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How is it possible to have a L-G fault on an ungrounded delta system? The delta is ungrounded (no neutral or ground), so physically speaking, how can we have a L-G fault? Thank you
Hey Fas thanks for your question. There are a few ways to think about this. You can't have a single line to ground fault because the system is ungrounded. If that situation happens the system becomes a grounded system by way of that connection to a metal object that is connected to ground. If a second fault occurs, from a different line (phase), we now have a short circuit condition, using the metal object(s), that is actually a 2-fault situation. Ground detectors are required for ungrounded systems under certain conditions as stated in 250.21(B). This is so when the first fault (ground fault) occurs an indication is provided so that hopefully a qualified person locates and corrects the fault before a second one occurs.
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