Strange Voltage Outlets / 347 volts ?????

I was just looking up some oddball outlet I got in a pail of electrical stuff at an auction. I went to this website. http://www.leviton.com/sections/techsupp/nema.htm
What I have is the # 24-15R Listed for 347V AC.
Now I know what it is, but where do they use 347V AC ? Or, for that matter, where do they use 277V AC which is also listed?
120 240 208 480 are all common, but these 277 and 347 I never heard of.
By the way, this is a very handy website. Bookmark it !!!!
Mark
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snipped-for-privacy@UNLISTED.com wrote:

277 volt is common for lights in some commercial buildings.
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The higher the voltage, the smaller the copper you need to carry it. In large buildings like supermarkets, and factories, these higher voltages are common

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If you have a 480 volt 3 phase circuit connected in the Y configuration, the center of the Y (which is often grounded and also the neutral) to one of the ends will be 277 volts. This is often used for lighting in buildings that have 480 volt 3 phase power. The 347 volts is the same way for a 600 volt Y connected circuit.
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277 is the phase to neutral voltage of a 3 phase 480 volt system. Very commonly used for the lighting in commercial buildings. 347 is the phase to neutral voltage of a 3 phase 600 volt system.
Phase to neutral voltages can be calculated by dividing the phase to phase voltage by the square root of 3.
John
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JohnR66 wrote: > 277 is the phase to neutral voltage of a 3 phase 480 volt system. Very

Indeed. Fluorescent lamp ballasts and even otherwise ordinary looking medium base (like standard household bulbs) incandescent bulbs can be had in 277V versions.
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Could you please post the mathematical formula. I'm pretty math challenged, but a sample might help. The square root is the part where I get lost....
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in the Y connection you devide 480 by 1.73 and get about 277. The same with the 600 volt circuit to get 347. The numbers are not exect, but just the nominal values.
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On Sun, 06 Aug 2006 15:29:28 GMT, "Ralph Mowery"

THANKS
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