We are installing new 277V LED emergency light fixtures that have a battery backup. The light fixtures are controlled by a switch with the normal lighting circuit (also LED same brand) and an un-switched circuit for the battery. The emergency light fixtures are failing after approximately 2 months. They completely burn as if it were a phase to phase short in the light fixture when switched. The breaker(s) do(es) not trip. This is happening randomly across several circuits and different phases. We have tested using battery power on the same phase as the switched power but they still fail in the same manner. We have tested amperage as well as voltage as well as breakers and there are no issues. The manufacturer keeps sending replacements only to have them fail again after approx 2 months. The existing fluorescent emergency light fixtures have functioned fine for years according to the building owner. Any ideas?