1 3.4.2 FALSE TRIPPING - BREAKERS
EQUIPPED WITH GROUND FAULT
When nuisance tripping occurs on breakers equipped
with the Ground Fault tip element, a probable cause is the
existence of a false "ground" signal. As indicated by the
cabling diagram of Fig. 1 06, each phase sensor is con
nected to summing circuitry in the programmer. Under
no-fault conditions on 3-wire load circuits, the currents in
this circuitry add to zero and no ground signal is devel
oped. This current sum will be zero only if all three sensors
have the same electrical characteristics. If one sensor
differs from the others (i .e., different rating) the circuity
can produce output sufficient to trip the breaker. Simi
larly, d i sconti n u ity between any sensor a n d t h e
programmer unit can cause a false tri p signal.
If nuisance tri p ping is encountered on any breaker
whose RMS-9 or Epic MicroVersaTrip components have
previously demonstrated satisfactory performance via
the Test Set, the sensors and their connections should be
closely scrutinized. After disconnecting the breaker from
all power sources.
a) Check that all phase sensors are the same type
(ampere range).
c) Verify that the harness connections to the sensors
meet the polarity constraints indicted by the cabling
diagram .
d) On Ground Fault breakers serving 4-wire loads,
check that the neutral sensor is properly connected (see
cabling diagram Fig. 1 07). I n particular,
( 1 ) Verify that the neutral sensor has the same rating as
the phase sensors.
(2) Check continuity between the neutral sensor and its
equipment-mounted secondary disconnect block. Also
check for continuity from the breaker-mounted neutral
secondary disconnect block through to the female har
ness connector.
(3) If the breaker's lower studs connect to the supply
source, then the neutral sensor must have its LOAD end
connected to the source. See Fig . 1 08.
(4) Ensure that the neutral conductor is carrying only
that neutral current associated with the breaker load
current (neutral not shared with other loads).
3) If the preceding steps fai l to identify the problem,
then the sensor resistances should be measured . Since
the phase and neutral sensors are electrically identical,
their tap-tO-tap resistances should closely agree. See
Table
1 5.
1 3.5 CABLING DIAGRAMS
q,A
q, s
q, c
PROGRAMMER
UNIT
;__ ;__ ;__
s
t�����
E
rt-1-t-1
FLUX
SHIFT
TRIP DEVICE
,
-
- - - - ,
� )===)===)=
LEFT POLE
I
CURRENT
SENSOR
I
I
,
,
_ _ _ _ _
j
LOAD
HARNESS
CONNECTOR
PROGRAMMER
(AMP
1 -350356-9)
CONNECTOR
FIG. 1 05 - CABLING DIAGRAM - RMS-9 &
EPIC MICROVERSATRIP® WITHOUT
GROUND FAULT
q,A
q, s
q, c
A A A
s
t������
E
rt-1-t-:
FLUX
SHIFT
TRIP DEVICE
PROGRAMMER
UNIT
,
-
- - -
--
� )===)===)=
I
•
LEFT POLE
I
CURRENT
SENSOR
LOAD
HARNESS
CONNECTOR
(AMP
1 -350356-9)
PROGRAMMER
CONNECTOR
FIG. 1 06 - CABLING DIAGRAM - RMS-9 &
EPIC MICROVERSATRIP® WITH GROUND
FAULT ON 3-WIRE LOAD
75
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