Today had a call that parking lot lights were not illuminating. Here is the set-up: Primary V 208/120 3P feeding a 75KVA transformer. Steps up to 480/277v. From transformer, circuit goes to a photo cell controlled contactor, which than energizes a panel with lighting circuits. Photo control working correctly. Contactor opens and closes correctly. However...with contactor CLOSED I have these voltages from phase to ground on HV side. A:210 B:340 C:340. When contactor is OPEN I have A:177 B 178 C:160 Phase to phase whether A-B or A-C or B-C is 479-481V no matter if contactor is open or closed. I have never seen this before. Any theories.
Yes. This system has been in place since 2002. All of a sudden parking lot lights do not go on. I checked bond in xfmr, and also followed electrode back to main. First thing I checked after reading screwy voltages.
I believe it is in the xfmr coils themselves. I removed HV wires off xfmr lugs for giggles to see if voltage would change with nothing connected on that side. Voltages were the same.
Neutral is bonded to frame with copper band, on xfmr than lugged electrode runs from chassis to main disc. bond. I were to run a second electrode temp from bond in disc to xfmr frame, and I still do not have 277...would it mean the neutral/ground is open in the transformer itself?