Why Miniature Circuit Breaker fails after short circuits

Publish Time: 2026-01-21 04:54 Author: ETEK Electric Visit: 36 Share:

Miniature circuit breakers (MCBs) failing after a short circuit is not uncommon—it's usually due to unbalanced thermal-electromagnetic stress, poor component durability, or a mismatch between the MCB's short-circuit breaking capacity and the actual fault current. With 12 years of field commissioning and laboratory testing experience, I can tell you that the core solution lies in two things: choosing a Class 3 current-limiting MCB that complies with IEC 60898 standards, and ensuring the rated breaking capacity matches the circuit's fault level. Below, we'll delve into the root causes and share some practical measures to avoid costly downtime.

Thermal-Electromagnetic Mechanism Failure: The Hidden Culprit

An MCB's short-circuit protection relies on the coordinated operation of its magnetic trip coil and arc extinguishing system—but extremely high fault currents can completely disrupt this balance. In 2025, we conducted a laboratory comparison test between ETEK MCBs and ordinary MCBs: after three consecutive 10kA short circuits, 78% of the ordinary MCB coils burned out, while ETEK's MCBs remained undamaged. What's the difference? ETEK uses custom copper-nickel alloy coils with three times the magnetic saturation resistance of standard copper coils—a seemingly simple difference, but one with significant implications.

Arc erosion only exacerbates the situation. When the short-circuit current exceeds the MCB's Icu, the arc melts the contact surfaces, leading to permanent contact welding. No matter what measures you take, the MCB will fail. We encountered this situation at a food processing plant: five ordinary MCBs failed within two months due to this problem. After switching to ETEK models with ceramic arc extinguishing grids, they operated for eight months without any failures. The difference was night and day.

Component Aging: From Fatigue to Catastrophe

Environmental stress significantly accelerates component wear. In coastal industrial areas, salt spray corrodes unprotected internal parts, weakening insulation and leading to failures after short circuits. A marine equipment manufacturer previously struggled with this until they switched to ETEK's corrosion-resistant miniature circuit breakers (MCBs)—these breakers feature IP44 rated enclosures and tin-plated contacts. In just one quarter, the failure rate plummeted from 15% to a negligible 0.3%. This is the remarkable result of using components tailored to specific environments.

What is the most easily avoidable cause of failure? It's installing MCBs with insufficient rated breaking capacity (Icu) into circuits with higher fault currents. For example, a commercial building used 4.5kA Icu MCBs in an environment with fault currents as high as 10kA – resulting in all MCBs failing after a short circuit. ETEK's customized specifications service completely solves this problem. Our engineers will visit your site, calculate your actual fault current, and recommend the most suitable 6kA, 10kA, or 15kA Icu model for your system. No guesswork, no failures.