Fault Currents Outside the Model Range in Arc Flash

Question: How does Arc Flash handle bolted fault currents that are out of the model range?


In IEEE 1584 method, PTW uses the Ralph Lee Equation for any parameter that is outside of the range of model (Voltage, Fault Current, Gap):


(1a) PTW Calculation:

(1b) Hand Calculation:

In the NFPA (Doughty Neal) Method, a scale factor is used when the bolted fault current is out of the model range:

Basically, the scale factor is the (Bolted fault/lower or upper limit). The factor was obtained in the Tutorial B presentation in PCIC. (see attached)

Tutorial B Presentation.pdf
1 MB