250A, 400A and 630A are the three most commonly used ratings for MCCBs (moulded case circuit breakers) in industrial power distribution, building main distribution and equipment protection. Using People Electric’s RDM5 series high-breaking-capacity MCCB as a practical example, this article explains a clear, practical selection logic to help engineers and purchasers quickly identify the right model.
Core Selection Principles
1.Rated current (In): Select according to the total load current multiplied by 1.25, matching the power of equipment or circuits.
2.Breaking capacity (Icu/Ics): Choose based on the system short-circuit current to ensure reliable tripping under fault conditions.
3.Number of poles: 2P for single-phase circuits, 3P for three-phase equipment, 4P for three-phase four-wire systems with neutral protection.
4.Protection type: Distribution protection or motor protection, corresponding to different tripping curves.
5.Accessories: Shunt trip, undervoltage release, auxiliary or alarm contacts can be added for remote control and status feedback.
RDM5 Series 250A/400A/630A Application Cases
RDM5-250 (250A Frame)
● Rated current: 100–250A
● Breaking capacity (AC400V): Icu 35–50kA, Ics 25–35kA
● Typical applications: Branch distribution in small and medium factories, three-phase motors (fans, pumps, air compressors), small PV box-type substations
● Selection tips: Priority to 3P/4P with thermal-magnetic release; motor protection version for motor loads, with optional auxiliary/alarm contacts.
RDM5-400 (400A Frame)
● Rated current: 200–400A
● Breaking capacity (AC400V): Icu 50–70kA, Ics 35–50kA; Icu 20–25kA at AC690V
● Typical applications: Main distribution in workshops, medium-sized data centers, main switches in commercial buildings
● Selection tips: Recommended 3P/4P with M-type (medium breaking); H-type high-breaking version for larger systems, with shunt/undervoltage release for remote and undervoltage protection.
RDM5-630 (630A Frame)
● Rated current: 400–630A
● Breaking capacity (AC400V): Icu 50–100kA, Ics 50–75kA; Icu 20–35kA at AC690V
● Typical applications: Main incoming of large equipment, low-voltage outgoing in substations, industrial bus coupler circuits
● Selection tips: Priority to 3P/4P with H-type high-breaking capacity; essential auxiliary/alarm contacts for critical circuits, available in fixed and draw-out versions.
Quick Selection Summary
● 250A: Small and medium loads / branch distribution → RDM5-250
● 400A: Medium main distribution / building main switch → RDM5-400
● 630A: High-current main incoming / critical circuits → RDM5-630
A complete and compliant selection can be made in three steps: match rated current → verify breaking capacity → choose poles and accessories.
Post time: Apr-07-2026
