34
Instructional Leaflet
IL70C1037H05
Effective October 2009
Digitrip models 520, 520i; and 520M, 520Mi,
520MC, 520MCi trip units for use only in
Magnum and Magnum DS circuit breakers
eaton corporation
www.eaton.com
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.
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.
Note:
N
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.
Figurt 48. Typical ZNnt InotrlNcking
2
1
3
C
C
C
ZO
ZO
ZO
ZI
ZI
ZI
3200A
Main
1600A
200A
Feeder
Branch
Zone 1
Zone 2
Zone 3
0.1 Sec.
100A
0.3 Sec.
400A
0.5 Sec.
1200A
Zone
1
Zone
2
Zone
3
See Note A4
C
= Common (ungrounded)
–B7—Contact
ZO = Zone Out output signal to higher level zone –B9—Contact
ZI
= Zone In input signal from lower level zone
–B8—Contact
= Fault at location 2
NNotse:
A1e:
Wiring to be twisted pair of AWG #14 to #20. Route zone
interlocking wiring separate from power conductors. DO NOT
GROUND any zone interlocking wiring.
A2e:
The maximum distance between two farthest breakers on
different zones (from the ZO downstream to ZI upstream terminals
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.
2
Legend