Klein ET600 Megohmmeter Display Question

[G-ManBart]

I have a couple of questionable 3-phase motors to test and decided to buy a decent megohmmeter to help out and now I'm confused (more than usual). I bought a Klein ET600 which has a decent reputation for an inexpensive meter, but some of the readings don't make sense to me.

Testing the winding insulation on a known good motor (from windings to the case) I'll get readings showing greater than 4000 mega ohms, but sometimes it reads "4000" "4,000" "400,0" and "40,00" (didn't get a picture of that readout) while the bar graph is maxed out. I can't figure out why the comma would move, or even be there if it's maxing the scale at 4000.

I looked in the manual and it makes no mention of the readout, much less the comma. I looked online and watched a number of reviews, with no mention of the display. I also watched reviews of folks using it to meg out a motor and didn't see the same differences, but some of that they fast forwarded through the different windings as it's all the same process.

Any ideas?

 

[markba633csi]

I read the manual and it's not very clear- I'm not even sure what the Lock button is for. It's possible that the meter is defective. When you leave the test leads apart and run a test what do you get?
Also, when you use the resistance setting (rightmost setting with ohm symbol) what happens when you short the test leads together? What happens when they are apart? Is it acting like a normal ohmmeter? Got any resistors laying around you can check?
The unit apparently can generate high voltages up to 1KV when testing so be careful not to touch the leads. In the lower right hand area of the display it should be telling you what voltage it is using (depending on the selector)

 

[Flyinfool]

This is just my interpretation of the manual.
The comma/decimal point is telling you what range the meter is in.
It has 4 ranges. 4MΩ, 40MΩ, 400MΩ and 4000MΩ.
The bar graph at the top always shows 0 - 4000 regardless of the range it is in. It is up to you to mentally move the decimal point.
It is auto ranging I do not know if you can pick a range.
When you are not testing it is telling you what range it is in.
The only time it is giving you an actual reading is when the test button is being pressed and the test voltage is being displayed in the lower right corner.

 

[G-ManBart]

I read the manual and it's not very clear- I'm not even sure what the Lock button is for. It's possible that the meter is defective. When you leave the test leads apart and run a test what do you get?
Also, when you use the resistance setting (rightmost setting with ohm symbol) what happens when you short the test leads together? What happens when they are apart? Is it acting like a normal ohmmeter? Got any resistors laying around you can check?
The unit apparently can generate high voltages up to 1KV when testing so be careful not to touch the leads. In the lower right hand area of the display it should be telling you what voltage it is using (depending on the selector)

I went back and ran some more tests and found something interesting, but I'll back up a step before getting to that.

The Lock button is so that it continues to apply voltage after you release the Test button. There are times when insulation is starting to break down and won't show it for a few seconds, but if you apply voltage for a minute or two the resistance will start to drop. I know that's a fairly common thing in the HVAC world...they'll run the test for a minute or two. Essentially, it's just so you don't have to sit there holding the button the whole time, or at least that's how I interpret it.

I ran through all the tests again and noticed that if I hold the Test button a few seconds longer the readout will always get to "4000" without a comma and the bar graph will be maxed out. It's only if I release the button sooner that I'll get a readout with a comma, and that corresponds with the voltage not getting to maximum as well. If you just quickly press the test button you don't get a result at all. It seems like maybe it takes a second or two at full voltage to stabilize for a consistent display reading.

If I run the test with the leads disconnected I get a readout of "4000" and the bar graph is maxed. If I have the leads shorted together I get "0.001" on the display.

It I set it to Ohms and the leads are disconnected I get OL and if they are shorted together I get "0.000" on the display.

 

[G-ManBart]

This is just my interpretation of the manual.
The comma/decimal point is telling you what range the meter is in.
It has 4 ranges. 4MΩ, 40MΩ, 400MΩ and 4000MΩ.
The bar graph at the top always shows 0 - 4000 regardless of the range it is in. It is up to you to mentally move the decimal point.
It is auto ranging I do not know if you can pick a range.
When you are not testing it is telling you what range it is in.
The only time it is giving you an actual reading is when the test button is being pressed and the test voltage is being displayed in the lower right corner.

I'm not sure how that could be when the bar graph at the top shows 0 to 4000 (it doesn't always show the dots all the way to 4000 like in my pictures). I've seen readings where the bar graph is under 1000 and the readout is a number under 1,000 as well (and seems to match). Likewise I've seen a reading where the bar graph is in between 1,000 and 2,000 and the display has a number with a comma. I'll have to try to capture a picture of that to make it clear.

The other thing is that the pictures taken above are of a known good motor with the lead on the same winding so if there was that much difference between the readings something would be seriously wrong. This is a 5hp, 3-phase 230/460V compressor motor that was working perfectly...swapped it for a single-phase motor not long ago.

 

[markba633csi]

OK so then it seems to be working, but insulation resistance of over 4000 meg seems too good to be true, and I don't know what typical motors should read. I would expect somewhere under 1000 meg , especially on a older non-inverter rated motor
What kind of readings are other people getting?

 

[GeneT45]

Part of the problem is the tool. "4000 M" just means the tester can't measure any degree of continuity. It's very hard to measure very large resistances with a low voltage input. The proper tool for the job is an IRT (Insulation Resistance Tester). Unfortunately you need a pretty good reason to own one. I see my Fluke 1507 is now over $700...

GsT

 

[Chip Hacket]

This is just my interpretation of the manual.
The comma/decimal point is telling you what range the meter is in.
It has 4 ranges. 4MΩ, 40MΩ, 400MΩ and 4000MΩ.
The bar graph at the top always shows 0 - 4000 regardless of the range it is in. It is up to you to mentally move the decimal point.
It is auto ranging I do not know if you can pick a range.
When you are not testing it is telling you what range it is in.
The only time it is giving you an actual reading is when the test button is being pressed and the test voltage is being displayed in the lower right corner.

My first thought was auto-ranging as well, especially since he's using a digital megger and seeing 4000MΩ with the decimal point moving. That seems quite high, but I haven’t used a megger in years—not since the old hand-cranked style.

 

[G-ManBart]

OK so then it seems to be working, but insulation resistance of over 4000 meg seems too good to be true, and I don't know what typical motors should read. I would expect somewhere under 1000 meg , especially on a older non-inverter rated motor
What kind of readings are other people getting?

The insulation resistance reading over 4000 meg is pretty typical going off the YT videos of folks megging motors (known to be good).

 

[G-ManBart]

Part of the problem is the tool. "4000 M" just means the tester can't measure any degree of continuity. It's very hard to measure very large resistances with a low voltage input. The proper tool for the job is an IRT (Insulation Resistance Tester). Unfortunately you need a pretty good reason to own one. I see my Fluke 1507 is now over $700...

GsT

The ET600 actually is an IRT and provides voltage up to 1000V DC for the test....125, 250, 500 and 1000V are all an option.

I spent hours and hours reading reviews and watching YT videos comparing different IRTs and the ET600 kept coming up as the best bang for the buck among IRTs. There are some less expensive options now that are popular, but not from companies with U.S. support like Klein.

Insulation Resistance Tester - ET600 | Klein Tools

The ET600 is a multi-function Megohmmeter capable of producing 125V, 250V, 500V, and 1000V test voltages for insulation resistance measurements up to 4000MΩ. Also tests AC/DC voltages up to 1000V with automatic ranging True RMS technology. Convenient lock function and built-in stand for hands...

www.kleintools.com