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Type CKO Overcurrent Relay
Time
Characteristic
Short Time
Long Time
Definite Time
Moderately Inverse Time
Inverse Time
Very Inverse Time
Extremely Inverse Time
The relays are available in the following current
ranges:
INSTANTANEOUS OVERCURRENT UNIT (1)
Range
0.5 - 2 Amps
0.5
1 - 4
1.0
2 - 8
2
4 - 16
4
10 - 40
1 0
1 5
20 - 80
2 0
3 0
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
.5 - 2.5
0.5
0.6
2
- 6
2
2.5
4
- 12
4
5
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.
Designation
2
5
6
7
8
9
11
Taps
0.75
1.0
1.25
1.5 2
1.5
2.0
2.5
3.0 4.0
3
4
5
6
6
8
9
1 2
2 0
2 4
3 0
4 0
4 8
6 0
Taps
0.8
1.0
1.5
2.0
3
3.5
4
5
6
7
8
1 0
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.
8
1 6
4 0
8 0
2.5
6
1 2
Figure 1.
Internal Schematic of the Type CKO
Relay in the Type FT31 Case.
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
Sub 4
880A450
3
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