In the prevouis Topic “Selective Coordination Tools and Spreadsheets – Part One”, I showed that our study for selective Coordination will be based on the following main parts:
Part One: What is selective coordination?
Part Two: NEC code and Selective Coordination
Part Three: Method of performing a selectivity coordination study
First: By using Selective Coordination Time – Current Curves
Second: By using Selective Coordination Charts/Tables.
Third: By using Siemens calculators / spreadsheets.
in this previous Topic, we covered part one, part two and the first method of performing a selectivity coordination study By using Selective Coordination Time – Current Curves.
today, I will continue explaining other Methods of performing a selectivity coordination study as follows:
Second: performing a selectivity coordination studyBy using Selective Coordination Charts/Tables
Charts are available which list, in varying styles, breakers that selectively coordinate with other breakers at specific available fault current levels. An advantage of the charts is that they are often more accurate than curve comparisons as they are based on more specific test data derived for selective coordination. If there is disagreement between overlaid curves and charts, the chart data should be used.
The following steps will assure the best use of the Selective Trip Coordination Table:
1. Conduct a short circuit study to determine the available fault current values at each level of the system where coordination is critical by using the Estimated Available Fault Current Calculator or any other Tool/Software.