1 meg ohm rule

[joshfromoshoto]

I am going to use a megger to test underground conductors that u believe are bad. I have heard of the 1 meg ohm per 1000v of operating voltage rule, so if the wires I'm testing are rated for 600v. Would a 0.6 meg ohm reading be considered good?

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[Strathead]

I am going to use a megger to test underground conductors that u believe are bad. I have heard of the 1 meg ohm per 1000v of operating voltage rule, so if the wires I'm testing are rated for 600v. Would a 0.6 meg ohm reading be considered good?

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Yes, when I used to meg wires for a Nuclear submarine, our minimum reading was supposed to be >100,000. I don't believe I saw a reading below 1,000,000 more than twice in my career though. When they are bad enough that you are megging to troubleshoot though, you are going to get reading that are very low though, not a reading in the hundreds f thousands of megs.

 

[ptonsparky]

I would never consider .6 meg to be good. We could find those. Our Flukes would give us the fault voltage as well.

The only time I could not, was some ancient direct buried cu. The whole thing leaked.


eta: 1 conductor at .6 and the rest at 100 is a flag!

 

[Opie11]

I personally use 1 Meg ohm as a benchmark. If above then good to go. If below then I label the conductor as suspect and or potential future issue. If grounded that would be obvious but if one conductor was around 300,000 ohms vs the other conductors being well over 1 Meg ohm I would be inclined to look at replacement of that conductor.

 

[Strathead]

I would never consider .6 meg to be good. We could find those. Our Flukes would give us the fault voltage as well.

The only time I could not, was some ancient direct buried cu. The whole thing leaked.


eta: 1 conductor at .6 and the rest at 100 is a flag!

While I have the same kneejerk reaction to a lower reading that you and Opie11 have, I have to suspect that the specifying engineers for nuclear submarines probably know more than you are I do. Also, you wouldn't usually be able to read .6 megs detected by a 500 volt megger with your Fluke at 9 volts.

 

[ptonsparky]

While I have the same kneejerk reaction to a lower reading that you and Opie11 have, I have to suspect that the specifying engineers for nuclear submarines probably know more than you are I do. Also, you wouldn't usually be able to read .6 megs detected by a 500 volt megger with your Fluke at 9 volts.

Fluke megger to giga ohms

 

[ptonsparky]

And were not working on submarines.

 

[Strathead]

Fluke megger to giga ohms

Misread. I thought you were saying a standard Fluke multimeter would read the resistance. My bad.