When applied with redundant protection, the Fig. 5
architecture would use cross-initiation within System A and
System B devices separately. When only one system
incorporates the BF protection, a failure or an out-of-service
condition of one of the devices would lead to a loss of BF
protection when initiated from the adjacent zone. This can be
resolved by monitoring the out-of-service IED outputs
between the two adjacent zones and allowing self-initiation
should the BF protection in the adjacent device become
unavailable.