Overload (L)
Short-time (S)
Instantaneous (I)
TCC curve
Your fault current
Trip time
clearing time
Zone
L · S · I
Arc exposure
Zone L — overload
Slow thermal response. The breaker waits seconds or minutes. Motors need this patience to start.
Zone S — short-time
Intentional delay lets the nearest downstream breaker trip first. This is selective coordination.
Zone I — instantaneous
One electrical cycle — 16 ms. No delay. This zone sets the cal/cm² on the arc flash label.