Voltage Rating Match the breaker's voltage capacity (AC/DC) to your system's operating voltage (e.g., 230V AC or 1000V DC for solar). Ensure compliance with local/national standards (IEC, UL, etc.). Current Rating Select a current rating slightly higher than the circuit's max load (e.g., 125% of continuous current). For motors/transformers, account for inrush currents (use D-curve for high inrush). Pole Configuration Choose 1P (single-phase), 2P/3P (split-phase/three-phase), or 4P (three-phase + neutral) based on system design. Breaking Capacity Ensure the breaker's short-circuit rating (e.g., 10kA, 25kA) exceeds your system's fault current. Trip Characteristics B-curve: Residential/light commercial (3-5× In). C-curve: Commercial/industrial (5-10× In). D-curve: High inrush loads (10-20× In). Application-Specific Needs Solar PV: DC-rated breakers (e.g., 1000V DC). Motors: Thermal-magnetic breakers for overload/short-circuit. Critical systems: AFCI/GFCI for added protection. Environmental Factors Outdoor use: IP65-rated for dust/water resistance. High temps: Verify ambient temperature derating. Pro Tip: Always consult manufacturer datasheets and local electrical codes (e.g., NEC, IEC 60898). For complex systems, involve a certified electrician.