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  • What Is The Answer?

    Below I have a link to a diagram with a question about it. Lets see how may of you can get the right answer. You can enlarge the diagram by clicking enlarge. Please post your answer here at the forum. Good luck.

    electric.jpg - Image - Photobucket - Video and Image Hosting

    electricLou

  • #2
    Re: What Is The Answer?

    I'm not an electrician but I'm guessing (b), lights go dim, but not out.
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    A good climbing rope will last you 3 to 5 years, a bad climbing rope will last you a life time !!!

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    • #3
      Re: What Is The Answer?

      A) Strange panel. Two phase? I think you really mean leg A and leg B in a single phase panel.

      B) Cut the neutral as shown and the circuits become 220V with a resistor (the bulbs). The bulbs will get brighter until they burn out. The correct answer is a.

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      • #4
        Re: What Is The Answer?

        E, none of the above.
        You will see no difference in the brightness of the bulbs. In fact you could put a switch at X and you would not be able to tell when it was open or closed. This only works because the resistance of the bulbs is identical so the voltage drop across them will be 120V each.

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        • #5
          Re: What Is The Answer?

          I'm with wbrooks

          because bulbs are same resistance and voltage is doubled there is no difference...

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          • #6
            Re: What Is The Answer?

            Problem

            Is this a 3 phase system but only using 2 phases, or is it a single phase system with A = L1 and B = L2 ?

            I want to see more to this diagram. What exactly is the power source?

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            • #7
              Re: What Is The Answer?

              I'm going to say: b) the lights will dim

              The diagram is definitely strange, but if you cut the neutral at that spot, it now places the light bulbs in series with each other. It doesn't make a difference what their wattage is. In series, you would add the resistance of both bulbs to the circuit and the drop in amperage will effect the voltage and the brightness of the bulbs.

              CWS

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              • #8
                Re: What Is The Answer?

                I would agree with brooks, if it is a 240 volt single phase system, or a 240 volt delta three phase.

                If the bulbs are the same resistance, the neutral wire would not be carrying any load as the two feeds are balanced,
                The load is the same and it is balanced, If you put two 120 volt bulbs in series in a 240 volt circuit it would be the same difference, (but with out the neutral).

                Depending on the system you may have 208 volts instead of 240 volts.

                now if it is derived from a Y three phase 208 volt they probly would dim, some.
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                • #9
                  Re: What Is The Answer?

                  Well electriclou, whats your answer??
                  Great Link for a Construction Owner/Tradesmen, and just say Garager sent you....

                  http://www.contractorspub.com

                  A good climbing rope will last you 3 to 5 years, a bad climbing rope will last you a life time !!!

                  Comment


                  • #10
                    Re: What Is The Answer?

                    Since the voltage between Phase A and Neutral and Phase B and Neutral are the same, the voltage between phase A and Phacse B is double of what it would be between each of the Phases and Neutral.

                    As the bulbs are identical (both 100W), when Neutral gets disconnected they become connected serially between the two phases.

                    Therefore the bulbs will be burning with the exact same intensity as when Neutral was connected, so none of the above is the correct answer.
                    Last edited by fkaufman; 03-18-2007, 09:37 AM. Reason: correct spelling
                    Frank sigpic

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                    • #11
                      Re: What Is The Answer?

                      if you want my answer it willbe E because the netural will be cut off at the place where it marked " X " and both bulb are same wattage and same manufacter it will show the same brightness in series baised off the single phase supply but if off on 3 phase wye connection supply it will slightly dimmer but not a whole alot on delta system it can be very unpreditale depending on which leg it ran


                      Merci , Marc

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                      • #12
                        Re: What Is The Answer?

                        It is a complete circuit under load , so "E" should be the
                        correct answer. of course if one of the bulbs are removed or blows out
                        the other will also go out.

                        Do we get a prize for the right answer?

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                        • #13
                          Re: What Is The Answer?

                          I figured it looked like a house panel but lets explore the other possibilities
                          Delta - has to be a center taped 4 wire lighting transformer otherwise the only ground would be a safety ground and we have to assume the common to be ground. Phase A and Phase B would have to be either side of the center tap (Phase C would be the wild leg with 1.73 X Vtap so not used for lights).
                          With the ground connected each light would see half of phase AB, drop the ground and each light would see half of phase AB because they are the same wattage and will divide the voltage equally so there is no change in brightness.

                          In a Y transformer lets assume we have a phase to neutral voltage of 120 V
                          So with the ground connected each light sees 120V. If we drop the neutral the lights will now be across Phase AB which is 208 (120 X 1.732) so each light will see 104 Volts and may appear slightly dimmer.
                          Attached Files

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                          • #14
                            Re: What Is The Answer?

                            I was gonna say E but then again I'm no electrician and haven't slightest idea about phase A and B. I thought at first it was a simple 120v circuit but then it wouldn't make sense to wire a light set like that. So...... I don't know!!!1

                            DAN

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                            • #15
                              Re: What Is The Answer?

                              After thinking more about this, I can figure where several answers could be correct. Who said that this is a normal power system? With a transformer that has 2 or more secondary windings (or a single one with taps where N is not centered) and one primary winding it is possible to not have anywhere near the same Voltage from neutral to A as from neutral to B. Also, they could be connected in some wild ways not shown. Let's see the total picture, please.

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