# Meggar Readings º¿º



## CADPoint (Jul 5, 2007)

Lennox G1604-100 motor "GS16"
Inside motor for Gas/AC coils w/ out door compressor

Meggar "250V" Insulation test
Black lead to Neutral 220K Ohm
Red lead to Neutral 220K Ohm
Black to Red 220K

Meggar Ohm Test
Black to Neutral 220K Ohm
Read to Neutral 220K Ohm
Black to Red 4 Ohm

Four seems low, is the motor toast?

Thanks for any insight


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## backstay (Feb 3, 2011)

I don't see how you can get 220k on 250volt but 4 ohms on the resistance test. A motor wiring schematic would help.


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## splatz (May 23, 2015)

backstay said:


> I don't see how you can get 220k on 250volt but 4 ohms on the resistance test. A motor wiring schematic would help.


I'd repeat the test, move the motor. Doesn't add up.


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## Big John (May 23, 2010)

None of this adds up. The neutral should be shorted through the run winding to a line conductor.

If it's a remote start capacitor then you should have continuity through the start winding as well, so all three conductors would have continuity to each other.

How'd you get two different resistance measurements on the same circuit? Is Black/Red 4 ohms or 220,000?


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## CADPoint (Jul 5, 2007)

I measured the ohm's to confirm 4 ohm w/ multimeter.

I had totally isolated motor before test.


"Ohm" just so happen to be on a test on megger old 1577.

Found a contactor that I misread and its not pulling in a NO contact,
but holding in a normally closed, it a fan contactor with a coil below. I'm not going to jumper it. wasted today, supply house closed.
Everybody is closed for I day.

Hope everyone enjoys the 4th.


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## joebanana (Dec 21, 2010)

That motors done. Depending on it's voltage rating, @ 500v. it should be 25 Meg ohm's minimum.


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## backstay (Feb 3, 2011)

joebanana said:


> That motors done. Depending on it's voltage rating, @ 500v. it should be 25 Meg ohm's minimum.


25 M ohms to what? I see no test to ground and if the motor has a neutral, it sure shouldn't be 25 meg hot to neutral. That's why I asked about wiring. A 3 lead motor with neutral means, start lead, run lead and neutral(120 volt motor)


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## joebanana (Dec 21, 2010)

backstay said:


> 25 M ohms to what? I see no test to ground and if the motor has a neutral, it sure shouldn't be 25 meg hot to neutral. That's why I asked about wiring. A 3 lead motor with neutral means, start lead, run lead and neutral(120 volt motor)


That's a good point, I don't know why I was assuming those readings were to the frame. Except, that nobody meggers phase to phase on a motor. It was a trick question. Anyway, the readings he got between leads, is extremely high, so I stick to my original assessment.


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## backstay (Feb 3, 2011)

I think we all agree, the readings aren't right. Question is, why and what symptoms brought him to a megger. I first check voltage of the circuit, then load. The megger is the last thing I pull out.


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## gnuuser (Jan 13, 2013)

i also agree without a wiring diagram its difficult at best to guess the issue, just going by name of the motor doesn't tell much.
knowing if the motor is internally wired for high or low voltage also helps.
also megger testing a motor is best done at the connections in the peckerhead (completely isolated from anything else)


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## scotch (Oct 17, 2013)

Sometimes you actually have to understand how to use the equipment and what the readings mean ....no amount of explanation from afar helps !


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## sparkiez (Aug 1, 2015)

You need to use your megger to check from windings to ground. They are for detecting shorts in the motor where insulation has failed. Hence their name, insulation testers.

I guess I should also mention that there are rare occasions to meg windings as well to see if there is a weak spot in the laminate somewhere, but check them with a meter first to see what you should be seeing. I'm thinking that your 220kohm readings are because you are reading across the cap, but I'm not certain there.


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## CADPoint (Jul 5, 2007)

> That's a good point, I don't know why I was assuming those readings were to the frame. Except, that nobody meggers phase to phase on a motor. It was a trick question. Anyway, the readings he got between leads, is extremely high, so I stick to my original assessment.





> 25 M ohms to what? I see no test to ground and if the motor has a neutral, it sure shouldn't be 25 meg hot to neutral. That's why I asked about wiring. A 3 lead motor with neutral means, start lead, run lead and neutral(120 volt motor)


Thanks for everyone responses, Consider a motor/ circle for a 7 point motor, attached to each point is: two hots, one neutral, two to the cap, and two cap'd off, that's the layout
It's a 120 V motor, chassis logo "forked off frame"

In power diagram both red and black touch power on a ladder diagram and each have controllers; with the black having indoor blower relay and the red 
NO/NC inside same controller but tied to Black wire inside of same controller.

Frankly I don't understand why it not viable to meggar across poles, it's no trick statement, the reading are what they are. 

I didn't test to ground, point made! Didn't think about the red start and the black the run, thanks for that tidbit.


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## MechanicalDVR (Dec 29, 2007)

CADPoint said:


> Thanks for everyone responses, Consider a motor/ circle for a 7 point motor, attached to each point is: two hots, one neutral, two to the cap, and two cap'd off, that's the layout
> It's a 120 V motor, chassis logo "forked off frame"
> 
> In power diagram both red and black touch power on a ladder diagram and each have controllers; with the black having indoor blower relay and the red
> ...


On a 100K btu furnace that should be a 1/2hp 3 speed psc motor. 

Black lead - high speed
Blue lead - medium 
Red lead - low speed
White - neutral
Brown - cap
Brown w/white trace - cap


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## sparkiez (Aug 1, 2015)

Though mergers are great, you can easily blow the cap with one. It also isn't difficult to blow up the insulation. I once heard of a guy megging romex with 1KV. That could easily damage/weaken the insulation and would almost certainly break down the dielectric in a cap. Keep this in mind. 

Now, on to troubleshooting. Make this simple. Turn off power, check your neutral, then make sure you are getting voltage to the motor. If you are getting voltage and a good neutral, you have an issue with the cap or motor. The cap can be tested with a meter. Otherwise just replace the motor.

Save the megger for when you specifically need to test insulation.


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