How do you get 240V in USA

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  • niki
    Senior Member
    • Nov 2006
    • 566
    • Poland
    • EB PK255

    How do you get 240V in USA

    In Europe the standard voltage is 230V (Phase to Neutral)

    I don't know the system in USA but, I'm just wondering...

    As I remember from the times that I was mechanic on the B-707 / B-747, the generators were specified as "115/200V - 3 Phase - 90 KVA" when;
    Phase to Neutral = 115V
    Phase to Phase = 200V

    That's because the generator Phases are at 120° one to the other and the "Picks" are never at 180° opposite one to the other.

    As I remember, the calculation of the "Phase to Phase" Voltage is (if the "hard drive" is still working properly ...)
    Square root of 3 multiplied by the "Phase to neutral" Voltage or
    sin 120° x 230V (Phase to Phase Voltage);
    1.732 x 115 = 199.186 V or
    0.866 x 230 = 199.186 V

    So the "Phase to Phase" voltage of 120V should be;
    1.732 x 120 = 207.85 (or 208V when rounded)

    It looks to me that if you want to operate an 230V motor - the motor runs on lower than the specified voltage that, as we all know, is a "killer" for any electric motor...

    So, how do you get 230 or 240V in USA (probably, I'm missing something...)

    Many thanks
    niki
  • Uncle Cracker
    The Full Monte
    • May 2007
    • 7091
    • Sunshine State
    • BT3000

    #2
    I think your confusion stems from the discrepancy between "peak-to-peak" (p2p) and "root-mean-square" (rms) voltage measurement. We get our 240V by using two 120V legs out of phase with one another. A typical voltmeter is going to measure p2p, but a more sophisticated "true rms" device will measure working voltage based on the structure of the involved sine waveforms. This is where I get off, however, as Loring and many others more knowledgeable can do a better job with this than I...

    Comment

    • cabinetman
      Gone but not Forgotten RIP
      • Jun 2006
      • 15218
      • So. Florida
      • Delta

      #3
      I have limited electrical knowledge nowhere near your knowledge base, but simply I've seen a variance of 110V to 120V per single circuit. Our 220V to 240V is from two single legs. That's about the best way I can describe it.
      .

      Comment

      • LarryG
        The Full Monte
        • May 2004
        • 6693
        • Off The Back
        • Powermatic PM2000, BT3100-1

        #4
        I don't know the how, but FWIW:

        In the United States, you'll hear different people refer to standard wall-outlet voltage as 110, 115, 117, or 120. It's all actually 120V.

        Similarly, people will talk about 220, 230, or 240. It's all actually 240V. Usually -- see below.

        Some buildings do have 208V if that is what the equipment within it needs. We run into this often on our commercial projects, perhaps most commonly those that have lots of food service equipment (i.e., school cafeterias). IIMN the 208V is provided by a different transformer than the one that supplies the more common 120/240.
        Larry

        Comment

        • LCHIEN
          Internet Fact Checker
          • Dec 2002
          • 20914
          • Katy, TX, USA.
          • BT3000 vintage 1999

          #5
          Niki,

          The short answer is that you get 208V from Wye-connected 120V 3-phase, you'll only find this in industrial locations and specially wound motors are made for this when used.
          In homes, 3-phase is never installed. Power enters the home as 240V center tapped neutral. 240V appliances are wired to both lines, 120V equipment is wired from one side to neutral. I laughingly call this 2-phase power.

          Detailed explanation:

          in the US power is transmitted at high voltage in three phases, 120 degrees between phases.
          Usually in industrial locations, all three phases are installed to run larger machinery, and 220/240V 3 phase is common as is 440/480 and often 660V. These are obtained using step down transformer taps from high voltage distribution.
          Sometimes 120V 3 phase (120V from phase to neutral) is obtained from the transformer. This can be used as you say to generate 208V between any two phases in the so-called delta wiring and 120V between phase and neutral with Wye-wiring.
          This takes special machinery set to 208VAC but standard 120V tools or instruments can be run from the same circuits (using any phase to neutral). This can be an advantage in using normally available 110/120V components with higher voltage motors. So you do find some common equipment options for 208VAC. in Either 3 phase or 1 phase. But you never find 208V stuff in homes simply because most homes don't get 3 phase power.

          In the normal US home or residence, there is three-phase high voltage distribution to the neighborhood. The residential branch typically is from a pair of the three-phase lines; different pairs of the three-phase might service separate blocks to balance the load. The final step down transformer from the two chosen phases gets to 220/240V center-tapped. The center tap is called the neutral. In this case either hot line has 110/120V to the neutral and are 180 degree out of phase with each other. If you measure H1 to H2 then you'll see 220-240 volts.

          The breaker box has all three lines, H1, H2 and neutral. Branch wiring into the house for 240V appliances (usually Air conditioning, electric heat, water heater, electric clothes dryer, stove and oven, as well as any 240V shop tools which most people don't have) is made by carrying both H lines through two ganged Circuit breakers to the appliance outlet (Which is usually dedicated to that appliance - you will not find 240V utility outlets in homes) For lighting and general purpose outlets, wiring from either H1 or H2 is brought through a circuit breaker (usually 15 or 20A) plus the neutral wire. The common color coding in the US is Hot is black and neutral is white. and silver terminals are hot and gold/brass terminals are hot. The US circuit breaker boxes are set to that alternate breakers pull from H1 and H2 so as to balance the load more or less.

          Neutral is connected to the grounding rod at the transformer. So neutral is almost always very close to ground potential (within a couple of volts), all branch wiring and outlets should use ground ( a green wire). Essentially No current flows in the ground wire. We use Ground fault interruptors which detect differential current between hot and neutral (should be zero) if its more than about 100 uA then the GFI opens the circuit assuming that the leakage current is into the frame or chassis and a shock potential exists.

          I see there are some other answers since I started but they missed the 208V mark...
          I think my description of the US power distribution is corrrect from an engineering standpoint and the explanation of 208V is somewhat technical but what you are inquiring about. Note my use of H1 and H2 are not a standard naming, I just use them so I would have to say "the other hot line".
          Last edited by LCHIEN; 09-02-2008, 10:38 AM.
          Loring in Katy, TX USA
          If your only tool is a hammer, you tend to treat all problems as if they were nails.
          BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

          Comment

          • Uncle Cracker
            The Full Monte
            • May 2007
            • 7091
            • Sunshine State
            • BT3000

            #6
            Atta boy, Loring... I knew you'd hold your end up!

            Comment

            • niki
              Senior Member
              • Nov 2006
              • 566
              • Poland
              • EB PK255

              #7
              Thank you for your replies and special thanks to you Loring for taking the time to explain it to me.

              Well, as I said..."probably I'm missing something"

              Maybe my confusion came from looking at my table saw spec.

              This TS comes in two versions - 1 phase and, 3 phase (I have the 1 phase).

              As you can see on the pic below, the 1 phase voltage is 230V but, the 3 phase voltage is 400 that if I'll apply the formula of "square root of 3 multiply by 230V" it will give me 398.37V (or rounded, 400V).

              So, it looks like in Europe the 3 phases are coming from the same generator or from many generators synchronized to the same phase and the method is simple "phase to phase" (but, I don't know about the industrial supply)

              My house and all the new houses around are supplied with 3 phases (no, I don't have special outlet for 3 phases just, each phase is connected to different breakers)

              On the 707/747 we had 4 generators and we had to connect them all in parallel to one "Bus Tie" so, if one generator fails, the other 3 will supply it's loads automatically (and the passengers would not know even that the generator failed).

              To connect 2 or more generators in parallel, I had to turn some small potentiometer that turned the generator faster or slower and, when the phases were synchronized (it was indicated by two lights - when they were blinking very slowly or "Off" - it meant that the phases are synchronized) I switched the "Bus Tie Breaker" (BTB) to ON.

              Connecting two generators in parallel while the phases are not synchronized (i.e. the "picks" are not at the same time) would lead to "Shaft Shear" of one of the generators.

              Thanks again
              niki
              Click image for larger version

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              Comment

              • LCHIEN
                Internet Fact Checker
                • Dec 2002
                • 20914
                • Katy, TX, USA.
                • BT3000 vintage 1999

                #8
                in the US there are four or so major power grids. Within each grid there are hundreds of generators running in parallel holding up the load. Every generator must be synchronized with the others or the power would go crazy (and probably shear shafts off, too). In the case of a generator, being started, it has to be brought up to speed (60 revolutions per second). At the turn of the 20th century, the standard means of checking synchronism is the three light bulbs tied between the each phase of the generator to the one phase on the grid. The bulbs will flash on and off at the difference speed, as they approach the bulbs will appear to rotate, the rotation slows as the speeds match and will stop when synched and reverse even if you are going too fast. when they are synchronized the bulbs will be holding or at least precessing slow enough that the connection used to be thrown by hand. I'm sure todays synchronizing in done automatically since a manual mismatch on a generator throwing out 500 MW would be catastrophic to something (very large generator shafts maybe). Much more exciting than synchronizing four jet engines.

                Once synchronized, you power output is controlled by increasing generator torque and increasing the phase a bit so that when you lead the phase you are generating power into the grid and your phase is lagging then you are actually pulling current from the grid (bad, unless you are a co-generator with varying power availability and a heavy user sometimes.).

                At any rate once tied in you are locked to the frequency of the grid which is kept very accurate on a short term and even more accurate on a long term. What I mean by that is they actually count the cycles during the day and if they ran a little slow in the morning they will speed up ever so much to make the days total come out exactly 60 per second over the day. because many clocks, esp. the mechanical analog ones, use synchronous motors, they will be perfect time keepers.
                Better even than the quartz clocks and watches because the time source they use to count cycles comes from a clock probably 10,000 times better than your commercial grade quartz timers.

                P.s. Niki, I'm sure by "picks" you are probably talking about "Peaks" referring to the phase difference which is usually measured by looking at the peaks on an oscillograph or oscilloscope. Maybe instructor had a strong accent?

                Also virtually all power generators are three phase motors run in a generator configuration, shaft is driven and the three windings are the output. Different generators are not used to generate different phases (was that a question you were asking?); the phase and phase angles are set by the winding relationship in the motor which are physically set at 120°.
                Last edited by LCHIEN; 09-02-2008, 12:46 PM.
                Loring in Katy, TX USA
                If your only tool is a hammer, you tend to treat all problems as if they were nails.
                BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

                Comment

                • LCHIEN
                  Internet Fact Checker
                  • Dec 2002
                  • 20914
                  • Katy, TX, USA.
                  • BT3000 vintage 1999

                  #9
                  Some might find this wiki article interesting. The US residential power distribution I described is correctly called Split-phase distribution. The article compares to Europe, it says that Europe homes usually have split phase in the neighborhood developing 230 and 460V as US homes develop 120 and 240, but many homes are only serviced by one side of the split phase meaning they won't have over 240V available.

                  Loring in Katy, TX USA
                  If your only tool is a hammer, you tend to treat all problems as if they were nails.
                  BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

                  Comment

                  • cgallery
                    Veteran Member
                    • Sep 2004
                    • 4503
                    • Milwaukee, WI
                    • BT3K

                    #10
                    Loring, I think I know the answer to this anyhow, but did you have to look any of this up? Or did you just know.

                    I'm betting you knew it already.
                    Last edited by cgallery; 09-02-2008, 01:24 PM.

                    Comment

                    • LCHIEN
                      Internet Fact Checker
                      • Dec 2002
                      • 20914
                      • Katy, TX, USA.
                      • BT3000 vintage 1999

                      #11
                      well, I looked it up afterwards to see if there was a better way of explanation... thats when I gave the link to the wiki article.

                      I first learned most all this three-phase-stuff in College EE classes - still remember.
                      Last edited by LCHIEN; 09-02-2008, 01:34 PM.
                      Loring in Katy, TX USA
                      If your only tool is a hammer, you tend to treat all problems as if they were nails.
                      BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

                      Comment

                      • BobSch
                        • Aug 2004
                        • 4385
                        • Minneapolis, MN, USA.
                        • BT3100

                        #12
                        It's amazing what a person can learn on this board.
                        Bob

                        Bad decisions make good stories.

                        Comment

                        • niki
                          Senior Member
                          • Nov 2006
                          • 566
                          • Poland
                          • EB PK255

                          #13
                          Thank you so much Loring

                          As for frequency, we use 50 Hz in Europe but I know that in Japan they use 50 Hz (Tokyo and up) and 60 Hz (Osaka and below) so, every clock has a switch 50 - 60.

                          I did not know the USA method of producing 240V and I thought that it cannot be made (that shows you my really basic knowledge) but I believe that the American Engineers found the way to do it (It's too complicated for me to understand )


                          As for the 230/460V in Europe, I have a little bit of confusion because my TS is made in Germany for the European and Australian markets and if they say "3 phase 400V" (as you can see on the spec of the TS - taken from the Operating Instructions that are written in all the main European languages including Polish) so, I believe that the Germans knows the electric power in Europe.

                          Again, I don't have any idea about the 3 phase voltage to the industry in Europe

                          BTW, I was reading some article that the EU decided to convert all the voltage in EU to 230V (some countries were using 220V and some - UK - 240V) as they explained, it is done so they will be able to supply electricity from one country to another and to make all the electric devices in standard 230V (so they can sell one product in all countries).

                          On your link, there is a title on "Construction Sites" that says that in UK, in construction sites, they must use 110V equipment.....lately, I've seen a 110V Angle grinders and alike in the shops here in Poland and, to my question, the guy replied that it became an EU safety regulation...now, everybody have to buy an 230/110V step-down transformer.

                          Maybe tomorrow, I'll try to check the Voltage between 2 phases on my electric box....
                          So, if you'll not here from me.......well, the voltage was high enough to kill me

                          Regards
                          niki

                          Comment

                          • LCHIEN
                            Internet Fact Checker
                            • Dec 2002
                            • 20914
                            • Katy, TX, USA.
                            • BT3000 vintage 1999

                            #14

                            The above is a link to the voltages and plugs used in most countries, I consult it when working abroad.

                            On the subject of 110V tools for UK, they require a split phase 55 + 55V system so that neither line is above 55V from ground potential and the total is 110V across the lines. The reason is that it is assumed that the most likely accident is one conductor shorting to the case or through water and contacting personnel who are in contact with ground. Thus given this scenario you cannot be exposed to more than 55V which is widely believed to be non-lethal given the impedance (resistance at 50 or 60 Hz) of most people. However the tool still operates with the power of a 110V tool. That a person might contact both lines and be electrocuted is considered to be much lower probability as in most likelihood he will get a good buzz from touching one line first before the insulation fails on the other line. Anyway to use these 110V tools in the manner that UK intended, you need a center-tapped, 240 to 110 step down transformer with the center tap grounded.

                            Actualy its no problem to produce most any voltage you want. All distribution today is done at a very high voltage from the power plant, often as high as 110,000 volts with local substations reducing it to several thousand volts near your homes. The final voltage is created with transformers which decrease the voltage and increase the current so the delivered power is about the same. This reduces resistance losses over long distance since at 110,000 the current is low, and allows smaller wires. USing high voltage directly is impractical due to the tendency to jump gaps and require lots of insulation and be dangerous. Fortunately a man named Westinghouse knew that transformers allowed AC voltages to be adjusted up and down and correctly laid out the basis for the distribution system everyone uses today. It also makes the powerful induction motors of today possible. Transformers do not work with DC and Thomas Edison, bless his wasteful little incandescant lighting, spent a huge fortune trying to light cities with DC power. This was doomed to failure and made him a bitter man later in life, because it is so costly compared to AC and did not support less expensive induction motors. Transformers can be made to handle large amounts of power and by adjusting the windings can change from almost any AC voltage to any other AC voltage.
                            Last edited by LCHIEN; 09-02-2008, 04:45 PM.
                            Loring in Katy, TX USA
                            If your only tool is a hammer, you tend to treat all problems as if they were nails.
                            BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

                            Comment

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