Page 2 of 2 FirstFirst 12
Results 11 to 14 of 14

Thread: Arc-Flash: Proper I for determining Ct of Upstream OCPD

  1. #11
    Join Date
    Jan 2016
    Location
    PA
    Posts
    3,763
    Quote Originally Posted by GoldDigger View Post

    If you do not have a transmission line of sufficient length (1 nanosecond per foot, roughly) the energy available from any possible short circuit impedance change will not be significant at the time scale of cycles of 60Hz.
    Hard to judge without ckt parameters
    fault f = 1/(2Pi (LC)^2) could be several 100 Hz
    surge Z = (L/C)^2
    vel of prop = 1/(LC)^2, but usually 1/2 or so of c

    but in the scale of bldg wiring moot
    not familiar with arc flash calc, may be required?



  2. #12
    Join Date
    Oct 2016
    Location
    Cleveland, Ohio
    Posts
    72
    Transmission line discussion is way over my head.

    Where are we on the original question ?

  3. #13
    Join Date
    Feb 2003
    Location
    Wisconsin
    Posts
    9,786
    Quote Originally Posted by MyCleveland View Post
    Where are we on the original question ?
    You do not need to consider any 'reflected values'. The person that first mentioned this condition went on to say they were not familiar with arc flash calculations.

    Determine your bolted fault current. Use an industry accept methodology, like IEEE1584, to determine your arcing fault current. Use the arcing fault current to determine your operating time. Use the arcing current and opening time to determine your incident energy. Multiple calculations are likely required in order to cover device and system tolerances.
    Just because you can, doesn't mean you should.

  4. #14
    Join Date
    Oct 2016
    Location
    Cleveland, Ohio
    Posts
    72
    Thanks Jim
    Embarrassed here....have been so wrapped up in coding, I neglected to draw out a simple cct diagram.
    Sorry for the waste of everyone's time.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •