Different AC Voltages?

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Hunter J

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I hope this was the correct area to post.

I am searching for information about AC voltage and I am not sure exactly how to phrase the question so that may, be the reason why I did not find the information I was looking for but I will try.
An example of what I am looking for is?
480 VAC 3 Phase input and you get 277 VAC L-L 1 Phase
240 VAC 3 Phase and get 208 1 Phase by connecting to two legs.
I don?t understand how these voltages are derived but I would like to.
Also, home come there are so many voltages that are so close..208, 220, 230, and 240.
I see these voltages list and wonder why/how and would really like a understand this.

If anyone can point me in the direction of a PDF or can recommend a book I would appreciate it.

Thank you for your time,
Hunter J
 
Welcome to the forum Hunter.

Yes this was the right place to ask the question and without a doubt the members here can help you out. :cool:
 
the answer lies in

the answer lies in

the square root of three

480 divided by 1.732 = 277.136

208 divided by 1.732 = 120.092

I hope this helped if not maybe someone who is not so far removed from school can help. I am learning algebra and calculas all over again thanks to 2 kids in high school.
 
As far as the difference between 240 and 208, to keep it very simple, when you take your power from the local utility it feeds through a transformer, that will take your higher power (277/480) and step it down depending on your transformer. Simply, a Delta configured transformer will give you 240 phase to phase, and a Wye configured transformer will give you 208 p->p. As far as the voltage range on equipment, look up nominal voltage in your NEC in Definitions if you have one, voltage can vary for many reasons and field conditions, so equipment is designed to better handle these potential situations, as well as for versatility to use either the Delta or Wye system without buying a specific piece of rated equipment.
 
supply voltage are also specified based on circuit lenght and the type of load your feeding. In most cases the utility will determine what voltage level you are supplied at.

the same applies to the utility also. thier goal to minimized I^2R losses. higher voltage less loss. everytime double the voltage you double the voltage, you can deliver 4 times as much power with the same circuit.
 
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480sparky said:
220, 230 and 240 are really the same, just like 110, 115 and 120 are.
Click to expand...

I'll go as far as admitting that that was true at one point. With the globalization of, well, everything, it's getting a little cloudy. Better be safe than sorry.

In Brazil, they really do have 220. It's 220 three phase, 127 Line-to-Neutral.
In Germany, they have 230/400 230(L-N), 400(L-L)
In the U.S., we have 240. (With motors nameplated at 230).

The U.S. has what we call a 480 Volt system. The motors are nameplated at 460.

In Parts of Brazil, The system is called "440." The motors and the equipment are nameplated at "440," but the transformer secondary often-times operates around 455 or so. If you use a U.S. motor, that is rated at 460 on one of these systems, you should probably consider derating the motor.

In Germany, the system may be called 690, the motors and equipment are nameplated as such, but the secondary operates at around 725 or so.

Why does any of this matter? The world is getting smaller and we're starting to see equipment from other countries. Assuming that 220 is the same as 240 can have interesting results.
 
480sparky said:
OK, I'm assuming US standards.
Click to expand...

Most of us do, but Eric brings up a good point. I spent last Jan to July assigned to a factory and a lot of the equipment there had to be supplied with 400Y/231. Some of the lab equipment required 230 instead of 208.
 
Thank you.

Thank you.

Wow! Nice discussion going on here, thank you.
I will reply today when time permits.

Thank you,
Hunter J
 
illust_glossary_13.gif
 
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