Meggering CB to inverter conductors in PVC conduit - useless?

[photonboy]

First time meggering conductors in PVC. We have a meggering requirement for final completion and I'm not sure we can get any useful information about the integrity of the insulation if there is no metal conduit for the megger voltage to leak into.

I have seen some suggestions that we should megger cable to cable in PVC (we have two conductors per conduit) but it seems that unless both cables have a nick near each other that wouldn't detect anything either.

So, is there any test to accurately verify the integrity of the insulation of a conductor in non-metallic raceway without filling it with water or something?

Thanks

 

[jaggedben]

My take:
The usefulness is that you do it and then you can get paid.
Another usefulness might be to show that water hasn't gotten into the conduit (although it probably will eventually).

 

[don_resqcapt19]

Even in metal conduit, unless you have damp or wet contamination, you can have exposed bare copper and pass a megger test.

 

[MWh_Pro]

Meggering establishes the insulation resistance of the system (Rins = V / I). High resistance is indicative of a healthy electrical system. If the conductors are installed in PVC, that positively helps/increases the insulation resistance, so I'd suggest that it is a valid test. And as jaggedben said, the usefulness of doing the test is that you ticked the box--part of your job--and that you confirmed there were no glaring faults at the time you finished installation. While PVC may mask damage to the insulation of the wires, you essentially did the best you could to verify that the system is healthy and the work is complete.

 

[don_resqcapt19]

In general, my opinion it that insulation tests for under 600 volt systems are worthless unless the conduit is wet or contaminated. If there is bare copper, it will pass the megger test unless there is water, or other conductive contamination or the bare copper is touching some other conductive item.