Resistance Wire Overview

What is Resistance Wire?

Resistance wire is a high-resistance electrical wire that is often found in industrial applications including electrical ovens, toasters, and heating elements. The two major types of resistance wire are Kanthal and Nichrome wire.

Kanthal wire is a ferritic iron-chromium-aluminum alloy that can be in high temperature applications. It is often used in large, industrial applications and chosen for its high resistivity and excellent oxidation resistance.

Nichrome is made from nickel-chromium alloys is generally only used in temperatures below 1250°C. Nichrome has a slightly lower maximum operating temperature than Kanthal and operates best applications such as hair dryers, toasters, and kilns.

Corrosion, Rusting, and Oxidation

Resistance wire does not easily rust or oxidize, even in extreme environments. Kanthal is often chosen for its excellent oxidation resistance. It can be exposed to sulfuric compounds and not corrode quickly, making it well suited for corrosion resistance in hot states. Nichrome has similar properties but oxidizes more quickly than Kanthal in sulfur-containing atmospheres.

"Annealed" vs. "Half-Hard"

The terms "annealed" and "half-hard" refer to the temper of the metal, or the condition produced by mechanical treatment. Annealed wire can be shaped and cut easily, making it relatively flexible, soft, and bendable when pressure is applied. An annealed surface is achieved by exposing the metal to high heat and allowing it to cool slowly. Half-hard treatment refers to rolled and drawn wire.

Temperature Ratings

The Maximum Operating Temperature refers to the highest temperature the wire can withstand without suffering damage. Kanthal wire can operate up to 1400°C (2550°F) safely, while Nichrome wire has a melting temperature around 1150°C (2100°F).

Resistance

The more heat the wire generates, the more resistance it creates. Resistance is affected by volume, diameter, and the length of wire. The longer the wire, the higher the overall resistance. Thinner wire has higher resistance than thicker wire.

Thermal Expansion

Resistance wire expands in diameter and length when exposed to high temperatures. All resistance wire has different reactions to heat and will expand different amounts. To determine the expansion of either Kanthal wire or Nichrome wire, check the specifications of the wire. The expansion rate and flexibility also depends on the diameter, or gauge, of the wire.

Soldering

You can solder to resistance wire, but you will need a special flux and high temperature solder. Common electrical solder will not stick to resistance wire. An alternative would be to use crimp connectors or screw terminals in place of solder.

Nichrome 60

Melting Temperature: 1350°C (2462°F)
Maximum Operating Temperature: 1150°C (2100°F)
Density: 0.2979 lbs/cubic in.
Specific heat capacity @ 68°F: 0.11 Btu/lb°F
Thermal Expansion: 14 x 10 to the -6 per °C

Nichrome 80

Melting Temperature: 1400°C (2552°F)
Maximum Operating Temperature: 1180°C (2150°F)
Density: 0.304 lbs/cubic in.
Specific heat capacity @ 68°F: 0.11 Btu/lb°F
Thermal Expansion: 14 x 10 to the -6 per °C