2011-05-31

Thermocouple wireThermocouples are defined by single letters – B, E, J,K, N, R, S, and T – having tolerances according to theIEC 60584-2. The American ANSI standard dictatesbrown-coloured outer sheathing for thermocouples.Thermocouple wires intended for high temperaturesnormally have sheaths which can’t be coloured.However, it occurs that a fibre – coloured according tothe codes above – is integrated to the sheath foridentification.

Extension wire and compensating cableExtension wires are nominally made by the same alloysas the corresponding thermocouples. These are definedby the additional letter X – e.g. KX – with temperaturerange -25 to 200 C. The limits of tolerance equalthermocouple class 1 or class 2 of the IEC 60584-2within this interval. Note that the sheath (e.g. PVC) canfurther limit the allowed ambient temperature of thecable location.

Compensation cables are produced from alloys differingfrom the original materials. Hence, the ambient

temperature will be more limited and the tolerances willnot be better than those of class 2. Compensationcables are marked with the additional letter C combinedwith another letter identifying the used alloys, e.g. SCAor SCB. Compensated materials are used because theyare cheaper and easier to produce.

For instance type K has the extension cable - KX –made by the very same material as the pure thermo-couple. Moreover there is the compensation cable KCAwith the temperature range 0 – 150 C and iron in thepositive wire. Compensation cables are only qualified tothe class 2. Generally cable sheathing can limit thetemperature ranges still more. For example PVCsheathing limits the location ambient temperature below100 C.

ConnectorsConnectors should be colour marked as thecorresponding cable.

NiCr / CuNi

NiCr / NiAl

Fe / CuNi

NiCr / NiSi

Cu / CuNi

Pt-30%Rh / Pt-6%Rh

S: Pt-10%Rh / PtR: Pt-13%Rh / Pt

Colour coding of thermocouple extension wires

+ / –

IEC 60584-3International

standard

ANSI MC 96.1Americanstandard

DIN 43714German std re-placed by IEC

BS 1843British std re-placed by IEC

NFC 42323French std re-placed by IEC

JIS 1620Japanese std