Yea. It would be really hard to figure out what the exact dynamics were. It could be the trencher cut the neutral, and or ground wires first. Or at least before the hot legs were severed. And some how a higher than normal voltage was injected into the coach. Also and arc flash can create huge spikes to be on the line.
Surge protectors generally work by shunting the spike to the ground wire. If the ground wire was cut, it couldn't do that.
And apparently it wasn't quite fast enough in shutting the power down. It needed to decide to drop the relay and then the relay needs time to physically open and break the connection. It is VERY quick, but in this instance just not quick enough to save everything. On powering up the coach it can take it's time analyzing the power before engaging.
Bottom line - the 12 volt adapters probably have some small diodes or something that was more sensitive and burned up quicker than the EMS responded. My best guess is some of the spike voltage got through because it was more than the shunt device could handle, or there was no place to shunt it too remaining. The cutting of the cable, most likely made this a worst case scenario.
