What are “405/426” alloys, and how do they differ from other Type C compensating extension wires?

“405/426” are alloy designations assigned many years ago by Hoskins Manufacturing Company. The original 405/426 alloys are nickel base materials and are produced to closely follow (within ± .110 millivolts) the nominal emf curve of the Type C thermocouple (tungsten 5% rhenium vs. tungsten 26% rhenium). As such they are considered compensating extension wires.

The advantage of Alloys 405/426 is that they are designed to match the Type C curve within the specified limits up to 1600°F. Competing alloys are copper-based. In addition to being more susceptible to oxidation at higher temperatures, they generally only follow the nominal curve up to about 400°F.

It should be noted that there are copper based alloys on the market that are called “405/426” simply because they are used as Type C extension wires. Concept Alloys does not sell these inferior, copper-based materials.

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