10
Single-phase Current Relay
K8AB-AS
Cat. No. N142-E1-02
Checking Operation
Overcurrents
Gradually increase the input from 80% of the setting.
The input will equal the operating value when the input
exceeds the setting and the alarm indicator starts flashing.
Operation can be checked by the relay outputs that will
start after the operating time has passed.
Undercurrent
Gradually decrease the input from 120% of the setting and
check the operation using the same method as for
overcurrent.
Example: Overcurrent Operating Mode, Normally Open Relay Drive,
and an Operating Time of 5 s
Connection Diagram
How to Measure the Operating Time
Overcurrent
Change the input suddenly from 0% to 120% of the set
value and measure the time until the Unit operates.
Undercurrent
Change the input suddenly from 120% to 0% of the set
value and measure the time until the Unit operates.
Monitoring Switch-mode Power Supplies
Switch-mode Power Supplies cannot be monitored. In
circuits with a capacitor input, including switch-mode power
supplies, the input capacitor recharge current flows in pulse
form as the load current. The K8AB-AS
@
has a built-in filter
as a countermeasure against high frequencies and cannot
be used to remove pulse current.
Grounding the Power Supply for K8AB Models with a DC
Power Supply
The input and power supply must be isolated.
Models with a DC power supply have a non-isolated power
supply. The input and power supply are connected internally
so the K8AB-AS
@
will not operate normally if an unwanted
current path exists. If an unwanted current path exists, use a
K8AB model with an AC power supply or use an isolated DC
power supply.
Using Multiple K8AB Relays with a DC Power Supply
The input and power supply must be isolated.
The input and power supply are connected internally so an
unwanted current path will be created if more than one K8AB
is used with one DC power supply, as shown in the diagram,
and the K8AB will not operate correctly. If an unwanted
current path exists, use a K8AB model with an AC power
supply or use a different isolated DC power supply for each
K8AB.
Operating Adjustment Knobs
Use a screwdriver to turn the knobs. There is a stopper to
prevent the knob from turning any further once it has been
turned completely to the left or right. Do not force the knob
past these limits.
Can the K8AB be used to monitor a motor with a rated
current of 5 A?
If it's possible to do so, are there any precautions
required?
The K8AB-AS1 and K8AB-AS2 cannot be used with a motor
load.
Use the K8AB-AS3 together with a K8AC-CT200L Current
Transformer.
A current that is many times the rated current can flow to a
motor due to startup current or stall current.
The startup current of a motor is shown in the following
graph.
Questions and Answers
Q
Set value
Current input
Alarm indicator
Relay output
Flashing
Lit
5 s
100 VAC
100 VAC
30
Ω
0 to 10 A
A
A1
A2
±
C 100 V
Variable autotransformer
Input terminals
Power
supply
Output
Cycle counter
400 W (two in parallel)
Q
Q
Q
Q
Input signal
Input ground
K8AB
K8AB
24 VDC
power supply
Q
Q
