K8AB-AS

9

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.

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 a motor with a rated current of 5 A be monitored

using the K8AB?

Are there any application precautions?

The K8AB-AS1 and K8AB-AS2 cannot be used with motor

loads. Use the K8AB-AS3 in combination with the K8AC-

CT200L Current Transformer (CT). With motor loads, the

startup current and stall current will cause a current of many

times the rated current to flow. Refer to the following figure

for information on the motor startup current.

For a motor with a rating of 5 A, the startup current will be

approximately 30 A. The startup current will exceed the

overload capacity (rating: 150% for 1 s) of the K8AB-AS1

and K8AB-AS2 and result in failure of the Relay.

To monitor the motor load, use the K8AB-AS3. (Overload

capacity: 120% of rating for continuous load, 200% of rating

for 30 s, and 600% of rating for 1 s).

The K8AB-AS3 has a large input range. Pass the conductors

multiple times through the special CT.

Concept behind Passing Conductor through the CT When

Using the K8AB-AS3

Example: Monitoring Overload of a Motor with a Rated Current

of 5 A

K8AB settings:

Overcurrent detection, operating value setting: 25%, operating

time: 0.1 s

Startup lock timer: 0.1 to 30 s (Set the timer according to the

duration of the startup current.)

The setting range for the K8AB-AS3 is 10% to 100% of the rated

current (i.e., 10 to 100 A). Pass the conductors through the CT five

times so that at least 10 A of current flows. The input current to the

K8AB will be 25 A (i.e., 5 A x 5 loops).

If a startup current of six times the rated current is generated, it will

be 150 A (i.e., 25 A x 6). The overload capacity for the K8AB-AS3 is

200% of the rating for 30 s. The Relay will not fail even if the startup

current continues for 30 s, and it is possible to perform overload

detection.

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

Several seconds to

several tens of seconds

Time from beginning of startup

100%

500%

K8AC-CT200L

Primary-side conductor

To the K8AB-AS3

In the interest of product improvement, specifications are subject to change without notice.

ALL DIMENSIONS SHOWN ARE IN MILLIMETERS.

To convert millimeters into inches, multiply by 0.03937. To convert grams into ounces, multiply by 0.03527.