Time-Current Curves

[timm33333]

I’ve question about doing coordination in ETAP. When we lump together several loads, is there a way to do the combined coordination of the lumped load?

For example if an LV (low voltage) MCC has 10 loads, a main breaker, and an upstream MV (medium voltage) fuse. We can show that the devices coordinate if the TCC (time current curve) of the MV fuse is at the far right, the TCC of the main breaker is to the left of the TCC of the fuse, and the TCC's of all 10 load breakers are to the left of the TCC of the main breaker.

Now we combine 10 loads into one lumped load, the breakers of all loads are of different sizes but they are of the same make and model. Maybe I can draw the TCC of one breaker only (instead of 10) which will represent the TCC of all 10 breakers?

 

[davidbeach]

Use the highest set, slowest tripping breaker of the load breakers. Or, it could be that you need two or three of them to generate the composite slowest load breaker. If that coordinates, then the lower, faster, breakers will have to coordinate.