What this MCCB is and what it does
The Siemens SENTRON 3VA1112-3EF36-0AF0 is a 3-pole molded case circuit breaker (MCCB) rated for line protection, with a TM240 thermal-magnetic overcurrent release. It carries 125 A continuously at 40 °C, and its interrupting capacity hits 75.6 kA at 240 V — enough to handle high-fault service-entrance or distribution panels where the available fault current is substantial. Rated insulation voltage is 800 V, so it's comfortable on 480/277 V and 600 V systems with headroom. The TM240 release means the thermal element is calibrated for a 240 A frame — the breaker is physically built on that frame but shipped with a 125 A continuous rating, which gives you some flexibility if you need to up-rate the trip unit later without swapping the whole breaker.
Interrupting ratings — match them to your available fault current
This MCCB's interrupting capacity drops as system voltage rises: 75.6 kA at 240 V, 52.5 kA at 415 V, 32 kA at 440 V, and 11.9 kA at both 500 V and 690 V. That 11.9 kA at 690 V is the limiting number if you're on a 690 V industrial distribution — make sure your calculated fault current stays under it, or you'll need a current-limiting upstream device or a higher-rated breaker.
Thermal derating — don't lose capacity to a hot panel
The 125 A rating holds steady from 40 °C up to 50 °C. Above that it starts to taper: 122 A at 55 °C, 120 A at 60 °C, 117 A at 65 °C, 114 A at 70 °C. If your panel ambient runs hot — say, 55 °C near the top of a sealed enclosure — you lose 3 A of headroom. That's not a showstopper for most loads, but worth factoring into the thermal coordination study.
Auxiliary and alarm switching built in
Comes with one auxiliary switch and one trip alarm switch (HQ type) factory-installed. The auxiliary tracks the breaker's open/closed position; the trip alarm signals only when the breaker trips on fault, not on manual opening. That's useful for remote fault annunciation or a shunt-trip supervision circuit — saves adding an external accessory block for basic status feedback.
Panel fit — dimensions and power loss
Mounts on a DIN rail or panel-mount baseplate. Overall dimensions: 130 mm height, 76.2 mm width (3 inches — standard MCCB footprint for this class), 70 mm depth. That 70 mm depth is shallow enough to fit in a 200 mm deep enclosure with room for wiring gutters. Maximum power dissipation is 28.1 W — not negligible; if you're packing several of these side-by-side in a sealed box, you'll want to account for the heat in the enclosure sizing.
Environmental limits and approvals
Operating temperature range is -25 °C to 70 °C; storage range is -40 °C to 80 °C. The storage low end matters if the breaker sits in an unheated warehouse before installation — it's fine down to -40 °C, but let it warm above -25 °C before you close the contacts under load. The part carries Siemens SENTRON branding and is designed to IEC/EN 60947-2; compliance documentation (CE, RoHS, REACH) is standard with the shipment.