x/r and MVA Info From SDG&E
x/r and MVA Info From SDG&E
Thank you for your responses. I am doing a short circuit analysis. I have seen tables recommending x/r values of 2 to 12 for power supplied over long transmission lines. So an x/r value of 8 would be a good conservative approach Ron.
Also, this study is for an existing electrical installation that I have been hired to perform inspection and maintenance for. I have done the calcs for this facility using the simplistic method of "f" factor and "M" multiplier. All the equipment ratings are fine. But I would bet that, using a more realistic method that takes into account asymmetrical short circuit currents, that the 10k rated CB's in at least one of the panels will "flunk". Now, the City of San Diego electrical inspector would require SSC calcs if this were a new installation, but they would accept the simplistic method I described above. So, as far as the AHJ is concerned all would be fine. The least expensive "fix" in this scenario would be to replace the panel feeder breaker with one that is series rated for the panel breakers. But the only question my client will have is, "Is it safe as it is." In light of the lack of input from the utility, my report would recommend that the breaker be replaced. Thoughts?