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Thread: Safely Maximize Power from a 100amp 3-Phase Delta Panel

  1. #21
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    Quote Originally Posted by iwire View Post
    Why are you saying a 100 amp breaker will trip at 80?

    What am I missing?
    Post 11 assumes the breaker will trip at exactly 80 amps in his calculations.
    Tom
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  2. #22
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    Quote Originally Posted by ptonsparky View Post
    Post 11 assumes the breaker will trip at exactly 80 amps in his calculations.
    And that is an incorrect assumption.

    Roger
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  3. #23
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    Quote Originally Posted by ptonsparky View Post
    Post 11 assumes the breaker will trip at exactly 80 amps in his calculations.
    Which make no sense and why I asked about it in post 12.

    Quote Originally Posted by iwire View Post
    Quote Originally Posted by EricJ View Post
    Assuming the breakers will trip at 80% capacity,
    Why are we assuming that? It is not reality.

  4. #24
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    Quote Originally Posted by iwire View Post
    Which make no sense and why I asked about it in post 12.
    Why? Because he doesn't care about reality, only the theoretical at this point.
    Tom
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  5. #25
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    Quote Originally Posted by ptonsparky View Post
    Why? Because he doesn't care about reality, only the theoretical at this point.
    The problem is the assumption that a breaker will trip at some arbitrary level is not theory. The theory problem I see here is that the OP is not seeing that L- L loads are all served by 240V windings and will only see 240V, not 120 or 208.


    Roger
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  6. #26
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    Quote Originally Posted by ptonsparky View Post
    Because he doesn't care about reality, only the theoretical at this point.
    Do you know that? I do not.

    Further I still do not know what the OP means by 'carrying the load safely'.

    Safely to who, to what standard and in what circumstances? I could safely carry 100 amps on 14 AWG under the right conditions.

  7. #27
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    Quote Originally Posted by roger View Post
    The problem is the assumption that a breaker will trip at some arbitrary level is not theory. The theory problem I see here is that the OP is not seeing that L- L loads are all served by 240V windings and will only see 240V, not 120 or 208.


    Roger
    Ok, imaginary, hypothetical?
    Tom
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  8. #28
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    170318-0946 EDT

    EricJ:

    Finally in post #11 you presented your question in a form that can be answered.

    That the panel is from a wild leg delta has nothing to do with the question except that the source is a delta. Actually the source could be a wye and it does not change the answer.

    The answer is obviously 80*138*3 = 11040*3 = 33120 W. Note 138 is a rounded value. The exact value is closer to 138.5641 . Because of this rounding some of the values below are not as close as you might want.

    Two different resistive loads will accomplish this or some combination.

    The possible load configurations are balanced delta or wye.

    In delta each resistor is R = 240^2/11040 = 5.22 ohms. In wye each is R = 138^2/11040 = 1.73 ohms. The two resistance values should be related by 3. So 1.73*3 = 5.18 ohms. Close but not real close.

    If I do the calculation with the full resolution of my HP 32S, then the results are:
    138.5641...
    80*this = 11085.1252...
    Rd = 240/Ipp = 5.1962... ohms.
    Rw = 138...../80 = 1.7321... ohms.
    1.7321...*3 = 5.1962... . Now the check is closer.

    .

  9. #29
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    EricJ:

    What are the classes required for a BSEE today? Back when I went to school we had to cover basics. And then there were two specialty areas, power and electronics-communications.

    The broad outline of common courses was:
    English, math, chemistry, physics, drawing, chem-met, economics, statics, dynamics, strength of materials, fluid mechanics, heat engines, machine design, dc machines and circuits, ac machines and circuits, electricity and magnetism, electromechanics, electrical measurements, ac apparatus, electrical design, electronics and electron tubes. This totaled 120 credit hours. Then there were another 20 credit hours in your speciality.

    Although I have lived within a mile or two of my school ever since graduation I have little contact with with the University as a whole or the EE department. I have no idea what a present class program looks like. Some classes that were basic requirements for us have probably been eliminated and others watered down.

    Today I think 4 years is too short for a good basic education in EE, 6 years might be a better number for a BSEE. Thinking, reasoning, and an education in basic concepts is what I expect of an electrical engineer. Just being able to plug numbers into an equation does not mean the resulting answer is valuable or useful. One has to understand how a particular equation relates to a real world problem.

    .

  10. #30
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    If one had 100 amps of 120 volt load on A, 100 amps of 120 volt load on C and 100 amps of 208 volt load on B, I guess the first approach taken sort of works, the breaker won't care what voltages are or how well the source can handle that type of loading, but it will still see 100 amps per line and will be fine with that, at least before we get into how long it can hold with a continuous 100 amp load.

    Reality is you will have very little if any 208 load connected to the high leg, you may have 120 volt loads connected to A and C, you may have unbalanced 240 volt loads connected between any two phase conductors, and your balanced three phase loads will each draw a factor of 1.732 of the total amps from each phase conductor. The ghost phase of an open delta will not provide any VA to the system, the other two phases will each have to contribute more VA to a balanced three phase load then they would if it were a full delta system.

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