Appendix A: Zone Interlocking Examples - Eaton Digitrip 520 Instructional Leaflet

Instructional Leaflet IL70C1037H05
Effective October 2009

appendix a: Zone interlocking examples

CASE 1e: Thtrt is nN zNnt stltcoivt inotrlNcking (soandard oimt
dtlay cNNrdinaoiNn is ustd).
Assume that a ground fault of 2000A occurs and refer to Figurt 48.
Fault at location 3
The branch breaker will trip, clearing the fault in 0.1 seconds.
Fault at location 2
The feeder breaker will trip, clearing the fault in 0.3 seconds.
Fault at location 1
The main breaker will trip, clearing the fault in 0.5 seconds.
CASE 2e: Thtrt is zNnt stltcoivt inotrlNcking.
Assume a ground fault of 2000A occurs and refer to Figurt 48.
Fault at location 3
The branch breaker trip unit will initiate the trip in 0.045 seconds
to clear the fault and the branch will send a restraint signal to the
feeder trip unit; the feeder will send a restraint interlocking signal
to Z1.
1
Zone 1
Zone 2
2
Zone 3
3
Figurt 48. Typical ZNnt InotrlNcking
34
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3200A
Main
0.5 Sec.
1200A
1600A Feeder
0.3 Sec.
400A
200A Branch
0.1 Sec.
100A
See Note A4
Digitrip models 520, 520i; and 520M, 520Mi,
520MC, 520MCi trip units for use only in
Magnum and Magnum DS circuit breakers
Main and feeder trip units will begin to time out and, in the event
that the branch breaker does not clear the fault, the feeder breaker
will clear the fault in 0.3 seconds (as above). Similarly, in the event
that the feeder breaker does not clear the fault, the main breaker
will clear the fault in 0.5 seconds (as above).
Fault at location 2
The feeder breaker trip unit will initiate the trip in 0.045 seconds to
clear the fault and will send an interlocking signal to the main trip
unit. The main trip unit will begin to time out and, in the event that
the feeder breaker Z2 does not clear the fault, the main breaker will
clear the fault in 0.5 second (as above).
Fault at location 1
There are no interlocking signals. The main breaker trip unit will
initiate the trip in 0.045 seconds.
Figurt 49 presents a zone selective interlocking connection diagram
for a system with two main breakers from incoming sources and a
bus tie breaker.
N Note: The blocking diode D1 is needed so that the feeder breakers can send
interlocking signals to both the main and the tie breakers, and prevent the tie
breaker from sending an interlocking signal to itself.
C
ZO
Zone
1
ZI
NNotse:
A1e: Wiring to be twisted pair of AWG #14 to #20. Route zone
interlocking wiring separate from power conductors. DO NOT
C
GROUND any zone interlocking wiring.
Zone
ZO
A2e: The maximum distance between two farthest breakers on
2
different zones (from the ZO downstream to ZI upstream terminals
ZI
is 250 feet (76m).
A3e: A maximum of 20 breakers may be contained in parallel in
one zone.
A4e: Provide a self-interlocking jumper (on Zone 3) if coordination
is desired with other downstream circuit breakers not providing
the zone interlock feature.
Legend
C = Common (ungrounded)
C
Zone ZO = Zone Out output signal to higher level zone –B9—Contact
ZO
3 ZI = Zone In input signal from lower level zone
= Fault at location 2
ZI
2
–B7—Contact
–B8—Contact