What is protection selectivity and why you need it

What is selectivity

Protection selectivity is the system's ability to disconnect only the damaged section, leaving everything else energized.

Example without selectivity: short circuit in an outlet → main breaker trips → entire house without power.

Example with selectivity: S/C in an outlet → only that line's group breaker trips → other groups keep working.

1. Current-based — upstream breaker has higher rating

2. Time-based — upstream breaker trips with a delay

3. Energy-based — modern breakers with energy selectivity

GorkyCAD automatically checks selectivity in the panel hierarchy:

1. Builds protection chain from final breaker to main

2. Compares ratings and characteristics (B/C/D)

3. On violation — warning and recommendation

Apartment panel: main C40 → RCD 40A/30mA → group breakers C16.

S/C in outlet (Isc ≈ 200 A): C16 trips in 0.01 s, C40 doesn't react in time. Selectivity achieved.

S/C at input (Isc ≈ 1500 A): both trip. Need to reconsider — e.g., main breaker with D characteristic.