FIG. 88 TEST SET, CAT. NO. TVTS 1
1 2.4.1 RESISTANCE VALUES
For use i n troubleshooting the MicroVersaTrip'M
current sensors, the resistance of the tapped and fixed
windings is g iven in Tables 13 and 1 4 respectively.
TABLE 1 3 - TAPPED SENSO R R ESISTANCE
VALUES
Resistance in Ohms
Ampere
Between Common
Tap
and Tap Terminals
1 00
7.0-8.2
1 50
1 0- 1 2
225
1 5-18
300
20-24
300
20-24
400
27-32
600
42-50
800
58-68
600
42-50
800
53-68
1 200
93-1 09
1 600
1 30-1 54
800
74-88
1 200
1 1 6-1 36
1 600
1 62-1 90
2000
21 0-246
TABLE 1 4 - FIXED SENSOR R ESISTANCE
VALUES
Ampere
Resistance in Ohms
Rating
Between Terminals
1 00
6.7-7.8
1 50
1 0- 1 2
225
1 5- 1 7
300
20-24
400
27-32
600
42-50
800
58-68
1 200
92-1 08
1 600
1 29-1 5 1
2000
207-243
The coil resistance of the M icroVersaTrip flux shifter
device is approximately
7
ohms.
SECTION 1 2-Micro Versa Trip
TM
Trip Device (Cont.)
1 2.4.2 FALSE TRIPPI NG-BR EAKERS
EQU I PPED WITH GROUND FAU LT
When nuisance tripping occu rs on breakers equipped
with the G round Fault trip element, a p robable cause is
the existence of a false "ground" signal. As indicated by
the cabling d iagram of Fig. 90, each phase sensor is
connected to su mming circu itry in the p rogrammer. Un
der no-fault cond itions on 3-wi re load circuits, the
currents i n this circuitry add to zero and no ground
signal is developed . This cu rrent sum will be zero only if
all three sensors have the same electrical charac
teristics. If one sensor d iffers from the others (i .e. , d if
ferent rating or wrong tap setting), the circuitry can
p rod uce output sufficient to trip the breaker. Similarly,
d iscontinuity between any sensor and the p rogrammer
unit can cause a false trip signal.
If n uisance tripping is encountered on any breaker
whose MicroVersaTrip components have p reviously
demonstrated satisfactory performance via the TVTS1
Test Set, the sensors and their connections should be
closely scrutinized . After d isconnecting the breaker from
all power sources.
a) Check that all phase sensors are the same type (am
pere range) .
b) Ensure that the tap settings on all 3-phase sensors
are identical .
c) Verify that the harness connections to the sensors
meet the polarity constrai nts i ndicated by the cabli ng
diagram.
d) On G rou nd Fault breakers serving 4-wire loads,
check that the neutral sensor is properly connected (see
cabling diagram Fig. 91 ) . In particular,
( 1 ) Verify that the neutral sensor has the same rating
and tap setti ng as the phase s ensors.
(2)
Check conti nuity between the neutral sensor and its
equipment-mou nted secondary disconnect block. Also
check for continuity from the breaker-mou nted neutral
secondary disconnect block through to the female harness
connector.
(3) If The breaker's lower studs con nect to the supply
source, then the neutral sensor must have its LOAD end
con nected to the sou rce. See Fig. 92.
(4) Ensure that the neutral conductor is carrying only
that neutral current associated with the breaker's load cur
rent (neutral not shared with other loads) .
e) If the preceding steps fail to identify the problem, then
the sensor resistances should be measured . Since the
phase and neutral sensors are electrically identical , th eir
tap-to-tap resistances should closely agree. See Tables 1 3
and 1 4 .
65
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