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208V low arc current long clearing time

Discussion in 'System Modeling and Calculations' started by alb, May 27, 2010.

  1. alb New Member

    I am reviewing an arc flash study with several low voltage (208) panelboards that have a low calculated arc current, less than 3000A, with long clearing times, 2 seconds or more. This is resulting in high energy and Cat #3 or #4 PPE. Are these calculations reasonable? Will that low a voltage and current even sustain an arc? Most of these currents are below the current calculated from a 112.5 kVA transformer which can be ignored at 208V. Any thoughts would be appreciated.

    Thanks
    alb, May 27, 2010
    #1

  2. brainfiller Administrator

    You will find numerous posts about this on the forum. Here is a short summary:

    The "less than 125 kVA" limit was initally used in IEEE 1584. Later, a few concerns arose about its validity. A few people (I'm one of them) have been involved in testing.

    It looks like eventually the cut off will be based on short circuit current not kVA and from what I have been involved with it will be much lower than the current from a 112.5 kVA transformer.

    I am now the task group leader for this with IEEE 1584 and it is formally being reviewed.

    You will find more detail throughout the forum.

    Good Luck, Let me know if you have any more questions.
    brainfiller, May 28, 2010
    #2

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