Type J Thermocouple Cable
Type J Thermocouple Cable
Thermocouple cables are the cables that carry the thermocouple measuring line to the instrument, and the sheath and core colours of thermocouple cables are marked according to IEC 60584-3.
A thermocouple measures temperature by means of a small voltage generated at the junction of two different metals. This voltage is in the millivolt range; the line from the sensor to the controller must therefore have the same thermoelectric properties. If ordinary copper cable is used, a new thermocouple forms at the connection point and the measurement drifts.
Thermocouple cable is made with conductors of the same alloy as the sensor. Compensating cable uses conductors that provide the same millivolt characteristic at lower ambient temperatures, offering an economical solution for long extension runs. The cable type must always match the sensor type, and the positive (+) and negative (−) leads must not be reversed.
PT100 cables are shielded cables with 2, 3 or 4 cores used to connect resistance thermometers (PT100) to the instrument. Unlike a thermocouple, the measurement relies on a change in resistance rather than a millivolt signal, so the IEC 60584-3 colour code does not apply to PT100 cables.
Thermocouple and Compensating Cable Colour Codes (IEC 60584-3)
| Type | Positive conductor (+) | Negative conductor (−) | + core colour | − core colour | Outer sheath |
|---|---|---|---|---|---|
| K | NiCr | NiAl (Ni) | Green | White | Green |
| J | Fe (iron) | CuNi (constantan) | Black | White | Black |
| T | Cu (copper) | CuNi (constantan) | Brown | White | Brown |
| N | NiCrSi | NiSi | Pink | White | Pink |
| E | NiCr | CuNi (constantan) | Violet | White | Violet |
| R | Pt-13% Rh (compensating: Cu) | Pt (compensating: CuNi) | Orange | White | Orange |
| S | Pt-10% Rh (compensating: Cu) | Pt (compensating: CuNi) | Orange | White | Orange |
| B | Pt-30% Rh (compensating: Cu) | Pt-6% Rh (compensating: Cu) | Grey | White | Grey |
In IEC 60584-3 the negative core is white for every type; the outer sheath carries the colour of the positive core. In intrinsically safe (Ex i) circuits the outer sheath is blue.
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