Thermowires and compensating wires

In most cases, the measuring device cannot be operated in the immediate vicinity of the measuring point since this is situated inside machinery or in similar hot, dirty environments. The measuring signal needs to therefore be transferred over a certain distance. Thermowires (extension cables) or compensating wires can be used for this. The wires in a thermowire are made from the same material as the wires in the thermocouple. The thermal voltage therefore appears only when it is connected to the device, and is not distorted. With compensating wires, on the other hand, materials are used that are similar to those of the thermocouple. Thermowires are supplied as standard with a limit deviation in tolerance class 1. Compensating wires, however, are only available in tolerance class 2. We only use thermowires from tolerance class 1. The limit value deviations only apply for the temperature range specified under the usage temperature (DIN EN 60584-3). The usage temperature relates to the temperature of the wire, while different limit deviations apply to connected thermocouples. A thermowire or compensating wire cannot be connected to a thermocouple of a different type.

1. Insulation

Thermowires are primarily insulated with Kapton, fibreglass, Teflon or silicone. A copper mesh is integrated with some wires in order to shield the wires from electromagnetic interference.

Where wires are exposed to particularly intensive mechanical stress, they should be protected with a stainless steel sheath. A stainless steel sheath can be combined with all types of insulation material.

PVC or silicone is frequently used to insulate compensating wires since their usage temperatures match those of the compensating wire.

(Polyimide) is chemically very resistant, has good insulating properties and is heat-resistant to +285 °C. Even with a small diameter of the Kapton, good electrical insulation properties can be achieved.

Fibreglass is laid or woven as a fabric around the wires and sealed with resin. Fibreglass-insulated wires have a heat resistance of up to +1,100 °C. For applications under mechanical strain, further wrapping of the fibreglass-insulated wire with a VA mesh is recommended.

Teflon is chemically resistant to acids, bases, alcohols, petrols and oils. It is flexible and slides very easily thanks to its low friction coefficient. It is also difficult to adhere to anything, since there are scarcely any materials that stick to Teflon. The usage temperature ranges, depending on the type of Teflon used, from -190 °C to +260 °C. For wire insulation, we use FEP Teflon (-100 °C to +205 °C), PTFE Teflon (-190 °C to +260 °C) or PFA Teflon (-190 °C to +260 °C).

Silicone is highly flexible and does not become brittle even at low temperatures. Its usage temperature is from -50 °C to +180 °C.

PVC is a commonly used insulating material in the electrical engineering sector. Its usage temperature is from -20 °C to +90 °C.

1.1 Properties of insulation materials

Material Usage temperature

constant (°C)

Approx. 25,000 h

Usage temperature

temporary (°C)


Dielectric strength

kV/mm (20 °C)




PVC –20 to +90 +120 25 Limited
FEP –100 to +205 +230 25 Very good
PTFE –190 to +260 +300 20 Very good
PFA –190 to +260 +280 25 Very good
Kapton –190 to +220 +400 287 Very good
Silicone –50 to +180 +250 30 Limited

3 Colour identifications for thermowires and compensating wires

Country Flagge Welt Flagge Deutschland Flagge USA Flagge Großbritannien Flagge Frankreich
Type Material IEC 60584-3 DIN 43714 ANSI MC 96.1 BS 1843 NF C 42-324
T Cu CuNi Typ T nach IEC 60584-3 Typ T nach ANSI MC 96.1 Typ T nach BS 1843 Typ T nach NF C 42-324
U Cu CuNi Typ U nach DIN 43714
J Fe CuNi Typ J nach IEC 60584-3 Typ J nach ANSI MC 96.1 Typ J nach BS 1843 Typ J nach NF C 42-324
L Fe CuNi Typ L nach ANSI MC 96.1
E NiCr CuNi Typ E nach IEC 60584-3 Typ E nach DIN 43714 Typ E nach ANSI MC 96.1 Typ E nach BS 1843 Typ E nach NF C 42-324
K NiCr Ni Typ K nach IEC 60584-3 Typ K nach DIN 43714 Typ K nach ANSI MC 96.1 Typ K nach BS 1843 Typ K nach NF C 42-324
N NiCrSi Ni Typ N nach IEC 60584-3
R PtRh13 Pt Typ R und Typ S nach IEC 60584-3 Typ R und Typ S nach DIN 43714 Typ R und Typ S nach ANSI MC 96.1 Typ R und Typ S nach BS 1843 Typ R und Typ S nach NF C 42-324
S PtRh10 Pt
B PtRh30 Pt6Rh Typ B nach IEC 60584-3 Typ B nach DIN 43714 Typ B nach ANSI MC 96.1 Typ B nach NF C 42-324

Images of thermowires and compensating wires