I work on lasers that use a buck/boost with 16 tap possibilities on 3
phase all the time, and I used to use the same units in theatrical
touring service until more modern solid state lasers dominated the
laser show industry. . From that perspective, I'm amazed at the
replies here that have failed to ask two simple questions. I will
state that I never met a house electrician who ever looked at the
rating plate on the gear, although I did have a few that asked about
phase sequences.

Two, I never met a house electrician who ever checked anything
hooked to the pigtail I gave him to connect, including "professional"
rental generator technicians (actually they were the worst) In the
theatrical business, it is up to the touring operator to check the
local guys work, and in most cases, we preferred they stand in a
corner and watch us, after your first blown passbank with 3 or 4 out
of 22 power transistors blown in the laser, you get the idea to check
the taps both preshow and under load condition. In one case I asked
for 220/3, went to lunch, and came out to find 380V European power
from the generator in my distro box, which is why the box had its
own"tagged out" disconnect switch. Its a rotary switch in big modern
generators, easy to mess up.

Questions:

One, Did the "electrician" hook straight to the machine's tappable
control transformers, or did he meet a simple junction box on the
side of the machine. If it were the later, I'd say he's off the
hook. On the other hand if he was staring at a tap strip , he should
have asked. There is also the possibility of a "cascade" of
transformers in some machines, ie little CTs all over the place in the
machine, that need tapped. ??????

Two, Did anybody bother to read the manual chapter on setup? Machine
shop gear needs leveled and "trammed" when moved, its not a simple
matter of tossing a CNC off the truck onto any old pad of concrete and
expecting good parts to tolerances, and the first paragraph usually
reads, something like "check settings" and have appropriate safety
gear. ??????

The fault occurred months down the road, a instant "oof and shower
of sparks:" would point to the electrician, but months down the road
is lack of due diligence on the part of the owner.