Meggering to prove an undamaged run

[W6SJK]

If you have a project where two 480V circuit runs were found to have damaged insulation after 6 months (ground fault) due to a contractor's poor installation techniques, how confident would you be of the integrity of all other circuits on the project that pass one-time 60sec meggering? What would you recommend to an owner for pass/fail?

 

[77401]

ONLY 6 MONTHS & 2 HAVE FAILED?
I'd have to insist all the wires be replaced.

 

[don_resqcapt19]

And don't count on the megger finding all problems. If you have a conduit that is dry when you megger but can be wet under some conditions, you can have bare conductor in the raceway and the megger can still read perfect. This will all change when the conduit gets water in it.
Don

 

[zog]

For 600V rated non-inductive equipment NETA MTS recommends a minimum of 100M ohms.

 

[Bob NH]

I once bought 250 ft of underground triple cable and found that the insulation had been cut by the measuring machine. Before installaion, we discovered half a dozen places where insulation was exposed.