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Old 04-13-2013, 02:24 PM   #1
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Default 2hp motor over current

Is it normal for a motor to ever run at above its nameplate value. Its FLA is 5amps and across the line it is pulling 6.4-6.8. It keeps tripping out the drive that is running it. The motor is brand new btw.
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Old 04-13-2013, 02:40 PM   #2
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Its FLA is 5amps and across the line it is pulling 6.4-6.8. The motor is brand new btw.

If seen where the wrong size pulley is put on, that could cause the amperage to be higher.
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Old 04-13-2013, 02:43 PM   #3
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99.5% of the time high motor current is because of a stubborn connected mechanical load. What is this thing driving?
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Old 04-13-2013, 02:48 PM   #4
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Its pumping milk out of a collection tank on a dairy. It has a pump connected to the cface
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Old 04-13-2013, 02:58 PM   #5
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Is this a replacement for the same sized motor? Totally new installation? What changed?
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Old 04-13-2013, 03:16 PM   #6
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Its was running on an old AC Tech drive that died. Replaced it with an ATV312 and it ran about 15hrs then tripped out on o.cf-(overcurrent fault). So after running in bypass across the line the motor spit out a spark and so it was replaced then put back on the drive and has ran fine for 4-5days. Now it is tripping on o.cf and even after resetting the vfd it goes right into o.cf fault upon start up. So the motor is back on bypass contact or but is pulling 6+ amps. Gotta be something upstream? Maybe needs a line reactor? Maybe just a detective drive?
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Old 04-13-2013, 05:41 PM   #7
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99.5% of the time high motor current is because of a stubborn connected mechanical load. What is this thing driving?
Quote:
Originally Posted by xsryman View Post
Its was running on an old AC Tech drive that died. Replaced it with an ATV312 and it ran about 15hrs then tripped out on o.cf-(overcurrent fault). So after running in bypass across the line the motor spit out a spark and so it was replaced then put back on the drive and has ran fine for 4-5days. Now it is tripping on o.cf and even after resetting the vfd it goes right into o.cf fault upon start up. So the motor is back on bypass contact or but is pulling 6+ amps. Gotta be something upstream? Maybe needs a line reactor? Maybe just a detective drive?
My guess would be a mechanical issue also. Pump bearings could be starting to seize or something is restricting the product flow. If you can't find any obvious issues maybe the original motor was a bit undersized to begin with but the old drive could handle the current better or had less sensitive protection.

Last edited by 8V71; 04-13-2013 at 05:47 PM.
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Old 04-13-2013, 05:46 PM   #8
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If you must keep it running until it's convenient to fix, more than likely the pump, you could close the discharge valve a little to bring the current down.
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Old 04-13-2013, 05:50 PM   #9
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or something is restricting the product flow.
As long as it is a centrifugal pump restricting the flow will reduce the current.

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If you must keep it running until it's convenient to fix, more than likely the pump, you could close the discharge valve a little to bring the current down.
I agree.
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Old 04-13-2013, 06:27 PM   #10
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Its was running on an old AC Tech drive that died. Replaced it with an ATV312 and it ran about 15hrs then tripped out on o.cf-(overcurrent fault). So after running in bypass across the line the motor spit out a spark and so it was replaced then put back on the drive and has ran fine for 4-5days. Now it is tripping on o.cf and even after resetting the vfd it goes right into o.cf fault upon start up. So the motor is back on bypass contact or but is pulling 6+ amps. Gotta be something upstream? Maybe needs a line reactor? Maybe just a detective drive?
Most likely scenario from this is that your load is changing, causing the original motor to go into overcurrent. It was put in bypass, and with no overload protection it ran to overheat and insulation failure. The replacement motor went in, and is now seeing the same overload condition, and will also eventually fail if run at that amperage.

The two big questions are: Is the original drive failure related? And what is causing the change in mechanical operation of the pump? I agree with other posters that restricting the pump volume should lower your pump current.

Why is this normally VFD driven if it can run across the line?
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Old 04-13-2013, 06:45 PM   #11
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Speed regulation is needed to get the best cooling as the milk comes from the receiver tank and passes through the chiller. Its not a centrifugal pump so there are no bearings to wear. It has an impeller directly on the motor shaft. It can run across the line but it is not ideal. Only for bypass situations. There is another set up identical to this one right next to it that is pulling the proper amp draw. There is just something about this setup. Checked for phase imbalances at the I/p and o/p. Everything checks out. Just high amp draw at the output.
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Old 04-13-2013, 06:56 PM   #12
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Can you post a model# or pictures? I'm having a hard time imagining this, and when I Google it I'm getting pictures of positive-displacement pumps, which are actually contrary to what we've said here and can't tolerate any discharge restriction.
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Old 04-13-2013, 07:15 PM   #13
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Quote:
Originally Posted by xsryman
Speed regulation is needed to get the best cooling as the milk comes from the receiver tank and passes through the chiller. Its not a centrifugal pump so there are no bearings to wear. It has an impeller directly on the motor shaft. It can run across the line but it is not ideal. Only for bypass situations. There is another set up identical to this one right next to it that is pulling the proper amp draw. There is just something about this setup. Checked for phase imbalances at the I/p and o/p. Everything checks out. Just high amp draw at the output.
What voltage? 1 or 3 phase? Is the fault contained to one phase or all three?
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Old 04-13-2013, 07:26 PM   #14
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Can you post a model# or pictures? I'm having a hard time imagining this, and when I Google it I'm getting pictures of positive-displacement pumps, which are actually contrary to what we've said here and can't tolerate any discharge restriction.
I think it's still centrifugal but a specialized SS unit with no external pump bearing.
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Old 04-13-2013, 07:31 PM   #15
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To answer your original question, sometimes yes a motor can run over its nameplate rating depending on the motor service factor.
But not that high of a percentage as you are seeing.
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Old 04-13-2013, 08:08 PM   #16
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What voltage? 1 or 3 phase? Is the fault contained to one phase or all three?
2HP, 5 amps; it's either 208 or 240 3.

I'd also be willing to bet that all 3 phases are seeing overcurrent.

I agree with the others, it's not a motor issue, most likely mechanical.

If the impeller is connected directly to the shaft, it's most likely a centrifugal pump. Is the motor actually a C face or is it a J frame? Like 56J.

As noted, if it is indeed a centrifugal pump, restricting the discharge will lower the current. If it's just about any other type, restricting the discharge will cause the current to rise.

Are the suction and discharge pressures the same on both pumps? If so, look at mechanical issues. If not, then look at fluid issues.
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Old 04-13-2013, 08:18 PM   #17
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It is 2hp 240v 3ph. I guess I will have to do some more mechanical investigation on Monday.
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Old 04-13-2013, 08:19 PM   #18
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Oh and its 56c. Not jet pump.
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Old 04-13-2013, 08:31 PM   #19
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Oh and its 56c. Not jet pump.
If it's 56C, then more than likely there's a bearing in the pump casing. Probably only one, but most 56C pumps have a bearing, even though they are directly coupled to the shaft.
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Old 04-13-2013, 09:24 PM   #20
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Quote:
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It is 2hp 240v 3ph. I guess I will have to do some more mechanical investigation on Monday.
A Mis alignment when mounting the motor can produce ol fault. Also a restriction in the chiller plate could be the problem. Is it a plate exchanger or a tank chilling system?
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