When sourcing MCBs, you must prioritize the Rated Breaking Capacity (Icn), typically ranging from 6kA to 10kA for standard applications, to ensure the device can interrupt fault currents without failing. Additionally, select the appropriate Tripping Curve (B, C, or D): Curve B is for resistive loads, Curve C (most common) is for inductive loads like motors, and Curve D is for high-inrush current equipment. Ensure the Rated Current (In) matches your circuit requirements to prevent nuisance tripping or fire hazards.