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Type CKO Overcurrent Relay
Figure 9.
time dial position or 4 tap setting, 0.6 seconds at 6
times tap value current).
To provide selective circuit breaker operation, a min-
imum coordinating time of 0.3 seconds plus circuit
breaker time is recommended between the relay be-
ing set and the relays with which coordination is to be
effected.
The connector screws on the tap plate above the
time dial makes connections to various turns on the
operating coil. By placing this screw in the various
tap plate holes, the relay will just close its contacts at
the corresponding current 4, 5, 6, 7, 8, 10, 12 am-
peres, or as marked on the tap plates.
!
CAUTION
Since the tap block screw carries operating cur-
rent, be sure that the screws are turned tight.
Maximum Pickup and Dropout Time Curves for Instantaneous Overcurrent Unit.
In order to avoid opening current transformer
circuits when changing taps under load, the re-
lay must first be removed from the case. Chassis
operating shorting switches on the case will short the
secondary of the current transformer. The taps
should then be changed with the relay outside of the
case and then reinserted into the case.
4.2
Instantaneous Reclosing
The factory adjustment of the CO unit contacts pro-
vides a contact follow. Where circuit breaker reclos-
ing will be initiated immediately after a trip by the CO
contact, the time of the opening of the contacts
should be a minimum. This condition is obtained by
loosening the stationary contact mounting screw, re-
moving the contact plate and then replacing the plate
with the bent end resting against the contact spring.
With this change and the contact mounting screw
tightened, the stationary contact will rest solidly
against its backstop.
41-101.3A
*Sub 4
629A576
15
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