# VFD NIDEC H300 OI ac Trip



## gpop (May 14, 2018)

What kind of motor and what environment is the motor in. 

damp motor/connections ?


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## Kevhuff26 (Dec 17, 2018)

gpop said:


> What kind of motor and what environment is the motor in.
> 
> damp motor/connections ?


It serves a chilled water pump. The area is typically very dry. Also, we recently had the motor tested and it passed.


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## Kevhuff26 (Dec 17, 2018)

gpop said:


> What kind of motor and what environment is the motor in.
> 
> damp motor/connections ?


Sorry, I didn’t answer your entire question. I believe it’s just an induction motor and of-course inverter duty rated. It has high-pressed lugs bolted on stationary copper bus bar for each phase inside the junction box.


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## gpop (May 14, 2018)

Kevhuff26 said:


> Sorry, I didn’t answer your entire question. I believe it’s just an induction motor and of-course inverter duty rated. It has high-pressed lugs bolted on stationary copper bus bar for each phase inside the junction box.



No built in heater. Do you know how long the motor is shut down for? (they shut down at weekends and the problem only happens on a Monday kind of thing)


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## micromind (Aug 11, 2007)

Has the noise level changed? Maybe it actually is overloading due to a bad bearing. 

What speed does it usually run at? 

Has anything in the water system changed?


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## Kevhuff26 (Dec 17, 2018)

gpop said:


> No built in heater. Do you know how long the motor is shut down for? (they shut down at weekends and the problem only happens on a Monday kind of thing)


Typically it runs twice a day. It’s weird though. It seems to always happen on the weekend. Then we find out about it Monday. We then troubleshoot it and it will run for days sometimes months with no problem.


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## John Valdes (May 17, 2007)

Does it have a fault log you could look at? Maybe pin down a time? Pin down how much current?


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## Kevhuff26 (Dec 17, 2018)

micromind said:


> Has the noise level changed? Maybe it actually is overloading due to a bad bearing.
> 
> What speed does it usually run at?
> 
> Has anything in the water system changed?


The noise hasn’t changed from what I can tell.

It typically runs around 80 percent. I’m not sure what RPM that is. I can find that out though.

Nothing in the system has changed that I know of. NIDEC Tech support told us that something in operations like a valve, ect. typically wouldn’t cause this trip. We always thought it would and it’s still hard to believe that.


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## Kevhuff26 (Dec 17, 2018)

John Valdes said:


> Does it have a fault log you could look at? Maybe pin down a time? Pin down how much current?


I can locate the last ten trips and their dates/times. Then there is a sub-trip that is supposed to help narrow the cause down. As far as displaying the current at the time of the trip. I believe we couldn’t locate that. I will look in the manual and try it again. It would make sense to list the current at the time of the trip.


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## micromind (Aug 11, 2007)

80% on a centrifugal pump would be a fairly light load, not even close to an actual overload.

When it runs, can you look at current on the VFD display? The The display is more accurate than a typical clamp-on meter.


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## John Valdes (May 17, 2007)

micromind said:


> 80% on a centrifugal pump would be a fairly light load, not even close to an actual overload.
> 
> When it runs, can you look at current on the VFD display? The The display is more accurate than a typical clamp-on meter.


I agree. Its a variable torque load and for the drive to trip on OL will take some serious loading. But also these controls are usually reduced in size (current) for this reason.
I always trusted my amp clamp more than the display. The display is a not a direct current reading. Its a voltage across a resistor and then mathematically turned into current.
At least thats how I remember it.


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## gpop (May 14, 2018)

Kevhuff26 said:


> The noise hasn’t changed from what I can tell.
> 
> It typically runs around 80 percent. I’m not sure what RPM that is. I can find that out though.
> 
> Nothing in the system has changed that I know of. NIDEC Tech support told us that something in operations like a valve, ect. typically wouldn’t cause this trip. We always thought it would and it’s still hard to believe that.



The pump pulls the highest amps on start up until it builds up back pressure which can cause a overload problem but the manual states this is a instantaneous trip where the amps exceeded the drives max output so you are looking for a surge rather than a overload that the drive can deal with. 

Ive seen old vfd's throw this code for no reason and ive seen motors that test good when warm test bad after they have cooled off.


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## gpop (May 14, 2018)

John Valdes said:


> I agree. Its a variable torque load and for the drive to trip on OL will take some serious loading. But also these controls are usually reduced in size (current) for this reason.
> I always trusted my amp clamp more than the display. The display is a not a direct current reading. Its a voltage across a resistor and then mathematically turned into current.
> At least thats how I remember it.


Its reacting to what amps it thinks its pulling (that's why the display readings are important). Once i see what it thinks its doing then i can check to see if i agree with a meter at which point its probably not serviceable and will have to be replaced.


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## paulengr (Oct 8, 2017)

What is the insulation resistance using a digital megaohm meter tested at 500 V for 60 seconds from phase to ground after disconnecting from VFD? Also measure temperature in C when you do it. Watch readings. Is there any jitter? Does it jump up then flat light or rapidly increase then sort of level off but continue to increase?

Put multimeter in diode check mode. With drive off put one probe on DC+ and the other on L1, L2, L3, T1, T2, T3. Repeat with DC-. Then flip the probes and repeat again. Check to see that everything “looks right”. Readings should be about 0.3-0.7 V in one direction, open in the other. Check VFD capacitance. What is reading from DC+ to DC-?

Trying to determine if it’s an actual short either to ground or blown drive component.

How is drive speed or torque controlled?


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## Kevhuff26 (Dec 17, 2018)

micromind said:


> 80% on a centrifugal pump would be a fairly light load, not even close to an actual overload.
> 
> When it runs, can you look at current on the VFD display? The The display is more accurate than a typical clamp-on meter.


I believe I can. I just need to scroll through and find it. We did put a Fluke power quality analyzer on the motor for a few days. The current was no where near an overload condition.


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## Kevhuff26 (Dec 17, 2018)

gpop said:


> The pump pulls the highest amps on start up until it builds up back pressure which can cause a overload problem but the manual states this is a instantaneous trip where the amps exceeded the drives max output so you are looking for a surge rather than a overload that the drive can deal with.
> 
> Ive seen old vfd's throw this code for no reason and ive seen motors that test good when warm test bad after they have cooled off.


It is very strange. I can say this. I have personally megger tested the motor at-least twice and it passed. We also just had another vender perform extensive motor testing and it passed again.

We also isolated the VFD output cables and megger tested them at 2000v per NIDEC’s recommendation. We tested each phase to ground. All passed. However, we did not test phase-phase. I asked the NIDEC support and they said we shouldn’t have to do that. They also initially told us to just replace all the VFD output cables as there is maybe a small short. We are finding that hard to believe.


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## Kevhuff26 (Dec 17, 2018)

paulengr said:


> What is the insulation resistance using a digital megaohm meter tested at 500 V for 60 seconds from phase to ground after disconnecting from VFD? Also measure temperature in C when you do it. Watch readings. Is there any jitter? Does it jump up then flat light or rapidly increase then sort of level off but continue to increase?
> 
> Put multimeter in diode check mode. With drive off put one probe on DC+ and the other on L1, L2, L3, T1, T2, T3. Repeat with DC-. Then flip the probes and repeat again. Check to see that everything “looks right”. Readings should be about 0.3-0.7 V in one direction, open in the other. Check VFD capacitance. What is reading from DC+ to DC-?
> 
> ...




I will look for the motor megger test results. The VFD output cables we recently tested phase-ground all tested in the T ohms except for one it was like 950 G ohms. However, we did not test phase-phase on the cables.

I will try taking those readings and see what the results are.
I did have a sub-trip number of 3000. It said something about the trip coming from power module 3. I can’t find in the manual what exactly the power module means. I asked the NIDEC support and they haven’t given me an answer.
I believe the drive is speed controlled.


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## paulengr (Oct 8, 2017)

Kevhuff26 said:


> It is very strange. I can say this. I have personally megger tested the motor at-least twice and it passed. We also just had another vender perform extensive motor testing and it passed again.
> 
> We also isolated the VFD output cables and megger tested them at 2000v per NIDEC’s recommendation. We tested each phase to ground. All passed. However, we did not test phase-phase. I asked the NIDEC support and they said we shouldn’t have to do that. They also initially told us to just replace all the VFD output cables as there is maybe a small short. We are finding that hard to believe.


Based on what they are telling you NIDEC is clueless. NIDEC is a motor company, a very large one. They are private labeling that VFD. NIDEC is asking you to do a DC test at 2000 V but the correct test if you were going to do what they are asking for is to measure the surge impedance at 2000 V. If you isolated the cables at both motor and drive end you can test insulation resistance.

I specifically asked what the readings were and told you what to watch for, for a reason. I have meggered plenty of motors that had ground faults but were considered "good" by people that don't know what to look for. 1 Megaohm is not good. 5 Megaohms is not good (raw reading). Even 100 Megaohms is not good if the reading shoots up to 100 Megaohms within a couple seconds then "flatlines" at that reading.

A common problem with VFD's is called reflected wave, but the problem can happen from other sources of surges in the system. If the electrical cable path between the VFD and the motor is long enough, it can puncture the cable insulation and cause the problem you are seeing. Meggering phase to phase and phase to ground should both be done. This means isolating at both ends. The cable is going to energize almost instantly so be ready for that.

Other issues are damaged IGBT's or SCR's or MOSFET's leading to intermittent shorts (at first) eventually building up to dead shorts, or a short in a cable, or damaged motor feeder cables. The drive DC link capacitors can be shorted too but the short doesn't show up until it gets near capacity.


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## Kevhuff26 (Dec 17, 2018)

paulengr said:


> Based on what they are telling you NIDEC is clueless. NIDEC is a motor company, a very large one. They are private labeling that VFD. NIDEC is asking you to do a DC test at 2000 V but the correct test if you were going to do what they are asking for is to measure the surge impedance at 2000 V. If you isolated the cables at both motor and drive end you can test insulation resistance.
> 
> I specifically asked what the readings were and told you what to watch for, for a reason. I have meggered plenty of motors that had ground faults but were considered "good" by people that don't know what to look for. 1 Megaohm is not good. 5 Megaohms is not good (raw reading). Even 100 Megaohms is not good if the reading shoots up to 100 Megaohms within a couple seconds then "flatlines" at that reading.
> 
> ...


Thank you, I see what your saying. Unfortunately I can't find our in house motor megger test results. I can tell you this though. When we megger tested the motor we tested each phase for one minute at 500 V. When I am doing a one minute megger test I always make sure there is a steady incline in my readings. I also have seen motors megger tested and then fail once in service. 

We also should be receiving reports soon from our motor testing contractor. I believe they did more extensive testing. I assume they did a PI and maybe a Hi-pot? I'll follow up with that when we receive the report. 

However, based on your recommendations. I will do those checks. I will also will isolate the VFD output-motor cables and test them again and include phase-phase testing. If the cables results are a pass and the motor results all pass as they said they did. I would say its probably not a short in the cable or a problem with the motor?


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## paulengr (Oct 8, 2017)

Megger testing tests the ground wall insulation of a motor, the thick piece of material that gets laid in the slot before inserting the coils. It is also sensitive to contamination and moisture. By the time problems show up here the motor is usually done for. I rarely catch motors that are borderline but if you have even slight amounts of surface voltage tracking or flash overs the VFD will freak out at it intermittently. That’s the reason that the shape of the curve is more important than the result. Insulation resistance is strongly affected by temperature. If you test a motor in summer then winter the winter test will be 3-4 times higher for the same insulation. That is why 5 Megaohms is not a safe reading unless taken at 40 C. I was testing a bunch of motors in a cold snap a month ago (in North Carolina) and the correction factor was 0.11...needed almost 50 Megaohms on a 460 V motor to pass. PI is an attempt to get around this issue. You keep testing for 10 minutes until hopefully most of the insulation is polarized. Then you take the ratio of the 10 and 1 minute readings. PI doesn’t care about temperature. You are looking for about 2-6 for a reading but low isn’t necessarily bad, very high Megger readings invalidate PI (over 5000), and high readings often indicate very dry but cracking/crazing insulation.

That’s all the test will tell you. It catches about 80% of motor failures and when Klein and Extech have Meggers on the market for under $200 there’s no excuse not to have a motor techs #1 go to tool.

But this is only half of the story. A motor shop does the full Megger/PI test. They also measure resistance coil to coil which can pick up shorts or opens before the Megger test. Think about a 460 V coil with 100 turns. The voltage turn to turn is only 4.6 V. That is why insulation on magnet wire is so thin it’s transparent. This catches things the Megger test can’t. They look for resistive imbalance under 1-2% which is a way of comparing coil to coil. You need a Kelvin bridge tester (4 wire milliohm tester) to measure a motor though because resistance is in the milliohm range. Even on small motors under 5 HP where it is in ohms I’ve tried using a Fluke 87 V and the accuracy just isn’t there. This needs to be the expensive tool.

They also run one of two tests. In the shop they will run the surge test for historical reasons. This takes a huge capacitor charged to near insulation limits (which is why it is a shop test) and smacks each coil with it. They measure the wave as it bounces back and forth between the coil and cap and then compare coil to coil giving you a bunch of numbers. The key one is PP-EAR which tells you how much different they are. The field test uses an LCR bridge. It measures inductance using a low voltage of around 100 V and a frequency of 60-1500 Hz (tester dependent) to measure inductance in millihenries then calculates inductive imbalance. Anything over about 15-20% or any big shift from a baseline reading is a bad motor. This test picks up on insulation problems before the resistance tests do but also gives bad readings with rotor air gap issues or rotor issues. One of the more common problems with drives is reflected waves that destroy the first couple turns. It shows up on this test first then eventually the resistance test. It does not typically appear at all on the Megger test except in severe cases. I had a customer destroying motors this way over and over and it failed Megger for them about 25% of the time. It was so bad in their case a multimeter would find it (measure each coil). Again pricey equipment that most electricians won’t have.

There are many other non-invasive field tests. Rotor Influence Testjng does the inductance test as you rotate the rotor a little at a time and is much more sensitive to rotor and air gap issues but requires an uncoupled motor with free access to the end of the shaft and disconnected from any drives. Partial Discharge testjng does the surge test but also looks for sudden jumps in current/voltage if you have microscopic arcing going on inside air bubbles in the insulation. This test really only applies to medium voltage motors. Another one are variations of the shaft voltage or common mode current test. These look for bearing discharges that cause bearing fluting from VFD common mode voltage but has nothing to do with your problem.

There are several that have fallen by the wayside. Stepped voltage testing or tip up is an old variation on Megger tests intended to find surge voltage issues but it shows very little and the modern digital surge and inductance tests make it obsolete.

A DC hi pot is one to watch out for. All reputable motor shops have discontinued it. The test standard is IEEE 400 and reading the introduction is very enlightening. Summary: IEEE 400 says DO NOT do DC Hi Pot. Two reasons. First it shows nothing of value. The surge/inductance and Megger/PI tests show everything that hi potting can detect. But more importantly it can damage perfectly good insulation since it does something funky to it that never happens in the real world (applying DC at the insulation limits), and the hi pot can give passing results but the damage that it caused makes the motor fail hours to weeks later. Every credible third party quality controlled shop has discontinued the test for that reason or does the test but won’t warranty the motor after doing it. The solitary exception is on brand new motors.

The offline tests will find about 95% of motor issues. Online testjng gets you the last 5% but none of those tests except obvious things like bad bearings will cause a drive trip. All three offline tests can be done by a motor shop with an advanced motor tester in about 20 minutes (drop drive leads, clip on tester, screw with software, run test). I’ve run thousands of these tests on just about every kind of motor or generator there is on different testers at times and seen almost every type of failure there is. The machines are self checking...I had a lead issue on a motor Thursday where a scrap of varnished cambric was hiding and the machine kept giving me a hassle (bad connection) over and over until I found it.

Moving on...how far apart (cable length) are the motor and VFD? Do you have more than one VFD in the same raceway? What is the raceway made out of? What type of insulation/cable are you using? Solid or stranded? Do you have an independent supplemental ground (green or bare wire) connected directly between the VFD and the motor frames? No cheating.

The trouble with overloads is that It can be instant like a flash over somewhere and VFDs are very picky about these or it can be a problem like a chain binding up and jumping on a sprocket tooth or bearings and gearing or a process problem. The big thing to remember too is that the VFD is just a computer. An algorithm is deciding on the kind of fault. It could be a ground fault but the drive reports overload. So often you know it has SOME problem but you don’t know what it is.

Don’t get hung up on condemning a motor. If a motor shop runs it through the tests I described it’s not the motor. You need to look at other components. For one thing about 90% of the time overload us a load problem, not a motor or drive issue. So look at the event log first. How much load/current was there? What was the speed? How much load? Lots of hints buried in that data. Get a good vibration/mechanical tech to check things. I usually just Megger the motor to placate the customer then start looking for mechanical or process issues.

If you suspect a drive problem the diode test only checks diodes. You sort of have to rely on the VFD for shorted SCRs or IGBTs. But a final test is that if you have another drive or another motor, even a tiny but portable motor, try hooking up the motor to a different drive or the VFD to another motor. We keep a few rental VFDs which makes it easy for us. I can also check them with an oscilloscope but again that’s typically outside of the budget.


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## wiz1997 (Mar 30, 2021)

How about a real simple question?
I've come across this issue several times over the years.
So simple know one believes that was the problem.
Have you checked the acceleration and deceleration settings on the drive?
I've experienced trips during shutdown on a chilled water pump.
If the deceleration is too low the motor may overload trying to slow the flow of liquid.
Is the drive programmed to ramp to a stop, or coast to a stop?
A typical centrifugal pump, without a VFD, will coast to a stop.


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## just the cowboy (Sep 4, 2013)

What is the plant voltage on weekends????
You state it happens on weekends, could the taps be set to high for the plant and when POCO has no load or plant has no load Voltage goes up. I have seen line voltage raise 20+ volts on weekends.

Cowoby


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## JRaef (Mar 23, 2009)

I can't download that manual without registering and I don't want to because I'm not willing to give up my personal data to learn about it. We have no distributors selling that line of drives around here, so I never have to deal with it..

Is that OI as in O for Over and (capital) I for current? Or is that O for Over and (lower case) l for load?

Over Current may mean something in your drive is detecting a rapid increase in current, maybe too rapid for it to be picked up by the display. Drives often have hardware overrides for things like this that protect the components faster than the microprocessor can calculate things. Usually the display will tell you it is a Short Circuit, but again, I don't know this drive.

If so, then it could be failing motor lead insulation, capacitive coupling in the cables, water in the conduit (which changes the capacitive coupling issue and/or exacerbates leaking insulation), any number of things that create an intermittent high current situation.


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## Kevhuff26 (Dec 17, 2018)

paulengr said:


> Megger testing tests the ground wall insulation of a motor, the thick piece of material that gets laid in the slot before inserting the coils. It is also sensitive to contamination and moisture. By the time problems show up here the motor is usually done for. I rarely catch motors that are borderline but if you have even slight amounts of surface voltage tracking or flash overs the VFD will freak out at it intermittently. That’s the reason that the shape of the curve is more important than the result. Insulation resistance is strongly affected by temperature. If you test a motor in summer then winter the winter test will be 3-4 times higher for the same insulation. That is why 5 Megaohms is not a safe reading unless taken at 40 C. I was testing a bunch of motors in a cold snap a month ago (in North Carolina) and the correction factor was 0.11...needed almost 50 Megaohms on a 460 V motor to pass. PI is an attempt to get around this issue. You keep testing for 10 minutes until hopefully most of the insulation is polarized. Then you take the ratio of the 10 and 1 minute readings. PI doesn’t care about temperature. You are looking for about 2-6 for a reading but low isn’t necessarily bad, very high Megger readings invalidate PI (over 5000), and high readings often indicate very dry but cracking/crazing insulation.
> 
> That’s all the test will tell you. It catches about 80% of motor failures and when Klein and Extech have Meggers on the market for under $200 there’s no excuse not to have a motor techs #1 go to tool.
> 
> ...


Thank you so much. That was is a lot of valuable information. Now of-course the VFD is not tripping. We still have to investigate.

I need to take an actual measurement. However, I believe the motor is about 20 feet from the VFD. The VFD-motor cables there is 9 total 3 for each phase. There is three conduits from the VFD-motor. Each with three non-grounded conductors. Then there is three bare stranded equipment grounding conductors in each conduit. They all terminate in the motor junction box and at the VFD. The 9 non-grounded motor cables are stranded conductors. I am not sure the wire type and size. I will have to follow up with that.

I haven’t received the motor testing results yet. However, I know they used a Baker set? We are having a meeting next week to make a game plan to troubleshoot.


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## paulengr (Oct 8, 2017)

Kevhuff26 said:


> Thank you so much. That was is a lot of valuable information. Now of-course the VFD is not tripping. We still have to investigate.
> 
> I need to take an actual measurement. However, I believe the motor is about 20 feet from the VFD. The VFD-motor cables there is 9 total 3 for each phase. There is three conduits from the VFD-motor. Each with three non-grounded conductors. Then there is three bare stranded equipment grounding conductors in each conduit. They all terminate in the motor junction box and at the VFD. The 9 non-grounded motor cables are stranded conductors. I am not sure the wire type and size. I will have to follow up with that.
> 
> I haven’t received the motor testing results yet. However, I know they used a Baker set? We are having a meeting next week to make a game plan to troubleshoot.


Unlikely the cabling is damaged but worth a shot. When you get up over 100 feet (30 meters) is when you will often have trouble.

Baker testers use the surge test. They can do hi pot but it’s a waste of time at best and can potentially damage motors. If the motor passes and cabling passes then it’s either a power or drive problem once you rule those out.


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## Kevhuff26 (Dec 17, 2018)

wiz1997 said:


> How about a real simple question?
> I've come across this issue several times over the years.
> So simple know one believes that was the problem.
> Have you checked the acceleration and deceleration settings on the drive?
> ...


I would have to check. It does state to check the accel and decel rates. However, I believe we have checked these settings before and matched them to our other two drives.


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## Kevhuff26 (Dec 17, 2018)

just the cowboy said:


> What is the plant voltage on weekends????
> You state it happens on weekends, could the taps be set to high for the plant and when POCO has no load or plant has no load Voltage goes up. I have seen line voltage raise 20+ volts on weekends.
> 
> Cowoby


I'll pull a trend on our SCADA system. If I notice anything odd I will let you know.


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## Kevhuff26 (Dec 17, 2018)

JRaef said:


> I can't download that manual without registering and I don't want to because I'm not willing to give up my personal data to learn about it. We have no distributors selling that line of drives around here, so I never have to deal with it..
> 
> Is that OI as in O for Over and (capital) I for current? Or is that O for Over and (lower case) l for load?
> 
> ...


The OI ac in the manual is a instantaneous output over current detected. 

Those are good points.


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## Kevhuff26 (Dec 17, 2018)

paulengr said:


> Unlikely the cabling is damaged but worth a shot. When you get up over 100 feet (30 meters) is when you will often have trouble.
> 
> Baker testers use the surge test. They can do hi pot but it’s a waste of time at best and can potentially damage motors. If the motor passes and cabling passes then it’s either a power or drive problem once you rule those out.





paulengr said:


> Unlikely the cabling is damaged but worth a shot. When you get up over 100 feet (30 meters) is when you will often have trouble.
> 
> Baker testers use the surge test. They can do hi pot but it’s a waste of time at best and can potentially damage motors. If the motor passes and cabling passes then it’s either a power or drive problem once you rule those out.


We are going to test the cable again. To hopefully rule it out. Then as you said we can focus on the power or the drive side.


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## paulengr (Oct 8, 2017)

Kevhuff26 said:


> I would have to check. It does state to check the accel and decel rates. However, I believe we have checked these settings before and matched them to our other two drives.


Acceleration time issues usually cause overcurrent or overload...Basically speeding up too fast. Deceleration usually causes bus overvoltages. With any VFD issue you have symptoms and causes and it's not a 1 to 1 relation. So you pick one cause and try to verify it. If for instance you think it's a motor issue you check the motor. If that's not it try something else. Some issues are process of elimination...you suspect something but you prove it by disproving everything else. For instance you cant directly test Ights buried in an IPM or MPM.

Sent from my SM-T350 using Tapatalk


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## emtnut (Mar 1, 2015)

Rozanegols said:


> wow, I did not know that


You have 5 posts. Didn't say anything in all of them. I'd say you don't know anything.

Waiting for a link now, spammer.


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