GE -MM2 Motor Protection Relay - Starting Current in mm2 Mis Match with Measured

You are more then likely seeing the difference in the response time, to the changing level of the in-rush current, of the two measuring systems. The GE MM2 has a sample time of 1.67ms, while fast, the clamp on might have a faster response to the changing current level.

Do the two measuring system show the same current once the motor is up to speed?

Is the relay tripping at that current level? Your inrush current seems a bit high even on the relay. Perhaps it is hitting that level as it's max read current and just shutting down.

guest; are you using a soft start or variable frequency drive controller, you may need a RMS type clamp on. perry

is any body can suggest any reason for this issue...

we are using this for cooler fan motor.

is this is due to grounding?

or this is this due to sensor (CT)?

plz help.......

Check the motor for shorted windings, grounding, or phase imbalance.

On all 8 motors??? Not likely.

I think North of 60 provided you with the best answer anyone can give you with the limited information you provided. With an FVNR starter, you will likely see 500% - 600% peak starting current, however briefly. So I would fully expect to see between 310A and 372A peak from that motor, right where your clamp-on is finding it.

So it looks as though your GE MM2 relay is too slow to pick that up, or is filtering it out of the display by averaging the current over a wider time frame, something not unheard of in microprocessor based motor protection algorithms. I would suspect that the MM2 has a completely separate Starting Current protection feature, not connected to the displayed values.

Don't sweat it.

thanks NORTH OF 60

MOTOR RUNNING CURRENT IN BOTH THE READINGS R CRRCT

SO AS PER U IT WOULD BE BCZ OF SLOW SAMPLING OF GE MM2?

Yes pretty much. As mentioned by JRaef, it is quite common for microprocessor based motor protection devices to average "displayed" current over a given time base. Notice the word "displayed", it is also possible that the device knows that the instantaneous current is of the same order as seen by the clamp on, but, only displays the "averaged" current. That is another thing some of them do.

If you have no other indication of trouble, and if all 8 motors accelerate as expected and run within norms, I would, as JRaef put it, "don't sweat it".

I forgot to add...

One of the reasons that microprocessor based devices, such as this, may show a discrepancy between themselves and another "dedicated device" (dedicated in the sense that it has no other function then to display current) is that... the microprocessor based unit more then likely uses a time slicing scheduler for its tasks. It is a sure bet that the "display" routine that takes the current value and loads it to the panel display on the GE unit has a pretty low priority level over its other functions. Hence the "apparent" lack of response.