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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Here’s links to a collection of our other blog posts about ELECTRIC PANELS:

• What causes copper wires to turn green or black in an electric panel?   

• When should a corroded or damaged electric panel cabinet or disconnect box be replaced? 

• Can an electric panel be located in a closet? 

• Can an electric panel be located in a bathroom? 

• Can you add circuit breakers by different manufacturers to an electric panel if they fit?

• My circuit breaker won't reset. What's wrong?  

• What is a split bus electric panel?

• How do I identify a combination AFCI (CAFCI) circuit breaker? 

• What does a circuit breaker with a yellow or white test button indicate? 

• What is the maximum gap allowed between the front of a recessed electric panel box and the wall surface surrounding it? 

• What are the requirements for NM-cables entering an electric panel box?

• Why is a fuse box/panel an insurance problem for homebuyers? 

• Why is bundled wiring in an electric panel a defect?

• What is the difference between GFCI and AFCI circuit breakers? 

• Why are old electrical components not always "grandfathered" as acceptable by home inspectors?

• What happens when you press the "TEST" button on a circuit breaker in an electric panel?

• What is a Dual Function Circuit Interrupter (DFCI)? 

• What is the difference between a Combination Arc Fault Circuit Interrupter (CAFCI) and an Arc Fault Circuit Interrupter (AFCI) circuit breaker?  

• Who is the manufacturer of those "bad" electric panels?

• Why is the circuit breaker stuck in the middle? 

• What is a double tap at a circuit breaker?

• What is the right electric wire size for a circuit breaker in an electric panel?

• What is the life expectancy of a circuit breaker? 

• My circuit breaker won't reset. What's wrong? 

• Why do some breakers in my electric panel have a "TEST" button on them?

• What is the right size electric panel for a house? 

• What is the code required clearance in front of an electric panel?

• What is the main bonding jumper and where do it find it in an electric panel? 

   Visit our ELECTRIC PANELS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.