Insulation resistance testing

[Solar Sage]

Looking for a sanity check for anyone involved in commissioning of utility scale PV systems. DC system is set up with strings to a PV harness (BLA) to the load break disconnect box to the inverter. EPC tested the LBD homerun to the inverter for insulation resistance with the LBD closed and claims that the test covered everything from the LBD output circuit through the BLA. I don't see how this would work as the insulation resistance test is testing for insulation integrity, and there is no insulation within the LBD bus, not to mention all the other factors that seem off here. I know you can VLF test an entire MV circuit through multiple terminations, but I don't think that same logic applies to dc IR testing. Are they trying to get away with doing 50% of the required work or am I missing something here? If this was doable I would expect many more EPC's to be doing the same, but that is not what I have seen.

 

[jaggedben]

It's out of my area of expertise but I'd say basic physics says that if all switches were closed then the test applies to everything connected. The LBD bus bars may not have insulation but there's something isolating them from the enclosure and thus each other and the test would have tested that as well.
I don't think AC vs. DC applies to insulation resistance testing. Not that I can say it all fits within the parameters proscribed for the testing equipment, I just don't know.

 

[pv_n00b]

Like overhead conductors and bus in SWDBs the bus in an LBD is insulated by air and the insulated standoffs. Doing a resistance test will disclose if there is a failure in the insulated standoffs or if there is an unintended conductive path from the bare bus to ground. So what the EPC did was a valid test.