Fig. 15 presents the preferred solution with BF protection
integrated in the bus relay. This configuration has more
complicated external initiation paths, but the BF tripping paths
are simplified because they are common to the bus tripping
paths. In this configuration, if the bus relay is out of service or
has failed, there is no BF protection on that breaker. However,
this only represents a single contingency because the primary
system for fault interruption (the breaker) is still in service.