More on Temperature Rise Limits - AS 3768-1990
For manual control components located inside enclosures, which are accessible upon the opening of the enclosure, and which are not used frequently, higher temperatures can be allowed.
The distinction between metallic and non-metallic surfaces depends on the thermal conductivity of the surface considered.
Coats of paint and varnish are not considered to modify the thermal conductivity of the surface. On the other hand, certain plastic coatings can noticeably reduce the thermal conductivity of a metallic surface and allow it to be considered as non-metallic.
This does not apply to materials which comply with standards which state that the temperature or temperature-rise limits for accessible surface are fixed.