Adrian Francis
Member
- Location
- Jamaica
- Occupation
- Electrician
Why when doing an insulation resistance test you must double the value of whatever the rating is for voltage?
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- Thread starter Adrian Francis
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ATSman
ATSman
- Location
- San Francisco Bay Area
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- Electrical Engineer/ Electrical Testing & Controls
Adrian,
From what I remember from my testing days an insulation resistance test instrument uses a DC reference test voltage then measures the leakage current to determine if the insulation is compromised. So you are making an error when comparing the AC system voltage with the DC test voltage.
You cannot compare the two.
Megger testing has been around for a long time and the results have been proven to be very useful in T shooting all kinds of problems. Suggest you read up on literature on the subject such as "A Stitch in Time" by the Biddle Co (I think it's AVO now) and NETA Acceptance and Maintenance Testing Specs as starters.
From what I remember from my testing days an insulation resistance test instrument uses a DC reference test voltage then measures the leakage current to determine if the insulation is compromised. So you are making an error when comparing the AC system voltage with the DC test voltage.
You cannot compare the two.
Megger testing has been around for a long time and the results have been proven to be very useful in T shooting all kinds of problems. Suggest you read up on literature on the subject such as "A Stitch in Time" by the Biddle Co (I think it's AVO now) and NETA Acceptance and Maintenance Testing Specs as starters.
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
As ATSman recommended, this book is very interesting.
At low voltage, NETA generally recommends doubling the nominal AC voltage rating to test with a DC insulation resistance tester.
At low voltage, NETA generally recommends doubling the nominal AC voltage rating to test with a DC insulation resistance tester.
Russs57
Senior Member
- Location
- Miami, Florida, USA
- Occupation
- Maintenance Engineer
Keep in mind the peak AC voltage is 1.4 times the RMS voltage so be equal you need to go at least 1.4 times. With the idea in mind that you are trying to locate faults that might not show up at nominal AC voltage levels twice the RMS voltage is a pretty conservative place to start.
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