Resistance wire


Resistance wire is wire intended for making electrical resistors. It is better if the alloy used has a high resistivity, since a shorter wire can then be used. In many situations, the stability of the resistor is of primary importance, and thus the alloy's temperature coefficient of resistivity and corrosion resistance play a large part in material selection.
When resistance wire is used for heating elements, high resistivity and oxidation resistance is important.
Sometimes resistance wire is insulated by ceramic powder and sheathed in a tube of another alloy. Such heating elements are used in electric ovens and water heaters, and in specialized forms for cooktops.

Types

, a non-magnetic 80/20 alloy of nickel and chromium, is the most common resistance wire for heating purposes because it has a high resistivity and resistance to oxidation at high temperatures. When used as a heating element, resistance wire is usually wound into coils. One difficulty in using nichrome wire is that common tin-based electrical solder will not bond with it, so the connections to the electrical power must be made using other methods such as crimp connectors or screw terminals.
Kanthal, a family of iron-chromium-aluminium alloys used in a wide range of high-temperature applications.
Constantan has a low temperature coefficient of resistivity and as a copper alloy, is easily soldered. Other constant-resistance alloys include manganin , Cupron and Evanohm.
The Evanohm family of nickel-chrome alloys , , have high resistance, low temperature coefficient of resistance, low electromotive force when in contact with copper, high tensile strength, and also are very stable with regards to heat treatment.
Balco and similar alloys have very high, but more linear, temperature coefficient of resistivity, making them suitable for sensing elements.
Many elements and alloys have been used as resistance wire for special purposes. The table below lists the resistivity of some common materials. The resistivity of amorphous carbon actually has a range of 3.8 - 4.1 × 10−6 Ω m.
MaterialResistivity
Resistivity
Aluminum15.942.650
Brass42.17.0
Carbon 233.95
Constantan272.9745.38
Copper10.091.678
Iron57.819.61
Manganin29048.21
Molybdenum32.125.34
Nichrome675112.2
Nichrome V650108.1
Nickel41.696.93
Platinum63.1610.5
Stainless steel 54190
Steel 10016.62
Zinc35.495.90

Common Alloy Trade Names

MWS Wire Ind.Carpenter Tech.Driver-HarrisHarrisonHoskinsJelliffKanthal
MWS-875Alchrome 875HAI-FeCr AI 25Alloy 875Kanthal A-1
MWS-800EvanohmKarmaHAI-431Chromel RAlloy 800Nikrothal L
MWS-675Tophet CNichromeHAI-NiCr 60Chromel CAlloy CNikrothal 6
MWS-650Tophet ANichrome VHAI-NiCr 80Chromel AAlloy ANikrothal 8
MWS-294CupronAdvanceHAI-CuNi 102CopelAlloy 45Cuprothal 294
MWS-180180 AlloyMidohmHAI-180Alloy 380Alloy 180Cuprothal 180
MWS-120BalcoHytemcoHAI-380Alloy 120
MWS-9090 Alloy#95 AlloyHAI-90Alloy 290Alloy 90Cuprothal 90
MWS-6060 AlloyLohmHAI-60Alloy 260Alloy 60Cuprothal 60
MWS-3030 Alloy#30 AlloyHAI-30Alloy 230Alloy 30Cuprothal 30