Maximum Number Of Half Size Circuit Breakers In A Panel
January 9, 2006
Q: Is there a limit to the number of “piggy-back” circuit breakers that are allowed in a 24-space panel?
A: Yes, a Class CTL panelboard is marked to indicate how many circuit breaker poles can be installed. Class CTL is the designation used to identify a panelboard as ‘circuit limiting.’ In these panelboards, only certain positions in the panelboard will allow the use of tandem, half-size or piggy-back circuit breakers. For example, a 125A, 3-wire, single phase, Class CTL panelboard with 20 full-size circuit breaker spaces may be marked to allow two or more tandem circuit breakers.
Class CTL panelboards are the result of a requirement that appears in 408.15. This is the sentence that requires a limit to the number of overcurrent devices in a panelboard: “A lighting and appliance panelboard shall be provided with physical means to prevent the installation of more overcurrent devices than the number for which the panelboard was designed, rated, and approved.”
Although non-CTL tandem circuit breakers are available and will fit in any space in a CTL panelboard, they are marked “For Replacement Only, Not CTL Assemblies.” These circuit breakers are for use in existing old style non-Class CTL assemblies only.
The number of piggy-back circuit breakers that is permitted in a Class CTL lighting and appliance panelboard is marked on the product, and non-CTL tandem circuit breakers are not permitted.
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