You've hit on a common and frustrating inconsistency in the US measurement system! Here's a breakdown of why this seemingly random use of Celsius for insulation temperature ratings exists: Historical/Industry Standard

The electrical industry, particularly in Europe and Asia, heavily relied on Celsius from its early days. As global trade increased, electrical components and standards had to align. Many core electrical materials (like wire insulation) and components are manufactured and tested according to international standards (e.g., IEC - International Electrotechnical Commission). These standards are primarily metric.

Global Harmonization (to a point)

Even though the US hasn't fully embraced the metric system, there's a growing need for interoperability and consistency in international commerce and engineering. Using Celsius for temperature ratings on insulation, especially when dealing with imported wires or when the product is sold internationally, makes it easier to compare specifications and ensure proper application regardless of the country of origin or use.

Material Properties/Chemical Processes

Some scientific testing and material property characterization is often conducted and reported in Celsius. This is because the behavior of materials like polymers (used in insulation) under heat are easier to explain and report in Celsius.

Clarity and Precision

Celsius often offers a convenient range for typical electrical insulation operating temperatures (e.g., 60°C, 75°C, 90°C, 105°C). While you can convert to Fahrenheit, the Celsius numbers are often "cleaner" and easier to remember and use in calculations.

Building Codes and Standards:* Certain building codes and electrical standards (e.g., the National Electrical Code (NEC) in the US) may reference insulation temperature ratings in Celsius, even if other measurements are primarily in imperial units. This is to ensure compliance with international safety and performance benchmarks.In short, the electrical industry adopts a mix of metric and imperial units due to a complex blend of historical practice, international harmonization, scientific considerations, and regulatory requirements. While it can be annoying, using Celsius for insulation temperature ratings is one way the US electrical industry tries to bridge the gap between the imperial and metric systems, especially in a globalized market. Flag for review