What is the difference between CTL and non-CTL breakers?

CTL stands for circuit total limitation. This normally is applied to the "twin" or 2 in 1 breakers used in residential loadcenters. CTL breakers have a rejection feature on the bus connection side of the breaker. This prevents them from being used in certain areas of a loadcenter. Non-CTL breakers do not have this rejection feature and will fit in any space in the loadcenter.