Don Murray wrote:

Pete C. wrote:


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.

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.


Most machines I've seen can accommodate a wide input voltage range, for
the few machines that can't you use the small inexpensive buck/boost
autotransformers.

We've already kicked that around. Why buy more transformers when you can
get the proper voltage?


Again, because not many machines would actually require it, and the fact
that your "proper" 240V service is allowed to vary over a 34v range
anyway.

Peter,
Do you think it would be OK to run the 240 motor on 197.6V ? Because
that's what could happen when you hook it up to a 208 service. Most all
power companies have a 5% tolerance on their service voltage. So a 240
service can go from 238 to 252.

I think something is wrong with your math there or you have a typo. At a
+/- 5% tolerance the nominal 240V service would range from 228V to 252V.
According to that ANSI spec 220V to 254V is acceptable.

And a 208 service can go from 197.6 to
218.4. The purpose of a 208 service is to serve buildings with large
lighting loads and small 3-phase loads. There is a lot of commercial 240
3-phase and a lot of houses that have their own 3-phase wells will also
have a grounded center tap delta. I happen to have a 10HP 3-phase pump
with a straight 3-phase service, 3hot wires and no neutral to the pump.
The bank across the street from my house has a 25KVA and 2 10KVA
transformers, in a center tap grounded delta. My house 120/240 single
phase also comes off of this same bank.

The different sized transformers is what I referenced about cost savings
for the wild leg configuration, with the 10KVA transformers costing less
than the 25KVA transformer.

A quick look on the Grainger site doesn't even find any 240V 3ph motors
at all. They all seem to be spec'ed for 208-220/440 or 208-230/460. The
Baldor site is also devoid of any 240V rated three phase motors, they
list motors with 208-230 range and some at 220V or 230V.

The Baldor spec's indicate for a 2HP motor the FLA difference between
208V and 230V is .5A (12 vs. 11.5). If the entire current difference was
dissipated as heat, which it is not, that's a whopping 104W extra to
dissipate from the surface of a beefy 60# motor - hardly a big deal in
just about any application.

So once again I think that there are very few machines that would
actually have any adverse effects from running on a 208V service.

An existing building with wild leg delta service that was in good
condition would be fine with me. For a new installation I would not
spec. a wild leg delta service.

Pete C.