How is that you get 408V? Can you get 408v on a 3 phase panel? And how?

You get 408 V out of a 408 V transformer. Many of the 3 phase transformers have several taps to give slightly different voltages. 20 years ago when I was managing a small factory, 480 was more common than 408, but I can't remember what all was used. 500 something was common too. Many of the industrial 3 phase motors, welders, etc. work OK anywhere from 440 to 480. The engineer that mentored me liked to keep the taps set to give 480 under load.

480 is phase to phase. It is only 277 above ground. The 408 may be the above ground voltage for something else. Often single phase lighting will use one leg of a 3 phase system. You have to watch getting the phases out of balance doing that.

Please explain the situtaion you have, what kind of electric service do you currently have, what is the 3 phase panel you have rated at, and any other details related to your question.

You ask for 408 volts. Is this a typo? 408 Volts is not a common USA voltage. What device do you have needs 408 volts? If 408 is a mistake, what device do you have and what does the nameplate say for rated voltage and amperage?

To answer your direct question, the 3 phase panel must be rated a minimum of 480 volts. Read the nameplate. Also read the main service nameplate. And still you should use a volt meter to read the actual voltage you are dealing with.

Should you already have a 120/208 volt 3 phase service, ( the 208 is not a typo, I suspect this is what you have and used the same syntax with the 480 volt), than a 3 phase transformer can be connected with the 208 on the primary side, and obtain 480 volt on the secondary, available to feed a 480 volt rated circuit.

Should you truly need 408 volts, there are special transformers call buck/boost transformers that can be used to either lower or raise the existing supply voltage to achieve the desired volts. Once I learn what the supply voltage and the load rating is I can explain in detail further the method of chosing the proper one.

Very important the transfomer is rated to handle the load it will be feeding.

You are getting into dangerous area with 480 volt. You really need to know exactly what you are doing. If you have even the slightest doubt what you are doing, better to call in a professional.

It is real scary the questions and situations I find lay people asking and dealing with. It is like if you go into a Rolls Royce dealer, and need to ask how much one costs before you buy one. If you need to ask then you can't afford it. If you need to ask how to get 408 volts, then you should be calling in a qualified professional.

And even scarier is when lay people that do not have the knowledge and experience with electricity therory and standard installation practices are answering these questions.

Yes that was a typo. I meant 480v. I'm actually just inquiring... I'm curious. I have never worked with more than 220V. You see I know you get 208 with just 2 phases. And I'm not sure but I believe you get 220v with 2 phases and a neutral. Am I right? Now I also would like to know how do I get 277v. As well as 440v & 480v. Now, from the replies I received already, I'm understanding that you get 440v or 480v through a 3 phase transformer, is this correct?

I think the industrial maintenance supervision experience I have more than qualifies me to answer questions like this. I don't appreciate gratuitous insults from a house electrician.

You can select transformers to deliver any voltage and amperage in either single phase or 3 phase. Most single phase is 110-120 V above ground. Most 3 phase is 440-480 V phase to phase. Other things vary from uncommon to unknown, but still possible. The wire and devices used with 480 volts are always rated at 600 volt.

I am glad you are only curious, and not looking to add some 480 volt machine in your basement by yourself. 480 Volt flash arcs and shocks are deadly.

Standard voltages in the US are 120/240 volts single phase 3 wire, 277/480 volts 3 phase 4 wire, and 120/208 volts 3 phase 4 wire. There are some medium duty industrial facilities that will have 240 volt delta 3 phase 3 wire, and even less of 5 wire 2 phase, which has been removed as much as possible. Heavy industrial can use 550 volts 3 phase and even higher voltages. 4160 is very common in large wood and paper industrial plants.

Seems that I have offended a fellow Ask Me Help Desk expert, with my comments. That does not concern me. My goal is to be sure that the question gets the best possible answer with as much fact to help educate, and very concerned that anyone attempting to work with electricity does everything correctly and safely.

What concerns me is that innocent people will be using the electric devices wired by do it yourselfers, and living in the homes wired by do it yourselfers.

Be assured that I am a bit more than a house electrician, licenses in two states and certified as an electrical inspector are my qualifications, along with now performing detailed power quality studies. I don't know very many individual homes that have 3 phase in them. Although the several 400- unit luxury apartment buildings I have permitted do use 120/208 volts, along with the hotels, brass mills, paper mills, banking data centers I have done all use 480 Volt and higher 3 phase.

You state that 208 comes from two phases. That is incorrect. 208 is a standard 3 phase voltage. Each 3 phase transformer or generator has three basic coils. These coils are all connected at one end, in the center. This is called a Wye connection, or Y. Sometimes, just to add to the confusion it is called Star.

If you can imagine each of the three spokes of the letter Y being a coil, all connected at the center, the neutral wire will connect at that center. The neutral wire is then grounded intentionally. Testing across the any two of the three outer spokes will give the higher volts, either 208 or 480. Testing between the center wire, or neutral, and any one of the outer spokes will give the lower volts, either 120 or 277.

I hope this helps. If you have any other questions get back to me.

I really appreciate the help. Thanks a lot guys. I'm just an aspiring Electrical Engineer who is an Electrical Apprentice. I'm going to school for Electrical Engineering and working as an Electrical Apprentice for the time being.

The answer to your question, How do you get 277v
It depends if the transformer producing the voltage is wired in for Delta, or Wye connection.
Delta is basically a triangle with a connection point at each tip of the triangle, thus representing 1ph at each point, giving you a total of 3ph(A,B,C). Its has a transformer winding between each of the 3ph. Between 2 of the points (ph), there is a centertap giving you a neural. Therefore if metering between any 2 points(A,B)(A,C)(B,C) you will get 480v. Between any 1 point A,B or C (ph) and the center taped (N) winding you get 240v, which is 1/2 of 480v.
Wye is set up to look like the Mercedes bends symbol, disregarding the circle portion for now!
There is a point at each tip, and a point in the center where they all meet. The center point is a neural. The points at each tip represent 3ph (A,B,C)
Now we know that between any 2 of the points (A,B)(A,C)(B,C) (not the center) will give us 480v. Between the center point and any of the outer points(A,B, or C) we get 277v.
To get this we need to go back to the Mercedes bends circle. A complete circle gives us 360 degrees. So 360 is representing our 480v. Divide 480 by 3, we get 120. Thus, giving 3 legs that equally 120 degrees out of ph from each other, which makes it balanced.
To get the proper voltage we need to take 480v and divide it by the square root of 3. The square root of 3 is 1.73205081 or (1.73). Now, 480 decvided by 1.73 gives us 277.46 .

Ebb, this question is almost four years old. The original poster, Melrub, hopefully is now a full engineer, or has past his apprenticeship by now, and by now would have a complete full understanding of 3 phase theory.

He should be able to give me answers and advice.

Please pay attention to post dates.

This thread is closed.