TC-K-EXT/COMP

Type K Thermocouple Extension and Compensating Cable

Moves the reference junction from the sensor head to a stable terminal, with a known error.

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Lead time15–25 working days
Minimum500 m per size
SampleFree up to 5 m

Illustrative cross section. Construction layers listed below.

Type K — nickel-chromium against nickel-silicon — is the thermocouple most plant instrumentation is built around, and the cable that connects it to the transmitter is part of the measurement, not an accessory. Every junction between dissimilar metals is itself a thermocouple, so the cable has to reproduce the Type K EMF curve or the reading carries an error that no amount of calibration at the instrument will remove.

Voltcore supplies both grades for Type K. KX uses the sensor alloys themselves and holds Class 1 tolerance of ±1.5 °C. KCA uses copper and a copper-nickel alloy that mimics the curve over a narrower span and is the cheaper option where the cable route stays cool. Both are identified to IEC 60584-3 with a green sheath, green positive and white negative conductor, and both are available with ANSI yellow coding for North American projects.

Specification

Type K extension and compensating cable — Technical Specification
Item	Value
Thermocouple type	Type K (NiCr positive / NiSi negative)
Cable grade	KX extension (same alloys) or KCA compensating (copper / copper-nickel)
Tolerance class	Class 1 ±1.5 °C, Class 2 ±2.5 °C, to IEC 60584-3
Valid tolerance range	KX: −20 °C to +200 °C; KCA: 0 °C to +150 °C
Conductor	Stranded alloy conductor, KX NiCr / NiSi or KCA Cu / CuNi
Construction	1 twisted pair, screened or unscreened
Cross-section range	0.5 – 2.5 mm²
Insulation and sheath	PVC 105 °C as standard; LSZH, PTFE and FEP available
Screen	Aluminium foil with tinned drain wire, or copper wire braid
Colour code	IEC 60584-3 green sheath, green positive, white negative; ANSI yellow on request
Test voltage	1 kV rms core to core, 500 V rms core to screen, 5 min
Minimum bending radius	10 × cable overall diameter

Layer-by-layer construction

Listed from the conductor outward. Read this alongside the specification table — the two together tell you whether the cable will survive its installation method.

1. ConductorPositive leg nickel-chromium, negative leg nickel-silicon for KX grade; copper and copper-nickel for KCA grade
2. InsulationPVC rated 105 °C extruded per conductor, 0.5–0.7 mm wall, coloured green and white to IEC 60584-3
3. Pair twistingTwo conductors twisted at a 35–60 mm lay length so induced voltages stay common-mode
4. Binder tapePolyester tape over the pair where a screen is applied
5. ScreenAluminium foil with a tinned copper drain wire, or a copper wire braid at ≥ 85 % coverage
6. SheathPVC green to IEC 60584-3; yellow to ANSI practice, or blue where Ex i identification is required

Reference dimensions and weights

Type K extension cable — 1 pair, dimensions and weight (reference figures)
Pairs × cross-section (mm²)	Conductor structure (No./mm)	Insulation thickness (mm)	Pair lay length (mm)	Approx. overall diameter (mm)	Approx. weight (kg/km)	Max. loop resistance at 20 °C (Ω/km, KX grade)	Tolerance class
1×2×0.5	7/0.30	0.5	35	3.6	32	1 980	Class 1 (±1.5 °C)
1×2×0.75	7/0.37	0.5	40	4.0	44	1 320	Class 1 (±1.5 °C)
1×2×1.0	7/0.43	0.6	45	4.6	58	990	Class 1 (±1.5 °C)
1×2×1.5	7/0.52	0.6	50	5.2	80	660	Class 1 (±1.5 °C)
1×2×2.5	7/0.68	0.7	60	6.2	124	396	Class 1 (±1.5 °C)

Reference figures for preliminary sizing and drum planning. Overall diameter and weight vary with strand construction and sheath thickness tolerance; certified drawings are issued with each quotation.

Engineering characteristics

KX grade reproduces the Type K EMF curve with the sensor's own alloys, to Class 1 ±1.5 °C
KCA grade substitutes copper and copper-nickel legs, cutting cost and loop resistance by roughly an order of magnitude
Loop resistance of the KX grade is high — 1 980 Ω/km at 0.5 mm² — but irrelevant in practice, because thermocouple inputs draw almost no current
IEC 60584-3 identification: green sheath, green positive conductor, white negative conductor
ANSI yellow identification available for North American projects and replacement work
Screened construction with foil or braid, because the signal at 100 °C is around 4 mV
Screened pair tested for continuity and insulation resistance at 500 V before despatch

Typical applications

Connecting thermocouples in furnaces, kilns and ovens to a temperature transmitter or controller
Plastic injection and extrusion machine barrel and die temperature loops
Heat treatment, annealing and tempering line temperature monitoring
HVAC, boiler and flue gas temperature measurement
Food processing and packaging plant with Type K probes throughout

Ordering options

KX extension grade or KCA compensating grade, Class 1 or Class 2 tolerance
IEC green or ANSI yellow colour coding
Foil screen with drain wire or copper wire braid screen
LSZH, PTFE or FEP insulation for higher temperature routes
Multi-pair construction for multi-point temperature monitoring on one cable

Standards manufactured to

IEC 60584-3 (extension and compensating cable, tolerances and colour coding)
ANSI/ASTM E230 (temperature-EMF reference tables)
IEC 60228 (conductor construction)
IEC 60332-1-2 (flame propagation)
RoHS and REACH compliant compounds

Manufactured to other standards on request. Send the standard number with your RFQ and we will quote against it rather than against a near-equivalent.

Price and availability for Type K Thermocouple Extension & Compensating Cable

Include cross-section, core count, voltage grade, route length and installation method — those five determine price more than anything else on the page.

Engineer-reviewed before pricing
Reference drawings issued with the quotation
Free sample up to free sample up to 5 m

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Type K Thermocouple Extension & Compensating Cable — frequently asked questions

What is the difference between extension cable and compensating cable?

Extension cable (KX) uses the same nickel-chromium and nickel-silicon alloys as the Type K thermocouple, so it follows the sensor's EMF curve over a wide range. Compensating cable (KCA) uses copper and a copper-nickel alloy that mimics the curve only over a limited span, typically 0 °C to 150 °C.

Can I use ordinary copper cable to extend a thermocouple?

Only if you accept moving the reference junction to wherever the copper begins, which is usually an uncontrolled terminal temperature. The instrument's cold junction compensation then corrects for the wrong place, and the error equals the difference in temperature between that terminal and the instrument input.

Does the high loop resistance of KX cable cause an error?

No, in practice. A thermocouple input has an impedance of a megohm or more, so a loop resistance near 2 kΩ/km draws negligible current and drops negligible voltage. That is a fundamental difference from an RTD circuit, where lead resistance is a direct error source.

Which colour code will I receive?

IEC 60584-3 as standard: green sheath with a green positive and white negative conductor. ANSI/ASTM practice is yellow jacket with yellow positive and red negative, and Voltcore supplies that on request. Never assume — confirm the code on the drawing before terminating.