Circuit breaker nameplate ratings define capabilities and limitations. Correct understanding prevents undersizing (catastrophic fault failure) and oversizing (wasted budget).
Key Ratings
| Rating | Symbol | Meaning | Typical MV |
|---|---|---|---|
| Rated voltage | Ur | Operating voltage | 12/24/40.5kV |
| Rated current | Ir | Max continuous | 630-4,000A |
| Breaking capacity | Isc | Max fault interrupted | 20-50kA |
| Making capacity | Ima | Max fault closed into | 2.5x breaking |
| Short-time withstand | Ith | Brief fault carry | 20-50kA / 1-3s |
| Mechanical life | M1/M2 | Total operations | 2,000-10,000 |
| Electrical life | E1/E2 | Fault interruptions | 20-50 at rated |
Breaking Capacity
Most critical safety rating. Must equal or exceed prospective fault current at installation. Add 10-20% margin for system growth. NAIJI VCBs: 20-50kA.
Endurance Classes
M1: 2,000 ops (infrequent — main incomers, transformer protection). M2: 10,000 ops (frequent — capacitor switching, auto-transfer). E2: Extended electrical endurance, standard for modern VCBs.
Nameplate Example
VS1-12 / 1250-25 = VS1 model, 12kV, 1,250A, 25kA. NAIJI offers: VS1-12, VN2-24E, VN1-40.5E.
Request a technical consultation — send voltage, fault level, and load current for recommendations.