Selective Coordination

A gap between two curves at one current isn't coordination. A gap held across the entire range of possible fault current is.

When a fault occurs anywhere in a distribution system, more than one protective device is technically capable of clearing it — the branch breaker right at the fault, the feeder breaker upstream of it, the main upstream of that. Selective (or "selectively") coordinated protection means only the device closest to the fault opens, leaving every upstream device closed and every other load on the system undisturbed. Non-selective — cascading — coordination means an upstream device trips at the same time as, or even before, the downstream device, needlessly de-energizing a much larger portion of the system for a fault that only ever affected one branch.