Dale,
I have a helper, and related stories I suppose, but he is helpful.
The "Site":
So, we have worked in a warehouse/manufacturing site,
wherein the POCO supplies 408 Delta, and one corner has 'become' grounded.
The master still swears this isn't so,
but we have an odd circuit supplying mose of the HID luminaires in the place.
The "Finding":
Putting up the HID lights, I find a hot wire with 240 to the other conductor.
This other conductor reads zero volts to ground.
Still not a neutral, but used as if it were, red and white colors.
The "Punch-line":
The 480 transformer supplies 3 phase 266, with 135 to neutral buss.
Originally the 208 HID luminaires were attached to this circuit.
My helper was helpful in simply reading the voltage at the buss bars
and agreeing with his readings.
The helper "helped" even in the face of other JM telling him
that the 'theory' said otherwise.
Eventually, others were coerced into physically reading the voltage and agreeing,
and shaking their heads.
The "Results":
Of course, this should be from a Wye secondary.
I expect that we will eventually fix this anomaly,
which may raise the branch circuit voltage
from 266 / 135 to 277 / 142,
and that will cause other problems! ha, ha.
The "Prognosis":
All the 208 HID luminaires will have to be rewired to 277!
I expect we will be back here again.