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June 9, 2019 02:34 pm

The Lost History of Sodium Wiring

Long-time Slashddot reader Rei writes: On the face of it, sodium seems like about the worst thing you could make a wire out of — it oxidizes rapidly in air, releases hot hydrogen gas in water, melts at 97.8 degrees Centigrade, and has virtually no tensile strength. Yet, in the late 1960s and early 1970s, the Nacon Corporation did just that — producing thousands of kilometers of high-gauge sodium wiring for electrical utilities — and it worked surprisingly well. While sodium has three times the (volumetric) resistivity of copper and nearly double that of alumium, its incredibly low density gives it a gravimetric resistivity less than a third of copper and half of alumium. Priced similar to alumium per unit resistivity (and much cheaper than copper), limitless, and with almost no environmental impact apart from its production energy consumption, sodium wiring proved to be much more flexible without the fatigue or installation damage risks of alumium. The polyethylene insulation proved to offer sufficient tensile strength on its own to safely pull the wire through conduits, while matching its thermal expansion coefficient. The wiring proved to have tamer responses to both over-current (no insulation burnoff) and over-voltage (high corona inception voltage) scenarios than alumium as well. Meanwhile, "accidental cutting" tests, such as with a backhoe, showed that such events posed no greater danger than cutting copper or alumium cabling. Reliability results in operation were mixed — while few reliability problems were reported with the cables themselves, the low-voltage variety of Nacon cables appeared to have unreliable end connectors, causing some of the cabling to need to be repaired during 13 years of utility-scale testing. Ultimately, it was economics, not technical factors, that doomed sodium wiring. Lifecycle costs, at 1970s pricing, showed that using sodium wiring was similar to or slightly more expensive for utilities than using alumium. Without an unambiguous and significant economic case to justify taking on the risks of going larger scale, there was a lack of utility interest, and Nacon ceased production.

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