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  1. schan05

    Short Circuit Rating

    Thanks for the helps.
  2. schan05

    Short Circuit Rating

    When we talk about SC rating of a piece of electrical equipment, such as switchboard, it is not quantified with a maximum allowable time duration. However, when we apply the insulated power breakers in low voltage power distribution switchboard, those power breakers could withstand SC up to 0.5...
  3. schan05

    Motor switch size

    William, how was 700A breaker considered? can you please enlight me on that? thanks.
  4. schan05

    Motor switch size

    Thanks.
  5. schan05

    Motor switch size

    VFDs don't have manual bypass. I believe 175% is the maximum allowable rating for the dual element fuses for normal starting motors. Is it specifically spelled on the NEC that existing equipment need not to be retrofitted for GFP? I couldn't find it on my handbook. Thanks for your time.
  6. schan05

    Motor switch size

    rbulsara, my apology for not mentioning this earlier, this is an older building with old electrical distribution system, the upstream or electric service switch doesn't have any GFP. Also, in your opinion, should the fusible switchs I mentioned earlier be at least 125% rated in order to...
  7. schan05

    Motor switch size

    What about NEC 215.10 Ground Fault Protection for equipment? I thought that would apply here. Please clarify for me. Thanks.
  8. schan05

    Motor switch size

    We are installed three motors with 650A FLA @ 460V, each motor is to be controlled by a VFD within motor vicinity, and there are two old 3p/1600A fusible switches available on the distribution switchboard, neither switch is equipped with GF protection. I am thinking of two options, one is to...
  9. schan05

    Any ill effect of different length cable

    Thanks for the explanation.
  10. schan05

    Any ill effect of different length cable

    load is around 420A, 4160V, 3Ph, 60Hz AC, 3-1/c, 750kcmil copper, 5.5kV rated copper tape shielded cable, the total legth is about 1000 feet, length difference is approximately 5-7%. Thanks.
  11. schan05

    Any ill effect of different length cable

    One important clarification: both sets are run in parallel from one source and to the same load.
  12. schan05

    Any ill effect of different length cable

    I am running two of sets of same type medium voltage cable with same rated capacity, but, take 2 separate routing paths, resulting in different length and therefore different impedance, how will this impact its overall performance under normal opearting and fault conditions? thanks.
  13. schan05

    motor starting simulation

    Thanks.
  14. schan05

    motor starting simulation

    I am using SKM sofoware to plot motor starting curve for TCC with an closed-transition autotransfomer starter @ 65% tap. At around 5", there is a current spike all the way approaching LRC level, and then graduately drops down to FLC level in 6 next seconds. The spike might be shorting contacts...
  15. schan05

    TCC Setting

    It worked as your described, really appreciate your help.
  16. schan05

    TCC Setting

    Most TCC charts that I have seen so far have upper limits of 10,000A and 1,000 seconds on the current and time axies respectively. Is there particular reason for this? If I need to model a power breaker with higher short time and instantaneous rating (say 3000a or 5000a power circuit breaker)...
  17. schan05

    How to determind need of power factor correction?

    Thank you all.
  18. schan05

    How to determind need of power factor correction?

    Out plant is putting in a 1600HP electric chiller, connected to 4.16kV distribution system with autotransformer starter. Should we consider power factor correction for this installation? If so, what are the major issues we should cover while doing calculations? Many thanks.

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