Akums Razor.... the simplest solution. Checked via a meter and small light with dental mirror but could not see the cut in the insulation from the mounting screw through the box. Had one fixture still to go when it became apparent by adding the closest then the next fixture etc. when breaker tripped. Had previously replaced the breaker and meter checked all wiring for grounds before posting this item. Was sure it had something to do with a new type transformer, and not the circuit installation.
Really appreciate the help and realizing that others, even with care, unknowingly cut insulation.
Now to put it all back together and on with business.