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Fault current time 1, 3 or 5 sec

  1. Nov 15, 2014 #1
    Any idea how can we decide on the fault current time 1, 3 or 5 sec. for grounding cable sizing? Also, what is the related temperature to the selected timing?
    Last edited by a moderator: Nov 15, 2014
  2. jcsd
  3. Nov 15, 2014 #2


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    How much reactive energy are you going to be dumping from which parts of your system during an event (short circuit plus time to open a breaker)? What is the fusion current for the conductor chosen? What is the heat capacity of the conductor (how long at fusion current to melt)?
  4. Nov 16, 2014 #3
    Required cross section of cable conductor in mm2 is :
    S = C⋅Ifault⋅√t
    C...constant depending on material, type and design of a cable
    I... RMS value of fault current in kA during fault time
    t... fault time in seconds
    Temperature increase allowed is typicaly Δϑ= 100-150 °C
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