Insulation Testing during a condition report/periodic test.

There may be loads connected L-N that mean that you will stress if you raise one side and not the other to 500VDC for the  test. Traditional  loads like filament lamps and DOL motors are unlikely to care, and in effect the insulation meter is seeing  L and N in parallel anyway, but some modern electronics does not appreciate being held up in the air by one leg only.of course if you disconnecto all loads and fittings, then you can do separated L and N to gnd tests, but that really is a lot of work, compared to switching off at the incomer to remove the connection of the NE short at the substation, plugging in an L-N short and then testing from there to ground and in effect testing the whole site at once.

I agree if you have to break it down by sub circuit to find a problem it rapidly gets very tedious.
Mike

That makes sense, thank you for your response I really appreciate it. 

That makes sense, thank you for your response I really appreciate it.