S to the end of the part number. For typical, non-flexing, ambient temperatures, indoor use, a 20 gauge (1.3 mm) solid conductor with PVC (Polyvinyl Plastic) insulation wire is an excellent choice. This wire is economical and resistant to oils, chemicals, abrasion, moisture, and acids. Never install extension wire in the same conduit as power lines. This will cause interference and errors in the temperature readings. It is a good practice to keep the extension wire at least 1 foot away from power lines to maintain an accurate thermocouple circuit.

Spooling -

Thermocouple extension wire can be supplied on spools or coils. Spools will be plus or minus 10% of the quantity unless otherwise specified by the customer and indicated on the purchase order.

If you require wire on spools, just specify the part number and the footage. The part numbers below specify the wire gauge, Type, and insulation material.   Example:  50 Feet of 24JX-TT     (in 24JX-TT-ex the “ex” indicates “extruded” Teflon®)

Notes -

Special limits can be specified by doubling the type letter in the part number.                            Example:  20KKX-TT

Stainless Steel Over Braid is available for many wires. It is used to protect from abrasion and fraying of wires and as an electric shielding when grounded. Eight is the designation for 304 Stainless Steel - “OB8”; just add to the end of the part number. Example:  20JX-GG-OB8

Examples -

  • Nickel vs. Nickel Moly thermocouples - can use Type KX extension wire at room temperature.
  • Type C thermocouples - can use Type RSX at room temperatures.
  • Platinum Type B thermocouples - can use ordinary copper wire for extension wire at room temperatures.
  • Type P (Platinel II) thermocouples - can use Type KX extension wire at room temperature.

Thermocouple Wire Extension Configurations

p120 Extension Wire Limits Pub 20171024-1
p112 Gauges Insulations Wire Pub 20171024-3
p120 Extension Wire Pub 20171024-4
p121 Extension Wire Pub 20171027-5
p122 Extension Multi Wire Pub 20171027-6
p122 Extension Multi Wire Pub 20171027-7


  • Standard Limits of Error
  • Wire Sizes From 24 Gauge to 16 Gauge
  • Thermocouple Types, BX, EX, CX, JX, KX, NX, TX, RX, and SX
  • Available in Spools, Coils, or Cut to Length
  • High Temperature Insulation