As I mentioned in my last entry about SC, there are a couple of methods that are most common for figuring out proper selective coordination. With any of these, the results should be interpreted correctly by a qualified individual.

 

1. Short-circuit current calculation study: This method is appropriate if circuit breakers are being used. It involves plotting time-current characteristic curves and then interpreting that data properly. An engineer can look at this information and determine whether or not selective coordination has been achieved.

 

2. Adhering to selectivity ratios: You'll go this route if fuses are being used. Just use fuse types and ampere ratings that adhere to the particular manufacturer's selectivity ratios. This is the easier method of the two.

 

Cooper Bussmann, however, makes it even easier to design and install systems with proper selective coordination. They publish Fuse Selectivity Ratio Tables for people to refer to. All that's required is that you make sure all fuse types and ampere rating ratios for the mains, feeders and branch circuits meet or exceed these listed selectivity ratios. You then can leave fuses where they are or adjust things accordingly. There's nothing else to analyze, and no other settings to tweak with!

 

If you'd like to get an even better grasp on Bussmann's method for meeting SC, you can read more detailed information here: