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  • #16
    Re: single phase and three phase?

    Originally posted by Andy_M View Post
    I'm sure that HooKooDooKu understands this, but it probably should be clarified that any specific device MUST be intended for connection to the 240 circuit. Some motors and other devices offer optional wiring for either connection, but in general if you connect a 120V device to 240V, you don't halve the current... you'll burn the thing out, and possibly get a visit from the fire department. The panel breakers won't keep the 120V device from catastrophy.

    So, never connect a 120V device across 240V unless the device is "dual voltage". And even then, make sure you know what you're doing.

    And don't connect a 240V device across 120V, either. In the case of an ac induction motor (most common type), under load, it WILL draw a lot of excess current and is very likely to burn out...
    Yea, good thing to point out. Sorry for potentially creating some confusion.

    When I was writing my description, I mistakenly had the narrow mind-set of speaking from the point of view of an appliance manufacturer... that when you go to build an appliance, you can chose to build your home appliance to be a 240 or a 120 system, without stipulating that point of view.

    Because yet, if you wire a 120 volt device into a 240 volt circuit, the electrical law of Current = Voltage / Resistance dictacts that you will get twice the current when you double the voltage.

    But from a design perspective, if you make an appliance that needs a certain POWER, you can get that power from either a 120 volt circuit or a 240 volt circuit, and the 240 volt circuit will require half as much current to acheieve the same POWER a 120 volt circuit would require.


    Need a little extra light in your work shop? Yea, hook that shop light upto a 240v circuit... you'll have plenty of light then... at least for a short while

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    • #17
      Re: single phase and three phase?

      Originally posted by James P View Post
      This may help.



      James
      I know this is random and I old thread, but I looked at the Pie chart in the random image drawing.

      Just structurally that chart doesn't make sense to me. How could I be expressed in terms of sqrt(I)/R.

      Comment


      • #18
        Re: single phase and three phase?

        That chart is wrong, look at the expression for V = sqrt(I)*R when V=IR.

        This is a better chart if you need it

        Reading through the post I get an uneasy feeling the guy was trying to run 3 phase equipment by attaching it to single phase power - hope not

        Last edited by wbrooks; 04-16-2010, 09:38 PM.

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        • #19
          Re: single phase and three phase?

          Originally posted by wbrooks View Post
          That chart is wrong, look at the expression for V = sqrt(I)*R when V=IR.

          This is a better chart if you need it

          Reading through the post I get an uneasy feeling the guy was trying to run 3 phase equipment by attaching it to single phase power - hope not
          its possible but you would have de-rate a bunch in order to not make the wires not have over capacity

          plus you would need a VFD or some type of inverter

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          • #20
            Re: single phase and three phase?

            Originally posted by tailgunner View Post
            Because that particular appliance is basically a giant resistor, the simplest of circuits. So yes, when rigged for 208, a heater will use less wattage, but give off less heat for that same appliance. Yes, for a heater rated at 750 watts @ 240 volts will only produce 563 watts of heat @ 208 volts. So what do you do when you need 750 watts of baseboard heat? Simple, get a bigger heater for 208v supply, which means, the circuit requires a larger set of conductors to handle the increase in current for the same amount of wattage.


            or put in a buck boost

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            • #21
              Re: single phase and three phase?

              Originally posted by cpw View Post
              I know this is random and I old thread, but I looked at the Pie chart in the random image drawing.

              Just structurally that chart doesn't make sense to me. How could I be expressed in terms of sqrt(I)/R.
              You're correct I pulled it off a web site should have checked it.

              Comment


              • #22
                Re: single phase and three phase?

                Originally posted by breid1903 View Post
                i don't know what you are working on, but you will have less power on a 208v 2 wire circuit than on a 240v 2 wire circuit. about 90% if i remember correctly. it's been years. volt will know. breid..............

                Residential electrical hot water tanks use 240V, but commercial HWTs use 208v/3ph(3 poles 120v each) or 208v/1ph (2 poles 120V each)

                Am I right? 208V 3 phase and 208V single phase?

                Thank you.

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