Case 3 is very possible. The fault from one side can ionize the air and cause a separate fault on the other side. You would have two separate faults taking place on the open tie.
Thanks to all for the info. Some follow-up questions:
If lamps and various appliances have floating metallic enclosures, why ground any enclosure? Who decides which electrical devices require safety grounds for enclosure protection and which do not? What is the criteria they use? Waiting...
I understand why toasters aren't grounded due to the exposed burners, and I understand why some appliances aren't grounded when the enclosures are non-metallic. But what about Lamps (desk, table, & night-stand); these never have a safety ground even if the lamp is made of metal. Why is this?
