K2CM

14

Safety Precautions

■ Correct Use

• The operation check using the test button is intended to check the

operation of the overcurrent functions. Therefore, be sure to turn

ON the overcurrent switch. Also, at this time, turn OFF the open-

phase switch and reverse-phase switch to prevent unnecessary

operations from being performed.

• The operating time of inverse-type models and the lock time of the

instantaneous-type models depend upon the set operating time.

Therefore, do not hold down the test button for more than the set

operating time.

• The reverse-phase can be detected in the wiring up to the current

transformer (including an external current transformer). Check the

wiring between the current transformer and the motor before start-

ing the motor.

• Current reverse-phase detection models cannot be used in applica-

tions that do not allow even momentary reversals of motor direc-

tion.

• Jogging of the motor can be performed. For details, consult your

OMRON representative.

• When using the K2CM to control inching shorter than 0.5 s, the

reverse-phase level detection circuit may operate. In this case, be

sure to use the K2CM with the reverse-phase switch set to OFF.

• The K2CM is basically intended to protect three-phase loads. Its

overcurrent function, however, can also be applied to single-phase

loads. In this case, the conductors can be passed through the holes

in any direction and sequence.

• When applying the K2CM to a circuit with a high imbalance factor

due to the nature of the power supply or load, actually measure the

imbalance factor and select the open-phase sensitivity accordingly

(i.e., set the open-phase switch to either the high or low position).

The K2CM cannot be used if the imbalance factor is 60% or higher.

• When applying the K2CM to the protection of three-phase trans-

formers, give consideration to the imbalance factor due to single-

phase loads.

• A power supply with a frequency other than commercial frequency

cannot be used as the control power supply.

• Use of circuits containing a high percentage of harmonics, such as

circuits incorporating SCR control circuits, VVVF inverters, or recti-

fiers, may cause errors and malfunctions. Consult your OMRON

representative for details.

• When applying the K2CM to the protection of a high-voltage motor

or low-voltage, high-capacity motor, use an external rectifier that

does not saturate at currents up to 600% of the rated motor current

and thus permits a large overcurrent; otherwise, the K2CM will out-

put a tripping signal because of imbalanced operation when an

overcurrent occurs and, with reverse-type models, the motor may

be damaged by burning.

• Never tamper with the trip indicator. Use the reset switch to reset

the K2CM.

• When a power failure occurs in the control power supply, the K2CM

is not reset even when the reset switch is pressed. This is not an

error. The K2CM can be reset only when control power is applied to

it.

• Be sure to remount the front cover after detaching it for operating or

setting the switches on the front panel.

• The rectifier and control circuits are combined by tightening the two

screws on the right and left sides. Never loosen these screws.

• The variable resistors used to make settings are equipped with

mechanisms to stop them rotating outside the valid scale range. Do

not rotate the variable resistors at a torque of 1 kg·cm or more.

• When using the K2CM-

@@@A (instantaneous, automatic reset-

ting), be sure to apply power to the Motor Protective Relay from the

same power line as the magnet contactor for switching the motor.

• Be sure to provide the control power supply for the K2CM-

@@@@V

(voltage reverse-phase detection) from the same line as the motor.

• If current reverse-phase detection models are used in a circuit with

distorted current waveforms, the reverse-phase element may per-

form an unwanted operation. In such circuits, use of the K2CM-

@@@@V (voltage reverse-phase detection) is recommended

because it is not affected at all by current waveform distortion.

Combination

Function setting switches

LED indicators

NOTE

Overcur-

rent

Open-

phase

Reverse-

phase

Overcur-

rent

Open-

phase

Reverse-

phase

1

ON

ON

If the inputs for combinations of two or more functions are

simultaneously generated, the K2CM detects the inputs in

the order reverse-phase, open-phase, overcurrent. Take

combination 4 as an example. If the open-phase and over-

current occur at the same time, there is insufficient time to

detect the overcurrent because the open-phase is first de-

tected and the K2CM outputs the tripping signal (causing

the magnet contactor to turn off). Therefore, the overcur-

rent indicator does not light.

2ON

ON

3ON

OFF

ON

4ON

ON

ON

5ON

ON

OFF

ON

6ON

ON

OFF

ON

7

ONONONOFF

OFF

ON