John E. wrote:
I have been asked to offer an opinion in a sensitive situation.

A machinist moved his shop across town and required some rewiring (3-phase
outlets, conduit, etc.) in order to locate some machines where he wanted
them.

He hires a guy who's not a pro (and later discovers is not insured) but has
done shop wiring before and had a good attitude and track record. The guy
does good work. No complaints about the quality of his work.

Owner throws the switch, all works fine.

The story continues 4 weeks later when the very expensive CNC fries its
controller PCB to the tune of $4000.

Turns out the voltage in the shop was upward of 245 and the taps in the CNC's
power supply were set for 220.

What is the legal and moral responsibility of each party?

What will not be helpful are replies about the character or intelligence of
either of the players or their actions.

Thanks.
Sorry, but that little upward swing didn't cause the issue..

Sounds to me like some one couldn't properly determine the real
problem with the control board and opted to simply replace the whole
thing or, the person doing the work on the repairs caused more damage
them self's and are covering their tracks.

I'm sorry, but 4 weeks into operation and it worked fine all that
time, I think you should look else where for the problem or just simply
eat the coast of a broken down CNC machine.

My guess is the moving process may have caused some sensitive
electronics on the board to get ajar if the CNC was possibly dropped
or whacked hard enough to cause a fracture crack in a solder joint that
finally showed it's oats.

Of course, that is just my opinion. You can take it with a grain of salt.