1. Rated limit short-circuit breaking capacity (Icu):
The circuit breaker has two breaking capacity indices:
● Rated limit short-circuit breaking capacity (Icu)
● Rated operational short-circuit breaking capacity (Ics)
Ics is not only a breaking capacity parameter but also a durability index, indicating normal operation after multiple short-circuit faults
2. Overcurrent protection performance:
During short-circuit events:
● Contacts separate rapidly to create arc resistance
● Faster interruption brings Ics closer to Icu value
● Reduces electromagnetic/thermal stresses on equipment
3. Short-circuit protection:
● Instantaneous trip for fault currents
● Preset values must be adjusted after load changes to:
● Avoid nuisance tripping (too low)
● Ensure adequate protection (too high)
4. Overload time-delay protection:
● Triggers when current exceeds equipment limits
● Allows thermal accumulation period
● Ineffective against short-term surges
5. Safety protection:
● Post-interruption leakage current control
● Human safety threshold: <30mA
● Hazard threshold: >300mA for 2 hours (insulation damage risk)