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=== Backup ===
The power protection system needs to be resilient to its own malfunctions. Thus it includes backup protection devices. For example if the fault is in the top left red zone, but outside the blue zone, it is expected to be handled by the "primary" relay A. If the relay A malfunctions and cannot clear the fault, the ''backup relays'' C and D in the adjacent (blue) zone will trip. This can be arranged without coordination (for example, the delay setting of C and D can be higher so they do not act if A succeeds in clearing the fault){{sfn|Anderson|1998|pp=9-10}} or through coordination via a pilot.{{cn|date=June 2025}} The term ''local backup'' is used when the backup relays are within the same zone as the "primary" one being duplicated.{{sfn|Anderson|1998|p=10}}

Local back-up protection, like the primary protective device, will isolate the elements of the plant affected by the fault to clear the latter. Adjacent-zone ("remote") back-up protection will generally isolate both the affected and unaffected items of plant to clear the fault.