You've hit on a good point! The omission of AC resistance data for coated copper wire in Table 9 compared to the DC resistance data in Table 8 is likely due to a combination of factors, primarily revolving around the skin effect and the practical considerations of AC resistance measurements: Skin Effect Sensitivity

AC resistance is significantly affected by the skin effect, where current tends to flow primarily near the surface of the conductor at higher frequencies. The type and thickness of the coating, especially if it's non-conductive, have a far more significant and unpredictable influence on AC resistance than on DC resistance. This makes it much harder to provide general, reliable AC resistance values for coated wire in a table.

Variability of Coatings

Copper wire coatings can vary considerably in material (e.g., enamel, varnish, polymer), thickness, and application method. These variations dramatically alter the AC resistance. A simple "coated" designation becomes meaningless without specifying the exact coating properties.

Complexity of Calculation and Measurement

Calculating the AC resistance of coated wire, especially considering the skin effect and the varying dielectric properties of coatings, is complex. Measuring it accurately requires sophisticated equipment and techniques, particularly at higher frequencies.

Limited General Applicability

In many applications where AC resistance is a critical design factor (e.g., high-frequency circuits), specific wire types and coatings are selected and characterized individually. General table values for coated wire would be less useful than the manufacturer's specifications for that specific wire.

Focus on Skin Effect Principles

Table 9 is likely intended to illustrate and explain the skin effect. The simple example of uncoated wire allows the reader to understand the fundamental principle without the added complexity of coating effects.

In summary: Providing AC resistance values for generic coated copper wire would be difficult to standardize, less reliable, and less practically useful due to the wide variety of coating types and their significant influence on AC resistance caused by the skin effect. Instead, manufacturers provide specific data for their* coated wires, or engineers will measure it during development of a product. Flag for review