Plastic? Plastic!? We're talking 277/480 Vac at order 1000 amps, (and available fault current probably the better part of 100kA!) and we're using flat sheets of molded plastic to protect it -
outdoors?
My first thought looking at the picture above is skate punks and "Hey dude, I bet I can jump the curb, have the board go under that thing while I bounce off it and hop back on!", followed by "Wow man, I think you broke that thing". Rain/dew/sprinkler water/... gets in and ZAP!... .
Wouldn't work at the Paso Robles site due to light pole in way, but errant weed whacker with steel edger blade, etc. and same result.
Or just a bad design to begin with - this thread at Mike Holt has several people saying (posts #8, #12, #16) "had problems with leaking busway, so replaced/ing with cable in conduit/cableway".