Under what condition shall strands of wire not be tinned?

Strands of wire shall not be tinned when they are used in crimp termination or mesh splices because tinned wire can create issues with the mechanical integrity and reliability of the crimp connection. Tinning adds a layer of solder or metal coating that can interfere with the proper mating of the individual wire strands within a crimp connector, potentially leading to a weak connection. The crimping process relies on the metal-to-metal contact between the wire strands and the connector to create a reliable electrical and mechanical bond. If the strands are tinned, this direct contact may be compromised, affecting the overall performance of the connection.

In contrast, the other conditions listed do not present similar issues: strands can be tinned when used for insulation, as insulation does not rely on the same mechanical properties as a crimp termination. In high voltage applications, while special considerations are necessary, tinned wires may still be appropriately used. Additionally, when wires are to be soldered directly, tinned strands can enhance solderability and ensure a better solder joint.