ABB CKO-5 User manual

41-101.3A Type CKO Overcurrent Relay
2
switch, which allows the operation indicator target to
drop.
The front spring, in addition to holding the target, pro-
vides restraint for the armature and thus controls the
pickup value of the switch.
2.3 Instantaneous Overcurrent Unit
2.3.1 Construction
The instantaneous overcurrent unit consists of an in-
duction cylinder unit, capacitor, varistor, and a trans-
former. The components are connected such that a
contact closing torque is produced when the current
exceeds a specified value.
2.3.2 Induction Cylinder Unit
Mechanically, the cylinder unit is composed of four
basic components: a diecast aluminum frame, an
electromagnet, a moving element assembly, and a
molded bridge.
The frame serves as the mounting structure for the
magnetic core. The magnetic core which houses the
lower pin bearing is secured to the frame by a locking
nut. The bearing can be replaced, if necessary, with-
out having to remove the magnetic core from the
frame.
The electromagnet has two pairs of coils. The coils
of each pair are mounted diametrically opposite one
another, and a capacitor is connected in series with
one pair of coils. In addition, there are two locating
pins. The locating pins are used to accurately posi-
tion the lower pin bearing, which is threaded into the
bridge. The electromagnet is secured to the frame by
four mounting screws.
The moving element assembly consists of a spiral
spring, contact carrying member, and an aluminum
cylinder assembled to a molded hub which holds the
shaft. The shaft has removable top and bottom jewel
bearings. The shaft rides between the bottom pin
bearing and the upper pin bearing with the cylinder
rotating in an air gap formed by the electromagnet
and the magnetic core.
The bridge is secured to the electromagnet and
frame by two mounting screws. In addition to holding
the upper pin bearings, the bridge is used for mount-
ing the adjustable stationary contact housing. The
stationary contact housing is held in position by a
spring type clamp. The spring adjuster is located on
the underside of the bridge and is attached to the
moving contact arm by a spiral spring. The spring ad-
juster is also held in place by a spring type clamp.
With the contact closed, the electrical connection is
made through the stationary contact housing clamp,
to the moving contact, through the spiral spring out
to the spring adjuster clamp.
2.3.3 Saturating Transformer
The transformer is a saturating type consisting of a
tapped primary winding and a secondary winding. A
varistor is connected across the secondary winding
to reduce the voltage peaks applied to the induc-
tion cylinder unit and phase shifting capacitor.
2.4 Operation
Operation of the instantaneous overcurrent unit oc-
curs when the primary current of the transformer ex-
ceeds a value as marked on the tap plate. Upon ap-
plication of current to the transformer, a voltage is
induced in the secondary winding. This voltage is im-
pressed upon the parallel connected pairs of cylinder
unit coils. The capacitor connected in series with one
pair of coils shifts the current flowing in these coils in
reference to the current flowing in the other pair of
coils. As a result, the air gap fluxes of the cylinder
unit are out of phase and a contact closing torque is
produced.
The primary of the transformer is tapped and brought
out to a tap connector block for ease in changing the
pickup current of the relay. The use of a tapped
transformer provides approximately the same ener-
gy level at a given multiple of pickup current for any
tap setting, resulting in one time curve throughout
the range of the relay.
Two terminals, 6 and 7, across one pair of pole wind-
up are brought out so that operating current can be
short circuited around the pole windings preventing
the unit from developing torque.
3.0 CHARACTERISTICS
The time characteristics of the overcurrent relays are
designated by specific numbers as indicated below
(e.g., CKO-8).

Type CKO Overcurrent Relay 41-101.3A
3
Time
Characteristic Designation
Short Time 2
Long Time 5
Definite Time 6
Moderately Inverse Time 7
Inverse Time 8
Very Inverse Time 9
Extremely Inverse Time 11
The relays are available in the following current
ranges:
INSTANTANEOUS OVERCURRENT UNIT (1)
Range Taps
0.5 - 2 Amps 0.5 0.75 1.0 1.25 1.5 2
1 - 4 1.0 1.5 2.0 2.5 3.0 4.0
2-8 234568
4-16 46 891216
10 - 40 101520243040
20 - 80 203040486080
The indicating contactor switch has two taps that
provide a pickup setting of 0.2 or 2 amperes. To
change taps requires connecting the lead located in
front of the tap block to the desired setting by means
of a screw connection.
3.2 Contacts
The moving contact assembly has been factory ad-
justed for low contact bounce performance and
should not be changed.
The set screw in each stationary contact has been
shop adjusted for optimum follow and this adjust-
ment should not be disturbed.
The tap value is the minimum current required to just
close the overcurrent relay contacts. For pickup set-
tings in between taps refer to the section under ad-
justments. The pickup and dropout time curves for
the instantaneous overcurrent units is shown in Fig-
ure 9. TIME OVERCURRENT UNIT
Range Taps
.5 - 2.5 0.5 0.6 0.8 1.0 1.5 2.0 2.5
2 - 6 2 2.5 3 3.5 4 5 6
4-12456781012
The tap value is the minimum current required to just
close the relay contacts.
This time vs. current characteristics for the time-
overcurrent unit are shown in Figures 2 to 8. These
characteristics give the contact closing time for the
various time dial settings when the indicated multi-
ples of tap value current are applied to the relay.
3.1 Trip Circuit
The relay contacts will safely close 30 amperes at
250 Vdc and the seal-in contacts of the indicating
contactor switches will safely carry this current long
enough to trip a circuit breaker.
Figure 1. Internal Schematic of the Type CKO
Relay in the Type FT31 Case.
880A450
Sub 4
3.2.1 Trip Circuit Constants
Indicating Contactor Switch
0.2 ampere tap - 6.5 ohms dc resistance
2.0 ampere tap - 0.15 ohms dc resistance
4.0 SETTINGS
4.1 Time Overcurrent Unit (CO)
The time overcurrent unit settings can be defined ei-
ther by tap setting and time dial position or by tap
setting and a specific time of operation at some cur-
rent multiple of the tap setting (e.g., 4 tap setting, 2

41-101.3A Type CKO Overcurrent Relay
4
ENERGY REQUIREMENTS
INSTANTANEOUS OVERCURRENT UNIT OPERATING CURRENT CIRCUIT- 60 HERTZ
†† ø†† ø
AMPERE RANGE TAP VA AT TAP VALUE P.F. ANGLE VA AT 4 AMPS P.F. ANGLE
.5 .37 39 2446
.75 .38 36 1337
1 .39 35 8.5 34
.5-2 1.25 .41 34 6.032
1.5 .43 32 4.6 31
2 .45 30 2.9 28
1.41 369.036
1.5 .44 32 5.0 32
2 .47 30 3.0 29
1-4 2.5 .50 28 2.1 27
3 .53 26 1.5 26
4 .59 24 0.93 24
21.1 496.548
31.2 433.342
41.3 382.137
2-8 5 1.4 35 1.4 35
61.5 331.133
81.8 290.729
41.5 512.451
61.7 451.245
4-16 8 1.8 40 0.7 40
91.9 380.638
12 2.2 34 0.37 34
16 2.5 30 0.24 31
10 1.7 28 0.43 28
15 2.4 21 0.27 21
20 3.1 16 0.20 17
10-40 24 3.6 15 0.15 15
30 4.2 12 0.11 13
40 4.9 11 0.08 12
20 6.6 31 0.40 31
30 9.3 24 0.25 24
20-80 4012.0 200.1820
4813.5 180.1418
6015.9 160.1016
8019.2 150.0715
CONTINUOUS RATING ONE SECOND RATING
RANGE (AMPERES) †(AMPERES)
0.5 - 2 5 100
1 - 4 8 140
2 - 8 8 140
4 - 16 10 200
10 - 40 10 200
20 - 80 10 200
†Thermal capacities for short times other than one second may be calculated on
the basis of time being inversely proportional to the square of the current.
øDegrees current lags voltage.
†† Voltages taken with Rectox type voltmeter.

Type CKO Overcurrent Relay 41-101.3A
5
ENERGY REQUIREMENTS
TYPE CKO-2 TIME OVERCURRENT UNITS
VOLT AMPERES††
CONTINUOUS ONE SECOND POWER AT AT 3 TIMES AT 10 TIMES AT 20 TIMES
AMPERE RATING RATING†FACTOR TAP VALUE TAP VALUE TAP VALUE TAP VALUE
RANGE TAP (AMPERES) (AMPERES) ANGLEøCURRENT CURRENT CURRENT CURRENT
0.5 0.91 28 58 4.8 39.6 256 790
0.6 0.96 28 57 4.9 39.8 270 851
0.8 1.18 28 53 5.0 42.7 308 1024
0.5-2.5 1.0 1.37 28 50 5.3 45.4 348 1220
1.5 1.95 28 40 6.2 54.4 435 1740
2.0 2.24 28 36 7.2 65.4 580 2280
2.5 2.50 28 29 7.9 73.6 700 2850
2.0 3.1 110 59 5.04 38.7 262 800
2.5 4.0 110 55 5.13 39.8 280 920
3.0 4.4 110 51 5.37 *40.8 312 1008
2-6 3.5 4.8 110 47 5.53 42.8 329 1120
4.0 5.2 110 45 5.72 46.0 360 1216
5.0 5.6 110 41 5.90 50.3 420 1500
6.0 6.0 110 37 6.54 54.9 474 1800
4.0 7.3 230 65 4.92 39.1 268 848
5.0 8.0 230 50 5.20 42.0 305 1020
6.0 8.8 230 47 5.34 44.1 330 1128
4-12 7.0 9.6 230 46 5.53 45.8 364 1260
8.0 10.4 230 43 5.86 49.9 400 1408
10.0 11.2 230 37 6.60 55.5 470 1720
12.0 12.0 230 34 7.00 62.3 528 2064
†Thermal capacities for short times other than one second maybe calculated on the basisoftimebeinginversely proportional
to the square of the current.
øDegrees current lags voltage at tap value current.
†† Voltages taken with Rectox type voltmeter.

41-101.3A Type CKO Overcurrent Relay
6
†Thermal capacities for short times other than one second maybe calculated on
the basis of time being inversely proportional to the square of the current.
øDegrees current lags voltage at tap value current.
†† Voltages taken with Rectox type voltmeter.
ENERGY REQUIREMENTS
TYPE CKO-5 AND TYPE CKO-6 TIME OVERCURRENT UNITS
VOLT AMPERES††
CONTINUOUS ONE SECOND POWER AT AT 3 TIMES AT 10 TIMES AT 20 TIMES
AMPERE RATING RATING†FACTOR TAP VALUE TAP VALUE TAP VALUE TAP VALUE
RANGE TAP (AMPERES) (AMPERES) ANGLE ø CURRENT CURRENT CURRENT CURRENT
0.5 2.7 88 69 3.92 20.6 103 270
0.6 3.1 88 68 3.96 20.7 106 288
0.8 3.7 88 67 3.96 21.0 114 325
0.5-2.5 1.0 4.1 88 66 4.07 21.4 122 360
1.5 5.7 88 62 4.19 23.2 147 462
2.0 6.8 88 60 4.30 24.9 168 548
2.5 7.7 88 58 4.37 26.2 180 630
2 8.0 230 67 3.88 21.0 110 308
2.5 8.8 230 66 3.90 21.6 118 342
3 9.7 230 64 3.93 22.1 126 381
2-6 3.5 10.4 230 63 4.09 23.1 136 417
4 11.2 230 62 4.12 23.5 144 448
5 12.5 230 59 4.20 24.8 162 540
6 13.7 230 57 4.38 26.5 183 624
4 16.0 460 65 4.00 22.4 126 376
5 18.8 460 63 4.15 23.7 143 450
6 19.3 460 61 4.32 25.3 162 531
4-12 7 20.8 460 59 4.35 26.4 183 611
8 22.5 460 56 4.40 27.8 204 699
10 25.0 460 53 4.60 30.1 247 880
12 28.0 460 47 4.92 35.6 288 1056
CKO-7 TIME OVERCURRENT UNITS
VOLT AMPERES††
CONTINUOUS ONE SECOND POWER AT AT 3 TIMES AT 10 TIMES AT 20 TIMES
AMPERE RATING RATING†FACTOR TAP VALUE TAP VALUE TAP VALUE TAP VALUE
RANGE TAP (AMPERES) (AMPERES) ANGLE ø CURRENT CURRENT CURRENT CURRENT
0.5 2.7 88 68 3.88 20.7 103 278
0.6 3.1 88 67 3.93 20.9 107 288
0.8 3.7 88 66 3.93 21.1 114 320
0.5-2.5 1.0 4.1 88 64 4.00 21.6 122 356
1.5 5.7 88 61 4.08 22.9 148 459
2.0 6.8 88 58 4.24 24.8 174 552
2.5 7.7 88 56 4.38 25.9 185 640
2 8.0 230 66 4.06 21.3 111 306
2.5 8.8 230 63 4.07 21.8 120 342
3 9.7 230 63 4.14 22.5 129 366
2-6 3.5 10.4 230 62 4.34 23.4 141 413
4 11.2 230 61 4.34 23.8 149 448
5 12.5 230 59 4.40 25.2 163 530
6 13.7 230 58 4.62 27.0 183 624
4 16.0 460 64 4.24 22.8 129 392
5 18.8 460 61 4.30 24.2 149 460
6 19.3 460 60 4.62 25.9 168 540
4-12 7 20.8 460 58 4.69 27.3 187 626
8 22.5 460 55 4.80 29.8 211 688
10 25.0 460 51 5.20 33.0 260 860
12 28.0 460 46 5.40 37.5 308 1032

Type CKO Overcurrent Relay 41-101.3A
7
ENERGY REQUIREMENTS
TYPE CKO-8 AND TYPE CKO-9 TIME OVERCURRENT UNITS
VOLT AMPERES††
CONTINUOUS ONE SECOND POWER AT AT 3 TIMES AT 10 TIMES AT 20 TIMES
AMPERE RATING RATING†FACTOR TAP VALUE TAP VALUE TAP VALUE TAP VALUE
RANGE TAP (AMPERES) (AMPERES) ANGLE øCURRENT CURRENT CURRENT CURRENT
0.5 2.7 88 72 2.38 21.0 132 350
0.6 3.1 88 71 2.38 21.0 134 365
0.8 3.7 88 69 2.40 21.1 142 400
0.5-2.5 1.0 4.1 88 67 2.42 21.2 150 440
1.5 5.7 88 62 2.51 22.0 170 530
2.0 6.8 88 57 2.65 23.5 200 675
2.5 7.7 88 53 2.74 24.8 228 800
2 8.0 230 70 2.38 21.0 136 360
2.5 8.8 230 66 2.40 21.1 142 395
3 9.7 230 64 2.42 21.5 149 430
2-6 3.5 10.4 230 62 2.48 22.0 157 470
4 11.2 230 60 2.53 22.7 164 500
5 12.5 230 58 2.64 24.0 180 580
6 13.7 230 56 2.75 25.2 198 660
4 16.0 460 68 2.38 21.3 146 420
5 18.8 460 63 2.46 21.8 158 480
6 19.3 460 60 2.54 22.6 172 550
4-12 7 20.8 460 57 2.62 23.6 190 620
8 22.5 460 54 2.73 24.8 207 700
10 25.0 460 48 3.00 27.8 248 850
12 28.0 460 45 3.46 31.4 292 1020
CKO-11 TIME OVERCURRENT UNITS
VOLT AMPERES††
CONTINUOUS ONE SECOND POWER AT AT 3 TIMES AT 10 TIMES AT 20 TIMES
AMPERE RATING RATING†FACTOR TAP VALUE TAP VALUE TAP VALUE TAP VALUE
RANGE TAP (AMPERES) (AMPERES) ANGLE øCURRENT CURRENT CURRENT CURRENT
0.5 1.7 56 36 0.72 6.54 71.8 250
0.6 1.9 56 34 0.75 6.80 75.0 267
0.8 2.2 56 30 0.81 7.46 84.0 298
0.5-2.5 1.0 2.5 56 27 0.89 8.30 93.1 330
1.5 3.0 56 22 1.13 10.04 115.5 411
2.0 3.5 56 17 1.30 11.95 136.3 502
2.5 3.8 56 16 1.48 13.95 160.0 610
2.0 7.0 230 32 0.73 6.30 74.0 264
2.5 7.8 230 30 0.78 7.00 78.5 285
3.0 8.3 230 27 0.83 7.74 84.0 309
2-6 3.5 9.0 230 24 0.88 8.20 89.0 340
4.0 10.0 230 23 0.96 9.12 102.0 372
5.0 11.0 230 20 1.07 9.80 109.0 430
6.0 12.0 230 20 1.23 11.34 129.0 504
4.0 14.0 460 29 0.79 7.08 78.4 296
5.0 16.0 460 25 0.89 8.00 90.0 340
6.0 17.0 460 22 1.02 9.18 101.4 378
4-12 7.0 18.0 460 20 1.10 10.00 110.0 454
8.0 20.0 460 18 1.23 11.10 124.8 480
10.0 22.0 460 17 1.32 14.90 131.6 600
12.0 26.0 460 16 1.80 16.30 180.0 720
†Thermal capacities for short times other than one second maybe calculated on the basis of time being
inversely proportional to the square of the current.
øDegrees current lags voltage at tap value current.
†† Voltages taken with Rectox type voltmeter.

41-101.3A Type CKO Overcurrent Relay
8
Figure 2. Typical Time Curves of the Time-Overcurrent Unit of the Short Time (2) Relays.
418244
Sub 3

Type CKO Overcurrent Relay 41-101.3A
9
Figure 3. Typical Time Curves of the Time-Overcurrent Unit of the Long Time (5) Relays.
418245
Sub 2

41-101.3A Type CKO Overcurrent Relay
10
Figure 4. Typical Time Curves of the Time-Overcurrent Unit of the Definite Time (6) Relays.
418246
*Sub 3

Type CKO Overcurrent Relay 41-101.3A
11
418247
*Sub 3
Figure 5. Typical Time Curves of the Time-Overcurrent Unit of the Moderately Inverse (7) Relays.

41-101.3A Type CKO Overcurrent Relay
12
Figure 6. Typical Time Curves of the Time-Overcurrent Unit of the Inverse (8) Relays.
418248
Sub 2

Type CKO Overcurrent Relay 41-101.3A
13
Figure 7. Typical Time Curves of the Time-Overcurrent Unit of the Very Inverse (9) Relays.
418249
Sub 2

41-101.3A Type CKO Overcurrent Relay
14
Figure 8. Typical Time Curves of the Time-Overcurrent Unit of the Extremely Inverse (11) Relays.
288B655
Sub 2

Type CKO Overcurrent Relay 41-101.3A
15
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.
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.
Figure 9. Maximum Pickup and Dropout Time Curves for Instantaneous Overcurrent Unit.
629A576
*Sub 4

41-101.3A Type CKO Overcurrent Relay
16
4.3 Instantaneous Overcurrent Unit (I)
The only setting required is the pickup current setting
which is made by means of the connector screw lo-
cated on the tap plate. By placing the connector
screw in the desired tap, the relay will just close its
contacts at the tap value current.
CAUTION
!
Since the tap block connector screw carries op-
erating current, be sure that the screw is turned
tight.
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 switcheson 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.
4.4 Indicating Contactor Switch (ICS/I
and ICS/T)
The setting required on the ICS units is the selection
of the 0.2 or 2.0 ampere tap setting. This selection is
made by connecting the lead located in front of the
tap block to the desired setting by means of the con-
necting screw.
5.0 INSTALLATION
The relays should be mounted on switchboard pan-
els or their equivalent in a location free from dirt,
moisture, excessive vibration and heat. Mount the
relay vertically by means of the rear mounting stud or
studs for the type FT projection case or by means of
the four mounting holes on the flange for the semi-
flush type FT case. Either the stud or the mounting
screws may be utilized for grounding the relay. Ex-
ternal toothed washers are provided for use in the lo-
cations shown on the outline and drilling plan to fa-
cilitate making a good electrical connection between
the relay case, its mounting screw or studs, and the
relay panel. Ground wires should be affixed to the
mounting screws or studs as required for poorly
grounded or insulating panels. Other electrical con-
nections may be made directly to the terminal by
means of screws for steel panel mounting or to the
terminal stud furnished with the relay for thick panel
mounting. The terminal stud may be easily removed
or inserted by locking two nuts on the stud and then
turning the proper nut with a wrench.
For detail information on the FT case refer to I.L.41-
076.
6.0 ADJUSTMENTS AND MAINTE-
NANCE
The proper adjustments to insure correct operation
of this relay have been made at the factory. Upon re-
ceipt of the relay, no customer adjustments, other
than those covered under Section 4, Settings,
should be required.
6.1 Performance Check
The following check is recommended to insure that
the relay is in proper working order.
6.1.1 Instantaneous Overcurrent Unit (I)
a. Contact Gap
The gap between the stationary and moving con-
tacts with the relay in the de-energized position
should be approximately .020".
b. Minimum Trip Current
The pick-up of the overcurrent unit can be checked
by inserting the tap screw in the desired tap hole and
applying rated tap value current. The contact should
close within ±5% of tap value current.
6.1.2 Time Overcurrent Unit (CO)
a. Contacts
The index mark on the movement frame will coincide
with the "0" mark on the time dial when the stationary
contact has moved through approximately one-half
of its normal deflection. Therefore, with the station-
ary contact resting against the backstop, the index
mark is offset to the right of the "0" mark by approxi-
mately .020". The placement of the various time dial
positions in line with the index mark will give operat-
ing times as shown on the respective time-current
curves.
b. Minimum Trip Current
Set the time dial to position 6, alternately apply tap
value current plus 3% and tap value current minus
3%. The moving contact should leave the backstop
at tap value current plus 3% and should return to the
backstop at tap value current minus 3%.

Type CKO Overcurrent Relay 41-101.3A
17
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 isheld
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 Type CKO Overcurrent Relay
18
Figure 10. Diagram of Test Connections of the Time-Overcurrent Unit.
1455C31 Sub 1

Type CKO Overcurrent Relay 41-101.3A
19
Figure 11. External Schematic of the CKO Relay
1452C84
Sub 2

41-101.3A Type CKO Overcurrent Relay
20
7.0 TIME OVERCURRENT UNIT (CO)
a. Contacts
The index mark on the movement frame will coincide
with the "0" mark on the time dial when the stationary
contact has moved through approximately one-half
of its normal deflection. Therefore, with the station-
ary contact resting against the backstop, the index
mark is offset to the right of the "0" mark by approxi-
mately .020". The placement of the various time dial
positions in line with the index mark will give operat-
ing times as shown on the respective time current
curves.
b. Minimum Trip Current
The adjustment of the spring tension in setting the
minimum trip current value of the relay is most con-
veniently made with the damping magnet removed.
With the time dial set on "0", wind upthe spiralspring
by means of the spring adjuster until approximately
6 3/4convolutions show.
Set the relay on the minimum tap setting, the time
dial to position 6.
Adjust the control spring tension so that the moving
contact will leave the backstop at tap value current
+1.0% and will return to the backstop at tap value
current -1.0%.
c. Time Curve Calibration
Install the permanent magnet. Apply the indicated
current per Table 1 for permanent magnet adjust-
ment (e.g., CKO-8, 2 times tap value) and measure
the operating time. Adjust the permanent magnet
keeper until the operating time corresponds to the
value of Table 1.
Apply the indicated current per Table 1 for the elec-
tromagnet plug adjustment (e.g., CKO-8, 20 times
tap value) and measure the operating time. Adjust
the proper plug until the operating time corresponds
to the value in Table 1. (Withdrawing the left hand
plug, front view increases the operating time and
withdrawing the right hand plug, front view, decreas-
es the time. In adjusting the plugs, one plug should
be screwed in completely and the other plug run in or
out until the proper operating time has been ob-
tained.
Recheck the permanent magnet adjustment. If the
operating time for this calibration point has changed,
readjust the permanent magnet and then recheck
the electromagnet plug adjustment.
7.1 Indicating Contactor Switches (ICS/I) AND
(ICS/T)
For proper contact adjustment, insert a .030" feeler
gauge between the core pin and the armature. Hold
the armature closed against the core pin and gauge
and adjust the stationary contacts such that they just
TABLE 1
TIME CURVE CALIBRATION DATA - 60 HERTZ
PERMANENT MAGNET ADJUSTMENT ELECTROMAGNET PLUGS
TIME- TIME CURRENT OPERATING CURRENT OPERATING
OVERCURRENT DIAL (MULTIPLES OF TIME MULTIPLES OF TIME
UNIT TYPE POSITION TAP VALUE) SECONDS TAP VALUE) SECONDS
2 6 3 0.57 20 0.22
5 6 2 37.80 10 14.30
6 6 2 2.46 20 1.19
7 6 2 4.27 20 1.11
8 6 2 13.35 20 1.11
9 6 2 8.87 20 0.65
11 6 2 11.27 20 0.24