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Thread: test questions

  1. #11
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    Quote Originally Posted by infinity View Post
    I would guess that the answer undefined wasn't on the test so you would need to look for the theoretical answer which should be 0 since it says that it's ungrounded.
    That's not the theoretical answer. 0V says that they are at the same potential, i.e., the conductor on which you are measuring the voltage to ground is grounded.

  2. #12
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    Question 3, this may help
    pg 4, fig 6-6
    http://static.schneider-electric.us/...tion6_0307.pdf



  3. #13
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    Quote Originally Posted by ggunn View Post
    That's not the theoretical answer. 0V says that they are at the same potential, i.e., the conductor on which you are measuring the voltage to ground is grounded.
    So if I take my Wiggy and go from any phase to ground it will read what? In my mind the author of the question was thinking ungrounded = 0 volt to ground from the B phase. If we knew the answer choices that would clear it up.
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

  4. #14
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    Quote Originally Posted by infinity View Post
    So if I take my Wiggy and go from any phase to ground it will read what?
    Very likely a different reading then if you had a high impedance meter.

  5. #15
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    Normal stray capacitance will cause the ungrounded three phase to float very close to ground.
    For an ungrounded 240V delta, A, B, and C will be about 139V to ground on a high impedance meter.

    Sent from my XT1585 using Tapatalk

  6. #16
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    Quote Originally Posted by GoldDigger View Post
    Normal stray capacitance will cause the ungrounded three phase to float very close to ground.
    For an ungrounded 240V delta, A, B, and C will be about 139V to ground on a high impedance meter.

    Sent from my XT1585 using Tapatalk

    The link I posted gives a good explanation



  7. #17
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    Quote Originally Posted by infinity View Post
    So if I take my Wiggy and go from any phase to ground it will read what? In my mind the author of the question was thinking ungrounded = 0 volt to ground from the B phase. If we knew the answer choices that would clear it up.
    Cant recall exactly, but i do remember 0, 240 & 208 being choices. I went back and forth between 0 & 208, finally choosing 208 because there would have to be some kind of grounding system, whether it terminated in xo of that secondary, the primary, or ges to the service. At least that was my thinking, under the gun, at the time. Thanks for the great responses.

  8. #18
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    240/sqrt3=139.
    cant recall if that was a choice.
    thanks ingenieur!

  9. #19
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    conductor parallel . queston #4

    Quote Originally Posted by gunpowder View Post
    4. What's smallest size conductor allowed in parallel? I chose 1/0, but couldn't also be 6awg for gec?

    Sent from my SAMSUNG-SM-G891A using Tapatalk
    The smallest conductor allowed in parallel is 20 awg.

  10. #20
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    Quote Originally Posted by domnic View Post
    The smallest conductor allowed in parallel is 20 awg.
    Maybe some esoteric rule or exception says that, but most tests would want 1/0 per 310.10(H).
    "Electricity is really just organized lightning." George Carlin


    Derek

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