A pine branch fell on my friend's service entrance wires once and broke the neutral wire in two. With no neutral to the house, a bunch of transformers blew, including one on the furnace.
In a separate incident, an electrician had done some wiring at her house during the construction of her addition;
I stayed out of the way during that circus of incompetency. Later I tapped into a 110v junction box to power her furnace and a few components blew immediately. The "electrician" had rewired the junction box to carry 220v, with no indication of it on the white neutral wires. I inadvertantly ran 220 to the furnace. I took something for granted, that's the way it always goes.