From: David Cole (DavidCole@tk7.net)
Date: Sun Jul 13 2003 - 12:55:18 PDT
I am working on a program for a new machine that is being built in an old
machine shop that is wired in a similar way, actually it is a 4 wire
system, with 120 -> grnd, 120 -> grnd, 240 -> grnd, and the three Lines
have 240 3phase between them. It took a while to figure out how to hook up
the motion controller I'm working on so I would not smoke the unit. The
service supplying the building is 1920's vintage and should be condemned.
(Seriously!)
208 Y 120 3 phase is very common with 120 between the legs and the neutral.
480 Y 277 is also very common in larger industrial plants. In the old
days they did all kinds of goofy things that are not friendly to computers.
Like ungrounded 440/480 volt delta systems which tend to kill computer
equipment. General Motors standardized on that system because you could
short a phase to ground and still run the plant! That was nice, but the
other two ungrounded legs went to 440/480 volts above ground when that
occurs and computers power supplies don't like that.
Dave
On Sat, 12 Jul 2003 08:39:02 -0400, Fred Martin <mung@in-touch.net> wrote:
> The last time I put 3 phase in a bldg., it was the four wire delta
> system...120, 120, 208 (wild leg) and a common. As I recall, years ago a
> nameplate on an electric motor might read 110, 208, 220 volts. Haven't
> seen it for a long time though. Fred Martin
>
> Ryan Gill wrote:
>> At 1:54 PM -0700 7/10/03, Horrocks, Aaron wrote:
>>
>>> While I have no experience with military AC/Heating units, I can tell
>>> you about the juice needed for it!
>>>
>>> For 60Hz here's the standards:
>>>
>>> Voltage Phase Wires
>>> 120/240 1 3 Used commonly in homes, small business
>>> 120/208 1 3
>>> 120/208Y 3 4
>>
>>
>> Isn't 120/208 based on it being off of a 3 phase system (4 wires total
>> at the box?) 208 volts being the sum of 2 hot wires that are 120° out of
>> phase. Home 120/240 involves 2 hot wires that are in phase and yielding
>> a total sum of 240 volts.
>>
>> How do you get 120/208 off of a single phase system? Isn't it by
>> default, off of a 3 phase 4 wire system?
>>
>>
>>> 240 3 3 " " pumps
>>> 120/240 3 4 " " small business
>>> 277/480Y 3 4 " " industrial
>>
>>
>> 277/480 is useful for large installations of flourescent lights. Most of
>> the floor on CNN center I'm on has 277 based lights.
>>
>>>
>>>
>>> 208 volts is one of those funky voltages that (pardon the pun) should
>>> be phased out!
>>
>>
>> Hardly, at home in residential, three phase is unusual. What you get off
>> the pole is single phase. In industrial/Commercial applications 120/208
>> is the lower voltage component of 277/480. My electrical room for the
>> Data Center I run has two types of panels for my Data Center. 120/208
>> and 277/480. The
>>
>> Perhaps the question here is if that generator is labeled as 208 and is
>> really 208Y (perhaps no difference, one label is more particular than
>> another?).
>>
>>> Usually 208V equipment is cheap because few manufacturers support it,
>>> and most
>>
>>
>> Its standard for computers, UPS and other applications in the tech
>> industry.
>>
>
>
>
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-- Dave
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