On Mon, 12 Sep 2005 15:51:38 -0500, Jess
wrote:
Hi all,
I would like some help / advice in outfitting my shop.
For the first time in my metalworking home shop, I am able to get 3
phase service from the local power company.
In the past, I have always used a 3 phase rotary converter that I
built with the help of the group here - special thanks to Fitch and
Bob Campbell.
My question is, which voltage should I specify - and why?
I can get 208v, 220v or 440v.
What are the pros and cons, if any, between the choices?
If you have any 480V loads to run and you can get a 480V 3Ph feed
from the utility without a hassle or a huge price penalty compared to
240V 3Ph, it's always far simpler to drop a 480V feed down to 240V for
most of your loads with a cheap used transformer than it is to boost a
240V feed up to 480V.
And a 200A @ 480V feed goes a whole lot further. But as has been
pointed out, 480V demands some serious respect because it will reach
out and bite you hard, and things tend to "blow up reel gud" ;-) with
very little provocation.
You put in the 480V meter section and main, a small (12 or 18
position) 480V distribution breaker panel to feed any machines that
must be run at 480V, or fused safety switches - and be sure to run it
in as 4-wire with a neutral in case you ever need 277V for lights.
Then you install your 480V-240V transformer, and a larger (and much
cheaper) 240V 3Ph panel for the bulk of your equipment.
If you want to run 277V lighting in a large shop, pay a bit more for
the light fixtures with individual fuses inside. Without them, one
ballast in a long string of lights goes bad and grounds out, and you
go nuts opening every single stupid fixture to find the culprit. Or
you split the circuit and test, and hope the circuit breaker lives
through the repeated short-circuit torture test. BT, DT...
I do have some small bench top and hand held machines that require
110v single phase.
Run a separate "lights and plugs" feed out to the shop building from
your house's 120-240V 1Ph panel feed, or leave the existing one hooked
up. This way, you can kill all the shop power at the 3Ph Main to work
on it, or just to kill the parasitic loads from the transformers and
keep "unauthorized personnel" from messing with your toys, and not be
in the dark.
With that power coming in on a totally separate feeder you keep the
motor start surges and welder spikes away from the more sensitive
gear. And no lights dimming when you hit the big switches.
Also, see mentions of demand metering and higher rates for
'commercial power' mentioned elsewhere - that way the lights, furnace
blower, computers, clocks, and other incidental loads that tend to add
up fast are being metered at the residential rate.
I have one lathe powered by a 200v three phase motor - I would be
willing to replace this motor, if it would seem to be an advantage to
go with one of the higher voltages for other reasons.
Consider getting three buck-boost transformers to drop a 240V or
208V line to 200V, depending on the price it's probably cheaper than a
new motor. And you can use some ridiculously small and cheap
transformers for that, even when buying new.
I have hopes of going to some newer machinery in the future, most /
all of it seems to be rated for 220v, but with the notation that it is
operable on 208.
A lot of equipment does both 208V and 240V, the current is slightly
higher at 208V. Makes it easier to wire up small industrial parks at
208V without people constantly making "Oopsies" hooking up 120V stuff
to the ~190V 'High Leg' of a 120/240V Delta service.
If I had my way, ALL houses would be able to get either 120/208V Wye
or 120/240V Delta feeds on demand - Just putting the largest motor
loads like air conditioning/heat pump compressors on 3-phase increases
the energy efficiency enough to make for a short payback period.
"But that will never happen - It would simply make too much sense."
(© BLB)
-- Bruce --
--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
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