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MaGnuM PRoDuct GuiDe
CA013002EN—April 2017 www.eaton.com
51
Magnum trip units and communication devices
Ground fault provisions and protective schemes
Ground fault sensing options
and zone selective interlocking
schemes relative to Digitrip
trip units are offered here as
a general introduction . For
more detailed information and
applicable wiring diagrams,
refer to trip unit Instruction
Leaflet
70C1037
(Digitrip 520)
or instruction leaflet
70C1036
(Digitrip 1150) .
As a standard feature,
Magnum circuit breakers
are internally wired with
provisions for ground fault
protection . However, ground
fault protection is provided
only if the breaker’s trip unit
is equipped with optional
LSIG protection .
Ground fault protection can
be added to breakers not
originally equipped with a
ground fault trip unit . This can
be accomplished by simply
replacing the existing trip unit
with a like model trip unit that
has LSIG protection .
To provide for maximum
application flexibility, breaker
ground fault provisions are
wired out to the breaker
secondary terminals for
external use . The secondary
terminals can be easily
configured to accommodate
the most common ground
fault schemes .
•
Residual sensing:
This is the standard or
default wiring configuration .
It is also the industry’s
most common mode
of ground fault sensing
used in 3-pole and 4-pole
breaker applications . One
current sensor per pole
on each phase conductor
is provided internal to the
circuit breaker . When 3-pole
breakers are applied on 3
phase, 4 wire systems,
an external sensor matched
to the breaker sensor ratio
is mounted on the
switchgear neutral bus .
It is then wired to the
breaker secondary contacts
to connect all sensors in the
residual circuit .
otee:
N
For a main-tie-main system,
current sensors and rating plugs
must be the same rating for the
system to work properly .
•
Source ground sensing:
Source ground sensing is
commonly found on 3 pole
breakers applied as a main
breaker on single-ended
radial or on double-ended
systems where a mid-point
grounding electrode is
employed . To configure a
breaker for source ground
sensing, a shorting jumper is
applied to breaker secondary
contacts B6 and B7 to
defeat the residual sensing
mode . An external current
sensor is mounted directly
on the bonding conductor
to ground to measure the
ground current flowing in
the grounding electrode
conductor and all other
grounding conductors . The
sensor is then wired to the
breaker secondary contacts
B4 and B5 . The secondary
current rating of the sensors
must be 1 ampere .
•
Zero sequence sensing:
Zero sequence is applied
on main and feeder
breakers, and other
breakers employed in
zone interlocking ground
protection schemes . To
configure a breaker for
zero sequence sensing, a
shorting jumper is applied to
breaker secondary contacts
B6 and B7 to defeat the
residual sensing mode .
Zero sequence sensors
with 1000:1 and 100:1
ratios are available for
mounting in the switchgear
cable compartment . The
sensor internal window
dimensions are 4 .5 x 13 .5
inches (114 x 342 mm) for
accommodating power
cables . The zero sequence
sensors are wired to breaker
secondary contacts B4
and B5 .
•
Multiple source/Multiple
ground:
Multiple source/multiple
ground sensing schemes are
also possible on systems
with multiple sensors .
•
Zone selective
interlocking:
Zone interlocking is a hard
wired communication
scheme used with circuit
breakers to improve the
level of protection in a
power distribution system .
This is achieved through
communication between
downstream and upstream
breakers in a system
continuously sending signals
to each other to help identify
the location of a fault
condition so the appropriate
breaker isolates the fault .
Zone Selective Interlocking
is a standard feature
provided on Magnum
breakers that are supplied
with Digitrip 520 or higher
trip units . The trip unit Short
Time and Ground Fault
Time Delay Zone Interlock
function is wired out to
breaker secondary terminals
B8 and B9 for customer use .
The zone interlock function
provides for hard-wired
selective circuit breaker
coordination in the power
distribution system .
In the event that a fault
current on the system
exceeds the trip unit Short
Time or Ground Fault pick-up
settings or the Short Delay
Setting 2xIr is exceeded,
the breaker nearest to the
fault trips instantaneously .
At the same time the trip
unit sends a logic signal to
the connected upstream
trip unit to restrain it from
tripping immediately and
follow its protective delay
settings . Coordination is
maintained, the breaker
closest to the fault trips first
and power is only selectively
disrupted .
otee:
N
When zone interlocking
is not employed, it may be
defeated by installing a shorting
jumper across breaker secondary
terminals B8 and B9 .
otee:
N
For IEC circuit breakers
with Digitrip trip units, the zone
interlocking function is not wired
out to the breaker secondaries .
The trip unit will always follow the
programmed short time or ground
time setting . This is accomplished
via a wiring harness internal to the
circuit breaker . If the zone
interlocking function is desired
for IEC breakers with Digitrips
trip units, please refer to Eaton
for appropriate instructions on how
to adjust the internal wiring
harness to activate the zone
interlocking function
Click
here
or search
for ‘70C1037’ on
www .eaton .com,
for more detailed
information on Magnum
Digitrip 520, 520M, and
520MC trip unit
Click
here
or search
for ‘70C1036’ on
www .eaton .com,
for more detailed
information on Magnum
Digitrip 1150 trip units
