Harold and Susan Vordos wrote:

"Pete C." wrote in message
...
Harold and Susan Vordos wrote:

"Pete C." wrote in message
...
Harold and Susan Vordos wrote:
snip----

That's how everything used to be and I believe both the wild leg and
open delta configurations were primarily used as a way to save
transformer costs.

Regardless of reason, machine shops are typically provided with this
service. The higher voltage is very desirable, and in some cases
mandatory.
I question your logic about saving transformer costs if individual
machines
would require buck/boost transformers. Between the area required to
store
them, and the increased cost of labor for installing them, seems to me
it's
a terrible waste of money when it can be dealt with by installing the
delta
system instead of the wye.

The transformer cost savings was for the large oil filled cans on the
pole, by using only two for open delta, or two smaller and one larger
for the unbalanced wild leg.

The buck/boost autotransformers are quite small and inexpensive. They
are dry type autotransformers, not full isolating transformers with
multiple windings so they are much smaller than you would expect for
their capacity. The KVA size required for the autotransformer is not the
full KVA of the load. The sizes you would need for an average machine
are about shoe box size and around $150 new.

Yeah, times 2 or three per machine, then the labor to install them. I
think you shot yourself in the foot here, Pete. My point is that 3 phase
delta is already the proper voltage----you need not find space for more
electrical apparatus, nor pay for its installation. So far, I'm not
convinced, and I'd refuse a wye service given a choice, which is exactly
what I did when I requested my delta service.

For the perhaps 5% of machines that might actually require them? A
smaller shop may well not have a single machine that legitimately
required the boost transformers.



But you've overlooked the fact that it does *not* yield 240 volts, the
optimum voltage for machine tools. I'm having more than a little
trouble
understanding why you feel delta is such a bad deal when it solves all
problems aside from the wild leg issue. I can't think of one small
machine shop that is wired wye------not one. Many of my friends are
still
in business in Utah, all of which have the delta service. Could be
it's a
regional thing. Dunno.

How is 240v "optimum" for machine tools? A lot of machines larger than
bench top size can be strapped for operation on 480v input as well. When
I did CNC service, I don't recall seeing a single machine that didn't
have a 480v input option.

Agreed. The vast majority of the large shops in which I worked had 480
volt service. I have no idea if they were delta or wye.


I would consider "optimum" voltage for a machine to be any voltage that
it can be strapped for. If it was designed with those taps then it
should operate just as well on any of them.

I would consider optimum voltage one that, given anything but a proper
match, would be higher voltage instead of lower voltage, so motors didn't
run hot. You may not think that's a problem, but I can tell you from the
perspective of a guy that knows how to move metal when roughing, it's damned
important. It's not unusual for a machine tool to be subjected to a 125%
demand on horsepower. I've seen machines that shut down because they've
been ridden hot and put away wet. No thanks, no 208 voltage for me.

I think you're under the impression that a motor will run hotter if it's
strapped for it's lower voltage rating. A motor should run at the same
temp for the same load and duty cycle conditions when operated at any
voltage it can be strapped for.

Operation at the higher voltage setting is for the benefit of smaller
wire gauge to feed the motor, lower voltage loss on those wires and
smaller switch gear to service it, not for the benefit of the motor.

If you are pushing your machines past their continuous ratings for
significant amounts of time you should fully expect them to shut down on
you. Brief excursions past the continuous rating are ok, but sustained
use there is not.



The "optimum" voltage that you would want to use based on external
factors would be one of the higher voltage options based on smaller
required wire gauge, reduced voltage drop, etc. From that standpoint
208v and 240v are essentially equal.

But *not* equal.

Correct 208V /= 240V. However the ~ 14% difference is not significant
from a practical standpoint. With either 208V or 240V vs. 120V you're
getting the benefits of the smaller wire and switch gear requirements
and lower voltage drop.



If a machine has taps for both 208v and 240v then there is no advantage
or disadvantage to either, only the convenience of what you have
available. If there are a sufficient number of machines that can take
480v to fill a decent portion of a 480v panel then that is an even
better choice.

My (very limited) experience has been that motors that are capable of
running both voltages are wound 230 volts. I know my Bridgeport is so
wound. That means, while you're still within tolerance, the motor is still
running hotter than is necessary when operated on 208V. I may be wrong,
but I don't think you have the luxury of changing internal wiring to reflect
208 or 240 volts. The only changes are to accommodate higher voltage,
i.e. 460 volts, in my case.

My Bridgeport motor is 220/440.




It would certainly be my preference to use a few autotransformers on
one
or two problem machines rather than go with a wild leg system.

You keep speaking of these problems, but I've had 3 phase delta systems
since 1967, and aside from the one failure, which would have occurred be
it
delta or wye, I've never had any problems. From that I conclude that
the
problems, while possibly serious, are highly unlikely to plague the
average
person. I'm more than willing to gamble on these ethereal problems
than
request wye service and know for damned sure I'm going to face other
problems, which I would. I get the idea you're geared to light
commercial,
where wye service is the norm. Machine shops do not use it----for
obvious
reasons. Places that have a lighting load that tends to be the largest
power demand is where you find lots of wye service, at least in my
experience.


Wye service is indeed good for buildings with a lot of lighting load,
480/277 is particularly good for that.

The main thing is that you are indicating that there is a big
disadvantage to 208v vs. 240v which I just don't see. I think your
making more of the difference between 208v and 240v than there is
justification for.

Funny, I was thinking the same about your position. I can't imagine how
the things you have spoken of are not a problem, buck/boost transformers for
individual machines (cost and inconvenience of placement), motors that run
hotter than is necessary.

Again you're assuming that most machines will require the transformers,
which is not the case. The hotter part is a small amount, perhaps
significant for a big shop in the desert, but not significant in most
cases.



The allowable voltage range for your 240/120 3ph delta wild leg service
is from 220v-254v at the service entrance (from a chart referencing ANSI
C84.1-1989). If the service is considered acceptable over a range of 34v
I just don't see a 32V difference between services as significant.

The voltage spread would, likewise be similar for 208, if not the same.
It's greater than 10%, the normal tolerance for motor voltage. Am I wrong?
Isn't that why newer motors are wound 230 volts? To keep them within
tolerance? Wouldn't that mean that older, 240 volt motors, would be
running out of tolerance if applied to 208 volt service?

I think that any older motors that are truly rated for 240V are also old
enough to be overbuilt beasts from the days when the line regulation was
nowhere near where it is today and consequently would likely not care
about running at 208V which is likely what they saw anyway on old
services with significant voltage drops within the building.



Large motors are built to handle widely varying power and load
conditions, and power supplies for controls either have plenty of tap
adjustment range for older machines, or switching supplies for newer
machines that are happy on anywhere from 98v - 250v. Your motors might
run a few degrees warmer but still well within their specified operating
range and your controls should be perfectly happy as well.

Tell my friend in Utah that he only imagined the problems he had with his
CNC grinders when he moved his shop to one wired wye. You make light of
it, but it was a serious problem for him. His machines wouldn't run. I
do not recall how they rectified the problem, this was about 12 years ago.

By changing the taps on the control transformers within the machines and
adjusting the set points for the motor starters?


Basically I think the 14% or so difference is of little to no
significance for 95% of the possible machines you might run, and for
those few the fix is easy and inexpensive.

But it *is* outside the 10% tolerance zone. I don't agree. I also don't
think of buying buck/boost transformers @ a few hundred dollars as not being
expensive. Especially commercially, where they *must* be installed by a
licensed electrician. I can see how such an installation could turn into
several hundred dollars per small machine, and in the thousands for large
ones.

Actually if they are installed integrally to the machine then they would
bypass any licensing requirement. Licensing requirements do not extend
past the power input terminals on the machine. Bolt the boost
transformers to the side of the control cabinet and run all the
connections inside the cabinet and they become part of the machine tool.



And actually the 240V is some 9% high for the machine, as it's motor is
rated for 220/440.

Yeah, 9% high, and in tolerance, unlike 14% low, and out of tolerance.


Funny, I get the distinct idea you think I made a mistake by installing
the
delta system. You couldn't be more wrong if you tried. It serves my
purpose perfectly, very unlike a wye system.

I think my main point is that I feel the Wye system would have served
your needs equally well and would have simplified the installation by
avoiding your use of separate panels for your single and three phase
loads to avoid the wild leg issue.


Wrong! I have *no* wild leg issues. In fact, my split panels provide a
good an valuable service beyond just addressing that problem. I'm on a
demand meter with my 3 phase, but not the single phase panel. The moment
I go above 50 KW (my induction furnace is a 50 KW unit), I pay more for my
power. The way I've wired the shop, I avoid the demand load except where
absolutely necessary, which is for the 3 phase equipment. My lighting load
alone could reach about 75 amps, if I was to run all my fluorescent lights
at one time. Each one is individually switched at the fixture so I can use
only those that are necessary. In turn, they are wired in six banks, so
each series (according to shop location) can be switched at the door.

And you're paying extra for the second service (meter) vs. a single
meter if you used Wye service. The whole peak meter thing can get pretty
hinky, particularly when it is based on rolling averages, not hard
setpoints. If it's based on rolling averages then a consistent lighting
load has little effect. You really have to analyze your loads to see
what is best.


My 42 position (Square D) single phase panel is all but full, without
accounting for any 3 phase devices. In other words, I'd have had to
install two panels, regardless. As it is, I have three, one being a 400 amp
disconnect that feeds the induction furnace.

I am better off for the way I've installed my service, and I still have no
regrets for having selected delta. If anything, you've further convinced
me I did the right thing. For that, I thank you.

If you've got individual 50KW loads you may well be big enough to have
benefited from 480V service.

Pete C.