When is a raised plaster cover permitted to increase the maximum number of conductors in an outlet box?

A raised plaster cover is permitted to increase the maximum number of conductors in an outlet box specifically when it is marked with its cubic-inch volume. This marking is crucial as it indicates the cover's size and how many conductors it can accommodate in conjunction with the outlet box's capacity.

The cubic inch volume rating informs electricians and inspectors about the total volume available for safe wiring, ensuring that the installation meets code requirements. Proper volume calculation helps prevent overheating and ensures that there is adequate space for splices, connectors, and conductors, which is essential for maintaining safety standards.

Other factors such as being painted, made of metal, or covered with a ceiling fan do not have any bearing on the allowed increase in conductor count, as they do not provide essential information about the cover's capacity for electrical conductors. Thus, the requirement for cubic-inch volume marking is the key element that makes this option the correct answer.