SYSTEM COMPONENTS AND PROTECTION DEVICES
Electrical Distribution Systems
Overlapping Protective Zones
A separate zone of protection is provided around each system element (Figure 2). Any failure
that may occur within a given zone will cause the tripping or opening of all circuit breakers
within that zone. For failures that occur within a region where two protective zones overlap,
more breakers will be tripped than are necessary to disconnect the faulty component; however,
if there were no overlap of protective zones, a fault in a region between the two zones would
result in no protective action at all. Therefore, it is desirable for protective zone overlap to
ensure the maximum system protection.
Figure 2 Protective Relaying Zones
ES-15
Page 4
Rev. 0
