This from Appendix D EIDG and relates to a method of assessing the impact on R and X values when using steel conduit as the cpc. I thought that the fault current was the principle consideration and not the design current. It does make a difference as the earth loop impedance calculated in an example earlier in the guide would have been less, albeit not by much.
This is just for academic purposes in preparation for an upcoming 2396 course I will be taking.
This is the calculation on page 90 of the EIDG. Third row from bottom. The calculation set out to the left is obviously incorrect but the sums to the right are correct but use Ib rather than If. Had If been used, Zef would have been 0.48 rather than 0.59.
Edit; perhaps what I should say is that the figures in the calculation to the left are the r and x for 25mm diameter steel conduit but clearly the calculation to the right is not the direct answer. The figures to the right have been adjusted using F1 and F2 factors for an Ib of less than 100A as a 32A CB is used. However, F1 and F2 would be less if a If of more than 100A was used instead of Ib.
Maybe GK could pop a comment.
