All communications cable can be used in cable trays except for which type?

The correct choice is CMX because this designation indicates that the cable is intended for use in a specific environment, often associated with outside plant applications or areas where moisture or exposure to the elements is a concern. This type of cable is typically not rated for installation in vertical cable trays, which are generally used for communication network cabling in controlled indoor environments.

The other types of cables listed—CM, CC, and CL2—are rated for different conditions that make them suitable for installation in cable trays. CM cables are designed for general-purpose communications wiring and can be used freely in various indoor environments. CC type cables are often used in commercial applications as a communications cable, while CL2 cables are rated for in-wall residential use, making them more adaptable for internal cabling situations and suitable for cable tray installations. Thus, understanding these ratings clarifies why CMX is the exception in this case.