Revision Standard - Active. Methods to protect a power system from faults that are not cleared because of failure of a power circuit breaker to operate or interrupt when called upon by a protective relay are described in this guide. The intent is to give the reader a guide in how to detect that a breaker has failed to clear a fault, and how to electrically isolate the fault after the breaker has failed to clear the fault. Additionally, schemes that provide primary protection of the power system from performance failures of the power circuit breaker other than fault clearing failures such as failure to operate, either tripping or closing, manual or automatic, are also described. Such schemes, when applied, are typically integrated as a part of the overall breaker failure protection scheme. Also covered are recent practices that take advantage of new technologies.