Circuit Breaker Coordiantion

[living2learn]

I am coordinating some awesome IAC53B relays. I have attached the graphs. My question is are these coordinated, and at what levels? I know circuit 1 instantaneous will open up above 3200 amps, but if I have a fault greater than 10152 Amps that my main relay is set to, both units will operate?

So I am coordianted as long as the fault is below 10,152 amps in the instantaneous portion?

 

[davidbeach]

Yep, they'll both operate for a fault on CKT #1 or CKT #2 that exceeds the instantaneous value of the main.

 

[LionelHutz]

Yes, both operate above 10152A. Typically, you make the curve of the main turn dirctly right a few cycles from instaneous so that the branch circuits first have an opportunity to clear. In other words, the main doesn't have a true instantaneous trip but rather a short delay before any trip.