Calculation to get 277 volts

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Johnd3573

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I have what I thought was a basic question but after speaking to several electricians and not getting a definitive answer, here I am. I build and run small venue sound and lighting systems. I typically work with 110 or 220 volt systems. We are looking at some upgrades to the lighting system and there are some larger dimmer packs, (lighting control units) that run on 3 phase 277 volt. I am not very familiar with 3 phase but would like to understand how you get to 277 volts with 3 legs of 110? In my search for information I have seen all different voltage rating for 3 phase and am at a loss as to how 3 legs of 110 can work out to these different values. I am looking for a breif explanation and possibly a mathmatical formula that will apply. Thanks in advance for your help. John
 
Johnd3573 said:
I have what I thought was a basic question but after speaking to several electricians and not getting a definitive answer, here I am. I build and run small venue sound and lighting systems. I typically work with 110 or 220 volt systems. We are looking at some upgrades to the lighting system and there are some larger dimmer packs, (lighting control units) that run on 3 phase 277 volt. I am not very familiar with 3 phase but would like to understand how you get to 277 volts with 3 legs of 110? In my search for information I have seen all different voltage rating for 3 phase and am at a loss as to how 3 legs of 110 can work out to these different values. I am looking for a breif explanation and possibly a mathmatical formula that will apply. Thanks in advance for your help. John
Click to expand...

You're right, 110 and 277 don't go together. First off. Let's use 120 instead of 110. 120 is the standard Voltage in the U.S.

The systems that are applicable are the following:

240V/120V single phase
208V/120V three phase
480V/277V three phase

If the 120 Volts comes from a three phase panel, then the cirucits are 120V from any of the phases to the Neutral bar. The voltage from any phase to any other phase is 208 Volts.

If you are dealing with a 277 Volt circuit, you are coming out of a 480 Volt three phase panel. The voltage from any phase to the neutral bar is 277V. The voltage from any phase to any other phase is 480V.

277 = 480 / sqrt(3)
120 = 208 / sqrt(3)
 
Thank you for answering so quickly. If you dont mind a quick follow up.. I noticed when I was doing a web search on this topic that 3 phase could be 220 277 480 volts etc. How does this formula apply to these other situations? I thank you again, this is more information for my own piece of mind, I dont like making decisions or working with something I dont understand. I do have a mechanical engineering background and farely good grasp of physics but college was a while ago, and when you dont use it.. you know.
 
In other words, the only way you can directly utilize 277v is to replace all of your lighting. If you want to continue using 120v lighting, you're stuck with the 120/240v 1-ph you're using now, or change over to 120/208v 3-ph.

The only thing between is to use 277/480v as your servioce voltage, and using thransformers to step that down to the lower voltages, but this only benefits the service, not the existing lighting.

By the way, the only advantage to using a higher voltage is that you can obtain more wattage at the same amperage. Whether it's worth the cost to change over must be determined by need.
 
Since you build these little sight and sound displays, chances are they're mobile equipment. You won't always have the luxury of 277 available at every site you arrive at, and certainly not receptacles. I'd suggest that you look into getting an appropriately sized 240 x 277 transformer for your equipment that requires 277.
 
Light dawns on yonder forehead. Thank you so much for the explanation. Thank makes so much sense now. I really cant believe that 3 electricians I asked about this had no answer for me. I just really hate not understanding. Thanks again for your time. John
 
Johnd3573 said:
I really cant believe that 3 electricians I asked about this had no answer for me.
Click to expand...
What sort of electrician did you ask? If you're in theater, the stage type electricians mostly get tasked with plugging cord A into box B. Many seem like electricians in name only, in my observation.
 
I thank you all for your quick responses and great information. Those are some of the decissions we are trying to make right now. We have 28 250 watt cans plus 4 500 watt cand and 8 intelligent light for the stage lighting and presently we cannot run everything at 100% thru the control board. We never run more than half the lighting at any one time and we have them set to 80% max output. Occasionally we can give quick all on flashes for a second or two at a time but this is why we are looking to upgrade. Trying to decide what is the best direction to go. This is a system for a night club that has live bands 6 nights a week. You guessed it.. No band on Monday night. Anyway, I would like to thank you all for your time and help. I appreciate it very much, Thanks john
 
John:

Here are a few Transformer Schematics which may be of some assistance:

wye_detail1.gif


208Y/120V 3? 4 Wire Wye Schematic
(FYI: the 480Y/277V 3? 4 Wire version is similar, only each Transformer / Winding is 277 Volts, instead of 120 Volts).

Referenced from ECN at this link:
http://electrical-contractor.net/ubb/Forum15/HTML/000053.html

delta_detail1.gif


240/120V 3? 4 Wire Closed Delta
"An Old System, Still In Use"

deltad3.gif


240 Volt 3? 3 Wire "Closed Delta"
(FYI: 480 and 600 Volt versions are similar to this Schematic)

Referenced from ECN at this link:
http://electrical-contractor.net/ubb/Forum15/HTML/000054.html

1phd4.gif


120/240 Volt 1? 3 Wire system
(typical for most Residential)

1phd8.gif


1 Phase Multitap Transformer
Included for example of "Output Voltage Options" and some informational impact...

These items referenced from ECN at this link:
http://electrical-contractor.net/ubb/Forum15/HTML/000057.html

Scott
 
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