On Wed, 15 Jul 2009 21:48:36 -0700 (PDT), stan
wrote:

On Jul 5, 12:34*pm, wrote:
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.

BTW just measured our North American domestic single phase here!
Leg A = 119 volts, Leg B = 121 volts. Leg A to b = 232 volts.
119/115 = 3.4% high
121/115 = 5.2% high
232/230 = 0.8% high
It's about 02.00h in mid summer so system load is probably light and
utility will have adjusted. No AC loads here; not needed.

Except for the fact that the NA standard is 120/240 volts (there are a
number of authorative references, feel free to Google them). So your
two 'phases' are almost dead on (probably measurement error) and the
240 is slightly low (measurement error, seems odd that it can be off
consdiering that it is supposed to be the sum of the two 120 legs.)

The reason that it was standardized at 120 volts was because of the
massive interconnecting done in North America in the past 25 years.
Old standards included the 115 volts you mention, and 117 volts in
some areas, and even some with 110 volts. It was determined that it
would be necessary to standardize all voltages (just not the low
voltages we are discussing here) to allow interconnection, and direct
substitution of equipment.