Categories: Resistance materials

Copper-nickel (CuNi) alloy Cuprothal® 49 (universally known as Constantan) is manufactured under controlled conditions from electrolytic copper and pure nickel.

Cuprothal® 49 has a number of special characteristics – some electrical, some mechanical – which make it a remarkably versatile alloy. For certain applications, its high specific resistance and negligible temperature coefficient of resistance are the most important attributes. For others, the fact that Cuprothal® 49 offers good ductility, is easily soldered and welded and has good resistance to atmospheric corrosion is more significant.

Although the range of applications of Cuprothal® 49 is so wide, its normally fall into four principal categories:

  • An ideal alloy for winding heavy-duty industrial rheostats and electric motor starter resistance. High specific resistance, together with good ductility and resistance to corrosion are all important requirements in this category, and Cuprothal® 49 satisfies the most demanding specifications.
  • Cuprothal® 49 is widely used in wire-wound precision resistors, temperature-stable potentiometers, volume control devices and strain gauges. In the resistor field, its high resistance and negligible temperature coefficient of resistance are main attractions.
  • The third main category of application exploits another characteristic of Cuprothal® 49. This is the fact that it develops a high thermal EMF (electromotive force) against certain other metals.
  • Low temperature resistance heating applications, such as heating cables.

Copper-nickel alloys with medium and low resistivity

Kanthal produces copper-nickel alloys with resistivity lower than those of Cuprothal 49. The main applications are in high current electrical resistances, fittings, heating cables, electric blankets, fuses, resistors but they are also used in many other applications.

Cuprothal® 30
Resistivity 30 μΩcm (180 Ω/cmf)

Cuprothal® 15
Resistivity 15 μΩcm (90 Ω/cmf)

Cuprothal® 10
Resistivity 10 μΩcm (60 Ω/cmf)

Cuprothal® 05
Resistivity 5 μΩcm (30 Ω/cmf)

CaptionDifferent resistors and potentiometers using Kanthal® alloys.

Cuprothal®49 Cuprothal®30 Cuprothal®15 Cuprothal®10 Cuprothal®5
Nominal composition, % Ni 44 21 11 6 2
Cu balance balance balance balance balance
Fe + – – – –
Mn 1 1.5 – – –
Density ρ g/cm3 8.90 8.90 8.90 8.90 8.90
Ib/in3 0.321 0.321 0.321 0.321 0.321
Resistivity at 20°C Ω mm2/m 0.49 0.30 0.15 0.10 0.05 
at 68°F Ω/cmf 295 180 90 60 30
Temperature factor of the resistivity, Ct
-55 – 150°C -67 – 300°F ±20 /±60
20 – 105°C (68 – 220°F) 250 400 700 1300
Temperature range °C -55 – 150 20 – 105 20 – 105 20 – 105 20 – 105
°F -67 – 300 68 – 220 68 – 220 68 – 220 68 – 220
Linear thermal expansion coefficient α, × 10-6/K 14 16 16 16 16.5
20 – 100°C (68 – 210°F)
Thermal conductivity λ at 50°C W/m K 21 35 60 90 130
at 122°F Btu in/ft2 h °F 146 243 460 624 901
Specific heat capacity at 20°C kJ/kg K 0.41 0.37 0.38 0.38 0.38
at 68°F Btu/lb °F 0.098 0.088 0.091 0.091 0.091
Melting point (approx.) °C 1280 1150 1100 1095 1090
°F 2336 2102 2012 2003 1994
Mechanical properties* (approx.)
Tensile strength, min N/mm2 420 340 250 230 220
psi 60900 49300 36200 33350 31900
Tensile strength, max N/mm2 690 690 540 680 440
psi 100100 100100 78300 98600 63800
Elongation at rupture % 30 30 30 30 30
Magnetic properties non-magnetic non-magnetic non-magnetic non-magnetic non-magnetic