Technical data

13
©1995 Square D—All Rights Reserved
11/98
Neutral Sensor
Ground-fault protection may be applied on
3Ø4W or 3Ø3W circuits. On 3Ø4W circuits an
external neutral sensor must be used. This
neutral current sensor must have the same
ampere rating as the circuit breaker sensor.
06313023
Note: #18 to #14 AWG cables, max. length 90 ft./30m.
06313021
T1
T2
S1
S2
Neutral
Ground-fault
Neutral CTs
T1
T2
S1
S2
Main Circuit Breaker
06313022
Zone-selective Interlocking (ZSI)
Option Z on the STR58U control unit provides
selective interlocking on short time or ground
fault. A pilot wire links several trip units in the
distribution network, as shown in the opposite
figure. In the event of a fault, the trip unit will
respond to the preset delay only if receiving a
signal from the downstream unit. If not receiving
a signal, the tripping will be instantaneous.
Therefore, the fault is cleared instantaneously
by the nearest circuit breaker: the thermal
stresses (I
2
t) in the network are minimized,
without any effect on the correct time-delay
coordination in the installation.
Fault 1
Circuit breaker A will clear the fault
instantaneously, regardless of its time-delay
setting.
Fault 2
Circuit breaker B will inform upstream circuit
breaker A that it is clearing the fault and will
prevent it from tripping instantaneously. Circuit
breaker A will trip at the end of its time delay
setting if the fault is not cleared during this time.
Note:
n Drawout circuit breaker terminals are
delivered with "in" terminals jumpered.
Remove the jumper when interlocking with a
downstream circuit breaker.
n The MASTERPACT circuit breaker may also
be interlocked with COMPACT
®
NS and CK
type molded case circuit breakers with ZSI
option.
n Do not ground ZSI wiring.
Cable Size #18–#14 AWG/1.5mm
2
Max. Length 90 ft./30 m
Wiring Twisted in Pairs One Turn per 4 in./10 cm
No. of Circuit Breakers Upstream: 2
Downstream: No Limit
Control Units
A
Out
In
In In
Z12
Z11
Z22
Z21
Out
In
Out
In
2
1
Z12
Z11
Z22
Z21
Z12
Z11
Z22
Z21
Z12
Z11
Z22
Z21
Z12
Z11
Z22
Z21
Z12
Z11
Z22
Z21
Out
In
Out Out
B