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4
IB 6.1.12.1-1C
device from a test set or with primary current
injection through the breaker itself.
Trip Latch Drag Force
CAUTION
This check is made on a closed breaker that is subsequently
tripped open. Keep clear of moving parts.
This measurement confirms the ability of the trip
system to trip the primary latching. Measure the drag
force by applying a spring scale on the tripper bar as
indicated in Figure 8.
Electromechanical trip devices actuate the tripper bar
directly with the tripping element armature upon
pickup. Electronic trip systems employ a magnetic
latch to strike the tripper bar. The higher kinetic
energy of a magnetic latch device overcomes a higher
drag load than does an armature of an OD device;
consequently, the acceptable drag loads differ. On
electromechanical trip devices, the drag force should
not exceed 29 ounces. On circuit breakers with
electronic trip systems, the drag force should not
exceed 50 ounces. If the drag force exceeds these
allowable loadings and no mechanical binding is
found,
then
the
mechanism
refurbishment. Continued use risks a "hang-fire"
condition during an automatic trip event.
Current Path Resistance
Measure pole resistance between the upper and
lower terminals behind the breaker, exclusive of the
primary disconnects. After breaker maintenance and
pre-operative checks, compare the renewed values to
previous service records and Table A6 of Appendix A.
Readings that exceed the maximum allowable values
suggest improper contact pressure or worn contact
structure. This may generate heating beyond the
thermal design limit of the circuit breaker if loaded to
the continuous current rating.
The pole resistance of OD equipped breakers
includes the additional resistance of the OD device
coil assembly, which is in series with the current path.
Reference Table A5 for coil assembly resistance.
Insulation Withstand
Remove the circuit breaker from its enclosure and
conduct a Withstand-Voltage Test to prove the
dielectric integrity of the circuit breaker.
According to breaker condition, apply the applicable
test voltage between the primary circuit, secondary
circuit, and grounded parts as indicated in Table A1 of
Appendix A. Establish test voltage within 5 to 10
seconds and maintain for 1 minute. Flashover defines
a failed test.
Testing a Power Shield trip unit:
1. Connect all sixteen terminals of the Power Shield
trip unit together.
Courtesy of NationalSwitchgear.com
2. Apply 500 V
ABB does not recommend withstand testing of the
MPS, MPS-C, or MPSC-2000 trip units.
Points of Test Voltage Application:
On an OPEN circuit breaker, apply primary-circuit test
voltage:
1. Between the primary circuit, including both the
2. Between the primary and secondary (control)
3. Between the upper and lower terminals of the
Note: For convenience, connecting the secondary
is
in
need
of
circuit to the grounded parts can combine tests 1 and
2 above. Should a breakdown occur, perform both
steps individually to determine which mode had failed.
On a CLOSED circuit breaker, apply primary-circuit
test voltage:
1. Between the primary circuit and ground all parts
2. Between the primary and secondary (control)
3. Between the primary terminals of adjacent
On an OPEN or CLOSED circuit breaker, apply
secondary-circuit test voltage between the secondary
circuit and ground all parts that are normally
grounded.
CAUTION
The charging motor is rated at a lower dielectric withstand-
voltage than the control circuit. Before testing the control
circuit, isolate the motor by turning the motor disconnect
switch OFF. Test the motor specifically by testing the control
circuit again, but with the motor disconnect switch turned ON
and at the lower voltage specified for the motor.
Renewal Parts
To minimize interrupted service, ABB recommends
stocking common replacement items. Part assemblies
are suggested for reliable and timely interchange. An
abbreviated list of common replacement parts is listed
in Appendix C.
A Renewal Parts Bulletin is available from the nearest
ABB District Sales Office. Verify the part number and
proper application prior to ordering.
between the sixteen terminals and
AC
metal parts normally grounded.
upper and lower terminals, and ground all metal
parts that are normally grounded. All poles of the
primary circuit may be jumpered together for one
test. The Ground Disconnect shown in Figure 1d
or an unpainted section of the metal frame may
be used for ground.
circuit.
primary
circuit.
Rather
permutation, jumper the upper terminals together,
then separately jumper the lower terminals
together. Conduct a single test between the upper
and lower terminals.
that are normally grounded.
circuit.
phases.
ABB
than
testing
each
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