In general, for calculation of downstream fault current (I

_{2}) from known upstream fault current (I

_{1}), the assumption is the line voltage drop is the same in either case, so the relationship exists: I

_{1}* Z

_{1}= I

_{2}* (Z

_{1}+Z

_{2}), which simplifies to I

_{2}= I

_{1}* 1 / (1 + Z

_{2}/Z

_{1}). In the above procedure, 1 / (1 + Z

_{2}/Z

_{1}) corresponds to the M multiplier and Z

_{2}/Z

_{1}corresponds to the f-factor, therefore Z

_{2}/Z

_{1}= (I

_{1}* V

_{1}* 1.732 * %Z) / (100,000 * KVA). Z

_{2}in this case is the impedance of the primary winding, which can be calculated from %Z by Z

_{2}= Z

_{abs}= %Z/100 * Z

_{base}= %Z/100 * V

^{2}* 1.732 / (1000 * S

_{KVA}). Z

_{1}is simply V

_{1}/I

_{1}. Dividing Z

_{2}by Z

_{1 }yields the same formula for the f-factor in the method above. I understand that this method ignores the X/R ratios of the line impedances. My questions:

1. In step C, I

_{1}= I

_{sca(p)}and I

_{2}= M * I

_{sca(p)}. Therefore I

_{2}is the fault current as seen by the primary side of the transformer during a secondary fault, which is then converted to the current on the secondary using the standard transformer conversion formula. Does this mean that I

_{2}would be the value I use to determine clearing time on the primary OCPD for arc flash purposes?

2. Step C does not use any efficiency or power factor for conversion. I can get efficiency and X/R ratios from the transformers here. In fault current situations, are these adjustments typically used?