- The main protection should clear a permanent or temporary fault before the backup protection operates, or continue to operate until the circuit is disconnected.
- Loss of supply caused by permanent faults should be restricted to the smallest part of the system for the shortest time possible.
The coordination criteria in this case are based upon the number of operations of the backup recloser. These operations can be any combination of rapid or timed
shots as mentioned previously, e.g., two fast and two delayed. The sectionalizer should be set for one shot less than those of the recloser, e.g., three disconnections in this case. If a permanent fault occurs beyond the sectionalizer, the sectionalizer will open and isolate the fault after the third opening of the recloser. The recloser will then re-energize the section to restore the circuit. If additional sectionalizers
are installed in series, the furthest recloser should be adjusted for a smaller number of counts. A fault beyond the last sectionalizer results in the operation of the recloser and the start of the counters in all the sectionalizers. Figure shows an example of coordination between 3 sectionalizers .