Testing Limitrip Devices
29
Test—Short Time Pick-Up
1.
Connect the Red GRABBER to the SHORT TIME PICK-
UP test point. See Figure 18.
2.
Set LONG TIME PICK-UP on “A,” INSTANTANEOUS
PICK-UP on “12X” (Close the 12X switch). Set SHORT
TIME PICK-UP on 3X (open all switches).
3.
Press and hold the START and RESET buttons.
4.
Slowly increase the current until the LONG TIME PICK-
UP light goes OUT. This should occur at 1.5 a
10%.
NOTE
Moving the red grabber connects the Long Time Pick-Up test
leads to the Short Time test point, and this signal goes to zero
at pick-up.
5.
Repeat for SHORT TIME PICK-UP settings of 6X, 8X and
1 2X. The RANGE switch must be on HIGH for these
tests. To avoid over heating, do not maintain the higher
currents any longer than necessary.
Test—Instantaneous Pick-Up
A trigger test point for INSTANTANEOUS TRIP is not avail-
able. Tripping of the circuit breaker and/or operation of the
test set relay will indicate instantaneous trip operation. To
operate the test set relay, the red and black banana plugs
must be connected to the trip device output using the jack
assemblies.
1.
Connect the test set to the circuit breaker as described
in the section under the heading CONNECTIONS.
2.
Set LONG TIME PICK-UP on “A,” LONG TIME BAND on
4 (all switches open), SHORT TIME PICK-UP on 12X
switch). Set INSTANTANEOUS on 3X (open all switches).
3.
Raise the current slowly until the relay in the test set
operates. This can be determined audibly and should
occur at 1 .5 a 10%.
4.
Repeat for the other settings as desired. Avoid maintain-
ing high currents longer than necessary to obtain the
readings.
5.
If it is desired to test the operation of the circuit breaker,
any of the above tests can be run with the circuit breaker
closed, allowing the trip device to open the circuit
breaker when it operates. It may be desirable to discon-
nect either the red or black banana plug from the jack
assembly to assure that the relay in the test set does not
interrupt the current before the circuit breaker can open
thus confusing the test results.
Test—Long Time Delay
1.
Connect the test set to the device as described under
the heading “Connections.” Connect the red GRABBER
to the LONG TIME TEST POINT shown in Figure 18.
2.
Set LONG TIME PICK-UP on “A” LONG TIME BAND on
1, SHORT TIME PICK-UP and INSTANTANEOUS on 1
2X.
3.
Press the START button and adjust the current to 3
amperes (6 times “A” pick-up).
4.
In turn press the STOP and the RESET buttons. Allow
time for the ammeter to return to zero.
5
Press the START button. It is not necessary to hold this
button. Power will be maintained until the trip device
times out.
6.
When the trip device operates, check the reading of the
stop clock against the curves shown in Figure 19. The
reading should be within the limits shown on the curve.
7.
Repeat steps 4, 5 and 6 several times to verify the
results.
8.
Repeat for the other phases, time delay bands and other
values of current, as desired. All test points should fall
within the bands shown on Figure 19. Each band should
have precisely twice the delay of the next lower band
when all other conditions are the same.
NOTE
When timing at values of current only slightly above pick-up
line voltage fluctuations may cause detriggering and result in
erroneous operating times. Therefore, it is advisable to watch
the long time pick-up light to note whether the trigger voltage
is maintained or not. In general, it is impractical to test at less
than 10% above pick-up.
