GE AKR-30 Series Maintenance Manual page 253

1 3.4.2 FALSE TRIPPING - BREAKERS
EQU IPPED WITH GROUND FAULT
When nu isance tripping occurs on b reakers eq uipped
with the Ground Fault tip element, a probable cause is the
existence of a false "ground" signal . As indicated by the
cabling d iagram of Fig. 1 06, each phase sensor is con­
nected to summing circuitry in the programmer. U nder
no-fault conditions on 3-wire load circuits, the currents in
this circuitry add to zero and no ground sig nal is devel­
oped. This current sum will be zero only if all three sensors
have the same electrical characteristics. If one sensor
d iffers from the others (i .e., different rating) the circuity
can produce output s ufficient to trip the breaker. Simi­
l a r l y , d i sc o n t i n u ity between any s e n s o r a n d t h e
programmer unit can cause a false tri p signal.
If n uisance 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 continu ity between the neutral sensor and its
eq uipment-mounted secondary d isconnect block. Also
check for continuity from the breaker-mounted neutral
secondary d iscon nect block through to the female har­
ness connector.
(3) If the b reaker'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 neut ral cond uctor 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 i dentical,
their tap-tO-tap resistances should closely agree. See
1 5.
Table
1 3.5 CABLING DIAGRAMS
q, s q, c
q,A
;__ ;__ ;__
r t - 1- t- 1
t � � � � �
E
s
� )= ==)= ==)=
LEFT POLE I
CURRENT
SENSOR
LOAD
FIG. 1 05 - CABLING DIAGRAM - RMS-9 &
EPIC MICROVERSATRIP® WITHOUT
GROUND FAULT
q, A q, s q, c
A A A
r t - 1- t- :
t �� � � � �
E
s
)= = =)= ==)=
�
I
LEFT POLE
CURRENT
SENSOR
LOAD
FIG. 1 06 - CABLING DIAGRAM - RMS-9 &
EPIC MICROVERSATRIP® WITH GROUND
FAULT ON 3-WIRE LOAD
FLUX SHIFT
PROGRAMMER
-
TRIP DEVICE
,
,
,
_ _ _ _ _
HARNESS
PROGRAMMER
CONNECTOR
CO NN E CT O R
(A MP 1 -3 5 03 56-9 )
FLUX SHIFT
PROGRAMMER
-
TRIP DEVICE
,
•
I
HARNESS
CONNECTOR
(AMP 1 -3503 56 - 9)
PRO GRAMMER
CONNECTOR
UNIT
- - - - ,
I
I
j
- -
UNIT
- - -
75