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.)
No.
The nominal 480 wye to neutral is 277 volts. That is why you see 277v lighting in big buildings
There is normally a transformer in the panel to give you 120 volts if
120 volts is needed there. Don't you have a meter?
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
Thank you. Saves me building a device, and not have it work.
Oh, thank you. I didn't know.
Oh, thank you. I didn't know.
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.
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
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???)
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
">>> 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.
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.
--
*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.
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
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.*LOL What about 208?
More likely, I forgot the number, and typed it wong. I don't deal with
480/3 very often.HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.