What this MCCB is and what it carries
The Siemens 3VA1112-3EF36-0CA0 is a SENTRON molded case circuit breaker (MCCB) built for line protection in distribution panels. It's a 3-pole unit rated for 125 A continuous current at 40 °C — and it holds that 125 A all the way up to 50 °C before it starts to derate, so you get the full rating in most ventilated enclosures. The thermal-magnetic release is a TM240, which means the thermal pickup is fixed and the magnetic short-circuit trip is adjustable. Breaking capacity runs 75.6 kA at 240 V, 52.5 kA at 415 V, 32 kA at 440 V, and 10.5 kA at 690 V — that's a lot of headroom for a 125 A frame, especially on the common 415 V industrial bus. Out here in the grease, that SCCR spread means you can put this breaker upstream of a motor control center and not worry about cascading faults.
Ratings that decide the fit
The 125 A continuous rating is the number that locks in your feeder size. It's not a peak — it's the Iu, the rated uninterrupted current the breaker can carry without tripping. The thermal derating curve is gentle: 125 A through 50 °C, then 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 runs hot near the top of the enclosure, you still get 112 A out of it. The insulation rating is 800 V, which covers 480 V and 600 V class systems with plenty of margin. The IP40 front protection means it's fine in a clean indoor panel but not for washdown areas — keep it behind a gland plate.
Undervoltage release and auxiliary options
This 3VA1112-3EF36-0CA0 comes with an integrated undervoltage release (UVR) — the design is a dedicated undervoltage release, part of the auxiliary release set. That UVR will trip the breaker if the control voltage drops below a set threshold, which is common for emergency-stop circuits or upstream loss-of-mains protection. There's no auxiliary contact version on this variant, so if you need a status feedback contact for a PLC or a remote indication, you'll add one externally. The integrated auxiliary trip is listed as 3VA9608-0BB24 — that's the factory-fit shunt trip or UVR module if you need to change it later.
Panel fit — dimensions and mounting
The breaker measures 130 mm high, 76.2 mm wide (that's 3 inches exactly — standard for a 3-pole MCCB frame), and 70 mm deep. The 70 mm depth is the body depth behind the panel face; it fits in most 8-inch deep enclosures with room for wiring gutters. Three-pole, screw-clamp terminals, line and load lugs are standard. If you're swapping this into a panel that was laid out for a different 3-pole MCCB, check the 76.2 mm width first — that's the mounting centers for the bus bars or the DIN-rail adapter.