Hello,
I once worked at an old mill (circa 1920's) and above the entry for the main switch gear room there were three indicator lights. These were mounted in such a way that they could be easily seen from the chief of Maintenance's office. The only time these indicators were lit is when that light's phase had a short to ground. A small 3 phase motor would barely make it glimmer. These small ones would often flicker for several hours. A shorted wire in a large branch would light it up like Christmas. Then of course that was usually followed by the sound of phase to ground "UUMMPPP" arc sound and trip.
Over the years I've often wondered how these indicators were wired. According to the head maintenance guy the bulbs had never been changed since the plant opened. He didn't know how they worked either. Any of you ever seen these type indicators before?
