The "electrician" is culpable as it was found that the wiring was to blame. That proof alone means that he would be culpable, regardless of his credentials, or lack thereof.
The owner should bear some blame (as in be lenient in court) for trying to economize costs in the wrong area (he should have paid the licensed and insured electrician).
Also knowing how to hook up systems well, and knowing how to do a proper requirements analysis are two different things and define some of the differences between the grunt pulling the wires and the supervisor laying out the plan and making sure that the machines and their power sources are matched. Since a failure mode did occur, it would be improper not to make a negative statement about the character of the installer.
Also, though it was not a lack of intelligence that compelled the owner to choose the riskier path, it does indicate a lack of wisdom, which I am sure has received a boost due to these events already.
PS Cross-posting is lame.