Line Protection MCCB with Undervoltage Release
The Siemens SENTRON 3VA1050-4ED42-0BC0 is a 4-pole molded case circuit breaker rated for 50 A continuous current (Iu) and a rated insulation voltage of 800 V. It carries a TM210 thermal-magnetic overcurrent release, meaning the thermal element handles overloads and the magnetic element handles short-circuit trips — no electronic adjustment, just fixed-curve protection for straightforward line-feeder duty. The 121 kA breaking capacity at 240 V gives headroom for high-fault installations; at 415 V it still interrupts 75.6 kA, and at 690 V it holds 11.9 kA. This version ships with an undervoltage release (UVR) integrated, so the breaker trips immediately if supply voltage drops below a threshold — common on safety circuits or emergency-stop chains where loss of control voltage must open the main power path. The auxiliary contact package is two HQ (high-auxiliary) switches, giving status feedback to a PLC or SCADA without an add-on module.
Thermal Derating and Panel Fit
The 50 A rating holds flat from 40 °C to 50 °C ambient, then derates to 48 A at 55 °C, 47 A at 60 °C, 46 A at 65 °C, and 45 A at 70 °C. In a sealed panel with multiple breakers ganged, the 70 °C derating figure (45 A) is the realistic continuous limit — plan for that if the enclosure runs hot. The operating temperature range is -25 °C to 70 °C; storage range extends to -40 °C to 80 °C. Dimensions are 70 mm deep, 101.6 mm wide, and 130 mm high — a standard 4-pole MCCB footprint for DIN-rail or screw-mount panel integration. Front protection is IP40, so it's fine for a clean indoor panel but not washdown areas.