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What is a CTL breaker?
Thursday, May 13, 2021
CTL is an acronym that stands for Circuit Total Limitation, a safety feature of modern electrical panels and breakers. It is primarily for control of where a type of breaker that combines two breakers into one and fits in a single panel slot—called a “tandem" breaker—can be added to the panel. Too many tandem breakers in a panel that’s not designed to hold them will overload it.
So panels and breakers are now made with a CTL rejection feature that will only allow tandem breakers to be installed where the panel is approved to accept them. Some panels accept no tandem breakers, a few allow them throughout, and others have only a portion of the slots allocated to take the double breakers. There is usually a diagram on the data plate at the panel door that shows where tandems can be installed.
Most manufacturers accomplish the rejection by adding a notch at the center of the bus fingers at the approved locations. Fingers without a notch will take only single breakers. Non-CTL breakers will fit at any slot in a panel. To learn more, go to our blog posts What is a tandem circuit breaker? and What is a “bus stab” in an electric panel? and What is the maximum number of circuit breakers allowed in an electric panel?
CTL was first mandated by the 1965 edition of the National Electrical Code (NEC), so pre-1965 panels do not have the rejection feature. Also, tandem breakers designed as replacements for older panels can be used to override the CTL feature in new panels, even though they have a sticker on the side that states “replacement use only - not for CTL assemblies.” This is probably why tandems are sometimes referred to by electricians as “cheater” breakers.
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