I can only provide partial answers.
The ballasts are made by Advance, and many were sent back to Advance for examination.
It is Advance that tells me that components failed on the input side, suggesting exposure to high voltage.
Ballasts are rated for the nominal voltage of the circuit; that is, a 120v rating on a circuit that measures 124 - 125v.
The pad mounted transformer serves seven customers, all in the same building. 4 are retail spaces (mini mart, fast food, butcher shop, novelty shop), 2 offices, and the house meter. Each tenant has their own HVAC (house does not have HVAC).
All problems so far seen are on circuits served by the house meter, and on the lighting circuits. 10 circuits, and seven involve the outside lights - leaving the alarm panel, and two I can't recall offhand.
