Resistance wire

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Resistance wire is wire intended for making electrical resistors.[1] It is desirable that the chosen alloy have high resistivity, as 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.

When resistance wire is used for heating elements (in electric heaters, toasters, and the like), high restivity 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[edit]

Nichrome, 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 stick to it, so the connections to the electrical power must be made using other methods such as crimp connectors or screw terminals.

Kanthal (Alloy 875/815), a family of iron-chromium-aluminium (FeCrAl) alloys used in a wide range of high-temperature applications.

Constantan [Cu55Ni45] has a low temperature coefficient of resistivity and as a copper alloy, is easily soldered. Other constant-resistance alloys include manganin [Cu86Mn12Ni2], Cupron [Cu53Ni44Mn3][2] and Evanohm.

The Evanohm family of nickel-chrome alloys [Ni72Cr20Mn4Al3Si1],[3] [Ni73Cr20Cu2Al2Mn1Si],[4] have high resistance, low temperature coefficient of resistance, low electromotive force (Galvani potential) when in contact with copper, high tensile strength, and also are very stable with regards to heat treatment.


Balco [Ni70Fe30] 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.

Material Resistivity
(ohm-cmil/ft)
Resistivity
(10-6 ohm-cm)
Aluminum 15.94 2.650
Brass 42.1 7.0
Carbon (amorphous) 23 3.95
Constantan 272.97 45.38
Copper 10.09 1.678
Iron 57.81 9.61
Manganin 290 48.21
Molybdenum 32.12 5.34
Nichrome 675 112.2
Nichrome V 650 108.1
Nickel 41.69 6.93
Platinum 63.16 10.5
Stainless steel (304) 541 90
Steel (0.5% carbon) 100 16.62
Zinc 35.49 5.90

Common Alloy Trade Names[edit]

[5]

MWS Wire Ind. Carpenter Tech. Driver-Harris Harrison Hoskins Jelliff Kanthal
MWS-875 Alchrome 875 HAI-FeCr AI 25 Alloy 875 Kanthal A-1
MWS-800 Evanohm Karma HAI-431 Chromel R Alloy 800 Nikrothal L
MWS-675 Tophet C Nichrome HAI-NiCr 60 Chromel C Alloy C Nikrothal 6
MWS-650 Tophet A Nichrome V HAI-NiCr 80 Chromel A Alloy A Nikrothal 8
MWS-294 Cupron Advance HAI-CuNi 102 Copel Alloy 45 Cuprothal 294
MWS-180 180 Alloy Midohm HAI-180 Alloy 380 Alloy 180 Cuprothal 180
MWS-120 Balco Hytemco HAI-380 Alloy 120
MWS-90 90 Alloy #95 Alloy HAI-90 Alloy 290 Alloy 90 Cuprothal 90
MWS-60 60 Alloy Lohm HAI-60 Alloy 260 Alloy 60 Cuprothal 60
MWS-30 30 Alloy #30 Alloy HAI-30 Alloy 230 Alloy 30 Cuprothal 30

References[edit]