14
the electrical connections may not be properly tightened or
it could also indicate improper contact wipe.
4.
To verify that the breaker has been properly retrofitted,
perform a primary injection test on each phase. This test
will check the CTs, bus, wiring harness, flux shifter, and
trip unit as a complete system.
a.
A high-current, low-voltage power supply should be
connected across each line and load terminal to simulate
an overcurrent fault.
b.
Set the long-time trip at 0.5 to minimize the breaker
stress.
c.
When ground fault is installed, the test can be
performed by wiring two adjacent poles in series or by
using the GE Digital Test Kit, cat. no. TVRMS2. This
will prevent the breaker from tripping because of an
unbalanced current flow. For Entelliguard TU use
GTUTK20.
CAUTION:
Do not attempt to use GE Test Kit cat. no.
TVTS1 or TVRMS on Entelliguard trip unit and do not use
GTUTK20 on MVT trip unit.
Trouble-Shooting
When malfunctioning is suspected, first examine the breaker
and its power system for abnormal conditions such as the
following:
• The breaker is not tripping in response to overcurrent
conditions or incipient ground faults.
• The breaker is remaining in a trip-free state because of
mechanical interference along its trip shaft.
• The shunt trip (if present) is activating improperly.
Nuisance Tripping on Ground Fault-Equipped Breakers
When nuisance tripping occurs on breakers equipped with
ground fault trip, a probable cause is the existence of a false
ground signal. Each phase sensor is connected to summing
circuitry in the trip unit. Under no-fault conditions on three-
wire load circuits, the currents add to zero and no ground signal
is developed. This current sum is zero only if all three sensors
have the same electrical characteristics. If one sensor differs
from the others (such as by a different rating or wrong tap
setting), the circuitry can produce an output sufficient to trip the
breaker. Similarly, a discontinuity between any sensor and the
trip unit can cause a false trip signal.
The sensors and their connections should be closely examined
if nuisance tripping is encountered on any breaker whose
Entelliguard, MicroVersaTrip Plus or MicroVersaTrip PM trip
unit has previously demonstrated satisfactory performance.
After disconnecting the breaker from all power sources,
perform the following procedure:
1.
Check that all phase sensors are the same type (current
range).
2.
Verify that the tap settings on all three phase sensors are
identical.
3.
Verify that the wiring harness connections to the sensors
have the proper polarity (white lead to common, black lead
to tap), as shown in the cabling diagrams1.
4.
On ground fault breakers serving four-wire loads, check
that the neutral sensor is properly connected, as indicated
in Figure 27. In particular, check the following:
a.
Verify that the neutral sensor has the same rating and
tap setting as the phase sensors.
b.
Verify 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 trip unit
wiring harness connector.
c.
If the breaker’s lower studs connect to the power
source, then the neutral sensor must have its load end
connected to the source.
d.
Verify that the neutral conductor is carrying only the
neutral current associated with the breaker’s load
current (the neutral is not shared with other loads).
5.
If the preceding steps fail to identify the problem, then
measure the sensor resistances. The appropriate values are
listed in Table 1. Since the phase and neutral sensors are
electrically identical, their resistances should agree closely.
Breaker
CT Rating, A
Resistance, ohms
LA-4000-Blue
4000
29–39
Table 1. CT resistance values.
