What is a CTL system?
What do the letters “CTL” represent? What is the danger of using “Replacement Use Only – Not for CTL assemblies” in a CTL assembly? Answer The history of CTL is somewhat clouded. You will hear many comments about what CTL means (but most are wrong). If memory serves, CTL means “Circuit Total Limiting”. “Circuit Total Limiting” (CTL) was introduced when the words “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” was added to Section 384-15 in the 1965 NEC. Here is a specific example: Lighting and Appliance Panelboards (load centers) made since 1967 have been marked “Class CTL Panelboard”. Some of these CTL panelboards (load centers) will accept a breaker that is other than full size (called tandems, half-size, wafers, etc.). These breakers have varying means to limit the number of them that can be installed in the lo
