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Type CKO Overcurrent Relay
c. Time Curve
Table 1 shows the time curve calibration points for
the various types of relays. With the time dial set to
the indicated position, apply the currents specified
by Table 1 (e.g., for the CKO-2, 3 times and 20 times
tap value current) and measure the operating time of
the relay. The operating times should equal those of
Table 1 plus or minus 5 percent.
6.1.3 Indicating Contactor Switches
(ICS/I) and (ICS/T)
a. Close the contacts of the CO and pass sufficient
dc current through the trip circuit to close the con-
tacts of (ICS/T). This value of current should not
be greater than the particular (ICS/T) tap setting
being used. The operation indicator target should
drop freely, bringing the letter "T" into view.
b. Close the contacts of the instantaneous over-cur-
rent unit (I) and pass sufficient dc current through
the trip circuit to close the contacts of (ICS/I). This
value of current should not be greater than the
particular (ICS/I) tap setting being used. The op-
eration indicator target should drop freely,
bringing the letter "I" into view.
c. For proper contact adjustment, insert a .030" feel-
er gauge between the core pin and the armature.
Hold the armature closed against the core pin and
guage and adjust the stationary contacts such
that they just make with the moving contact. Both
stationary contacts should make at approximately
the same time. The contact follow will be approx-
imately 1/64" to 3/64".
6.2
ROUTINE MAINTENANCE
All relays should be inspected periodically and the
time of operation should be checked at least once
every year or at such other time intervals as may be
dictated by experience to be suitable to the particular
application. The use of phantom loads, in testing in-
duction-type relays, should be avoided, since the re-
sulting distorted current wave form will produce an
error in timing.
All contacts should be periodically cleaned. A con-
tact burnishing tool #182A836H01 is recommended
for this purpose. The use of abrasive material for
cleaning contacts is not recommended, because of
the danger of embedding small particles in the face
of the soft silver and thus impairing the contact.
6.3
CALIBRATION
Use the following procedure for calibrating the relay
if the relay has been taken apart for repairs or the ad-
justments have been disturbed. This procedure
should not be used unless it is apparent that the re-
lay is not in proper working order. (See Section 6.1,
Performance Check.)
6.4
INSTANTANEOUS OVERCURRENT
UNIT (I)
a. The upper pin bearing should be screwed down
until there is approximately 0.025 clearance be-
tween it and the top of shaft bearing. The upper
pin bearing should then be securely locked in po-
sition with the lock nut. The lower bearing position
is fixed and cannot be adjusted.
b. The contact gap adjustment for the overcurrent
unit is made with the moving contact in the reset
position, i.e., against the right side of the bridge.
Move in the left-hand stationary contact until it just
touches the moving contact then back off the sta-
tionary contact 2/3 of one turn for a gap of
approximately .020". The clamp holding the sta-
tionary contact in position.
c. The sensitivity adjustment is made by varying the
tension of the spiral spring attached to the moving
element assembly. The spring is adjusted by
placing a screwdriver or similar tool into one of the
notches located on the periphery of the spring ad-
juster and rotating it. The spring adjuster is
located on the underside of the bridge and is held
in place by a spring type clamp that does not have
to be loosened prior to making the necessary
adjustments.
Insert the tap screw in the minimum value tap setting
and adjust the spring such that the contacts will
close as indicated by a neon lamp in the contact cir-
cuit when energized with the required current. The
pick up of the overcurrent unit with the tap screw in
any other tap should be within ±5% of tap value.
If adjustment of pick-up current in between tap set-
tings is desired insert the tap screw in the next low-
est tap setting and adjust the spring as described. It
should be noted that this adjustment results in a
slightly different time characteristic curve and bur-
den.
41-101.3A
17
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