125 A MCCB with TM240 release — what the ratings mean for panel fit
The Siemens SENTRON 3VA1112-4EF36-0CA0 is a 3-pole molded case circuit breaker rated for 125 A continuous current at 40 °C, meaning it handles that load without derating in a typical 40 °C panel ambient. The TM240 thermal-magnetic release provides fixed thermal and magnetic trip curves — no adjustment dials, which simplifies ordering but means you select the exact frame for the load. The interrupting capacity hits 121 kA at 240 VAC, 75.6 kA at 415 VAC, and still delivers 52.5 kA at 440 VAC; that 121 kA figure at 240 V is the headline number for high-fault panels downstream of large transformers. The 800 V rated insulation voltage (Ui) tells you the breaker's internal clearance and creepage are designed for 800 V systems, even though the interrupting ratings top out at 690 V. The undervoltage release (UVR) is factory-fitted — if the control voltage drops, the breaker trips open, which is standard for emergency-stop circuits or loss-of-mains protection in motor control centers.
Footprint and panel integration
The 3VA1112-4EF36-0CA0 measures 70 mm deep by 76.2 mm wide by 130 mm tall — a compact 3-pole frame that fits standard SENTRON mounting plates and busbar systems. The IP40 front protection means it's fine inside a closed panel; not rated for washdown or outdoor exposure without an enclosure. The 15 000 mechanical endurance cycles cover the typical switching life for a line-protection breaker in a distribution board.
Thermal derating curve — the real-world current limit
The 125 A rating holds flat from 40 °C to 50 °C. Above that, the breaker derates: 120 A at 55 °C, 117.5 A at 60 °C, 115 A at 65 °C, and 112.5 A at 70 °C. If your panel ambient runs above 50 °C — say, a non-ventilated enclosure near a furnace line — you need to factor that 10 A drop at the top end. The operating temperature range is -25 °C to 70 °C; storage range is -40 °C to 80 °C.