What it is and what it does
The Siemens SENTRON 3VA1112-4EF36-0AF0 is a 3-pole molded case circuit breaker (MCCB) rated for line protection in distribution panels. It carries a continuous current rating of 125 A at 40 °C, with minimal thermal derating up to 70 °C — still delivering 114 A at the top of the operating range. The TM240 thermal-magnetic release handles overload and short-circuit protection without an electronic trip unit, keeping the design simple and field-replaceable. Breaking capacity is the headline number for this class: 121 kA at 240 V AC, 75.6 kA at 415 V, 52.5 kA at 440 V, and 11.9 kA at both 500 V and 690 V. The 121 kA figure at 240 V means it can safely interrupt a fault current up to that level without cascading upstream — critical for high-fault panels near large transformers or service entrances. Rated insulation voltage is 800 V, so it handles 480 V and 600 V class systems with headroom. The breaker ships with one auxiliary switch and one trip alarm switch (HQ configuration) factory-installed, giving a dry-contact status signal for PLC or annunciator inputs. A mechanical trip indicator is present on the front face — no undervoltage release, no ground-fault monitoring, no communication module. This is a straightforward line-protection MCCB, not a multifunction power breaker.
Mounting and panel fit
Dimensions are 130 mm height, 76.2 mm width, 70 mm depth. The 70 mm depth is shallow enough for most 200 mm deep enclosures without crowding the gland plate. Width at 76.2 mm is standard for a 3-pole MCCB in this frame size — it occupies three 25 mm module spaces on a DIN rail or bolts directly to a mounting plate via the rear slots. The 3VA1 family uses a common footprint across current ratings, so swapping a 100 A unit for this 125 A unit does not require re-drilling the backplate.
Thermal performance across the panel ambient range
Rated current holds flat at 125 A from 40 °C through 50 °C. At 55 °C it drops to 122 A, at 60 °C to 120 A, at 65 °C to 117 A, and at 70 °C to 114 A. The derating curve is gentle — about 0.2 A per °C above 50 °C — so a panel running at 60 °C ambient still gets 96% of the nameplate rating. Maximum power loss at full load is 28.1 W, which is manageable for natural convection in a ventilated enclosure.
Environmental limits
Operating temperature range is -25 °C to +70 °C. Storage range extends from -40 °C to +80 °C — the storage limit governs handling and warehousing, not running conditions. The -40 °C storage floor means it can sit in an unheated warehouse through winter without damage.