125 A MCCB with shunt trip — what the ratings mean for fit
The Siemens 3VA1225-5FF42-0HC0 is a SENTRON molded case circuit breaker rated at 125 A continuous, 4-pole, designed for line protection in distribution panels. The 125 A rating is fixed — not adjustable — so the breaker is sized for a specific feeder or main that draws that current continuously. The interrupting ratings climb to 187 kA at 240 V and 121 kA at 415 V, dropping to 30 kA at 500 V and 17 kA at 690 V — these are the fault currents the breaker can safely clear at each voltage level, which governs where it can be placed in the fault-current hierarchy of the panel. The thermal derating curve is published: full 250 A rating holds up through 50 °C ambient, then tapers to 243 A at 55 °C, 237 A at 60 °C, 230 A at 65 °C, and 223 A at 70 °C. If the breaker lives in a hot enclosure — say, near a transformer or in a non-ventilated cabinet — that derating matters for coordination with downstream devices. The insulation voltage is rated 800 V, so it can be used on 480/277 V or 600 V systems without derating the insulation.
Integrated shunt trip and auxiliary switches
This variant ships with a shunt trip (STL) release and two auxiliary switches HQ factory-installed. The shunt trip allows remote tripping via a control voltage — useful for emergency-stop circuits or supervisory shutdown. The two auxiliary switches provide status feedback (open/closed) to a PLC or indicator lamp. No undervoltage release is fitted on this order code; if UVR is needed, that is a different variant. The breaker measures 70 mm deep by 140 mm wide by 158 mm high — standard 4-pole MCCB footprint for a 125 A frame. It mounts into the panel via the SENTRON base plate or direct screw-mount; no DIN-rail adapter is used for this frame size. The power loss at full load is 57 W, which should be factored into enclosure thermal calculations.
Selectivity and coordination notes
For a site electrical engineer planning selectivity: the 125 A fixed rating and the published SCCR curves at 240 V (187 kA), 415 V (121 kA), 440 V (75.6 kA), 500 V (30 kA), and 690 V (17 kA) allow coordination with upstream breakers. The line-protection design means it is optimized for feeder or main protection, not motor-starting duty — no adjustable thermal or magnetic settings are available on this fixed-trip variant. The operating temperature range is -25 °C to 70 °C, with storage from -40 °C to 80 °C.