Sparky: Class CTL means "circuit limiting" See Section 384-15, paragraph 2 in the 1999 NEC:
A lighting and appliance branch-circuit panelboard shall be provided with physical means to prevent the installation of more overcurrent devices than that number for which the panelboard was designed, rated, and approved.
From the UL White Book: "Class CTL panelboards are identified by the words "Class CTL" on the Underwriters Laboratories Inc. Follow-Up Service Listing Mark.
Class CTL panelboards incorporate physical features which in conjunction with the physical size, configuration, or other
means provided in Class CTL circuit breakers, fuse holders, or fusible switches, are designed to prevent the installation of
more overcurrent protective poles than that number for which the device is designed and rated."
I have images showing this information on the equipment.
