The guys in the crew have stumped me again.
We've been getting fluorescent fixtures with dual-rated electronic ballasts as of late. (As far as I know, the ballasts are not yet available for replacement use, I've only seen them on new fixtures). 120/277 photocells have been around for awhile.
When installed on a 120V system, they can be used later with a 277V system, but once 277V is applied, they cannot be used again @ 120V.
How does this work?? Is there an electronic device that "burns out" at a specified voltage?
(I've been wanting to smash one and look inside, but the opportunity hasn't yet presented itself). Thanks...S