440 volt three phase question

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• posted on May 27, 2010, 3:03 pm

I've had the moment to work on 440 volt roof top heating and AC.
Once in a while, need some power to run a 120 volt device. Is it 120 volts from one leg to ground?
(Yeah, I could just check it. But I was on the roof yesterday, and not sure how long until I get to another roof.)
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Christopher A. Young
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• posted on May 27, 2010, 3:23 pm

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• posted on May 27, 2010, 9:22 pm
Oh, thank you. I didn't know.
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Christopher A. Young
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• posted on May 28, 2010, 5:31 pm
On May 27, 5:22 pm, "Stormin Mormon"

It is entirely possible that the 440 volts is from a delta configured transformer that is not ground referenced or is corner grounded. Point is that one shouldn't assume that the transformer that is supplying the current is Y configured. -- Tom Horne
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• posted on May 27, 2010, 4:05 pm
On May 27, 10:03 am, "Stormin Mormon"

No.
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• posted on May 27, 2010, 9:22 pm
Oh, thank you. I didn't know.
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Christopher A. Young
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• posted on May 27, 2010, 4:33 pm
On Thu, 27 May 2010 11:03:40 -0400, "Stormin Mormon"

The nominal 480 wye to neutral is 277 volts. That is why you see 277v lighting in big buildings
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• posted on May 27, 2010, 9:21 pm
Thank you. Saves me building a device, and not have it work.
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Christopher A. Young
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• posted on May 27, 2010, 4:48 pm
Stormin Mormon wrote:

120 volts is needed there. Don't you have a meter?
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LSMFT

I haven't spoken to my wife in 18 months.
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• posted on May 27, 2010, 9:23 pm
Where I was working, there was a GFCI convenience outlet on the side (120 VAC) but that got me to thinking. And, I'm learning.
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Christopher A. Young
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• posted on May 27, 2010, 8:03 pm
On May 27, 11:03 am, "Stormin Mormon"

How old is this roof top unit... Seriously 440 volts ? Are you sure that it isn't 480 volts ?
I asked the _age_ of the unit because there is supposed to be a service outlet for 120 volt powered tools for maintaining the roof top equipment installed somewhere near the unit...
And no, with a 3 phase 480 volt system it is typically 277 volts on each leg...
~~ Evan
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• posted on May 27, 2010, 9:25 pm
How old is this roof top unit... Seriously 440 volts ? Are you sure that it isn't 480 volts ?
CY: The unit looks maybe ten years old. It may well been 480, and I typed it wong.
I asked the _age_ of the unit because there is supposed to be a service outlet for 120 volt powered tools for maintaining the roof top equipment installed somewhere near the unit...
CY: Actually, this one did have a convenience outlet. But,t hat gets me thinking.
And no, with a 3 phase 480 volt system it is typically 277 volts on each leg...
CY: Thanks.
~~ Evan
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• posted on May 27, 2010, 9:29 pm
On 5/27/2010 1:03 PM Evan spake thus:

Right; we should all tighten up our terminology, nominal voltage-wise.
It's 120, 240 and 480. *Not* 110, 220 and 440. (Not to mention all those weird older numbers that were used, like 117 volts: WTF did that come from???)
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The fashion in killing has an insouciant, flirty style this spring,
with the flaunting of well-defined muscle, wrapped in flags.
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• posted on May 28, 2010, 12:36 pm
">>> I've had the moment to work on 440 volt roof top heating and AC.

*I have found that the actual voltage varies by power company. One company in NJ supplies 460/265 volts while another supplies 480/277. It is quite possible that Stormin is dealing with 440 volts.
When I worked for my father decades ago he did a lot of industrial work and we quite often had to add buck and boost transformers to equipment because the juice from the power company did not match the nameplate requirements for a machine.
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• posted on May 28, 2010, 12:55 pm
John Grabowski wrote: ...

More than likely it's owing to variations in distribution or even local voltage drops rather than a difference in system generation setpoints between utilities.
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• posted on May 28, 2010, 1:31 pm

*Many years ago I had an issue with the voltage at a hospital that I was working at. It seemed that there was low voltage everywhere. I had the power company come in and monitor the building for a week, but they assured me that they only supply 460/265 and that is what we were getting. The ballasts for the fluorescent lighting were rated for 277 volts. I had to go to every transformer in the building and change the taps so that we could get 120 volts out of an outlet instead of the 102-105. I also had to install a few buck and boost transformers on some A/C equipment.
Of course variation in distribution, voltage drop and distance from transformers does have an effect.
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• posted on May 28, 2010, 6:56 pm
On 5/28/2010 5:36 AM John Grabowski spake thus:

Don't doubt you at all; however, the *nominal* voltages are still 120/240/480. What you're describing are basically under-voltage situations.
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The fashion in killing has an insouciant, flirty style this spring,
with the flaunting of well-defined muscle, wrapped in flags.
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• posted on May 28, 2010, 8:26 pm

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• posted on May 28, 2010, 11:00 pm
More likely, I forgot the number, and typed it wong. I don't deal with 480/3 very often.
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Christopher A. Young
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• posted on May 28, 2010, 5:02 am
Evan wrote:

Usually, equipment is rated for a range of voltages. A lot of HVAC equipment has different taps on the 24 volt control transformer to pick a different primary voltage. I've seen some air handlers that had a tap on the control transformer for 110 volts and another for 120 volts. Of course on larger package units there will be taps on the primary of the control transformer to choose between 208 or 240. I've seen a lot of blower motors that show a rating of 100-125 VAC 60 Hz on the nameplate.
TDD