Eaton Cutler-Hammer Digitrip RMS 910 Instructions Manual

Also see for Digitrip RMS 910: Instructions Instructional Leaflet Instruction leaflet

I.L. 29-889APage 30APPENDIX A Zone InterlockingAssume a ground fault of 2000 Amperes occurs and refer toFig A.1.CASE 1: There is no Zone Selective Interlocking.(standard time delay coordination is used)Fault 3The branch breaker will trip clearing the fault in 0.1 s.Fault 2The feeder breaker will trip clearing the fault in 0.3 s.Fault 1The breaker will trip clearing the fault in 0.5 s.CASE 2: There is Zone Selective InterlockingFault 3The branch breaker trip unit will initiate the trip in 0.03 sto clear the fault and Z3 will send an interlocking signal tothe Z2 trip unit; and Z2 will send an interlocking signal toZ1.Z1 and Z2 trip units will begin to time out, and in theevent that the branch breaker Z3 would not clear thefault, the feeder breaker Z2 will clear the fault in 0.3 s (asabove). Similarly, in the event that the feeder breaker Z2would not clear the fault, the main breaker Z1 will clearthe fault in 0.5 s (as above).Fault 2The feeder breaker trip unit will initiate the trip in 0.03 s toclear the fault; and Z2 will send an interlocking signal tothe Z1 trip unit. Z1 trip unit will begin to time out, and inthe event that the feeder breaker Z2 would not clear thefault, the main breaker Z1 will clear the fault in 0.5 s (asabove).Fault 1There are no interlocking signals. The main breaker tripunit will initiate the trip in 0.03 s.Figure A.2 presents a Zone Selective Interlocking con-nection diagram for a system with two main breakersfrom incoming sources and a bus tie breaker. Note theblocking diode D1 is needed so that the feeder breakerscan send interlocking signals to both the main and tiebreakers, without having the tie breaker send itself aninterlocking signal.Effective May 1997