🔍 Key Concepts

• Operation of ungrounded 3‑phase systems when there is one ground fault versus two ground faults • How the control circuit is supposed to work: STOP → START → holding contact (Ma) → overload contacts (OL1/OL2) → return • What happens when accidental grounds bypass parts of the control circuit and create an unintended current path

💭 Think About

• Trace the normal control‑circuit path from L1, through the fuse, STOP and START pushbuttons, Ma coil, overload contacts, and back to the source. Then, redraw that path mentally including both accidental grounds and see what components are now bypassed. • Ask yourself: with two grounds in an ungrounded system, do you now have a complete circuit even when one of the control devices is open (STOP, START, or overload contacts)? Which device can be made irrelevant by this new path? • Consider how the controller is supposed to behave on loss of voltage and on overload. Then ask: do the two grounds make the coil stay energized when it should drop out, or energize when it should be de‑energized?

✅ Before You Answer

• Verify which phase the upper accidental ground is connected to, and which point in the control circuit the lower accidental ground is tied to. • Check whether the new ground‑to‑ground path effectively shorts around the START button or shorts around the overload contacts in the control circuit. • Confirm whether, with both grounds present, the Ma coil can be energized without operating the START pushbutton, or can remain energized when an overload should de‑energize it.