A municipal customer recently had a problem when a flange broke on a fresh water well. The water filled the block wall building until the water reached a height of 7 feet. At this point the door blew open allowing the water to escape. When the water had reached the VFD, the VFD blew up which shut down the well. Unfortunately, the broken flange was downstream of the check valve. Water from the system continued to fill the building. This submerged all the controls in the building but did not trip the circuit breakers outside. The 3 phase 480 VAC CB was not tripped nor was the 1 phase 240 VAC CB that feeds a NEMA 1 subpanel. The customer said the lights were on when he got to the well site at 3am. Why did the CB's not trip on a phase to phase short or phase to ground assuming the grounding is properly done. Thanks for the input.