8538.90.40.00 - Other, for the articles of subheading 8535.90.40, 8536.30.40 or 8536.50.40, of ceramic or metallic materials, electrically or mechanically reactive to changes in temperature

This HTS category encompasses a specific group of parts and accessories designed for use with electrical apparatus falling under subheadings 8535.90.40, 8536.30.40, or 8536.50.40. The key defining characteristics are the material composition and functional properties. These parts must be fabricated from ceramic or metallic materials and exhibit an electrical or mechanical reactivity to changes in temperature. This temperature sensitivity is a crucial differentiator for classification within this specific node.

Distinguishing this category from its sibling, "Printed circuit assemblies," is paramount. While both are parts for the same general apparatus, this current node specifically excludes printed circuit boards (PCBs) and their assembled components. Instead, it focuses on components that leverage thermal properties, such as bimetallic strips, thermistors, or other temperature-sensitive mechanical or electrical elements that form part of the larger apparatus's functionality.

As this is a leaf node, there are no further subcategories. Therefore, classification within 8538.90.40.00 hinges on confirming that the part is intended for one of the specified subheadings, is made of ceramic or metal, and demonstrates a response to temperature fluctuations. Examples might include thermally actuated switches, temperature compensation elements within a larger electrical device, or ceramic insulators that expand or contract measurably with heat.