There is an interesting glitch with the IEEE 1584 equation for arcing short circuit current at or above 1 kV.
The equation for arcing current at higher voltages > 1 kV:
Log Ia = 0.00402 + [0.983 (Log Ibf)]
Ia = 10^(Log Ia)
Where:
Ibf = 3 phase bolted short circuit current in kA
Ia = 3 phase arcing short circuit current
IEEE range of validity 700A to 106 kA
Here’s the glitch. If the bolted current is 1,000 Amps i.e. 1 kA:
Log Ia = 0.00402 + 0.983 X Log (1)
Log of 1 = 0
Therefore:
Log Ia = 0.00402 + 0.983 X 0
Log Ia = 0.00402 + 0
Log Ia = 0.00402
Ia = 10^(Log Ia)
Ia = 10^0.00402 = 1.0093 kA
So….. Ibolted = 1,000 Amps and Iarcing =1,009.3 Amps
Except it is physically impossible to have Iarcing greater than Ibolted.
Oops!
