# megger is always maxed out



## John Valdes (May 17, 2007)

I always shorted the megger leads to themselves and wanted/should to see a dead short.
Then take it to the leads of the motor.
Testing the leads as connected for use is the way to go. You can test each coil if you want. For fun! I will post a link to the windings so you can not only test your heart out, you can be precise with other motors that have different configurations.
You are correct on small motors resistance should be very close. Does your megger have a resistance setting? It should.


10 ohms in a plant environment is barely passing. Do you have a threshold? You should so everyone is on the same page. Infinity is possible buy very unlikely in your setting. A motor shop shoots for infinity.

http://www.goevans.com/filesSite/EHB_pgs0803.pdf

Note: There are others that are much more spot on with this subject. Brian is one of them and there are others that are very good.
Our new journeyman 460 is another.
Take what they say as fact. I'm just an old retired guy.


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## mburtis (Sep 1, 2018)

yes the megger has a regular ohm meter as well. So far all the windings have tested very close to one another testing coil to coil, like less than an ohm difference. Having a plant electrician is kinda a new thing for us so we don't have any standards set up for what means good and what means bad. Its all up to me to figure out.


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## CoolWill (Jan 5, 2019)

I don't think you're understanding resistance right. Maxed out is a good thing, assuming the meter is working. The higher the resistance the better. The meter is saying, whatever the insulation resistance is, it is more than 11 Gohm.


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## mburtis (Sep 1, 2018)

If the resistance really is over 11 G ohms that would be great and would mean that the motors are in great shape. However every motor I test maxes the meter out which just makes me question if I am really doing it right.


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## gpop (May 14, 2018)

The fluke 1507 has a habit of destroying its own leads after a few years of heavy use. They are not expensive so its no big deal but it means you need to test them.

First you have to make sure your using the correct 2 lead ports. Megging is the middle (common) and the right side port. Now if you own the probe with the test button you can use that or you can use a standard probe and use the test button on the meter. (using the left port which is for ohms will give a false reading when megging)

Hook common to something metal then touch something close by with the other probe and test. Meter should read zero and the voltage (bottom right of screen) should be around 15. If that test passes then touch a lead on the motor and hit test.
As its a small motor it shouldn't take more than a few seconds to give a stable reading. 550Mh at 500v would be a excellent reading as it indicates that its higher than the meter is capable of reading. 
Most of us use 5Mh or lower as a warning sign.

After testing the motor again test to ground to check the meter. 

Just remember a megger only indicates a leak between 2 test points there are other problems a motor can have that a megger can not detect.


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## 460 Delta (May 9, 2018)

I’m no expert at all, and I still use a hand crank Biddle that I inherited from my old papaw years back. Infinity is great and a 10 meg or so is good also. I’ve been told to use your VOM to test your Megger by checking it against its published impedance, if it’s the same or close, it’s good to go. The thing does seem a little suspicious is the grease soaked windings testing high, you might pay a wind shop to check a few and then compare readings. A decent wind shop might we’ll give them a quick test on the house for a chance to do some real money work for you in the future.


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## paulengr (Oct 8, 2017)

A few things here.

On motors under 1000 V the standard test is 500 V for 1 minute and a good reading is 5 megaohms or better, higher is better. NETA went off and did a bunch of goofy untested things that don’t follow standards so ignore them. IEEE standard 43 is the one for motors.

Usually what happens is it either goes to zero and/or shorts out or within 10-20 seconds it goes very high. So if you just want to know good/bad once it is clearly above or below 5 megaohms you stop. That’s why electricians usually barely run the test before they are done. The issue is if you are not trained (monkey see monkey do) then often you see electricians treat it like a multimeter which doesn’t work for marginal cases. You can’t compare readings unless the motors (or the same one over time) are at the same temperature though. So if you want to do that take a temperature (I use a cheap IR pyrometer) and look up the correction numbers in a table.

As for connections you can either test every wire to the frame or bolt them all together and do one test or maybe only a few if you know how the motor is wired. The wire numbers and wiring on motors is all standardized so it’s really easy to find out how it’s wired. Ask a motor shop for the little book most of them give away (they cost about $2). It has all the motor diagrams in the front. Then instead of guessing you will know how it is wired. There are a bunch of schemes for two speed motors so you need the diagram to wire them properly.

Unless you clean it out really good with denatured alcohol or pressure wash it then dry it in an oven overnight there is no way you would get good readings with a motor that has grease in the air gap. Megger readings are poor when there is moisture present, the insulation is damaged or aged and cracked, or it is contaminated.

But on small motors even under ideal conditions (brand new) you wouldn’t get over a gigaohm and you said teraohms. That’s just way too good so sounds like something is wrong. Test the meter by first testing it on a piece of steel. One if the steps I do is when the frame connection is suspect, test against another spot on the frame. Second test it by measuring lead to lead on a multimetsr. All of them are in the 5-100 megaohm range. If it reads much lower or higher the megger is messed up. The multimeter can be off for this test since you are just using it as a resistor.


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## mburtis (Sep 1, 2018)

Thanks for the good replys. I will have to do some experimenting with the meter tomorrow to see if it checks out. We have been cleaning the motors out best we can with spray solvent but some of these motors were running with windings completely packed with a rainbow of grease. 

paulengr that is sorta of what I was getting at with my question is on a small 3 phase motor should I really be seeing gigaohm range readings. You always hear of results in the megaohm scale so I was skeptical. So your saying I can hook lead to lead on a multimeter and then do a 500V test and see what reading I get?

gpop thanks for the info about the leads, like I say this meter was at the plant when I started so who knows its history. I have caught myself not switch the leads to the right port when switching between resistance and insulation testing before though.

Really want to learn the ins and outs of insulation testing so I can start doing regular scheduled PMs that include it to hopefully catch motors/conductors/whatever as they begin to degrade in order to schedule replacements before failures.


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## 460 Delta (May 9, 2018)

One thing you should really consider is removing the grease zerks from the end bells on the motor after the rebuild. Some guys in operations and well meaning mechanics think that those bearings need greased weekly with a half dozen pump shots. No zerk fitting means no more greasing.


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## Aktom10 (Feb 22, 2017)

....


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## Wirenuting (Sep 12, 2010)

mburtis said:


> Thanks for the good replys. I will have to do some experimenting with the meter tomorrow to see if it checks out. We have been cleaning the motors out best we can with spray solvent but some of these motors were running with windings completely packed with a rainbow of grease.
> 
> paulengr that is sorta of what I was getting at with my question is on a small 3 phase motor should I really be seeing gigaohm range readings. You always hear of results in the megaohm scale so I was skeptical. So your saying I can hook lead to lead on a multimeter and then do a 500V test and see what reading I get?
> 
> ...


Google your Fluke meter for a video of how it works. They have some simple ones on YouTube. 
You can also google for a book called “A Stitch in Time” that’s a great one to learn how to Meg a motor. 

I just got a Fluke 1587 and it’s a great addition. I had an older crank Biddle that worked well over the years,,, but time to move on. 

When I got the new 1587FC I tried it on several motors. 
1) a two speed two winding cooling tower motor that I knew had one bad winding. Low speed was 10 Meg and high speed was 10 ohms.

2) a new 5 hp used for a diaphragm pump and it was 2 gig ohm

3) a used 3/4 fan coil motor and it was 1 Meg ohm with the AC guy telling me it was a good motor. Rattled and rolled the shaft and the reading dropped like a rock based on its location. 

With the exception of the cooling tower motor high speed windings, all these motors had read +2 Meg ohms using a fluke multimeter. 

The higher the reading the longer life the motor has left. 
If you didn’t Meg a motor when it was brand new you’ll never know what it was. But if you test the same motor yearly you will see a curve downward as the insulation begins to break down. You’ll begin to learn when that motor should be replaced before it fails. 
If you can’t rest yearly because your a service guy, you will begin to learn how to tell a customer a motors life left. ie: replace it or it will fail soon. 


Here is a link to the 1587 video.


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## Wirenuting (Sep 12, 2010)

460 Delta said:


> One thing you should really consider is removing the grease zerks from the end bells on the motor after the rebuild. Some guys in operations and well meaning mechanics think that those bearings need greased weekly with a half dozen pump shots. No zerk fitting means no more greasing.


We had a local supplier come in and give a class how to test motors. I wasn’t invited. 
They said to never grease a motor unless it came from the factory with a zerk fitting already installed. They said never remove the plug on the bearings as they were factory sealed. 
Needless to say the local supplier was trying to sell us more motors over time.


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## gpop (May 14, 2018)

Wirenuting said:


> We had a local supplier come in and give a class how to test motors. I wasn’t invited.
> They said to never grease a motor unless it came from the factory with a zerk fitting already installed. They said never remove the plug on the bearings as they were factory sealed.
> Needless to say the local supplier was trying to sell us more motors over time.


Bearings are either no shield (6309), single shield (6309-Z) or dual shield (6309-ZZ). A motor with a grease zerk should be a single shield if the data plate shows a dual or double shied then it wont except grease unless its under high pressure which will push the shield into the bearing causing premature failure. 

If you read the bearing data sheet a bearing in a clean area running with in its rpm range is roughly 1 shot every 3 months. (1 pump of a battery grease gun can be as high as 3 shots)

Another problem is that different greases do not mix.

The problem isn't the grease its the Muppet greasing it.


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## gpop (May 14, 2018)

mburtis said:


> Thanks for the good replys. I will have to do some experimenting with the meter tomorrow to see if it checks out. We have been cleaning the motors out best we can with spray solvent but some of these motors were running with windings completely packed with a rainbow of grease.
> 
> paulengr that is sorta of what I was getting at with my question is on a small 3 phase motor should I really be seeing gigaohm range readings. You always hear of results in the megaohm scale so I was skeptical. So your saying I can hook lead to lead on a multimeter and then do a 500V test and see what reading I get?
> 
> ...


Using spray solvent to clean grease might not be a good idea. Grease isn't much of a problem just wipe it away. Solvent can do wonders for the insulation on the winding.

Megging wont tell you when a motor is going to fail. Its just a test tool that's useful for diagnosing a fault.

If you want to set up a pm program start with the low hanging fruit. 

All motors get rotated (by hand if they are in the stock room) every week 3 turns. All vfd's get powered up once a year, etc


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## Lone Crapshooter (Nov 8, 2008)

If you have doubt that your Megger is working a quick to check is to meg a DMM that you know the input impedance of. Most Flukes have a input impedance of 10 meg ohms. 
Set up your DMM on the output voltage of the megger or higher then connect the megger to the DMM. Your megger should read 11 meg ohms and your DMM should read the voltage coming from the megger. 
This is not a official IEEE or NETA test. This is a test that I came up with that a blue collar worker can do in the field if he doubts his megger is working.
This is just a spot test and in no way guarantees the accuracy of the megger.
LC


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## macmikeman (Jan 23, 2007)

Lone Crapshooter said:


> If you have doubt that your Megger is working a quick to check is to meg a DMM that you know the input impedance of. Most Flukes have a input impedance of 10 meg ohms.
> Set up your DMM on the output voltage of the megger or higher then connect the megger to the DMM. Your megger should read 11 meg ohms and your DMM should read the voltage coming from the megger.
> This is not a official IEEE or NETA test. This is a test that I came up with that a blue collar worker can do in the field if he doubts his megger is working.
> This is just a spot test and in no way guarantees the accuracy of the megger.
> LC


The other way is to clip the leads together and look at the led display as you push the button. If it goes red right away your megger is good............ If you see green or amber then the megger is bad.


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## joebanana (Dec 21, 2010)

gpop said:


> Bearings are either no shield (6309), single shield (6309-Z) or dual shield (6309-ZZ). A motor with a grease zerk should be a single shield if the data plate shows a dual or double shied then it wont except grease unless its under high pressure which will push the shield into the bearing causing premature failure.
> 
> If you read the bearing data sheet a bearing in a clean area running with in its rpm range is roughly 1 shot every 3 months. (1 pump of a battery grease gun can be as high as 3 shots)
> 
> ...


Good point. Same with lube oils. Turbine oil is not the same as "lube oil".


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## mburtis (Sep 1, 2018)

Don't even get me started with different grease. These motors have had about 4 different kinds of grease packed into them and blown everywhere. These include white food grade (which was not needed), regular brown lithium multipurpose, red farm grease, and some nasty brown sticky stuff that almost looked like coupler grease. None of which is the proper polyurea based grease. The biggest problem as was mentioned is that grease are not typically compatible and depending on the mix either leak all the oil out and turn hard, or turn to a nasty soupy mess and run out everywhere. On all our motors we are putting sealed bearings in when we go back together with them, unless they are larger (bigger than 15 horse) and properly designed to grease. What I have ran into a lot is the small ones have a grease port and a fitting but there is no purge port drilled into the bearing housing, so even if you grease them sparingly there is no where for the old dried out thickener to go, so you still end up pushing crap into the windings. Most of the ones we have been tearing apart have been so jam packed that washing them out is the only option. Like I say we have been using several different kinds of solvent all of which are sold as some sort of contact cleaner. I have been careful about testing them to ensure they wont soften the varnish on the winding before going full bore with them. Nobody before me around here knew or cared about properly taking care of lubrication.


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## mburtis (Sep 1, 2018)

Getting back to the megger, I played with it a little bit today. I tested it by hooking both leads to the same piece of metal. Hit the button and it said 0 ohms and the voltage would flash then go back to 0. If I removed one lead and hit the button it would jump to 11 G ohm on the 1000V setting or 500 megaohms on the 500V setting. I did hook it to my fluke T5 while off and hit the button on the 500 Volt setting. It read like .94 megaohms if I remember right. Tommorrow should be a slow day so I can play with it some more.


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## paulengr (Oct 8, 2017)

Ok lord of suggestions on lubrication. But here’s the biggest one. The “oiler” on the crew is usually assigned to the junior man and that’s a really, really bad idea. Lubrication is one of the most critical tasks in a maintenance department and should not be assigned to the junior man. Lubrication has come a long way in the last 20 years. If you do it right and do precision alignment, balancing, and follow up with vibration testing to verify everything is in good working order, everything runs largely trouble free and your maintenance costs decrease dramatically. I’ve seen bearings fail in 48 hours but I’ve also seen bearings last for over 25 years, all based on how they are treated. Think about that...25 years with no replacements. No rewinds or motor replacements. And when the rewind bill for some of our customers is over $1 MM USD and takes months to finish, you can imagine why they do everything they can to get every last hour of life out of their motors compared to someone with a $150 rolled steel throw away motor. But if you can do minimal effort and put off replacing that $150 motor for a couple years, you double the life!

This is what big operations do. But even small plants can do this. My work is a contract maintenance group that does all of this. We sell equipment, do training, do alignments, balancing, lubrication, and vibration for plants that don’t have the resources or time. So we do it “by the book”.

With greases the highest temperature and performance grease on the market is blue colored, Polyrex EM. It was designed specifically for motors. This is used by all motor manufacturers and rebuild shops on almost every motor. The only exception is some roller bearings used on larger motors might use a lithium grease and of coarse oil lubricated bearings like sleeve bearings. The one thing about Polyrex is it is basically incompatible with practically every other grease. So if you shoot something else in there what you get is a soupy mess as both greases break down. And the EP additive should be avoided in motors. You can use other greases but make sure you get the grease supplier involved to ensure compatibility but if you don’t know a tube of Polyrex EM is about $15 retail so it’s not bad compared to say Molykote 3451 used for circuit breakers that costs hundreds for a tube.

Compare this to basically every other bearing on conveyors, pulleys, lawnmowers and so on. Most people use a lithium grease because it’s cheap and middle of the road performance. If you buy grease at say Tractor Supply that’s what you get. It has the EP additive almost always because it improves the grease under high pressure. The big difference is that motors are typically running 1200-3600 RPM with some servos running up to 10,000 RPM compared to mechanical loads that are only 50-600 RPM where pressures are higher but temperatures and speeds are much lower. So it should be no surprise that motors take different grease.

Grease is basically just oil with a thickener added (15%). The thickener is like a sponge and just holds the oil in place. But if you mix thickeners you get a chemical “tug of war” and one breaks down the other. So when you mix them you get what you see. Multicolored slime. Great for Nickelodeon game shows but not for bearings.

Undergreasing is of course bad. The grease is depleted and the bearing fails. Typically in industrial plants with typical conditions this happens in 2-5 years. Maybe 10 with motors that see occasional use. I’ve seen worse cases but this kind of life is typical for industrial manufacturing plants,

BUT overdressing is even worse. If you do what most mechanics do they keep pumping in grease until it squirts out the seals. So they push the seals right out of the bearings eventually. And they didn’t remove the drain plug either. A grease gun puts out about 10-20 times the pressure the bearing is rated for. Plus there is another problem. A lot of motor bearings have a different inner seal. If you wait for it to squirt out first it squirts out into the motor before it ever comes out the front. Even if you just over grease it, it overheats. Usually this wipes out motors very quickly so I’m surprised they were burned up and destroyed.

You can guess what a decent grease schedule is and the bearing number tells you the amount it holds. There are tables for estimating (guessing). BUT this is basically guess work so this approach is always a minimal grease schedule. So the bearing is going to be undergreased on purpose. The other poster that said grease every X months and use the exact same amount of grease is right sometimes, wrong on others. A hammer mill or pellet mill for instance needs grease almost weekly but this is gross overkill on a lot of fan motors. And one pump of grease on a fractional HP motor might be too much, but way too little on a 25 HP motor. So you need to be a little more precise than this.

The claim that battery grease guns put out 3 times the grease per pump is also dead wrong. There is NO standard for how much you get per pump. You have to look at the guns data sheet. Or if you don’t know, do this. Get a 36 mm film canister, if you can find one these days! These hold one fluid ounce. Fill it with the grease gun, counting pumps. When it’s full, 1 divided by the number of pumps gives you ounces per pump,

So with the table based approach the bearing will be under greased but at least not dry. So you get 5-10 years of life typically. It’s not ideal but it’s simple. There are several tables out there. They give similar results no matter how sophisticated they are. Engineers spend way too much time on something that in the end is an educated guess.

The best way is to do ultrasonic greasing. You use a sensor that measures the sound at around 30 KHz. Take the drain plug out and use a brush to scoop out the dried grease inside. As you add a pump of grease the sound goes up a little then quiets down. Keep slowly adding grease until it goes up but doesn’t drop anymore. That’s when the motor is optimally greased. Ultrasonic attachments are fairly inexpensive these days. This is what we do. This gets you maximum life out of your bearings. If you are doing everything else right (good environment, regular PMs, keep cooling fins clean, good power quality) 20+ years of life is easily achieved on modern motors.


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