Heating element

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A heating element converts electricity into heat through the process of Joule heating. Electric current through the element encounters resistance, resulting in heating of the element.

Most heating elements use Nichrome 80/20 (80% nickel, 20% chromium) wire, ribbon, or strip. Nichrome 80/20 is an ideal material, because it has relatively high resistance and forms an adherent layer of chromium oxide when it is heated for the first time. Material beneath the wire will not oxidize, preventing the wire from breaking or burning out.

• Resistance wire: may be wire or ribbon, straight or coiled. Used in common items such as toasters and hair dryers, furnaces for industrial heating, floor heating, roof heating, pathway heating to melt snow, dryers etc. Most common wires are from the following classes

Kanthal (FeCrAl) wires

Nichrome 80/20 wire and strip

Cupronickel (CuNi) alloys for low temperature heating

• Screen-printed metal–ceramic tracks deposited on ceramic insulated metal (generally steel) plates. These elements have found widespread application for kettles and other domestic appliances since the mid 1990s.

• Tubular (sealed element): a fine coil of Nickel chrome wire in a insulating binder (MgO, aluminia powder), sealed inside a tube made of stainless steel or brass. These can be a straight rod (as in toaster ovens) or curved to fit in a smaller space (such as in electric stoves, ovens, and coffee makers).

• Heat lamp: a high-powered incandescent lamp usually run at less than maximum power to radiate mostly infrared instead of visible light. These are usually found in radiant space heaters and food warmers, taking either a long, tubular form or an R40 reflector-lamp form. The reflector lamp style is often tinted red to minimize the visible light produced; the tubular form is always clear.

• PTC ceramic: This material is named for its Positive Thermal Coefficient of resistance. Most ceramics have a negative coefficient; most metals, a positive one. While metals do become slightly more resistant at higher temperatures, this class of ceramics (often barium titanate and lead titanate composites) has a highly nonlinear thermal response, so that it becomes extremely resistant above a composition-dependent threshold temperature. This behavior causes the material to act as its own thermostat, since current passes when it is cool, and does not when it is hot. Thin films of this material are used in automotive rear-window defrost heaters, and honeycomb-shaped elements are used in more expensive hair dryers and space heaters.

• Thick film technology:

Heating elements for high-temperature furnaces are often made of exotic materials, including platinum, molybdenum disilicide, molybdenum (vacuum furnaces) and silicon carbide. Silicon carbide igniters are common in gas ovens.

See also

• Thermoelectric effect
• Positive temperature coefficient
• Heated hose
• Heating mantle

External links

• Sam's Repair FAQ - heating elements
• Resistance wire technical information tables