Megger Formula Question

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RICHRICH36

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Hello, I am trying to educate myself on the "correct" use of a megger and its associated formulas. Previously using a megger looking for something that "just didnt look right" method many times. I have read a stitch in time and although very informative I cant seem to get past the following formula:

R in megohms = rated voltage in kv / 1) x 100 / (length of cable in feet)

Is this minimum value?

Lets say i want to see if some direct bury USE or XLPE in earth is breaking down.

rated voltage in kv (500v test of megger so .5 kv) stitch in time tells me to use minimum of 1 KV so so far I have R = 1KV x 100 this gives me 100

Now I have 100 / by the length of the cable (lets say 175') this gives me 0.57

Am I looking for 57 M OHM or better?
 
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G._S._Ohm

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R in megohms = rated voltage in kv / 1) x 100 / (length of cable in feet)
>I guess the kv/1 means you round up to the nearest kv. Can you post a link to the manual for your megger?

Is this minimum value?
>I'd say. A maximum value for perfect insulation would be infinite no matter how long the cable.

Am I looking for 57 M OHM or better?
>Well, it can't be 0.57 Mohm because that is way too low.

Using a formula you can also measure hundreds of megohms using almost any DVM and a 12v battery, just for a sanity check on your results.
 
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RICHRICH36

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G.S. Thank you for your reply. As I sometimes do, I was looking in to this a little too deep. Your links clearly explained. Thanks again.
 
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G._S._Ohm

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Glad I could help.

While we're on the subject, I should collect a few more megger formulas and see if I can extract some general rules of thumb.
 
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G._S._Ohm

Senior Member
Location
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zog said:
There are internationally recognized standards for insulatiuon resistance minimums that should be followed
Click to expand...
It gets interesting if a formula predicts a measured value below the min. standard value.
Also, most formulas only work over a range of values before the formula gives intolerable errors.

If you post some of these standards I'll be glad to use Excel and work through some examples and maybe come up with some tables.
 
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