Fault current time 1, 3 or 5 sec

[Khaled Abuzaid]

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?

 

[Bystander]

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)?

 

[zoki85]

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?

Required cross section of cable conductor in mm² is :
S = C⋅I_fault⋅√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