We have several mission critical facilities that use an ungrounded delta system.
An ungrounded delta is kinda capacitively coupled to the Earth, so a ground detector device is used.
There are 3 lights wired from phase to a ground rod and all glow continuously at the same brightness.
If one of the phases has a ground fault that light will go out and the other 2 get much brighter.
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are you sure that's not a high impedance grounded neutral system?
i was at a plant with a set-up like that and i can't remember the exact fault locator they had but we traced the ground fault with some type of frequency fault locator, even through metal conduit and enclosures, found it pretty quickly ( i think 1 hour)
