Why you use eureka wire instead of copper wire?

Eureka wire, which is a nickel copper alloy, has a higher resistance than copper wire and is used as a heating element for specialized purposes. These hot cutting wires have high strength at elevated temperatures and are used for cutting foam polystyrene (EPS) and or heat sealing woven polypropylene bags.

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This alloy also has another important feature. Its resistance to electricity remains the same over a wide range of temperatures. For more information please see the wikipedia article about constantan.