DIELECTRIC VS. MEGGAR TESTING

[Strathead]

smart$,
Do you have a list of the types of wires that gets damaged with 1mA of leakage current?

As a layman, I don't think a list is necessary. Common sense tells me that when you push the voltage through insulation to the point that it breaks down you are doing a destructive test. High potting MV wiring used to be a standard, but they don't practice that as much any more for the same reason.

 

[Strathead]

i'd never be one to argue meggers with ya, but i'm guessing the
guy just needs to megger some branch circuits that have been covered,
so i'm guessing romex, etc. and wonders what a good reading
would be.

i'd think if you meggered at the working voltage, assuming 120 volts,
and got a 10 megohm reading, you'd be in pretty good shape. you aren't
going to smoke anything with the megger, and you'll know the insulation
isn't damaged.

In another life, I worked for the Navy on nuclear submarines. All megger testing on 600 volt wiring and equipment was done with a 500V megger and an acceptable reading was always 100,000 ohms or more. It was rare to see less than 10 Megohms, but that was the standard and a piece of equipment protecting the reactor was acceptable at 100,000 so I am guessing that most of the things we do would be OK too.

 

[zog]

As a layman, I don't think a list is necessary. Common sense tells me that when you push the voltage through insulation to the point that it breaks down you are doing a destructive test. High potting MV wiring used to be a standard, but they don't practice that as much any more for the same reason.

Industry went away from DC hipot testing of MV cable due to accelerated propagation of water trees. You can still hipot but a VLF test set is recommended.

 

[Strathead]

And we all know what happens when that membrane is an inflated balloon.

I resemble that remark!