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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?
Answer:
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):

Sample:
(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)


Answer:
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):
Sample:
(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)
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Tutorial B Presentation.pdf 1.4 MB |